diff --git a/library/bignum.c b/library/bignum.c
index 11acc01..8717c8a 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1785,7 +1785,7 @@
     /*
      * handle trivial cases
      */
-    if( b == 1 )
+    if( b == 1 || A->n == 0 )
     {
         *r = 0;
         return( 0 );
diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index 23ea07b..43f490e 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -607,6 +607,9 @@
     if( ( f = fopen( path, "wb" ) ) == NULL )
         return( MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR );
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( f, NULL );
+
     if( ( ret = mbedtls_ctr_drbg_random( ctx, buf,
                                          MBEDTLS_CTR_DRBG_MAX_INPUT ) ) != 0 )
         goto exit;
@@ -640,6 +643,9 @@
     if( ( f = fopen( path, "rb" ) ) == NULL )
         return( MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR );
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( f, NULL );
+
     n = fread( buf, 1, sizeof( buf ), f );
     if( fread( &c, 1, 1, f ) != 0 )
     {
diff --git a/library/dhm.c b/library/dhm.c
index 2ce0ed4..1e95bda 100644
--- a/library/dhm.c
+++ b/library/dhm.c
@@ -620,6 +620,7 @@
 
     if( ( f = fopen( path, "rb" ) ) == NULL )
         return( MBEDTLS_ERR_DHM_FILE_IO_ERROR );
+    /* The data loaded here is public, so don't bother disabling buffering. */
 
     fseek( f, 0, SEEK_END );
     if( ( size = ftell( f ) ) == -1 )
diff --git a/library/entropy.c b/library/entropy.c
index 9e31f84..08c5bd7 100644
--- a/library/entropy.c
+++ b/library/entropy.c
@@ -457,6 +457,9 @@
         goto exit;
     }
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( f, NULL );
+
     if( fwrite( buf, 1, MBEDTLS_ENTROPY_BLOCK_SIZE, f ) != MBEDTLS_ENTROPY_BLOCK_SIZE )
     {
         ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
@@ -484,6 +487,9 @@
     if( ( f = fopen( path, "rb" ) ) == NULL )
         return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( f, NULL );
+
     fseek( f, 0, SEEK_END );
     n = (size_t) ftell( f );
     fseek( f, 0, SEEK_SET );
diff --git a/library/entropy_poll.c b/library/entropy_poll.c
index 058c307..2ae57fd 100644
--- a/library/entropy_poll.c
+++ b/library/entropy_poll.c
@@ -35,7 +35,7 @@
 #if defined(MBEDTLS_TIMING_C)
 #include "mbedtls/timing.h"
 #endif
-#if defined(MBEDTLS_ENTROPY_NV_SEED)
+#if defined(MBEDTLS_ENTROPY_NV_SEED) || !defined(HAVE_SYSCTL_ARND)
 #include "mbedtls/platform.h"
 #endif
 
@@ -195,6 +195,9 @@
     if( file == NULL )
         return( MBEDTLS_ERR_ENTROPY_SOURCE_FAILED );
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( file, NULL );
+
     read_len = fread( output, 1, len, file );
     if( read_len != len )
     {
diff --git a/library/hmac_drbg.c b/library/hmac_drbg.c
index ab353bf..8b13a86 100644
--- a/library/hmac_drbg.c
+++ b/library/hmac_drbg.c
@@ -436,6 +436,9 @@
     if( ( f = fopen( path, "wb" ) ) == NULL )
         return( MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR );
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( f, NULL );
+
     if( ( ret = mbedtls_hmac_drbg_random( ctx, buf, sizeof( buf ) ) ) != 0 )
         goto exit;
 
@@ -465,6 +468,9 @@
     if( ( f = fopen( path, "rb" ) ) == NULL )
         return( MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR );
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( f, NULL );
+
     n = fread( buf, 1, sizeof( buf ), f );
     if( fread( &c, 1, 1, f ) != 0 )
     {
diff --git a/library/md.c b/library/md.c
index f2c1a90..a387da5 100644
--- a/library/md.c
+++ b/library/md.c
@@ -605,6 +605,9 @@
     if( ( f = fopen( path, "rb" ) ) == NULL )
         return( MBEDTLS_ERR_MD_FILE_IO_ERROR );
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( f, NULL );
+
     mbedtls_md_init( &ctx );
 
     if( ( ret = mbedtls_md_setup( &ctx, md_info, 0 ) ) != 0 )
diff --git a/library/pkparse.c b/library/pkparse.c
index 6f40968..73d59a6 100644
--- a/library/pkparse.c
+++ b/library/pkparse.c
@@ -82,6 +82,9 @@
     if( ( f = fopen( path, "rb" ) ) == NULL )
         return( MBEDTLS_ERR_PK_FILE_IO_ERROR );
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( f, NULL );
+
     fseek( f, 0, SEEK_END );
     if( ( size = ftell( f ) ) == -1 )
     {
diff --git a/library/platform.c b/library/platform.c
index e742fde..6151e6c 100644
--- a/library/platform.c
+++ b/library/platform.c
@@ -226,6 +226,28 @@
 }
 #endif /* MBEDTLS_PLATFORM_FPRINTF_ALT */
 
+#if defined(MBEDTLS_PLATFORM_SETBUF_ALT)
+#if !defined(MBEDTLS_PLATFORM_STD_SETBUF)
+/*
+ * Make dummy function to prevent NULL pointer dereferences
+ */
+static void platform_setbuf_uninit( FILE *stream, char *buf )
+{
+   ((void) stream);
+   ((void) buf);
+}
+
+#define MBEDTLS_PLATFORM_STD_SETBUF   platform_setbuf_uninit
+#endif /* !MBEDTLS_PLATFORM_STD_SETBUF */
+void (*mbedtls_setbuf)( FILE *stream, char *buf ) = MBEDTLS_PLATFORM_STD_SETBUF;
+
+int mbedtls_platform_set_setbuf( void (*setbuf_func)( FILE *stream, char *buf ) )
+{
+   mbedtls_setbuf = setbuf_func;
+   return( 0 );
+}
+#endif /* MBEDTLS_PLATFORM_SETBUF_ALT */
+
 #if defined(MBEDTLS_PLATFORM_EXIT_ALT)
 #if !defined(MBEDTLS_PLATFORM_STD_EXIT)
 /*
@@ -288,6 +310,9 @@
     if( ( file = fopen( MBEDTLS_PLATFORM_STD_NV_SEED_FILE, "rb" ) ) == NULL )
         return( -1 );
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( file, NULL );
+
     if( ( n = fread( buf, 1, buf_len, file ) ) != buf_len )
     {
         fclose( file );
@@ -307,6 +332,9 @@
     if( ( file = fopen( MBEDTLS_PLATFORM_STD_NV_SEED_FILE, "w" ) ) == NULL )
         return -1;
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( file, NULL );
+
     if( ( n = fwrite( buf, 1, buf_len, file ) ) != buf_len )
     {
         fclose( file );
diff --git a/library/psa_its_file.c b/library/psa_its_file.c
index f058720..b7c2e6b 100644
--- a/library/psa_its_file.c
+++ b/library/psa_its_file.c
@@ -102,6 +102,9 @@
     if( *p_stream == NULL )
         return( PSA_ERROR_DOES_NOT_EXIST );
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( *p_stream, NULL );
+
     n = fread( &header, 1, sizeof( header ), *p_stream );
     if( n != sizeof( header ) )
         return( PSA_ERROR_DATA_CORRUPT );
@@ -201,9 +204,13 @@
 
     psa_its_fill_filename( uid, filename );
     stream = fopen( PSA_ITS_STORAGE_TEMP, "wb" );
+
     if( stream == NULL )
         goto exit;
 
+    /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+    mbedtls_setbuf( stream, NULL );
+
     status = PSA_ERROR_INSUFFICIENT_STORAGE;
     n = fwrite( &header, 1, sizeof( header ), stream );
     if( n != sizeof( header ) )
diff --git a/library/ssl_cache.c b/library/ssl_cache.c
index d198474..6505e11 100644
--- a/library/ssl_cache.c
+++ b/library/ssl_cache.c
@@ -50,6 +50,7 @@
 #endif
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_cache_find_entry( mbedtls_ssl_cache_context *cache,
                                  unsigned char const *session_id,
                                  size_t session_id_len,
@@ -124,6 +125,7 @@
     return( ret );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_cache_pick_writing_slot( mbedtls_ssl_cache_context *cache,
                                         unsigned char const *session_id,
                                         size_t session_id_len,
diff --git a/library/ssl_ciphersuites.c b/library/ssl_ciphersuites.c
index 62988f2..835159e 100644
--- a/library/ssl_ciphersuites.c
+++ b/library/ssl_ciphersuites.c
@@ -1778,6 +1778,7 @@
 static int supported_ciphersuites[MAX_CIPHERSUITES];
 static int supported_init = 0;
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ciphersuite_is_removed( const mbedtls_ssl_ciphersuite_t *cs_info )
 {
     (void)cs_info;
diff --git a/library/ssl_client.c b/library/ssl_client.c
index 22ca57c..20f1aff 100644
--- a/library/ssl_client.c
+++ b/library/ssl_client.c
@@ -46,6 +46,7 @@
 #include "ssl_debug_helpers.h"
 
 #if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_hostname_ext( mbedtls_ssl_context *ssl,
                                    unsigned char *buf,
                                    const unsigned char *end,
@@ -129,6 +130,7 @@
  * } ProtocolNameList;
  *
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_alpn_ext( mbedtls_ssl_context *ssl,
                                unsigned char *buf,
                                const unsigned char *end,
@@ -226,6 +228,7 @@
  *
  * DHE groups are not supported yet.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_supported_groups_ext( mbedtls_ssl_context *ssl,
                                            unsigned char *buf,
                                            const unsigned char *end,
@@ -308,6 +311,7 @@
 #endif /* MBEDTLS_ECDH_C || MBEDTLS_ECDSA_C ||
           MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_client_hello_cipher_suites(
             mbedtls_ssl_context *ssl,
             unsigned char *buf,
@@ -424,6 +428,7 @@
  *     };
  * } ClientHello;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_client_hello_body( mbedtls_ssl_context *ssl,
                                         unsigned char *buf,
                                         unsigned char *end,
@@ -654,6 +659,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_generate_random( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -691,6 +697,7 @@
     return( ret );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_prepare_client_hello( mbedtls_ssl_context *ssl )
 {
     int ret;
diff --git a/library/ssl_client.h b/library/ssl_client.h
index 8e0c216..be4d067 100644
--- a/library/ssl_client.h
+++ b/library/ssl_client.h
@@ -28,6 +28,7 @@
 
 #include <stddef.h>
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_write_client_hello( mbedtls_ssl_context *ssl );
 
 #endif /* MBEDTLS_SSL_CLIENT_H */
diff --git a/library/ssl_cookie.c b/library/ssl_cookie.c
index 0f2bc60..4b2d2d2 100644
--- a/library/ssl_cookie.c
+++ b/library/ssl_cookie.c
@@ -160,6 +160,7 @@
 /*
  * Generate the HMAC part of a cookie
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_cookie_hmac( mbedtls_md_context_t *hmac_ctx,
                             const unsigned char time[4],
                             unsigned char **p, unsigned char *end,
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index bd8c14d..39a47ca 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -381,11 +381,38 @@
  * \return       Zero if the needed space is available in the buffer, non-zero
  *               otherwise.
  */
+#if ! defined(MBEDTLS_TEST_HOOKS)
 static inline int mbedtls_ssl_chk_buf_ptr( const uint8_t *cur,
                                            const uint8_t *end, size_t need )
 {
     return( ( cur > end ) || ( need > (size_t)( end - cur ) ) );
 }
+#else
+typedef struct
+{
+    const uint8_t *cur;
+    const uint8_t *end;
+    size_t need;
+} mbedtls_ssl_chk_buf_ptr_args;
+
+void mbedtls_ssl_set_chk_buf_ptr_fail_args(
+    const uint8_t *cur, const uint8_t *end, size_t need );
+void mbedtls_ssl_reset_chk_buf_ptr_fail_args( void );
+
+MBEDTLS_CHECK_RETURN_CRITICAL
+int mbedtls_ssl_cmp_chk_buf_ptr_fail_args( mbedtls_ssl_chk_buf_ptr_args *args );
+
+static inline int mbedtls_ssl_chk_buf_ptr( const uint8_t *cur,
+                                           const uint8_t *end, size_t need )
+{
+    if( ( cur > end ) || ( need > (size_t)( end - cur ) ) )
+    {
+        mbedtls_ssl_set_chk_buf_ptr_fail_args( cur, end, need );
+        return( 1 );
+    }
+    return( 0 );
+}
+#endif /* MBEDTLS_TEST_HOOKS */
 
