diff --git a/CMakeLists.txt b/CMakeLists.txt
index 746b38a..39808f9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -185,7 +185,10 @@
 
 add_subdirectory(library)
 add_subdirectory(include)
-add_subdirectory(tinycrypt)
+
+if(USE_TINYCRYPT)
+    add_subdirectory(tinycrypt)
+endif()
 
 if(ENABLE_PROGRAMS)
     add_subdirectory(programs)
diff --git a/include/mbedtls/hmac_drbg.h b/include/mbedtls/hmac_drbg.h
index ed03854..f38337a 100644
--- a/include/mbedtls/hmac_drbg.h
+++ b/include/mbedtls/hmac_drbg.h
@@ -70,8 +70,8 @@
 
 /* \} name SECTION: Module settings */
 
-#define MBEDTLS_HMAC_DRBG_PR_OFF   0   /**< No prediction resistance       */
-#define MBEDTLS_HMAC_DRBG_PR_ON    1   /**< Prediction resistance enabled  */
+#define MBEDTLS_HMAC_DRBG_PR_OFF   0x55555555   /**< No prediction resistance       */
+#define MBEDTLS_HMAC_DRBG_PR_ON    0x2AAAAAAA   /**< Prediction resistance enabled  */
 
 #ifdef __cplusplus
 extern "C" {
@@ -202,7 +202,8 @@
  * \param add_len       Length of additional data, or 0
  *
  * \return              \c 0 on success, or an error from the underlying
- *                      hash calculation.
+ *                      hash calculation or
+ *                      MBEDTLS_ERR_PLATFORM_FAULT_DETECTED.
  *
  * \note                Additional data is optional, pass NULL and 0 as second
  *                      third argument if no additional data is being used.
@@ -237,7 +238,8 @@
  * \return              0 if successful, or
  *                      MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED, or
  *                      MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG, or
- *                      MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG.
+ *                      MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG, or
+ *                      MBEDTLS_ERR_PLATFORM_FAULT_DETECTED.
  */
 int mbedtls_hmac_drbg_random_with_add( void *p_rng,
                                unsigned char *output, size_t output_len,
@@ -255,7 +257,9 @@
  *
  * \return              0 if successful, or
  *                      MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED, or
- *                      MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG
+ *                      MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG,
+ *                      MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG, or
+ *                      MBEDTLS_ERR_PLATFORM_FAULT_DETECTED.
  */
 int mbedtls_hmac_drbg_random( void *p_rng, unsigned char *output, size_t out_len );
 
diff --git a/include/mbedtls/platform.h b/include/mbedtls/platform.h
index 82d5e33..ec1df15 100644
--- a/include/mbedtls/platform.h
+++ b/include/mbedtls/platform.h
@@ -39,14 +39,16 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
+#define MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED     -0x0070 /**< Hardware accelerator failed */
+#define MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED -0x0072 /**< The requested feature is not supported by the platform */
+#define MBEDTLS_ERR_PLATFORM_FAULT_DETECTED      -0x0071 /**< A hardware fault was detected in a critical path. As a security precaution this should be treated as a potential physical attack */
+
+#if defined(MBEDTLS_PLATFORM_C)
+
 #if defined(MBEDTLS_HAVE_TIME)
 #include "platform_time.h"
 #endif
 
-#define MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED     -0x0070 /**< Hardware accelerator failed */
-#define MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED -0x0072 /**< The requested feature is not supported by the platform */
-#define MBEDTLS_ERR_PLATFORM_FAULT_DETECTED      -0x0071 /**< A fault was detected in a critical path, likely indicative of an active physical attack */
-
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -365,4 +367,6 @@
 }
 #endif
 
