diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index c1a73f8..6346598 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -584,25 +584,25 @@
 #endif
 
 #if defined(MBEDTLS_SSL_PROTO_SSL3)
-static void ssl_calc_verify_ssl( mbedtls_ssl_context *, unsigned char * );
+static void ssl_calc_verify_ssl( const mbedtls_ssl_context *, unsigned char * );
 static void ssl_calc_finished_ssl( mbedtls_ssl_context *, unsigned char *, int );
 #endif
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1)
-static void ssl_calc_verify_tls( mbedtls_ssl_context *, unsigned char * );
+static void ssl_calc_verify_tls( const mbedtls_ssl_context *, unsigned char * );
 static void ssl_calc_finished_tls( mbedtls_ssl_context *, unsigned char *, int );
 #endif
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
 #if defined(MBEDTLS_SHA256_C)
 static void ssl_update_checksum_sha256( mbedtls_ssl_context *, const unsigned char *, size_t );
-static void ssl_calc_verify_tls_sha256( mbedtls_ssl_context *,unsigned char * );
+static void ssl_calc_verify_tls_sha256( const mbedtls_ssl_context *,unsigned char * );
 static void ssl_calc_finished_tls_sha256( mbedtls_ssl_context *,unsigned char *, int );
 #endif
 
 #if defined(MBEDTLS_SHA512_C)
 static void ssl_update_checksum_sha384( mbedtls_ssl_context *, const unsigned char *, size_t );
-static void ssl_calc_verify_tls_sha384( mbedtls_ssl_context *, unsigned char * );
+static void ssl_calc_verify_tls_sha384( const mbedtls_ssl_context *, unsigned char * );
 static void ssl_calc_finished_tls_sha384( mbedtls_ssl_context *, unsigned char *, int );
 #endif
 #endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
@@ -1109,7 +1109,7 @@
                                int minor_ver,
                                mbedtls_md_type_t hash_alg,
                                unsigned char *master,
-                               mbedtls_ssl_context *ssl )
+                               const mbedtls_ssl_context *ssl )
 {
     int ret;
 
@@ -1219,7 +1219,7 @@
 }
 
 #if defined(MBEDTLS_SSL_PROTO_SSL3)
-void ssl_calc_verify_ssl( mbedtls_ssl_context *ssl, unsigned char hash[36] )
+void ssl_calc_verify_ssl( const mbedtls_ssl_context *ssl, unsigned char hash[36] )
 {
     mbedtls_md5_context md5;
     mbedtls_sha1_context sha1;
@@ -1268,7 +1268,7 @@
 #endif /* MBEDTLS_SSL_PROTO_SSL3 */
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1)
-void ssl_calc_verify_tls( mbedtls_ssl_context *ssl, unsigned char hash[36] )
+void ssl_calc_verify_tls( const mbedtls_ssl_context *ssl, unsigned char hash[36] )
 {
     mbedtls_md5_context md5;
     mbedtls_sha1_context sha1;
@@ -1296,7 +1296,7 @@
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
 #if defined(MBEDTLS_SHA256_C)
-void ssl_calc_verify_tls_sha256( mbedtls_ssl_context *ssl, unsigned char hash[32] )
+void ssl_calc_verify_tls_sha256( const mbedtls_ssl_context *ssl, unsigned char hash[32] )
 {
     mbedtls_sha256_context sha256;
 
@@ -1317,7 +1317,7 @@
 #endif /* MBEDTLS_SHA256_C */
 
 #if defined(MBEDTLS_SHA512_C)
-void ssl_calc_verify_tls_sha384( mbedtls_ssl_context *ssl, unsigned char hash[48] )
+void ssl_calc_verify_tls_sha384( const mbedtls_ssl_context *ssl, unsigned char hash[48] )
 {
     mbedtls_sha512_context sha512;