 /**
  * \brief        This macro checks if the remaining size in a buffer is
@@ -1102,6 +1129,7 @@
  *                      (<> 0) or not ( 0 ).
  * \param[out]  out_len Length of the data written into the buffer \p buf
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls12_write_client_hello_exts( mbedtls_ssl_context *ssl,
                                                unsigned char *buf,
                                                const unsigned char *end,
@@ -1153,7 +1181,9 @@
 void mbedtls_ssl_set_outbound_transform( mbedtls_ssl_context *ssl,
                                          mbedtls_ssl_transform *transform );
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_handshake_client_step( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_handshake_server_step( mbedtls_ssl_context *ssl );
 void mbedtls_ssl_handshake_wrapup( mbedtls_ssl_context *ssl );
 static inline void mbedtls_ssl_handshake_set_state( mbedtls_ssl_context *ssl,
@@ -1162,15 +1192,19 @@
     ssl->state = ( int ) state;
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_send_fatal_handshake_failure( mbedtls_ssl_context *ssl );
 
 void mbedtls_ssl_reset_checksum( mbedtls_ssl_context *ssl );
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_derive_keys( mbedtls_ssl_context *ssl );
 #endif /* MBEDTLS_SSL_PROTO_TLS1_2  */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_handle_message_type( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_prepare_handshake_record( mbedtls_ssl_context *ssl );
 void mbedtls_ssl_update_handshake_status( mbedtls_ssl_context *ssl );
 
@@ -1250,16 +1284,20 @@
  *              following the above definition.
  *
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_read_record( mbedtls_ssl_context *ssl,
                              unsigned update_hs_digest );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_fetch_input( mbedtls_ssl_context *ssl, size_t nb_want );
 
 /*
  * Write handshake message header
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_start_handshake_msg( mbedtls_ssl_context *ssl, unsigned hs_type,
                                      unsigned char **buf, size_t *buf_len );
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_write_handshake_msg_ext( mbedtls_ssl_context *ssl,
                                          int update_checksum,
                                          int force_flush );
@@ -1271,19 +1309,28 @@
 /*
  * Write handshake message tail
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_finish_handshake_msg( mbedtls_ssl_context *ssl,
                                       size_t buf_len, size_t msg_len );
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, int force_flush );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_flush_output( mbedtls_ssl_context *ssl );
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_write_certificate( mbedtls_ssl_context *ssl );
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_parse_change_cipher_spec( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_write_change_cipher_spec( mbedtls_ssl_context *ssl );
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_parse_finished( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_write_finished( mbedtls_ssl_context *ssl );
 
 void mbedtls_ssl_optimize_checksum( mbedtls_ssl_context *ssl,
@@ -1299,10 +1346,12 @@
 
 #if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
 #if !defined(MBEDTLS_USE_PSA_CRYPTO)
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_psk_derive_premaster( mbedtls_ssl_context *ssl,
                                       mbedtls_key_exchange_type_t key_ex );
 #endif /* !MBEDTLS_USE_PSA_CRYPTO */
 #if defined(MBEDTLS_SSL_CLI_C) && defined(MBEDTLS_SSL_PROTO_TLS1_2)
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_conf_has_static_psk( mbedtls_ssl_config const *conf );
 #endif
 
@@ -1370,11 +1419,14 @@
 unsigned char mbedtls_ssl_hash_from_md_alg( int md );
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_set_calc_verify_md( mbedtls_ssl_context *ssl, int md );
 #endif
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_check_curve_tls_id( const mbedtls_ssl_context *ssl, uint16_t tls_id );
 #if defined(MBEDTLS_ECP_C)
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_check_curve( const mbedtls_ssl_context *ssl, mbedtls_ecp_group_id grp_id );
 #endif
 
@@ -1429,6 +1481,7 @@
  *
  * Return 0 if everything is OK, -1 if not.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_check_cert_usage( const mbedtls_x509_crt *cert,
                           const mbedtls_ssl_ciphersuite_t *ciphersuite,
                           int cert_endpoint,
@@ -1477,21 +1530,26 @@
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
 void mbedtls_ssl_send_flight_completed( mbedtls_ssl_context *ssl );
 void mbedtls_ssl_recv_flight_completed( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_resend( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_flight_transmit( mbedtls_ssl_context *ssl );
 #endif
 
 /* Visible for testing purposes only */
 #if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_dtls_replay_check( mbedtls_ssl_context const *ssl );
 void mbedtls_ssl_dtls_replay_update( mbedtls_ssl_context *ssl );
 #endif
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_session_copy( mbedtls_ssl_session *dst,
                               const mbedtls_ssl_session *src );
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
 /* The hash buffer must have at least MBEDTLS_MD_MAX_SIZE bytes of length. */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_get_key_exchange_md_tls1_2( mbedtls_ssl_context *ssl,
                                             unsigned char *hash, size_t *hashlen,
                                             unsigned char *data, size_t data_len,
@@ -1503,11 +1561,13 @@
 #endif
 
 void mbedtls_ssl_transform_init( mbedtls_ssl_transform *transform );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_encrypt_buf( mbedtls_ssl_context *ssl,
                              mbedtls_ssl_transform *transform,
                              mbedtls_record *rec,
                              int (*f_rng)(void *, unsigned char *, size_t),
                              void *p_rng );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
                              mbedtls_ssl_transform *transform,
                              mbedtls_record *rec );
@@ -1525,10 +1585,12 @@
 }
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_resend_hello_request( mbedtls_ssl_context *ssl );
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
 
 void mbedtls_ssl_set_timer( mbedtls_ssl_context *ssl, uint32_t millisecs );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_check_timer( mbedtls_ssl_context *ssl );
 
 void mbedtls_ssl_reset_in_out_pointers( mbedtls_ssl_context *ssl );
@@ -1536,6 +1598,7 @@
                               mbedtls_ssl_transform *transform );
 void mbedtls_ssl_update_in_pointers( mbedtls_ssl_context *ssl );
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_session_reset_int( mbedtls_ssl_context *ssl, int partial );
 void mbedtls_ssl_session_reset_msg_layer( mbedtls_ssl_context *ssl,
                                           int partial );
@@ -1543,6 +1606,7 @@
 /*
  * Send pending alert
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_handle_pending_alert( mbedtls_ssl_context *ssl );
 
 /*
@@ -1563,6 +1627,7 @@
 void mbedtls_ssl_handshake_wrapup_free_hs_transform( mbedtls_ssl_context *ssl );
 
 #if defined(MBEDTLS_SSL_RENEGOTIATION)
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_start_renegotiation( mbedtls_ssl_context *ssl );
 #endif /* MBEDTLS_SSL_RENEGOTIATION */
 
@@ -1627,7 +1692,9 @@
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3)
 extern const uint8_t mbedtls_ssl_tls13_hello_retry_request_magic[
                         MBEDTLS_SERVER_HELLO_RANDOM_LEN ];
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_process_finished_message( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_write_finished_message( mbedtls_ssl_context *ssl );
 void mbedtls_ssl_tls13_handshake_wrapup( mbedtls_ssl_context *ssl );
 
@@ -1640,6 +1707,7 @@
  * \param[in]   end     End address of the buffer where to write the extensions
  * \param[out]  out_len Length of the data written into the buffer \p buf
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_write_client_hello_exts( mbedtls_ssl_context *ssl,
                                                unsigned char *buf,
                                                unsigned char *end,
@@ -1650,6 +1718,7 @@
  *
  * \param ssl       SSL context
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_handshake_client_step( mbedtls_ssl_context *ssl );
 
 /**
@@ -1657,6 +1726,7 @@
  *
  * \param ssl       SSL context
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_handshake_server_step( mbedtls_ssl_context *ssl );
 
 
@@ -1749,6 +1819,7 @@
 /*
  * Fetch TLS 1.3 handshake message header
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_fetch_handshake_msg( mbedtls_ssl_context *ssl,
                                            unsigned hs_type,
                                            unsigned char **buf,
@@ -1757,17 +1828,20 @@
 /*
  * Handler of TLS 1.3 server certificate message
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_process_certificate( mbedtls_ssl_context *ssl );
 
 #if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
 /*
  * Handler of TLS 1.3 write Certificate message
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_write_certificate( mbedtls_ssl_context *ssl );
 
 /*
  * Handler of TLS 1.3 write Certificate Verify message
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_write_certificate_verify( mbedtls_ssl_context *ssl );
 
 #endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
@@ -1775,16 +1849,20 @@
 /*
  * Generic handler of Certificate Verify
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_process_certificate_verify( mbedtls_ssl_context *ssl );
 
 /*
  * Write of dummy-CCS's for middlebox compatibility
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_write_change_cipher_spec( mbedtls_ssl_context *ssl );
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_reset_transcript_for_hrr( mbedtls_ssl_context *ssl );
 
 #if defined(MBEDTLS_ECDH_C)
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_generate_and_write_ecdh_key_exchange(
                 mbedtls_ssl_context *ssl,
                 uint16_t named_group,
@@ -1800,12 +1878,14 @@
 /*
  * Parse TLS Signature Algorithm extension
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_parse_sig_alg_ext( mbedtls_ssl_context *ssl,
                                    const unsigned char *buf,
                                    const unsigned char *end );
 #endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
 
 /* Get handshake transcript */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_get_handshake_transcript( mbedtls_ssl_context *ssl,
                                           const mbedtls_md_type_t md,
                                           unsigned char *dst,
@@ -2172,6 +2252,7 @@
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3)
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_check_sig_alg_cert_key_match( uint16_t sig_alg,
                                                     mbedtls_pk_context *key );
 
@@ -2265,6 +2346,7 @@
 
 #if defined(MBEDTLS_ECDH_C)
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_read_public_ecdhe_share( mbedtls_ssl_context *ssl,
                                                const unsigned char *buf,
                                                size_t buf_len );
@@ -2297,31 +2379,44 @@
  *
  * \return 0 if valid, negative value otherwise.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_validate_ciphersuite(
     const mbedtls_ssl_context *ssl,
     const mbedtls_ssl_ciphersuite_t *suite_info,
     mbedtls_ssl_protocol_version min_tls_version,
     mbedtls_ssl_protocol_version max_tls_version );
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_write_sig_alg_ext( mbedtls_ssl_context *ssl, unsigned char *buf,
                                    const unsigned char *end, size_t *out_len );
 
 #if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_parse_server_name_ext( mbedtls_ssl_context *ssl,
                                        const unsigned char *buf,
                                        const unsigned char *end );
 #endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */
 
 #if defined(MBEDTLS_SSL_ALPN)
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_parse_alpn_ext( mbedtls_ssl_context *ssl,
                                 const unsigned char *buf,
                                 const unsigned char *end );
 
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_write_alpn_ext( mbedtls_ssl_context *ssl,
                                 unsigned char *buf,
                                 unsigned char *end,
                                 size_t *out_len );
 #endif /* MBEDTLS_SSL_ALPN */
 