+#endif /* MBEDTLS_PLATFORM_C */
+
 #endif /* platform.h */
diff --git a/include/mbedtls/x509.h b/include/mbedtls/x509.h
index c31847d..b2ad182 100644
--- a/include/mbedtls/x509.h
+++ b/include/mbedtls/x509.h
@@ -85,6 +85,8 @@
  * \{
  */
 /* Reminder: update x509_crt_verify_strings[] in library/x509_crt.c */
+/* Reminder: update X509_BADCERT_FI_EXTRA in library/x509_crt.c if using more
+ * that 24 bits */
 #define MBEDTLS_X509_BADCERT_EXPIRED             0x01  /**< The certificate validity has expired. */
 #define MBEDTLS_X509_BADCERT_REVOKED             0x02  /**< The certificate has been revoked (is on a CRL). */
 #define MBEDTLS_X509_BADCERT_CN_MISMATCH         0x04  /**< The certificate Common Name (CN) does not match with the expected CN. */
diff --git a/include/tinycrypt/ecc.h b/include/tinycrypt/ecc.h
index ebd16d6..6a85a55 100644
--- a/include/tinycrypt/ecc.h
+++ b/include/tinycrypt/ecc.h
@@ -73,7 +73,6 @@
  *
  */
 
-#if defined(MBEDTLS_USE_TINYCRYPT)
 #ifndef __TC_UECC_H__
 #define __TC_UECC_H__
 
@@ -477,4 +476,3 @@
 #endif
 
 #endif /* __TC_UECC_H__ */
-#endif /* MBEDTLS_USE_TINYCRYPT */
diff --git a/include/tinycrypt/ecc_dh.h b/include/tinycrypt/ecc_dh.h
index f471349..c443f85 100644
--- a/include/tinycrypt/ecc_dh.h
+++ b/include/tinycrypt/ecc_dh.h
@@ -71,7 +71,6 @@
  *  Security: The curve NIST p-256 provides approximately 128 bits of security.
  */
 
-#if defined(MBEDTLS_USE_TINYCRYPT)
 #ifndef __TC_ECC_DH_H__
 #define __TC_ECC_DH_H__
 
@@ -133,4 +132,3 @@
 #endif
 
 #endif /* __TC_ECC_DH_H__ */
-#endif /* MBEDTLS_USE_TINYCRYPT */
diff --git a/include/tinycrypt/ecc_dsa.h b/include/tinycrypt/ecc_dsa.h
index 259cf44..0001ecb 100644
--- a/include/tinycrypt/ecc_dsa.h
+++ b/include/tinycrypt/ecc_dsa.h
@@ -80,7 +80,6 @@
  *          the signer's public key and the signature values (r and s).
  */
 
-#if defined(MBEDTLS_USE_TINYCRYPT)
 #ifndef __TC_ECC_DSA_H__
 #define __TC_ECC_DSA_H__
 
@@ -141,4 +140,3 @@
 #endif
 
 #endif /* __TC_ECC_DSA_H__ */
-#endif /* MBEDTLS_USE_TINYCRYPT */
diff --git a/library/CMakeLists.txt b/library/CMakeLists.txt
index 89f7275..0156856 100644
--- a/library/CMakeLists.txt
+++ b/library/CMakeLists.txt
@@ -1,4 +1,5 @@
 option(USE_STATIC_MBEDTLS_LIBRARY "Build mbed TLS static library." ON)
+option(USE_TINYCRYPT "Include TinyCrypt." ON)
 option(USE_SHARED_MBEDTLS_LIBRARY "Build mbed TLS shared library." OFF)
 option(LINK_WITH_PTHREAD "Explicitly link mbed TLS library to pthread." OFF)
 
@@ -123,7 +124,9 @@
     set(libs ${libs} pthread)
 endif()
 
-set(libs ${libs} tinycrypt)
+if(USE_TINYCRYPT)
+    set(libs ${libs} tinycrypt)
+endif()
 
 if (NOT USE_STATIC_MBEDTLS_LIBRARY AND NOT USE_SHARED_MBEDTLS_LIBRARY)
     message(FATAL_ERROR "Need to choose static or shared mbedtls build!")
diff --git a/library/Makefile b/library/Makefile
index 4154c6a..96a9d60 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -99,8 +99,7 @@
 		ripemd160.o	rsa_internal.o	rsa.o  		\
 		sha1.o		sha256.o	sha512.o	\
 		threading.o	timing.o	version.o	\
-		version_features.o		xtea.o		\
-		ecc.o		ecc_dh.o	ecc_dsa.o
+		version_features.o		xtea.o
 