+#if defined(MBEDTLS_TEST_HOOKS)
+int mbedtls_ssl_check_dtls_clihlo_cookie(
+                           mbedtls_ssl_context *ssl,
+                           const unsigned char *cli_id, size_t cli_id_len,
+                           const unsigned char *in, size_t in_len,
+                           unsigned char *obuf, size_t buf_len, size_t *olen );
+#endif
+
 #endif /* ssl_misc.h */
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index d0b8a64..fb0b709 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -86,6 +86,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_record_header( mbedtls_ssl_context const *ssl,
                                     unsigned char *buf,
                                     size_t len,
@@ -157,11 +158,16 @@
 static void ssl_buffering_free_slot( mbedtls_ssl_context *ssl,
                                      uint8_t slot );
 static void ssl_free_buffered_record( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_load_buffered_message( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_load_buffered_record( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_buffer_message( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_buffer_future_record( mbedtls_ssl_context *ssl,
                                      mbedtls_record const *rec );
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_next_record_is_in_datagram( mbedtls_ssl_context *ssl );
 
 static size_t ssl_get_maximum_datagram_size( mbedtls_ssl_context const *ssl )
@@ -179,6 +185,7 @@
     return( out_buf_len );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_get_remaining_space_in_datagram( mbedtls_ssl_context const *ssl )
 {
     size_t const bytes_written = ssl->out_left;
@@ -195,6 +202,7 @@
     return( (int) ( mtu - bytes_written ) );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_get_remaining_payload_in_datagram( mbedtls_ssl_context const *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -246,6 +254,7 @@
  * Double the retransmit timeout value, within the allowed range,
  * returning -1 if the maximum value has already been reached.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_double_retransmit_timeout( mbedtls_ssl_context *ssl )
 {
     uint32_t new_timeout;
@@ -329,6 +338,7 @@
  *  - A negative error code if `max_len` didn't offer enough space
  *    for the expansion.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_build_inner_plaintext( unsigned char *content,
                                       size_t *content_size,
                                       size_t remaining,
@@ -356,6 +366,7 @@
 
 /* This function parses a (D)TLSInnerPlaintext structure.
  * See ssl_build_inner_plaintext() for details. */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_inner_plaintext( unsigned char const *content,
                                           size_t *content_size,
                                           uint8_t *rec_type )
@@ -469,6 +480,7 @@
 #if defined(MBEDTLS_GCM_C) || \
     defined(MBEDTLS_CCM_C) || \
     defined(MBEDTLS_CHACHAPOLY_C)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_transform_aead_dynamic_iv_is_explicit(
                                 mbedtls_ssl_transform const *transform )
 {
@@ -2066,6 +2078,7 @@
 /*
  * Append current handshake message to current outgoing flight
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_flight_append( mbedtls_ssl_context *ssl )
 {
     mbedtls_ssl_flight_item *msg;
@@ -2132,6 +2145,7 @@
 /*
  * Swap transform_out and out_ctr with the alternative ones
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_swap_epochs( mbedtls_ssl_context *ssl )
 {
     mbedtls_ssl_transform *tmp_transform;
@@ -2767,6 +2781,7 @@
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_hs_is_proper_fragment( mbedtls_ssl_context *ssl )
 {
     if( ssl->in_msglen < ssl->in_hslen ||
@@ -2792,6 +2807,7 @@
               ssl->in_msg[8] );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_check_hs_header( mbedtls_ssl_context const *ssl )
 {
     uint32_t msg_len, frag_off, frag_len;
@@ -2858,6 +2874,7 @@
 /*
  * Check that bitmask is full
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_bitmask_check( unsigned char *mask, size_t len )
 {
     size_t i;
@@ -3057,6 +3074,7 @@
             ( (uint64_t) buf[5]       ) );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int mbedtls_ssl_dtls_record_replay_check( mbedtls_ssl_context *ssl, uint8_t *record_in_ctr )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -3139,8 +3157,8 @@
 
 #if defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE) && defined(MBEDTLS_SSL_SRV_C)
 /*
- * Without any SSL context, check if a datagram looks like a ClientHello with
- * a valid cookie, and if it doesn't, generate a HelloVerifyRequest message.
+ * Check if a datagram looks like a ClientHello with a valid cookie,
+ * and if it doesn't, generate a HelloVerifyRequest message.
  * Both input and output include full DTLS headers.
  *
  * - if cookie is valid, return 0
@@ -3149,15 +3167,15 @@
  *   return MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED
  * - otherwise return a specific error code
  */
-static int ssl_check_dtls_clihlo_cookie(
-                           mbedtls_ssl_cookie_write_t *f_cookie_write,
-                           mbedtls_ssl_cookie_check_t *f_cookie_check,
-                           void *p_cookie,
+MBEDTLS_CHECK_RETURN_CRITICAL
+MBEDTLS_STATIC_TESTABLE
+int mbedtls_ssl_check_dtls_clihlo_cookie(
+                           mbedtls_ssl_context *ssl,
                            const unsigned char *cli_id, size_t cli_id_len,
                            const unsigned char *in, size_t in_len,
                            unsigned char *obuf, size_t buf_len, size_t *olen )
 {
-    size_t sid_len, cookie_len;
+    size_t sid_len, cookie_len, epoch, fragment_offset;
     unsigned char *p;
 
     /*
@@ -3186,26 +3204,55 @@
      *
      * Minimum length is 61 bytes.
      */
-    if( in_len < 61 ||
-        in[0] != MBEDTLS_SSL_MSG_HANDSHAKE ||
-        in[3] != 0 || in[4] != 0 ||
-        in[19] != 0 || in[20] != 0 || in[21] != 0 )
+    MBEDTLS_SSL_DEBUG_MSG( 4, ( "check cookie: in_len=%u",
+                                (unsigned) in_len ) );
+    MBEDTLS_SSL_DEBUG_BUF( 4, "cli_id", cli_id, cli_id_len );
+    if( in_len < 61 )
     {
+        MBEDTLS_SSL_DEBUG_MSG( 4, ( "check cookie: record too short" ) );
+        return( MBEDTLS_ERR_SSL_DECODE_ERROR );
+    }
+
+    epoch = MBEDTLS_GET_UINT16_BE( in, 3 );
+    fragment_offset = MBEDTLS_GET_UINT24_BE( in, 19 );
+
+    if( in[0] != MBEDTLS_SSL_MSG_HANDSHAKE || epoch != 0 ||
+        fragment_offset != 0 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 4, ( "check cookie: not a good ClientHello" ) );
+        MBEDTLS_SSL_DEBUG_MSG( 4, ( "    type=%u epoch=%u fragment_offset=%u",
+                                    in[0], (unsigned) epoch,
+                                    (unsigned) fragment_offset ) );
         return( MBEDTLS_ERR_SSL_DECODE_ERROR );
     }
 
     sid_len = in[59];
-    if( sid_len > in_len - 61 )
+    if( 59 + 1 + sid_len + 1 > in_len )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 4, ( "check cookie: sid_len=%u > %u",
+                                    (unsigned) sid_len,
+                                    (unsigned) in_len - 61 ) );
         return( MBEDTLS_ERR_SSL_DECODE_ERROR );
+    }
+    MBEDTLS_SSL_DEBUG_BUF( 4, "sid received from network",
+                           in + 60, sid_len );
 
     cookie_len = in[60 + sid_len];
-    if( cookie_len > in_len - 60 )
-        return( MBEDTLS_ERR_SSL_DECODE_ERROR );
-
-    if( f_cookie_check( p_cookie, in + sid_len + 61, cookie_len,
-                        cli_id, cli_id_len ) == 0 )
+    if( 59 + 1 + sid_len + 1 + cookie_len > in_len )
     {
-        /* Valid cookie */
+        MBEDTLS_SSL_DEBUG_MSG( 4, ( "check cookie: cookie_len=%u > %u",
+                                    (unsigned) cookie_len,
+                                    (unsigned) ( in_len - sid_len - 61 ) ) );
+        return( MBEDTLS_ERR_SSL_DECODE_ERROR );
+    }
+
+    MBEDTLS_SSL_DEBUG_BUF( 4, "cookie received from network",
+                           in + sid_len + 61, cookie_len );
+    if( ssl->conf->f_cookie_check( ssl->conf->p_cookie,
+                                   in + sid_len + 61, cookie_len,
+                                   cli_id, cli_id_len ) == 0 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 4, ( "check cookie: valid" ) );
         return( 0 );
     }
 
@@ -3240,8 +3287,9 @@
 
     /* Generate and write actual cookie */
     p = obuf + 28;
-    if( f_cookie_write( p_cookie,
-                        &p, obuf + buf_len, cli_id, cli_id_len ) != 0 )
+    if( ssl->conf->f_cookie_write( ssl->conf->p_cookie,
+                                   &p, obuf + buf_len,
+                                   cli_id, cli_id_len ) != 0 )
     {
         return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
     }
@@ -3280,6 +3328,7 @@
  * includes the case of MBEDTLS_ERR_SSL_CLIENT_RECONNECT and of unexpected
  * errors, and is the right thing to do in both cases).
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_handle_possible_reconnect( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -3295,15 +3344,13 @@
         return( 0 );
     }
 
-    ret = ssl_check_dtls_clihlo_cookie(
-            ssl->conf->f_cookie_write,
-            ssl->conf->f_cookie_check,
-            ssl->conf->p_cookie,
+    ret = mbedtls_ssl_check_dtls_clihlo_cookie(
+            ssl,
             ssl->cli_id, ssl->cli_id_len,
             ssl->in_buf, ssl->in_left,
             ssl->out_buf, MBEDTLS_SSL_OUT_CONTENT_LEN, &len );
 
-    MBEDTLS_SSL_DEBUG_RET( 2, "ssl_check_dtls_clihlo_cookie", ret );
+    MBEDTLS_SSL_DEBUG_RET( 2, "mbedtls_ssl_check_dtls_clihlo_cookie", ret );
 
     if( ret == MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED )
     {
@@ -3337,6 +3384,7 @@
 }
 #endif /* MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE && MBEDTLS_SSL_SRV_C */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_check_record_type( uint8_t record_type )
 {
     if( record_type != MBEDTLS_SSL_MSG_HANDSHAKE &&
@@ -3369,6 +3417,7 @@
  * Point 2 is needed when the peer is resending, and we have already received
  * the first record from a datagram but are still waiting for the others.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_record_header( mbedtls_ssl_context const *ssl,
                                     unsigned char *buf,
                                     size_t len,
@@ -3481,7 +3530,6 @@
     /*
      * Parse and validate record version
      */
-
     rec->ver[0] = buf[ rec_hdr_version_offset + 0 ];
     rec->ver[1] = buf[ rec_hdr_version_offset + 1 ];
     tls_version = mbedtls_ssl_read_version( buf + rec_hdr_version_offset,
@@ -3489,10 +3537,12 @@
 
     if( tls_version > ssl->conf->max_tls_version )
     {
-        MBEDTLS_SSL_DEBUG_MSG( 1, ( "TLS version mismatch" ) );
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "TLS version mismatch: got %u, expected max %u",
+                                    (unsigned) tls_version,
+                                    (unsigned) ssl->conf->max_tls_version) );
+
         return( MBEDTLS_ERR_SSL_INVALID_RECORD );
     }
-
     /*
      * Parse/Copy record sequence number.
      */
@@ -3594,6 +3644,7 @@
 
 
 #if defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE) && defined(MBEDTLS_SSL_SRV_C)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_check_client_reconnect( mbedtls_ssl_context *ssl )
 {
     unsigned int rec_epoch = ( ssl->in_ctr[0] << 8 ) | ssl->in_ctr[1];
@@ -3623,6 +3674,7 @@
 /*
  * If applicable, decrypt record content
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_prepare_record_content( mbedtls_ssl_context *ssl,
                                        mbedtls_record *rec )
 {
@@ -3757,7 +3809,7 @@
 
     /* Check actual (decrypted) record content length against
      * configured maximum. */
-    if( ssl->in_msglen > MBEDTLS_SSL_IN_CONTENT_LEN )
+    if( rec->data_len > MBEDTLS_SSL_IN_CONTENT_LEN )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad message length" ) );
         return( MBEDTLS_ERR_SSL_INVALID_RECORD );
@@ -3775,8 +3827,11 @@
  */
 
 /* Helper functions for mbedtls_ssl_read_record(). */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_consume_current_message( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_get_next_record( mbedtls_ssl_context *ssl );
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_record_is_in_progress( mbedtls_ssl_context *ssl );
 
 int mbedtls_ssl_read_record( mbedtls_ssl_context *ssl,
@@ -3864,6 +3919,7 @@
 }
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_next_record_is_in_datagram( mbedtls_ssl_context *ssl )
 {
     if( ssl->in_left > ssl->next_record_offset )
@@ -3872,6 +3928,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_load_buffered_message( mbedtls_ssl_context *ssl )
 {
     mbedtls_ssl_handshake_params * const hs = ssl->handshake;
@@ -3969,6 +4026,7 @@
     return( ret );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_buffer_make_space( mbedtls_ssl_context *ssl,
                                   size_t desired )
 {
@@ -4011,6 +4069,7 @@
     return( -1 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_buffer_message( mbedtls_ssl_context *ssl )
 {
     int ret = 0;
@@ -4215,6 +4274,7 @@
 }
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_consume_current_message( mbedtls_ssl_context *ssl )
 {
     /*
@@ -4302,6 +4362,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_record_is_in_progress( mbedtls_ssl_context *ssl )
 {
     if( ssl->in_msglen > 0 )
@@ -4328,6 +4389,7 @@
     }
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_load_buffered_record( mbedtls_ssl_context *ssl )
 {
     mbedtls_ssl_handshake_params * const hs = ssl->handshake;
@@ -4385,6 +4447,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_buffer_future_record( mbedtls_ssl_context *ssl,
                                      mbedtls_record const *rec )
 {
@@ -4443,6 +4506,7 @@
 
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_get_next_record( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -5193,6 +5257,7 @@
 /*
  * Check record counters and renegotiate if they're above the limit.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_check_ctr_renegotiate( mbedtls_ssl_context *ssl )
 {
     size_t ep_len = mbedtls_ssl_ep_len( ssl );
@@ -5232,6 +5297,7 @@
  * and having a helper function allows to distinguish between TLS <= 1.2 and
  * TLS 1.3 in the future without bloating the logic of mbedtls_ssl_read().
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_handle_hs_message_post_handshake( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -5549,6 +5615,7 @@
  * Therefore, it is possible that the input message length is 0 and the
  * corresponding return code is 0 on success.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_real( mbedtls_ssl_context *ssl,
                            const unsigned char *buf, size_t len )
 {
diff --git a/library/ssl_ticket.c b/library/ssl_ticket.c
index a924a2a..28c4d3e 100644
--- a/library/ssl_ticket.c
+++ b/library/ssl_ticket.c
@@ -66,6 +66,7 @@
 /*
  * Generate/update a key
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_ticket_gen_key( mbedtls_ssl_ticket_context *ctx,
                                unsigned char index )
 {
@@ -113,6 +114,7 @@
 /*
  * Rotate/generate keys if necessary
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_ticket_update_keys( mbedtls_ssl_ticket_context *ctx )
 {
 #if !defined(MBEDTLS_HAVE_TIME)
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index d3bb291..e60b82f 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -58,6 +58,30 @@
 #include "mbedtls/oid.h"
 #endif
 
+#if defined(MBEDTLS_TEST_HOOKS)
+static mbedtls_ssl_chk_buf_ptr_args chk_buf_ptr_fail_args;
+
+void mbedtls_ssl_set_chk_buf_ptr_fail_args(
+    const uint8_t *cur, const uint8_t *end, size_t need )
+{
+    chk_buf_ptr_fail_args.cur = cur;
+    chk_buf_ptr_fail_args.end = end;
+    chk_buf_ptr_fail_args.need = need;
+}
+
+void mbedtls_ssl_reset_chk_buf_ptr_fail_args( void )
+{
+    memset( &chk_buf_ptr_fail_args, 0, sizeof( chk_buf_ptr_fail_args ) );
+}
+
+int mbedtls_ssl_cmp_chk_buf_ptr_fail_args( mbedtls_ssl_chk_buf_ptr_args *args )
+{
+    return( ( chk_buf_ptr_fail_args.cur  != args->cur  ) ||
+            ( chk_buf_ptr_fail_args.end  != args->end  ) ||
+            ( chk_buf_ptr_fail_args.need != args->need ) );
+}
+#endif /* MBEDTLS_TEST_HOOKS */
+
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
 
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
@@ -275,6 +299,7 @@
 }
 
 #if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int resize_buffer( unsigned char **buffer, size_t len_new, size_t *len_old )
 {
     unsigned char* resized_buffer = mbedtls_calloc( 1, len_new );
@@ -380,6 +405,7 @@
                           const unsigned char *, size_t,
                           unsigned char *, size_t);
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls12_populate_transform( mbedtls_ssl_transform *transform,
                                    int ciphersuite,
                                    const unsigned char master[48],
@@ -393,6 +419,7 @@
                                    const mbedtls_ssl_context *ssl );
 
 #if defined(MBEDTLS_SHA256_C)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int tls_prf_sha256( const unsigned char *secret, size_t slen,
                            const char *label,
                            const unsigned char *random, size_t rlen,
@@ -403,6 +430,7 @@
 #endif /* MBEDTLS_SHA256_C */
 
 #if defined(MBEDTLS_SHA384_C)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int tls_prf_sha384( const unsigned char *secret, size_t slen,
                            const char *label,
                            const unsigned char *random, size_t rlen,
@@ -415,6 +443,7 @@
 static size_t ssl_session_save_tls12( const mbedtls_ssl_session *session,
                                       unsigned char *buf,
                                       size_t buf_len );
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_session_load_tls12( mbedtls_ssl_session *session,
                                    const unsigned char *buf,
                                    size_t len );
@@ -672,6 +701,7 @@
     memset( session, 0, sizeof(mbedtls_ssl_session) );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_handshake_init( mbedtls_ssl_context *ssl )
 {
     /* Clear old handshake information if present */
@@ -862,6 +892,7 @@
 
 #if defined(MBEDTLS_SSL_DTLS_HELLO_VERIFY) && defined(MBEDTLS_SSL_SRV_C)
 /* Dummy cookie callbacks for defaults */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_cookie_write_dummy( void *ctx,
                       unsigned char **p, unsigned char *end,
                       const unsigned char *cli_id, size_t cli_id_len )
@@ -875,6 +906,7 @@
     return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_cookie_check_dummy( void *ctx,
                       const unsigned char *cookie, size_t cookie_len,
                       const unsigned char *cli_id, size_t cli_id_len )
@@ -897,6 +929,7 @@
     memset( ssl, 0, sizeof( mbedtls_ssl_context ) );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_conf_version_check( const mbedtls_ssl_context *ssl )
 {
     const mbedtls_ssl_config *conf = ssl->conf;
@@ -948,6 +981,7 @@
     return( MBEDTLS_ERR_SSL_BAD_CONFIG );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_conf_check(const mbedtls_ssl_context *ssl)
 {
     int ret;
@@ -1092,6 +1126,8 @@
         memset( ssl->in_buf, 0, in_buf_len );
     }
 
+    ssl->send_alert = 0;
+
     /* Reset outgoing message writing */
     ssl->out_msgtype = 0;
     ssl->out_msglen  = 0;
@@ -1371,6 +1407,7 @@
 }
 
 /* Append a new keycert entry to a (possibly empty) list */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_append_key_cert( mbedtls_ssl_key_cert **head,
                                 mbedtls_x509_crt *cert,
                                 mbedtls_pk_context *key )
@@ -1524,6 +1561,7 @@
 
 #if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_conf_psk_is_configured( mbedtls_ssl_config const *conf )
 {
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
@@ -1569,6 +1607,7 @@
  * It checks that the provided identity is well-formed and attempts
  * to make a copy of it in the SSL config.
  * On failure, the PSK identity in the config remains unset. */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_conf_set_psk_identity( mbedtls_ssl_config *conf,
                                       unsigned char const *psk_identity,
                                       size_t psk_identity_len )
@@ -2763,6 +2802,7 @@
  *
  */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_session_save( const mbedtls_ssl_session *session,
                              unsigned char omit_header,
                              unsigned char *buf,
@@ -2837,6 +2877,7 @@
  * This internal version is wrapped by a public function that cleans up in
  * case of error, and has an extra option omit_header.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_session_load( mbedtls_ssl_session *session,
                              unsigned char omit_header,
                              const unsigned char *buf,
@@ -2903,6 +2944,7 @@
 /*
  * Perform a single step of the SSL handshake
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_prepare_handshake_step( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -3061,6 +3103,7 @@
 /*
  * Write HelloRequest to request renegotiation on server
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_hello_request( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -3659,6 +3702,7 @@
  * This internal version is wrapped by a public function that cleans up in
  * case of error.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_context_load( mbedtls_ssl_context *ssl,
                              const unsigned char *buf,
                              size_t len )
@@ -4224,6 +4268,7 @@
 #if defined(MBEDTLS_DEBUG_C) && defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
 /* Function for checking `ssl_preset_*_sig_algs` and `ssl_tls12_preset_*_sig_algs`
  * to make sure there are no duplicated signature algorithm entries. */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_check_no_sig_alg_duplication( uint16_t * sig_algs )
 {
     size_t i, j;
@@ -4769,6 +4814,7 @@
 #else /* MBEDTLS_USE_PSA_CRYPTO */
 
 #if defined(MBEDTLS_SHA384_C)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_get_handshake_transcript_sha384( mbedtls_ssl_context *ssl,
                                                 unsigned char *dst,
                                                 size_t dst_len,
@@ -4799,6 +4845,7 @@
 #endif /* MBEDTLS_SHA384_C */
 
 #if defined(MBEDTLS_SHA256_C)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_get_handshake_transcript_sha256( mbedtls_ssl_context *ssl,
                                                 unsigned char *dst,
                                                 size_t dst_len,
@@ -5034,6 +5081,7 @@
     return( PSA_SUCCESS );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int tls_prf_generic( mbedtls_md_type_t md_type,
                             const unsigned char *secret, size_t slen,
                             const char *label,
@@ -5110,6 +5158,7 @@
 
 #else /* MBEDTLS_USE_PSA_CRYPTO */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int tls_prf_generic( mbedtls_md_type_t md_type,
                             const unsigned char *secret, size_t slen,
                             const char *label,
@@ -5202,6 +5251,7 @@
 #endif /* MBEDTLS_USE_PSA_CRYPTO */
 
 #if defined(MBEDTLS_SHA256_C)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int tls_prf_sha256( const unsigned char *secret, size_t slen,
                            const char *label,
                            const unsigned char *random, size_t rlen,
@@ -5213,6 +5263,7 @@
 #endif /* MBEDTLS_SHA256_C */
 
 #if defined(MBEDTLS_SHA384_C)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int tls_prf_sha384( const unsigned char *secret, size_t slen,
                            const char *label,
                            const unsigned char *random, size_t rlen,
@@ -5232,6 +5283,7 @@
  * Outputs:
  * - the tls_prf, calc_verify and calc_finished members of handshake structure
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_set_handshake_prfs( mbedtls_ssl_handshake_params *handshake,
                                    mbedtls_md_type_t hash )
 {
@@ -5276,6 +5328,7 @@
  *      EMS: passed to calc_verify (debug + session_negotiate)
  *      PSA-PSA: conf
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_compute_master( mbedtls_ssl_handshake_params *handshake,
                                unsigned char *master,
                                const mbedtls_ssl_context *ssl )
@@ -5744,6 +5797,7 @@
 #endif /* !MBEDTLS_USE_PSA_CRYPTO && MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
 
 #if defined(MBEDTLS_SSL_SRV_C) && defined(MBEDTLS_SSL_RENEGOTIATION)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_hello_request( mbedtls_ssl_context *ssl );
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
@@ -5915,6 +5969,7 @@
 #if defined(MBEDTLS_SSL_RENEGOTIATION) && defined(MBEDTLS_SSL_CLI_C)
 