 OBJS_X509=	certs.o		pkcs11.o	x509.o
 
@@ -110,6 +109,17 @@
 		ssl_srv.o	ssl_ticket.o		\
 		ssl_tls.o
 
+# Default to always build TinyCrypt
+ifndef TINYCRYPT_BUILD
+TINYCRYPT_BUILD=1
+endif
+
+ifeq ($(TINYCRYPT_BUILD),1)
+# Add TinyCrypt to the targets and Makefile path
+VPATH = ../tinycrypt
+OBJS_CRYPTO += ecc.o           ecc_dh.o        ecc_dsa.o
+endif
+
 .SILENT:
 
 .PHONY: all static shared clean
diff --git a/library/error.c b/library/error.c
index 77c7133..74c9d0b 100644
--- a/library/error.c
+++ b/library/error.c
@@ -842,7 +842,7 @@
     if( use_ret == -(MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED) )
         mbedtls_snprintf( buf, buflen, "PLATFORM - The requested feature is not supported by the platform" );
     if( use_ret == -(MBEDTLS_ERR_PLATFORM_FAULT_DETECTED) )
-        mbedtls_snprintf( buf, buflen, "PLATFORM - A fault was detected in a critical path, likely indicative of an active physical attack" );
+        mbedtls_snprintf( buf, buflen, "PLATFORM - A hardware fault was detected in a critical path. As a security precaution this should be treated as a potential physical attack" );
 #endif /* MBEDTLS_PLATFORM_C */
 
 #if defined(MBEDTLS_POLY1305_C)
diff --git a/library/hmac_drbg.c b/library/hmac_drbg.c
index d0de5de..82703b0 100644
--- a/library/hmac_drbg.c
+++ b/library/hmac_drbg.c
@@ -34,6 +34,7 @@
 #if defined(MBEDTLS_HMAC_DRBG_C)
 
 #include "mbedtls/hmac_drbg.h"
+#include "mbedtls/platform.h"
 #include "mbedtls/platform_util.h"
 
 #include <string.h>
@@ -51,6 +52,9 @@
 #endif /* MBEDTLS_SELF_TEST */
 #endif /* MBEDTLS_PLATFORM_C */
 
+#define HMAC_NONCE_YES     0x4AAAAAAA
+#define HMAC_NONCE_NO      0x75555555
+
 /*
  * HMAC_DRBG context initialization
  */
@@ -74,42 +78,76 @@
         mbedtls_md_get_handle( &ctx->md_ctx ) );
     unsigned char rounds = ( additional != NULL && add_len != 0 ) ? 2 : 1;
     unsigned char sep[1];
+    volatile unsigned int flow_counter = 0;
     unsigned char K[MBEDTLS_MD_MAX_SIZE];
-    int ret;
+    int ret = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
 
     for( sep[0] = 0; sep[0] < rounds; sep[0]++ )
     {
         /* Step 1 or 4 */
+        flow_counter++;
         if( ( ret = mbedtls_md_hmac_reset( &ctx->md_ctx ) ) != 0 )
             goto exit;
+
+        flow_counter++;
         if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
                                             ctx->V, md_len ) ) != 0 )
             goto exit;
+
+        flow_counter++;
         if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
                                             sep, 1 ) ) != 0 )
             goto exit;
+
         if( rounds == 2 )
         {
+            flow_counter++;
             if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
                                                 additional, add_len ) ) != 0 )
             goto exit;
         }
+
+        flow_counter++;
         if( ( ret = mbedtls_md_hmac_finish( &ctx->md_ctx, K ) ) != 0 )
             goto exit;
 
         /* Step 2 or 5 */
+        flow_counter++;
         if( ( ret = mbedtls_md_hmac_starts( &ctx->md_ctx, K, md_len ) ) != 0 )
             goto exit;
+
+        flow_counter++;
         if( ( ret = mbedtls_md_hmac_update( &ctx->md_ctx,
                                             ctx->V, md_len ) ) != 0 )
             goto exit;
+
+        flow_counter++;
         if( ( ret = mbedtls_md_hmac_finish( &ctx->md_ctx, ctx->V ) ) != 0 )
             goto exit;
+        flow_counter++;
     }
 
 exit:
+
     mbedtls_platform_zeroize( K, sizeof( K ) );
-    return( ret );
+    /* Check for possible attack.
+     * Counters needs to have correct values when returning success
+     */
+    if ( ret != 0 )
+        return( ret ); // error case, return immediately
+
+    if ( ( ( flow_counter == 8  ) && ( sep[0] == 1 ) ) ||
+         ( ( flow_counter == 18 ) && ( sep[0] == 2 ) ) )
+    {
+        flow_counter = flow_counter - sep[0];
+        // Double check flow_counter
+        if ( ( flow_counter == 7 ) || ( flow_counter == 16 ) )
+        {
+            return ret;   // success, return 0 from ret
+        }
+    }
+
+    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
 }
 