 #if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_check_peer_crt_unchanged( mbedtls_ssl_context *ssl,
                                          unsigned char *crt_buf,
                                          size_t crt_buf_len )
@@ -5930,6 +5985,7 @@
     return( memcmp( peer_crt->raw.p, crt_buf, peer_crt->raw.len ) );
 }
 #else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_check_peer_crt_unchanged( mbedtls_ssl_context *ssl,
                                          unsigned char *crt_buf,
                                          size_t crt_buf_len )
@@ -5964,6 +6020,7 @@
  * Once the certificate message is read, parse it into a cert chain and
  * perform basic checks, but leave actual verification to the caller
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_certificate_chain( mbedtls_ssl_context *ssl,
                                         mbedtls_x509_crt *chain )
 {
@@ -6119,6 +6176,7 @@
 }
 
 #if defined(MBEDTLS_SSL_SRV_C)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_srv_check_client_no_crt_notification( mbedtls_ssl_context *ssl )
 {
     if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
@@ -6144,6 +6202,7 @@
  */
 #define SSL_CERTIFICATE_EXPECTED 0
 #define SSL_CERTIFICATE_SKIP     1
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_certificate_coordinate( mbedtls_ssl_context *ssl,
                                              int authmode )
 {
@@ -6173,6 +6232,7 @@
     return( SSL_CERTIFICATE_EXPECTED );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_certificate_verify( mbedtls_ssl_context *ssl,
                                          int authmode,
                                          mbedtls_x509_crt *chain,
@@ -6270,7 +6330,9 @@
     {
         const mbedtls_pk_context *pk = &chain->pk;
 
-        /* If certificate uses an EC key, make sure the curve is OK */
+        /* If certificate uses an EC key, make sure the curve is OK.
+         * This is a public key, so it can't be opaque, so can_do() is a good
+         * enough check to ensure pk_ec() is safe to use here. */
         if( mbedtls_pk_can_do( pk, MBEDTLS_PK_ECKEY ) &&
             mbedtls_ssl_check_curve( ssl, mbedtls_pk_ec( *pk )->grp.id ) != 0 )
         {
@@ -6361,6 +6423,7 @@
 }
 
 #if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_remember_peer_crt_digest( mbedtls_ssl_context *ssl,
                                          unsigned char *start, size_t len )
 {
@@ -6392,6 +6455,7 @@
     return( ret );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_remember_peer_pubkey( mbedtls_ssl_context *ssl,
                                      unsigned char *start, size_t len )
 {
@@ -7060,6 +7124,7 @@
  *      [in] optionally used for:
  *        - MBEDTLS_DEBUG_C: ssl->conf->{f,p}_dbg
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls12_populate_transform( mbedtls_ssl_transform *transform,
                                    int ciphersuite,
                                    const unsigned char master[48],
@@ -7889,6 +7954,7 @@
     return( used );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_session_load_tls12( mbedtls_ssl_session *session,
                                    const unsigned char *buf,
                                    size_t len )
@@ -8254,6 +8320,7 @@
  *          ServerName server_name_list<1..2^16-1>
  *     } ServerNameList;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_parse_server_name_ext( mbedtls_ssl_context *ssl,
                                        const unsigned char *buf,
                                        const unsigned char *end )
@@ -8309,6 +8376,7 @@
 #endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */
 
 #if defined(MBEDTLS_SSL_ALPN)
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_parse_alpn_ext( mbedtls_ssl_context *ssl,
                                 const unsigned char *buf,
                                 const unsigned char *end )
diff --git a/library/ssl_tls12_client.c b/library/ssl_tls12_client.c
index 050aaa1..7fa6443 100644
--- a/library/ssl_tls12_client.c
+++ b/library/ssl_tls12_client.c
@@ -75,6 +75,7 @@
 #endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
 
 #if defined(MBEDTLS_SSL_RENEGOTIATION)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_renegotiation_ext( mbedtls_ssl_context *ssl,
                                         unsigned char *buf,
                                         const unsigned char *end,
@@ -116,6 +117,7 @@
 #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
     defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_supported_point_formats_ext( mbedtls_ssl_context *ssl,
                                                   unsigned char *buf,
                                                   const unsigned char *end,
@@ -147,6 +149,7 @@
           MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
 
 #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_ecjpake_kkpp_ext( mbedtls_ssl_context *ssl,
                                        unsigned char *buf,
                                        const unsigned char *end,
@@ -220,6 +223,7 @@
 #endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
 
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_cid_ext( mbedtls_ssl_context *ssl,
                               unsigned char *buf,
                               const unsigned char *end,
@@ -266,6 +270,7 @@
 #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
 
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_max_fragment_length_ext( mbedtls_ssl_context *ssl,
                                               unsigned char *buf,
                                               const unsigned char *end,
@@ -298,6 +303,7 @@
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_encrypt_then_mac_ext( mbedtls_ssl_context *ssl,
                                            unsigned char *buf,
                                            const unsigned char *end,
@@ -328,6 +334,7 @@
 #endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */
 
 #if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_extended_ms_ext( mbedtls_ssl_context *ssl,
                                       unsigned char *buf,
                                       const unsigned char *end,
@@ -358,6 +365,7 @@
 #endif /* MBEDTLS_SSL_EXTENDED_MASTER_SECRET */
 
 #if defined(MBEDTLS_SSL_SESSION_TICKETS)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_session_ticket_ext( mbedtls_ssl_context *ssl,
                                          unsigned char *buf,
                                          const unsigned char *end,
@@ -400,6 +408,7 @@
 #endif /* MBEDTLS_SSL_SESSION_TICKETS */
 
 #if defined(MBEDTLS_SSL_DTLS_SRTP)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_use_srtp_ext( mbedtls_ssl_context *ssl,
                                    unsigned char *buf,
                                    const unsigned char *end,
@@ -629,6 +638,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_renegotiation_info( mbedtls_ssl_context *ssl,
                                          const unsigned char *buf,
                                          size_t len )
@@ -673,6 +683,7 @@
 }
 
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_max_fragment_length_ext( mbedtls_ssl_context *ssl,
                                               const unsigned char *buf,
                                               size_t len )
@@ -699,6 +710,7 @@
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_cid_ext( mbedtls_ssl_context *ssl,
                               const unsigned char *buf,
                               size_t len )
@@ -755,6 +767,7 @@
 #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
 
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_encrypt_then_mac_ext( mbedtls_ssl_context *ssl,
                                          const unsigned char *buf,
                                          size_t len )
@@ -780,6 +793,7 @@
 #endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */
 
 #if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_extended_ms_ext( mbedtls_ssl_context *ssl,
                                          const unsigned char *buf,
                                          size_t len )
@@ -805,6 +819,7 @@
 #endif /* MBEDTLS_SSL_EXTENDED_MASTER_SECRET */
 
 #if defined(MBEDTLS_SSL_SESSION_TICKETS)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_session_ticket_ext( mbedtls_ssl_context *ssl,
                                          const unsigned char *buf,
                                          size_t len )
@@ -831,6 +846,7 @@
 
 #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
     defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_supported_point_formats_ext( mbedtls_ssl_context *ssl,
                                                   const unsigned char *buf,
                                                   size_t len )
@@ -879,6 +895,7 @@
           MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
 
 #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_ecjpake_kkpp( mbedtls_ssl_context *ssl,
                                    const unsigned char *buf,
                                    size_t len )
@@ -913,6 +930,7 @@
 #endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
 
 #if defined(MBEDTLS_SSL_ALPN)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_alpn_ext( mbedtls_ssl_context *ssl,
                                const unsigned char *buf, size_t len )
 {
@@ -983,6 +1001,7 @@
 #endif /* MBEDTLS_SSL_ALPN */
 
 #if defined(MBEDTLS_SSL_DTLS_SRTP)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_use_srtp_ext( mbedtls_ssl_context *ssl,
                                    const unsigned char *buf,
                                    size_t len )
@@ -1103,6 +1122,7 @@
  * Parse HelloVerifyRequest.  Only called after verifying the HS type.
  */
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_hello_verify_request( mbedtls_ssl_context *ssl )
 {
     const unsigned char *p = ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl );
@@ -1184,6 +1204,7 @@
 }
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_server_hello( mbedtls_ssl_context *ssl )
 {
     int ret, i;
@@ -1716,6 +1737,7 @@
 
 #if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED) ||                       \
     defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_server_dh_params( mbedtls_ssl_context *ssl,
                                        unsigned char **p,
                                        unsigned char *end )
@@ -1761,6 +1783,7 @@
     defined(MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED) ||     \
     defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_server_ecdh_params( mbedtls_ssl_context *ssl,
                                              unsigned char **p,
                                              unsigned char *end )
@@ -1825,6 +1848,7 @@
     return( 0 );
 }
 #else
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_check_server_ecdh_params( const mbedtls_ssl_context *ssl )
 {
     const mbedtls_ecp_curve_info *curve_info;
@@ -1853,6 +1877,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_server_ecdh_params( mbedtls_ssl_context *ssl,
                                          unsigned char **p,
                                          unsigned char *end )
@@ -1893,6 +1918,7 @@
           MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED */
 
 #if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_server_psk_hint( mbedtls_ssl_context *ssl,
                                       unsigned char **p,
                                       unsigned char *end )
@@ -1939,6 +1965,7 @@
 /*
  * Generate a pre-master secret and encrypt it with the server's RSA key
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_encrypted_pms( mbedtls_ssl_context *ssl,
                                     size_t offset, size_t *olen,
                                     size_t pms_offset )
@@ -2021,6 +2048,7 @@
 #if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED) ||                       \
     defined(MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||                     \
     defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_signature_algorithm( mbedtls_ssl_context *ssl,
                                           unsigned char **p,
                                           unsigned char *end,
@@ -2079,6 +2107,7 @@
 
 #if defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) || \
     defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_get_ecdh_params_from_cert( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -2097,6 +2126,8 @@
     peer_pk = &ssl->session_negotiate->peer_cert->pk;
 #endif /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
 
+    /* This is a public key, so it can't be opaque, so can_do() is a good
+     * enough check to ensure pk_ec() is safe to use below. */
     if( ! mbedtls_pk_can_do( peer_pk, MBEDTLS_PK_ECKEY ) )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "server key not ECDH capable" ) );
@@ -2166,6 +2197,7 @@
 #endif /* MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) ||
           MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_server_key_exchange( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -2513,6 +2545,7 @@
 }
 
 #if ! defined(MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_certificate_request( mbedtls_ssl_context *ssl )
 {
     const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
@@ -2531,6 +2564,7 @@
     return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
 }
 #else /* MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_certificate_request( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -2734,6 +2768,7 @@
 }
 #endif /* MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_server_hello_done( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -2773,6 +2808,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_client_key_exchange( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -3295,6 +3331,7 @@
 }
 
 #if !defined(MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_certificate_verify( mbedtls_ssl_context *ssl )
 {
     const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
@@ -3320,6 +3357,7 @@
     return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
 }
 #else /* !MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_certificate_verify( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
@@ -3459,6 +3497,7 @@
 #endif /* MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
 
 #if defined(MBEDTLS_SSL_SESSION_TICKETS)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_new_session_ticket( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
diff --git a/library/ssl_tls12_server.c b/library/ssl_tls12_server.c
index 4ab3db5..bfe3e8e 100644
--- a/library/ssl_tls12_server.c
+++ b/library/ssl_tls12_server.c
@@ -78,6 +78,7 @@
 #endif /* MBEDTLS_SSL_DTLS_HELLO_VERIFY */
 
 #if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_conf_has_psk_or_cb( mbedtls_ssl_config const *conf )
 {
     if( conf->f_psk != NULL )
@@ -99,6 +100,7 @@
 }
 #endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_renegotiation_info( mbedtls_ssl_context *ssl,
                                          const unsigned char *buf,
                                          size_t len )
@@ -176,6 +178,7 @@
  *
  * DHE groups are not supported yet.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_supported_groups_ext( mbedtls_ssl_context *ssl,
                                            const unsigned char *buf,
                                            size_t len )
@@ -242,6 +245,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_supported_point_formats( mbedtls_ssl_context *ssl,
                                               const unsigned char *buf,
                                               size_t len )
@@ -287,6 +291,7 @@
           MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
 