 #if !defined(MBEDTLS_DEPRECATED_REMOVED)
@@ -125,10 +163,10 @@
  * Simplified HMAC_DRBG initialisation (for use with deterministic ECDSA)
  */
 int mbedtls_hmac_drbg_seed_buf( mbedtls_hmac_drbg_context *ctx,
-                        mbedtls_md_handle_t md_info,
-                        const unsigned char *data, size_t data_len )
+                                mbedtls_md_handle_t md_info,
+                                const unsigned char *data, size_t data_len )
 {
-    int ret;
+    int ret = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
 
     if( ( ret = mbedtls_md_setup( &ctx->md_ctx, md_info, 1 ) ) != 0 )
         return( ret );
@@ -146,7 +184,7 @@
     if( ( ret = mbedtls_hmac_drbg_update_ret( ctx, data, data_len ) ) != 0 )
         return( ret );
 
-    return( 0 );
+    return( ret );
 }
 
 /*
@@ -160,22 +198,19 @@
 {
     unsigned char seed[MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT];
     size_t seedlen = 0;
+    size_t total_entropy_len;
     int ret;
 
+    if( use_nonce == HMAC_NONCE_NO )
+        total_entropy_len = ctx->entropy_len;
+    else
+        total_entropy_len = ctx->entropy_len * 3 / 2;
+
+    /* III. Check input length */
+    if( len > MBEDTLS_HMAC_DRBG_MAX_INPUT ||
+        total_entropy_len + len > MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT )
     {
-        size_t total_entropy_len;
-
-        if( use_nonce == 0 )
-            total_entropy_len = ctx->entropy_len;
-        else
-            total_entropy_len = ctx->entropy_len * 3 / 2;
-
-        /* III. Check input length */
-        if( len > MBEDTLS_HMAC_DRBG_MAX_INPUT ||
-            total_entropy_len + len > MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT )
-        {
-            return( MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG );
-        }
+        return( MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG );
     }
 
     memset( seed, 0, MBEDTLS_HMAC_DRBG_MAX_SEED_INPUT );
@@ -190,7 +225,7 @@
 
     /* For initial seeding, allow adding of nonce generated
      * from the entropy source. See Sect 8.6.7 in SP800-90A. */
-    if( use_nonce )
+    if( use_nonce == HMAC_NONCE_YES )
     {
         /* Note: We don't merge the two calls to f_entropy() in order
          *       to avoid requesting too much entropy from f_entropy()
@@ -225,9 +260,20 @@
     ctx->reseed_counter = 1;
 
 exit:
+
     /* 4. Done */
     mbedtls_platform_zeroize( seed, seedlen );
-    return( ret );
+
+    if ( ret != 0 )
+        return ret;
+
+    if ( ret == 0 && ctx->reseed_counter == 1 )
+    {
+        /* All ok, return 0 from ret */
+        return ret;
+    }
+
+    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
 }
 
 /*
@@ -236,8 +282,7 @@
 int mbedtls_hmac_drbg_reseed( mbedtls_hmac_drbg_context *ctx,
                       const unsigned char *additional, size_t len )
 {
-    return( hmac_drbg_reseed_core( ctx, additional, len,
-                                   0 /* no nonce */ ) );
+    return( hmac_drbg_reseed_core( ctx, additional, len, HMAC_NONCE_NO ) );
 }
 
 /*
@@ -286,13 +331,12 @@
                        md_size <= 28 ? 24 : /* 224-bits hash -> 192 bits */
                        32;  /* better (256+) -> 256 bits */
 
-    if( ( ret = hmac_drbg_reseed_core( ctx, custom, len,
-                                       1 /* add nonce */ ) ) != 0 )
+    if( ( ret = hmac_drbg_reseed_core( ctx, custom, len, HMAC_NONCE_YES ) ) != 0 )
     {
         return( ret );
     }
 