 #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_ecjpake_kkpp( mbedtls_ssl_context *ssl,
                                    const unsigned char *buf,
                                    size_t len )
@@ -316,6 +321,7 @@
 #endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
 
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_max_fragment_length_ext( mbedtls_ssl_context *ssl,
                                               const unsigned char *buf,
                                               size_t len )
@@ -335,6 +341,7 @@
 #endif /* MBEDTLS_SSL_MAX_FRAGMENT_LENGTH */
 
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_cid_ext( mbedtls_ssl_context *ssl,
                               const unsigned char *buf,
                               size_t len )
@@ -407,6 +414,7 @@
 #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
 
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_encrypt_then_mac_ext( mbedtls_ssl_context *ssl,
                                       const unsigned char *buf,
                                       size_t len )
@@ -431,6 +439,7 @@
 #endif /* MBEDTLS_SSL_ENCRYPT_THEN_MAC */
 
 #if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_extended_ms_ext( mbedtls_ssl_context *ssl,
                                       const unsigned char *buf,
                                       size_t len )
@@ -455,6 +464,7 @@
 #endif /* MBEDTLS_SSL_EXTENDED_MASTER_SECRET */
 
 #if defined(MBEDTLS_SSL_SESSION_TICKETS)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_session_ticket_ext( mbedtls_ssl_context *ssl,
                                          unsigned char *buf,
                                          size_t len )
@@ -529,6 +539,7 @@
 #endif /* MBEDTLS_SSL_SESSION_TICKETS */
 
 #if defined(MBEDTLS_SSL_DTLS_SRTP)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_use_srtp_ext( mbedtls_ssl_context *ssl,
                                    const unsigned char *buf,
                                    size_t len )
@@ -657,6 +668,7 @@
  * Return 0 if the given key uses one of the acceptable curves, -1 otherwise
  */
 #if defined(MBEDTLS_ECDSA_C)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_check_key_curve( mbedtls_pk_context *pk,
                                 const mbedtls_ecp_curve_info **curves )
 {
@@ -678,6 +690,7 @@
  * Try picking a certificate for this ciphersuite,
  * return 0 on success and -1 on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_pick_cert( mbedtls_ssl_context *ssl,
                           const mbedtls_ssl_ciphersuite_t * ciphersuite_info )
 {
@@ -784,6 +797,7 @@
  * Check if a given ciphersuite is suitable for use with our config/keys/etc
  * Sets ciphersuite_info only if the suite matches.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_ciphersuite_match( mbedtls_ssl_context *ssl, int suite_id,
                                   const mbedtls_ssl_ciphersuite_t **ciphersuite_info )
 {
@@ -881,6 +895,7 @@
 /* This function doesn't alert on errors that happen early during
    ClientHello parsing because they might indicate that the client is
    not talking SSL/TLS at all and would not understand our alert. */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_client_hello( mbedtls_ssl_context *ssl )
 {
     int ret, got_common_suite;
@@ -1049,16 +1064,29 @@
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
         return( MBEDTLS_ERR_SSL_UNEXPECTED_MESSAGE );
     }
-
-    MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, handshake len.: %d",
-                   ( buf[1] << 16 ) | ( buf[2] << 8 ) | buf[3] ) );
-
-    /* We don't support fragmentation of ClientHello (yet?) */
-    if( buf[1] != 0 ||
-        msg_len != mbedtls_ssl_hs_hdr_len( ssl ) + ( ( buf[2] << 8 ) | buf[3] ) )
     {
-        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
-        return( MBEDTLS_ERR_SSL_DECODE_ERROR );
+        size_t handshake_len = MBEDTLS_GET_UINT24_BE( buf, 1 );
+        MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello v3, handshake len.: %u",
+                       ( unsigned ) handshake_len ) );
+
+        /* The record layer has a record size limit of 2^14 - 1 and
+         * fragmentation is not supported, so buf[1] should be zero. */
+        if( buf[1] != 0 )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message: %u != 0",
+                                        (unsigned) buf[1] ) );
+            return( MBEDTLS_ERR_SSL_DECODE_ERROR );
+        }
+
+        /* We don't support fragmentation of ClientHello (yet?) */
+        if( msg_len != mbedtls_ssl_hs_hdr_len( ssl ) + handshake_len )
+        {
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message: %u != %u + %u",
+                                    (unsigned) msg_len,
+                                    (unsigned) mbedtls_ssl_hs_hdr_len( ssl ),
+                                    (unsigned) handshake_len ) );
+            return( MBEDTLS_ERR_SSL_DECODE_ERROR );
+        }
     }
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
@@ -1093,16 +1121,24 @@
             ssl->handshake->out_msg_seq = cli_msg_seq;
             ssl->handshake->in_msg_seq  = cli_msg_seq + 1;
         }
-
-        /*
-         * For now we don't support fragmentation, so make sure
-         * fragment_offset == 0 and fragment_length == length
-         */
-        if( ssl->in_msg[6] != 0 || ssl->in_msg[7] != 0 || ssl->in_msg[8] != 0 ||
-            memcmp( ssl->in_msg + 1, ssl->in_msg + 9, 3 ) != 0 )
         {
-            MBEDTLS_SSL_DEBUG_MSG( 1, ( "ClientHello fragmentation not supported" ) );
-            return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
+            /*
+             * For now we don't support fragmentation, so make sure
+             * fragment_offset == 0 and fragment_length == length
+             */
+            size_t fragment_offset, fragment_length, length;
+            fragment_offset = MBEDTLS_GET_UINT24_BE( ssl->in_msg, 6 );
+            fragment_length = MBEDTLS_GET_UINT24_BE( ssl->in_msg, 9 );
+            length = MBEDTLS_GET_UINT24_BE( ssl->in_msg, 1 );
+            MBEDTLS_SSL_DEBUG_MSG(
+                4, ( "fragment_offset=%u fragment_length=%u length=%u",
+                     (unsigned) fragment_offset, (unsigned) fragment_length,
+                     (unsigned) length ) );
+            if( fragment_offset != 0 || length != fragment_length )
+            {
+                MBEDTLS_SSL_DEBUG_MSG( 1, ( "ClientHello fragmentation not supported" ) );
+                return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
+            }
         }
     }
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
@@ -2045,6 +2081,7 @@
 #endif /* MBEDTLS_SSL_DTLS_SRTP */
 
 #if defined(MBEDTLS_SSL_DTLS_HELLO_VERIFY)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_hello_verify_request( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -2163,6 +2200,7 @@
     mbedtls_ssl_session_free( &session_tmp );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_server_hello( mbedtls_ssl_context *ssl )
 {
 #if defined(MBEDTLS_HAVE_TIME)
@@ -2379,6 +2417,7 @@
 }
 
 #if !defined(MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_certificate_request( mbedtls_ssl_context *ssl )
 {
     const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
@@ -2397,6 +2436,7 @@
     return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
 }
 #else /* !MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_certificate_request( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
@@ -2568,6 +2608,7 @@
 #if defined(MBEDTLS_USE_PSA_CRYPTO) &&                      \
         ( defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) || \
           defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED) )
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_get_ecdh_params_from_cert( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -2662,6 +2703,7 @@
 }
 #elif defined(MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED) || \
     defined(MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_get_ecdh_params_from_cert( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -2694,6 +2736,7 @@
 
 #if defined(MBEDTLS_KEY_EXCHANGE_WITH_SERVER_SIGNATURE_ENABLED) && \
     defined(MBEDTLS_SSL_ASYNC_PRIVATE)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_resume_server_key_exchange( mbedtls_ssl_context *ssl,
                                            size_t *signature_len )
 {
@@ -2721,6 +2764,7 @@
 /* Prepare the ServerKeyExchange message, up to and including
  * calculating the signature if any, but excluding formatting the
  * signature and sending the message. */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_prepare_server_key_exchange( mbedtls_ssl_context *ssl,
                                             size_t *signature_len )
 {
@@ -3148,6 +3192,7 @@
  * that do not include a ServerKeyExchange message, do nothing. Either
  * way, if successful, move on to the next step in the SSL state
  * machine. */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_server_key_exchange( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -3169,7 +3214,12 @@
 #if defined(MBEDTLS_KEY_EXCHANGE_SOME_ECDH_ENABLED)
         if( mbedtls_ssl_ciphersuite_uses_ecdh( ciphersuite_info ) )
         {
-            ssl_get_ecdh_params_from_cert( ssl );
+            ret = ssl_get_ecdh_params_from_cert( ssl );
+            if( ret != 0 )
+            {
+                MBEDTLS_SSL_DEBUG_RET( 1, "ssl_get_ecdh_params_from_cert", ret );
+                return( ret );
+            }
         }
 #endif /* MBEDTLS_KEY_EXCHANGE_SOME_ECDH_ENABLED */
 
@@ -3245,6 +3295,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_server_hello_done( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -3284,6 +3335,7 @@
 
 #if defined(MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED) ||                       \
     defined(MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_client_dh_public( mbedtls_ssl_context *ssl, unsigned char **p,
                                        const unsigned char *end )
 {
@@ -3327,6 +3379,7 @@
     defined(MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED)
 
 #if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_resume_decrypt_pms( mbedtls_ssl_context *ssl,
                                    unsigned char *peer_pms,
                                    size_t *peer_pmslen,
@@ -3344,6 +3397,7 @@
 }
 #endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_decrypt_encrypted_pms( mbedtls_ssl_context *ssl,
                                       const unsigned char *p,
                                       const unsigned char *end,
@@ -3429,6 +3483,7 @@
     return( ret );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_encrypted_pms( mbedtls_ssl_context *ssl,
                                     const unsigned char *p,
                                     const unsigned char *end,
@@ -3517,6 +3572,7 @@
           MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED */
 
 #if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_client_psk_identity( mbedtls_ssl_context *ssl, unsigned char **p,
                                           const unsigned char *end )
 {
@@ -3577,6 +3633,7 @@
 }
 #endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_client_key_exchange( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -4014,6 +4071,7 @@
 }
 
 #if !defined(MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_certificate_verify( mbedtls_ssl_context *ssl )
 {
     const mbedtls_ssl_ciphersuite_t *ciphersuite_info =
@@ -4032,6 +4090,7 @@
     return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
 }
 #else /* !MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_parse_certificate_verify( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
@@ -4195,6 +4254,7 @@
 #endif /* MBEDTLS_KEY_EXCHANGE_CERT_REQ_ALLOWED_ENABLED */
 
 #if defined(MBEDTLS_SSL_SESSION_TICKETS)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_write_new_session_ticket( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index 416316b..2b68306 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -42,6 +42,7 @@
  *      ProtocolVersion versions<2..254>;
  * } SupportedVersions;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_supported_versions_ext( mbedtls_ssl_context *ssl,
                                                    unsigned char *buf,
                                                    unsigned char *end,
@@ -91,6 +92,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_supported_versions_ext( mbedtls_ssl_context *ssl,
                                                    const unsigned char *buf,
                                                    const unsigned char *end )
@@ -120,6 +122,7 @@
 }
 