-    return( 0 );
+    return( ret );
 }
 
 /*
@@ -329,6 +373,8 @@
                                const unsigned char *additional, size_t add_len )
 {
     int ret;
+    volatile unsigned char *output_fi = output;
+    volatile size_t out_len_fi = out_len;
     mbedtls_hmac_drbg_context *ctx = (mbedtls_hmac_drbg_context *) p_rng;
     size_t md_len = mbedtls_md_get_size(
         mbedtls_md_get_handle( &ctx->md_ctx ) );
@@ -390,7 +436,21 @@
 
 exit:
     /* 8. Done */
-    return( ret );
+
+    if ( ret != 0 )
+        return ret;
+
+    /*
+     * Check doubled variables and illegal conditions in case of possible
+     * attack.
+     */
+    if ( ( out_len_fi == out_len ) && ( output_fi == output) &&
+         ( left == 0 ) )
+    {
+        return ret; // Success, return 0
+    }
+
+    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
 }
 
 /*
diff --git a/library/md.c b/library/md.c
index d9d6509..4f03acc 100644
--- a/library/md.c
+++ b/library/md.c
@@ -32,6 +32,7 @@
 #if defined(MBEDTLS_MD_C)
 
 #include "mbedtls/md.h"
+#include "mbedtls/platform.h"
 #include "mbedtls/platform_util.h"
 
 #if defined(MBEDTLS_PLATFORM_C)
@@ -525,7 +526,7 @@
     int ret;
     unsigned char sum[MBEDTLS_MD_MAX_SIZE];
     unsigned char *ipad, *opad;
-    size_t i;
+    size_t i = 0;
 
     mbedtls_md_handle_t md_info;
 
@@ -575,16 +576,27 @@
     if( ( ret = mbedtls_md_info_starts( md_info, ctx->md_ctx ) ) != 0 )
         goto cleanup;
 
+    i++;    // Use i as flow control
+
     if( ( ret = mbedtls_md_info_update( md_info, ctx->md_ctx, ipad,
            mbedtls_md_info_block_size( md_info ) ) ) != 0 )
     {
         goto cleanup;
     }
 
+    i++;    // Use i as flow control now
+
 cleanup:
     mbedtls_platform_zeroize( sum, sizeof( sum ) );
 
-    return( ret );
+    if ( ret != 0 )
+        return ret;
+
+    /* Check possible fault injection */
+    if ( ( i - 2 ) == keylen )
+        return ret; // success, return 0 from ret
+
+    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
 }
 
 int mbedtls_md_hmac_update( mbedtls_md_context_t *ctx,
@@ -653,7 +665,7 @@
     if( ( ret = mbedtls_md_info_finish( md_info, ctx->md_ctx, output ) ) != 0 )
         return( ret );
 
-    return( 0 );
+    return( ret );
 }
 
 int mbedtls_md_hmac_reset( mbedtls_md_context_t *ctx )
diff --git a/library/x509_crt.c b/library/x509_crt.c
index e537983..fd3fa1a 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -43,6 +43,7 @@
 #include "mbedtls/x509_internal.h"
 #include "mbedtls/oid.h"
 #include "mbedtls/platform_util.h"
+#include "mbedtls/platform.h"
 
 #include <string.h>
 
@@ -2884,6 +2885,10 @@
     return( 0 );
 }
 
+/* This value is different enough from 0 that it's hard for an active physical
+ * attacker to reach it just by flipping a few bits. */
+#define X509_SIGNATURE_IS_GOOD      0x7f5a5a5a
+
 /*
  * Find a suitable parent for child in candidates, or return NULL.
  *
@@ -2915,7 +2920,8 @@
  *  - [in] child: certificate for which we're looking for a parent
  *  - [in] candidates: chained list of potential parents
  *  - [out] r_parent: parent found (or NULL)
- *  - [out] r_signature_is_good: 1 if child signature by parent is valid, or 0
+ *  - [out] r_signature_is_good: set to X509_SIGNATURE_IS_GOOD if
+ *                               child signature by parent is valid, or to 0
  *  - [in] top: 1 if candidates consists of trusted roots, ie we're at the top
  *         of the chain, 0 otherwise
  *  - [in] path_cnt: number of intermediates seen so far
@@ -2938,8 +2944,9 @@
                         mbedtls_x509_crt_restart_ctx *rs_ctx )
 {
     int ret;
+    volatile int ret_fi = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
     mbedtls_x509_crt *parent_crt;
-    int signature_is_good;
+    int signature_is_good = 0;
 
 #if defined(MBEDTLS_HAVE_TIME_DATE)
     mbedtls_x509_crt *fallback_parent;
@@ -3018,10 +3025,10 @@
             continue;
 
         /* Signature */
-        ret = x509_crt_check_signature( child_sig, parent_crt, rs_ctx );
+        ret_fi = x509_crt_check_signature( child_sig, parent_crt, rs_ctx );
 
 #if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
-        if( rs_ctx != NULL && ret == MBEDTLS_ERR_ECP_IN_PROGRESS )
+        if( rs_ctx != NULL && ret_fi == MBEDTLS_ERR_ECP_IN_PROGRESS )
         {
             /* save state */
             rs_ctx->parent = parent_crt;
@@ -3030,13 +3037,17 @@
             rs_ctx->fallback_signature_is_good = fallback_signature_is_good;
 #endif /* MBEDTLS_HAVE_TIME_DATE */
 
-            return( ret );
+            return( ret_fi );
         }
-#else
-        (void) ret;
 #endif
 
-        signature_is_good = ret == 0;
+        if( ret_fi == 0 )
+        {
+            mbedtls_platform_enforce_volatile_reads();
+            if( ret_fi == 0 )
+                signature_is_good = X509_SIGNATURE_IS_GOOD;
+        }
+
         if( top && ! signature_is_good )
             continue;
 
@@ -3318,6 +3329,23 @@
 #endif /* MBEDTLS_X509_REMOVE_VERIFY_CALLBACK */
 
 /*
+ * This is used in addition to the flag for a specific issue, to ensure that
+ * it is not possible for an active physical attacker to entirely clear the
+ * flags just by flipping a single bit. Take advantage of the fact that all
+ * values defined in include/mbedtls/x509.h so far are 24-bit or less, so the
+ * top byte is free.
+ *
+ * Currently this protection is not compatible with the vrfy callback (as it
+ * can observ and modify flags freely), so it's only enabled when the callback
+ * is disabled.
+ */
+#if defined(MBEDTLS_X509_REMOVE_VERIFY_CALLBACK)
+#define X509_BADCERT_FI_EXTRA   0xff000000u
+#else
+#define X509_BADCERT_FI_EXTRA   0u
+#endif
+
+/*
  * Build and verify a certificate chain
  *
  * Given a peer-provided list of certificates EE, C1, ..., Cn and
@@ -3374,6 +3402,7 @@
     int parent_is_trusted;
     int child_is_trusted;
     int signature_is_good;
+    volatile int signature_is_good_fi;
     unsigned self_cnt;
 
 #if defined(MBEDTLS_ECDSA_C) && defined(MBEDTLS_ECP_RESTARTABLE)
@@ -3422,9 +3451,9 @@
 #if !defined(MBEDTLS_X509_CRT_REMOVE_TIME)
                 /* Check time-validity (all certificates) */
                 if( mbedtls_x509_time_is_past( &child->valid_to ) )
-                    *flags |= MBEDTLS_X509_BADCERT_EXPIRED;
+                    *flags |= MBEDTLS_X509_BADCERT_EXPIRED | X509_BADCERT_FI_EXTRA;
                 if( mbedtls_x509_time_is_future( &child->valid_from ) )
-                    *flags |= MBEDTLS_X509_BADCERT_FUTURE;
+                    *flags |= MBEDTLS_X509_BADCERT_FUTURE | X509_BADCERT_FI_EXTRA;
 #endif /* !MBEDTLS_X509_CRT_REMOVE_TIME */
 
                 /* Stop here for trusted roots (but not for trusted EE certs) */
@@ -3444,10 +3473,10 @@
 
                 /* Check signature algorithm: MD & PK algs */
                 if( x509_profile_check_md_alg( profile, child->sig_md ) != 0 )
-                    *flags |= MBEDTLS_X509_BADCERT_BAD_MD;
+                    *flags |= MBEDTLS_X509_BADCERT_BAD_MD | X509_BADCERT_FI_EXTRA;
 
                 if( x509_profile_check_pk_alg( profile, child->sig_pk ) != 0 )
-                    *flags |= MBEDTLS_X509_BADCERT_BAD_PK;
+                    *flags |= MBEDTLS_X509_BADCERT_BAD_PK | X509_BADCERT_FI_EXTRA;
 