 #if defined(MBEDTLS_SSL_ALPN)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_alpn_ext( mbedtls_ssl_context *ssl,
                                      const unsigned char *buf, size_t len )
 {
@@ -168,6 +171,7 @@
 }
 #endif /* MBEDTLS_SSL_ALPN */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_reset_key_share( mbedtls_ssl_context *ssl )
 {
     uint16_t group_id = ssl->handshake->offered_group_id;
@@ -206,6 +210,7 @@
 /*
  * Functions for writing key_share extension.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_get_default_group_id( mbedtls_ssl_context *ssl,
                                            uint16_t *group_id )
 {
@@ -255,6 +260,7 @@
  *          KeyShareEntry client_shares<0..2^16-1>;
  *      } KeyShareClientHello;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_key_share_ext( mbedtls_ssl_context *ssl,
                                           unsigned char *buf,
                                           unsigned char *end,
@@ -368,6 +374,7 @@
  *        NamedGroup selected_group;
  * } KeyShareHelloRetryRequest;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_hrr_key_share_ext( mbedtls_ssl_context *ssl,
                                               const unsigned char *buf,
                                               const unsigned char *end )
@@ -442,6 +449,7 @@
  *        opaque key_exchange<1..2^16-1>;
  * } KeyShareEntry;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_key_share_ext( mbedtls_ssl_context *ssl,
                                           const unsigned char *buf,
                                           const unsigned char *end )
@@ -516,6 +524,7 @@
  * a "cookie" extension in the new ClientHello.  Clients MUST NOT use
  * cookies in their initial ClientHello in subsequent connections.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_cookie_ext( mbedtls_ssl_context *ssl,
                                        const unsigned char *buf,
                                        const unsigned char *end )
@@ -549,6 +558,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_cookie_ext( mbedtls_ssl_context *ssl,
                                        unsigned char *buf,
                                        unsigned char *end,
@@ -642,6 +652,7 @@
  * \return 1 if the ServerHello contains a supported_versions extension
  * \return A negative value if an error occurred while parsing the ServerHello.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_is_supported_versions_ext_present(
     mbedtls_ssl_context *ssl,
     const unsigned char *buf,
@@ -717,6 +728,7 @@
  *     the server is TLS 1.3 capable but negotiating TLS 1.2 or below.
  * - 0 otherwise
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_is_downgrade_negotiation( mbedtls_ssl_context *ssl,
                                                const unsigned char *buf,
                                                const unsigned char *end )
@@ -749,6 +761,7 @@
  */
 #define SSL_SERVER_HELLO 0
 #define SSL_SERVER_HELLO_HRR 1
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_server_hello_is_hrr( mbedtls_ssl_context *ssl,
                                     const unsigned char *buf,
                                     const unsigned char *end )
@@ -788,6 +801,7 @@
  * - SSL_SERVER_HELLO_TLS1_2
  */
 #define SSL_SERVER_HELLO_TLS1_2 2
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_preprocess_server_hello( mbedtls_ssl_context *ssl,
                                               const unsigned char *buf,
                                               const unsigned char *end )
@@ -878,6 +892,7 @@
     return( ret );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_check_server_hello_session_id_echo( mbedtls_ssl_context *ssl,
                                                          const unsigned char **buf,
                                                          const unsigned char *end )
@@ -925,6 +940,7 @@
  *    Extension extensions<6..2^16-1>;
  * } ServerHello;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_server_hello( mbedtls_ssl_context *ssl,
                                          const unsigned char *buf,
                                          const unsigned char *end,
@@ -1183,6 +1199,7 @@
     return( ret );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_postprocess_server_hello( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1258,6 +1275,7 @@
     return( ret );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_postprocess_hrr( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1281,6 +1299,7 @@
  * Wait and parse ServerHello handshake message.
  * Handler for MBEDTLS_SSL_SERVER_HELLO
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_process_server_hello( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1355,6 +1374,7 @@
  *     Extension extensions<0..2^16-1>;
  * } EncryptedExtensions;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_encrypted_extensions( mbedtls_ssl_context *ssl,
                                                  const unsigned char *buf,
                                                  const unsigned char *end )
@@ -1436,6 +1456,7 @@
     return( ret );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_process_encrypted_extensions( mbedtls_ssl_context *ssl )
 {
     int ret;
@@ -1486,6 +1507,7 @@
  * - SSL_CERTIFICATE_REQUEST_SKIP
  * indicating if a Certificate Request is expected or not.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_certificate_request_coordinate( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1523,6 +1545,7 @@
  *   Extension extensions<2..2^16-1>;
  * } CertificateRequest;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_certificate_request( mbedtls_ssl_context *ssl,
                                                 const unsigned char *buf,
                                                 const unsigned char *end )
@@ -1639,6 +1662,7 @@
 /*
  * Handler for  MBEDTLS_SSL_CERTIFICATE_REQUEST
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_process_certificate_request( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1684,6 +1708,7 @@
 /*
  * Handler for MBEDTLS_SSL_SERVER_CERTIFICATE
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_process_server_certificate( mbedtls_ssl_context *ssl )
 {
     int ret;
@@ -1699,6 +1724,7 @@
 /*
  * Handler for MBEDTLS_SSL_CERTIFICATE_VERIFY
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_process_certificate_verify( mbedtls_ssl_context *ssl )
 {
     int ret;
@@ -1715,6 +1741,7 @@
 /*
  * Handler for MBEDTLS_SSL_SERVER_FINISHED
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_process_server_finished( mbedtls_ssl_context *ssl )
 {
     int ret;
@@ -1746,6 +1773,7 @@
 /*
  * Handler for MBEDTLS_SSL_CLIENT_CERTIFICATE
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_client_certificate( mbedtls_ssl_context *ssl )
 {
     int non_empty_certificate_msg = 0;
@@ -1788,6 +1816,7 @@
 /*
  * Handler for MBEDTLS_SSL_CLIENT_CERTIFICATE_VERIFY
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_client_certificate_verify( mbedtls_ssl_context *ssl )
 {
     int ret = mbedtls_ssl_tls13_write_certificate_verify( ssl );
@@ -1802,6 +1831,7 @@
 /*
  * Handler for MBEDTLS_SSL_CLIENT_FINISHED
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_client_finished( mbedtls_ssl_context *ssl )
 {
     int ret;
@@ -1825,6 +1855,7 @@
 /*
  * Handler for MBEDTLS_SSL_FLUSH_BUFFERS
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_flush_buffers( mbedtls_ssl_context *ssl )
 {
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "handshake: done" ) );
@@ -1835,6 +1866,7 @@
 /*
  * Handler for MBEDTLS_SSL_HANDSHAKE_WRAPUP
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_handshake_wrapup( mbedtls_ssl_context *ssl )
 {
 
diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 8ec9f90..265d6d3 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -31,6 +31,7 @@
 #include <string.h>
 
 #include "ssl_misc.h"
+#include "ssl_tls13_invasive.h"
 #include "ssl_tls13_keys.h"
 #include "ssl_debug_helpers.h"
 
@@ -156,6 +157,7 @@
     *verify_buffer_len = idx;
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_certificate_verify( mbedtls_ssl_context *ssl,
                                                const unsigned char *buf,
                                                const unsigned char *end,
@@ -385,9 +387,11 @@
  */
 
 /* Parse certificate chain send by the server. */
-static int ssl_tls13_parse_certificate( mbedtls_ssl_context *ssl,
-                                        const unsigned char *buf,
-                                        const unsigned char *end )
+MBEDTLS_CHECK_RETURN_CRITICAL
+MBEDTLS_STATIC_TESTABLE
+int mbedtls_ssl_tls13_parse_certificate( mbedtls_ssl_context *ssl,
+                                         const unsigned char *buf,
+                                         const unsigned char *end )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     size_t certificate_request_context_len = 0;
@@ -438,6 +442,7 @@
 
     mbedtls_x509_crt_init( ssl->session_negotiate->peer_cert );
 
+    MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, certificate_list_len );
     certificate_list_end = p + certificate_list_len;
     while( p < certificate_list_end )
     {
@@ -517,9 +522,11 @@
     return( ret );
 }
 #else
-static int ssl_tls13_parse_certificate( mbedtls_ssl_context *ssl,
-                                        const unsigned char *buf,
-                                        const unsigned char *end )
+MBEDTLS_CHECK_RETURN_CRITICAL
+MBEDTLS_STATIC_TESTABLE
+int mbedtls_ssl_tls13_parse_certificate( mbedtls_ssl_context *ssl,
+                                         const unsigned char *buf,
+                                         const unsigned char *end )
 {
     ((void) ssl);
     ((void) buf);
@@ -532,12 +539,15 @@
 #if defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
 #if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
 /* Validate certificate chain sent by the server. */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_validate_certificate( mbedtls_ssl_context *ssl )
 {
     int ret = 0;
     int authmode = MBEDTLS_SSL_VERIFY_REQUIRED;
     mbedtls_x509_crt *ca_chain;
     mbedtls_x509_crl *ca_crl;
+    const char *ext_oid;
+    size_t ext_len;
     uint32_t verify_result = 0;
 
     /* If SNI was used, overwrite authentication mode
@@ -626,12 +636,25 @@
     /*
      * Secondary checks: always done, but change 'ret' only if it was 0
      */
-    if( mbedtls_ssl_check_cert_usage( ssl->session_negotiate->peer_cert,
-                                      ssl->handshake->ciphersuite_info,
-                                      !ssl->conf->endpoint,
-                                      &verify_result ) != 0 )
+    if( ssl->conf->endpoint == MBEDTLS_SSL_IS_CLIENT )
     {
-        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate ( usage extensions )" ) );
+        ext_oid = MBEDTLS_OID_SERVER_AUTH;
+        ext_len = MBEDTLS_OID_SIZE( MBEDTLS_OID_SERVER_AUTH );
+    }
+    else
+    {
+        ext_oid = MBEDTLS_OID_CLIENT_AUTH;
+        ext_len = MBEDTLS_OID_SIZE( MBEDTLS_OID_CLIENT_AUTH );
+    }
+
+    if( ( mbedtls_x509_crt_check_key_usage(
+              ssl->session_negotiate->peer_cert,
+              MBEDTLS_X509_KU_DIGITAL_SIGNATURE ) != 0 ) ||
+        ( mbedtls_x509_crt_check_extended_key_usage(
+              ssl->session_negotiate->peer_cert,
+              ext_oid, ext_len ) != 0 ) )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad certificate (usage extensions)" ) );
         if( ret == 0 )
             ret = MBEDTLS_ERR_SSL_BAD_CERTIFICATE;
     }
@@ -641,7 +664,8 @@
      * with details encoded in the verification flags. All other kinds
      * of error codes, including those from the user provided f_vrfy
      * functions, are treated as fatal and lead to a failure of
-     * ssl_tls13_parse_certificate even if verification was optional. */
+     * mbedtls_ssl_tls13_parse_certificate even if verification was optional.
+     */
     if( authmode == MBEDTLS_SSL_VERIFY_OPTIONAL &&
         ( ret == MBEDTLS_ERR_X509_CERT_VERIFY_FAILED ||
           ret == MBEDTLS_ERR_SSL_BAD_CERTIFICATE ) )
@@ -696,6 +720,7 @@
     return( ret );
 }
 #else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_validate_certificate( mbedtls_ssl_context *ssl )
 {
     ((void) ssl);
@@ -718,8 +743,8 @@
                           &buf, &buf_len ) );
 
     /* Parse the certificate chain sent by the peer. */
-    MBEDTLS_SSL_PROC_CHK( ssl_tls13_parse_certificate( ssl, buf,
-                                                       buf + buf_len ) );
+    MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_tls13_parse_certificate( ssl, buf,
+                                                               buf + buf_len ) );
     /* Validate the certificate chain and set the verification results. */
     MBEDTLS_SSL_PROC_CHK( ssl_tls13_validate_certificate( ssl ) );
 
@@ -757,6 +782,7 @@
  *        CertificateEntry certificate_list<0..2^24-1>;
  *    } Certificate;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_certificate_body( mbedtls_ssl_context *ssl,
                                              unsigned char *buf,
                                              unsigned char *end,
@@ -850,7 +876,6 @@
 /*
  * STATE HANDLING: Output Certificate Verify
  */
-
 int mbedtls_ssl_tls13_check_sig_alg_cert_key_match( uint16_t sig_alg,
                                                     mbedtls_pk_context *key )
 {
@@ -902,6 +927,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_select_sig_alg_for_certificate_verify(
                                           mbedtls_ssl_context *ssl,
                                           mbedtls_pk_context *own_key,
@@ -931,6 +957,7 @@
     return( -1 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_certificate_verify_body( mbedtls_ssl_context *ssl,
                                                     unsigned char *buf,
                                                     unsigned char *end,
@@ -1080,6 +1107,7 @@
  * Implementation
  */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_preprocess_finished_message( mbedtls_ssl_context *ssl )
 {
     int ret;
@@ -1099,6 +1127,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_finished_message( mbedtls_ssl_context *ssl,
                                              const unsigned char *buf,
                                              const unsigned char *end )
@@ -1177,6 +1206,7 @@
  * Implement
  */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_prepare_finished_message( mbedtls_ssl_context *ssl )
 {
     int ret;
@@ -1197,6 +1227,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_finished_message_body( mbedtls_ssl_context *ssl,
                                                   unsigned char *buf,
                                                   unsigned char *end,
@@ -1276,6 +1307,7 @@
  *
  */
 #if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_change_cipher_spec_body( mbedtls_ssl_context *ssl,
                                                     unsigned char *buf,
                                                     unsigned char *end,
diff --git a/library/ssl_tls13_invasive.h b/library/ssl_tls13_invasive.h
index f874a88..5470200 100644
--- a/library/ssl_tls13_invasive.h
+++ b/library/ssl_tls13_invasive.h
@@ -25,7 +25,9 @@
 #include "psa/crypto.h"
 
 #if defined(MBEDTLS_TEST_HOOKS)
-
+int mbedtls_ssl_tls13_parse_certificate( mbedtls_ssl_context *ssl,
+                                         const unsigned char *buf,
+                                         const unsigned char *end );
 #endif /* MBEDTLS_TEST_HOOKS */
 
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index d4a8e46..51743bb 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -644,6 +644,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_calc_finished_core( psa_algorithm_t hash_alg,
                                          unsigned char const *base_key,
                                          unsigned char const *transcript,
@@ -1071,6 +1072,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int mbedtls_ssl_tls13_get_cipher_key_info(
                     const mbedtls_ssl_ciphersuite_t *ciphersuite_info,
                     size_t *key_len, size_t *iv_len )
diff --git a/library/ssl_tls13_keys.h b/library/ssl_tls13_keys.h
index 693b6c4..76c1e93 100644
--- a/library/ssl_tls13_keys.h
+++ b/library/ssl_tls13_keys.h
@@ -121,6 +121,7 @@
  * \return           A negative error code on failure.
  */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_hkdf_expand_label(
                      psa_algorithm_t hash_alg,
                      const unsigned char *secret, size_t secret_len,
@@ -159,6 +160,7 @@
  * \returns             A negative error code on failure.
  */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_make_traffic_keys(
                      psa_algorithm_t hash_alg,
                      const unsigned char *client_secret,
@@ -205,6 +207,7 @@
  * \returns        \c 0 on success.
  * \returns        A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_derive_secret(
                    psa_algorithm_t hash_alg,
                    const unsigned char *secret, size_t secret_len,
@@ -255,6 +258,7 @@
  * \returns        \c 0 on success.
  * \returns        A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_derive_early_secrets(
           psa_algorithm_t hash_alg,
           unsigned char const *early_secret,
@@ -300,6 +304,7 @@
  * \returns        \c 0 on success.
  * \returns        A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_derive_handshake_secrets(
           psa_algorithm_t hash_alg,
           unsigned char const *handshake_secret,
@@ -350,6 +355,7 @@
  * \returns        \c 0 on success.
  * \returns        A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_derive_application_secrets(
           psa_algorithm_t hash_alg,
           unsigned char const *master_secret,
@@ -380,6 +386,7 @@
  * \returns        \c 0 on success.
  * \returns        A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_derive_resumption_master_secret(
           psa_algorithm_t hash_alg,
           unsigned char const *application_secret,
@@ -453,6 +460,7 @@
  * \returns           A negative error code on failure.
  */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_evolve_secret(
                    psa_algorithm_t hash_alg,
                    const unsigned char *secret_old,
@@ -482,6 +490,7 @@
  * \returns           \c 0 on success.
  * \returns           A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_create_psk_binder( mbedtls_ssl_context *ssl,
                                const psa_algorithm_t hash_alg,
                                unsigned char const *psk, size_t psk_len,
@@ -516,6 +525,7 @@
  *                     mbedtls_ssl_transform_encrypt().
  * \return             A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_populate_transform( mbedtls_ssl_transform *transform,
                                           int endpoint,
                                           int ciphersuite,
@@ -542,6 +552,7 @@
  * \returns    \c 0 on success.
  * \returns    A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_key_schedule_stage_early( mbedtls_ssl_context *ssl );
 
 /**
@@ -560,6 +571,7 @@
  * \returns    \c 0 on success.
  * \returns    A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_key_schedule_stage_handshake( mbedtls_ssl_context *ssl );
 
 /**
@@ -574,6 +586,7 @@
  * \returns    \c 0 on success.
  * \returns    A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_generate_handshake_keys( mbedtls_ssl_context *ssl,
                                                mbedtls_ssl_key_set *traffic_keys );
 
@@ -593,6 +606,7 @@
  * \returns    \c 0 on success.
  * \returns    A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_key_schedule_stage_application( mbedtls_ssl_context *ssl );
 
 /**
@@ -607,6 +621,7 @@
  * \returns    \c 0 on success.
  * \returns    A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_generate_application_keys(
     mbedtls_ssl_context* ssl, mbedtls_ssl_key_set *traffic_keys );
 
@@ -620,6 +635,7 @@
  * \returns    \c 0 on success.
  * \returns    A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_generate_resumption_master_secret(
     mbedtls_ssl_context *ssl );
 
@@ -645,6 +661,7 @@
  * \returns    \c 0 on success.
  * \returns    A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_calculate_verify_data( mbedtls_ssl_context *ssl,
                                              unsigned char *dst,
                                              size_t dst_len,
@@ -660,6 +677,7 @@
  * \returns    \c 0 on success.
  * \returns    A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_compute_handshake_transform( mbedtls_ssl_context *ssl );
 
 /**
@@ -671,6 +689,7 @@
  * \returns    \c 0 on success.
  * \returns    A negative error code on failure.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 int mbedtls_ssl_tls13_compute_application_transform( mbedtls_ssl_context *ssl );
 
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index 144c70d..7d99433 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -50,6 +50,7 @@
  *          ProtocolVersion versions<2..254>;
  *   } SupportedVersions;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_supported_versions_ext( mbedtls_ssl_context *ssl,
                                                    const unsigned char *buf,
                                                    const unsigned char *end )
@@ -106,6 +107,7 @@
  *       NamedGroup named_group_list<2..2^16-1>;
  *   } NamedGroupList;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_supported_groups_ext( mbedtls_ssl_context *ssl,
                                                  const unsigned char *buf,
                                                  const unsigned char *end )
@@ -168,6 +170,7 @@
  *    be needed.
  *  - A negative value for fatal errors.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_key_shares_ext( mbedtls_ssl_context *ssl,
                                            const unsigned char *buf,
                                            const unsigned char *end )
@@ -313,6 +316,7 @@
 }
 #endif /* MBEDTLS_DEBUG_C */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_client_hello_has_exts( mbedtls_ssl_context *ssl,
                                             int exts_mask )
 {
@@ -320,6 +324,7 @@
     return( masked == exts_mask );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_client_hello_has_exts_for_ephemeral_key_exchange(
         mbedtls_ssl_context *ssl )
 {
@@ -329,6 +334,7 @@
                           MBEDTLS_SSL_EXT_SIG_ALG ) );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_check_ephemeral_key_exchange( mbedtls_ssl_context *ssl )
 {
     if( !mbedtls_ssl_conf_tls13_ephemeral_enabled( ssl ) )
@@ -348,6 +354,7 @@
  * Pick best ( private key, certificate chain ) pair based on the signature
  * algorithms supported by the client.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_pick_key_cert( mbedtls_ssl_context *ssl )
 {
     mbedtls_ssl_key_cert *key_cert, *key_cert_list;
@@ -463,6 +470,7 @@
 #define SSL_CLIENT_HELLO_OK           0
 #define SSL_CLIENT_HELLO_HRR_REQUIRED 1
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_parse_client_hello( mbedtls_ssl_context *ssl,
                                          const unsigned char *buf,
                                          const unsigned char *end )
@@ -804,6 +812,7 @@
 
 /* Update the handshake state machine */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_postprocess_client_hello( mbedtls_ssl_context* ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -850,6 +859,7 @@
  * Main entry point from the state machine; orchestrates the otherfunctions.
  */
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_process_client_hello( mbedtls_ssl_context *ssl )
 {
 
@@ -888,6 +898,7 @@
 /*
  * Handler for MBEDTLS_SSL_SERVER_HELLO
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_prepare_server_hello( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -923,6 +934,7 @@
  *      ProtocolVersion selected_version;
  * } SupportedVersions;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_server_hello_supported_versions_ext(
                                                 mbedtls_ssl_context *ssl,
                                                 unsigned char *buf,
@@ -960,6 +972,7 @@
 
 /* Generate and export a single key share. For hybrid KEMs, this can
  * be called multiple times with the different components of the hybrid. */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_generate_and_write_key_share( mbedtls_ssl_context *ssl,
                                                    uint16_t named_group,
                                                    unsigned char *buf,
@@ -1013,6 +1026,7 @@
  *     KeyShareEntry server_share;
  * } KeyShareServerHello;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_key_share_ext( mbedtls_ssl_context *ssl,
                                           unsigned char *buf,
                                           unsigned char *end,
@@ -1056,6 +1070,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_hrr_key_share_ext( mbedtls_ssl_context *ssl,
                                               unsigned char *buf,
                                               unsigned char *end,
@@ -1131,6 +1146,7 @@
  *        Extension extensions<6..2^16-1>;
  *    } ServerHello;
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_server_hello_body( mbedtls_ssl_context *ssl,
                                               unsigned char *buf,
                                               unsigned char *end,
@@ -1257,6 +1273,7 @@
     return( ret );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_finalize_write_server_hello( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1272,6 +1289,7 @@
     return( ret );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_server_hello( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1319,6 +1337,7 @@
 /*
  * Handler for MBEDTLS_SSL_HELLO_RETRY_REQUEST
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_prepare_hello_retry_request( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1345,6 +1364,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_hello_retry_request( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1398,6 +1418,7 @@
  * } EncryptedExtensions;
  *
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_encrypted_extensions_body( mbedtls_ssl_context *ssl,
                                                       unsigned char *buf,
                                                       unsigned char *end,
@@ -1436,6 +1457,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_encrypted_extensions( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1487,6 +1509,7 @@
  * indicating if the writing of the CertificateRequest
  * should be skipped or not.
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_certificate_request_coordinate( mbedtls_ssl_context *ssl )
 {
     int authmode;
@@ -1513,6 +1536,7 @@
  * } CertificateRequest;
  *
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_certificate_request_body( mbedtls_ssl_context *ssl,
                                                      unsigned char *buf,
                                                      const unsigned char *end,
@@ -1559,6 +1583,7 @@
     return( 0 );
 }
 
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_certificate_request( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1606,6 +1631,7 @@
 /*
  * Handler for MBEDTLS_SSL_SERVER_CERTIFICATE
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_server_certificate( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1631,6 +1657,7 @@
 /*
  * Handler for MBEDTLS_SSL_CERTIFICATE_VERIFY
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_certificate_verify( mbedtls_ssl_context *ssl )
 {
     int ret = mbedtls_ssl_tls13_write_certificate_verify( ssl );
@@ -1644,6 +1671,7 @@
 /*
  * Handler for MBEDTLS_SSL_SERVER_FINISHED
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_write_server_finished( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1679,6 +1707,7 @@
 /*
  * Handler for MBEDTLS_SSL_CLIENT_FINISHED
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_process_client_finished( mbedtls_ssl_context *ssl )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
@@ -1701,6 +1730,7 @@
 /*
  * Handler for MBEDTLS_SSL_HANDSHAKE_WRAPUP
  */
+MBEDTLS_CHECK_RETURN_CRITICAL
 static int ssl_tls13_handshake_wrapup( mbedtls_ssl_context *ssl )
 {
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "handshake: done" ) );