                 /* Special case: EE certs that are locally trusted */
                 if( x509_crt_verify_chain_len( ver_chain ) == 1 && self_issued &&
@@ -3495,7 +3524,7 @@
         /* No parent? We're done here */
         if( parent_crt == NULL )
         {
-            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED;
+            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED | X509_BADCERT_FI_EXTRA;
             return( 0 );
         }
 
@@ -3516,8 +3545,13 @@
         }
 
         /* signature was checked while searching parent */
-        if( ! signature_is_good )
-            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED;
+        signature_is_good_fi = signature_is_good;
+        if( signature_is_good_fi != X509_SIGNATURE_IS_GOOD )
+            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED | X509_BADCERT_FI_EXTRA;
+
+        mbedtls_platform_enforce_volatile_reads();
+        if( signature_is_good_fi != X509_SIGNATURE_IS_GOOD )
+            *flags |= MBEDTLS_X509_BADCERT_NOT_TRUSTED | X509_BADCERT_FI_EXTRA;
 
         {
             mbedtls_pk_context *parent_pk;
@@ -3527,7 +3561,7 @@
 
             /* check size of signing key */
             if( x509_profile_check_key( profile, parent_pk ) != 0 )
-                *flags |= MBEDTLS_X509_BADCERT_BAD_KEY;
+                *flags |= MBEDTLS_X509_BADCERT_BAD_KEY | X509_BADCERT_FI_EXTRA;
 
             mbedtls_x509_crt_pk_release( parent_crt );
         }
@@ -3658,7 +3692,7 @@
     if( ret != 0 )
         ret = MBEDTLS_ERR_X509_FATAL_ERROR;
 
-    *flags |= MBEDTLS_X509_BADCERT_CN_MISMATCH;
+    *flags |= MBEDTLS_X509_BADCERT_CN_MISMATCH | X509_BADCERT_FI_EXTRA;
     return( ret );
 }
 #endif /* !MBEDTLS_X509_REMOVE_HOSTNAME_VERIFICATION */
@@ -3747,6 +3781,7 @@
     int ret;
     mbedtls_x509_crt_verify_chain ver_chain;
     uint32_t ee_flags;
+    volatile uint32_t flags_fi = (uint32_t) -1;
 
     *flags = 0;
     ee_flags = 0;
@@ -3780,10 +3815,10 @@
         pk_type = mbedtls_pk_get_type( pk );
 
         if( x509_profile_check_pk_alg( profile, pk_type ) != 0 )
-            ee_flags |= MBEDTLS_X509_BADCERT_BAD_PK;
+            ee_flags |= MBEDTLS_X509_BADCERT_BAD_PK | X509_BADCERT_FI_EXTRA;
 
         if( x509_profile_check_key( profile, pk ) != 0 )
-            ee_flags |= MBEDTLS_X509_BADCERT_BAD_KEY;
+            ee_flags |= MBEDTLS_X509_BADCERT_BAD_KEY | X509_BADCERT_FI_EXTRA;
 
         mbedtls_x509_crt_pk_release( crt );
     }
@@ -3823,10 +3858,19 @@
         return( ret );
     }
 
-    if( *flags != 0 )
-        return( MBEDTLS_ERR_X509_CERT_VERIFY_FAILED );
+    flags_fi = *flags;
+    if( flags_fi == 0 )
+    {
+        mbedtls_platform_enforce_volatile_reads();
+        if( flags_fi == 0 )
+            return( 0 );
+    }
 
-    return( 0 );
+    /* Preserve the API by removing internal extra bits - from now on the
+     * fact that flags is non-zero is also redundantly encoded by the
+     * non-zero return value from this function. */
+    *flags &= ~ X509_BADCERT_FI_EXTRA;
+    return( MBEDTLS_ERR_X509_CERT_VERIFY_FAILED );
 }
 
 /*
diff --git a/scripts/config.pl b/scripts/config.pl
index 619c5ca..ff522b6 100755
--- a/scripts/config.pl
+++ b/scripts/config.pl
@@ -213,11 +213,15 @@
 # Check the config file is present
 if (! -f $config_file)  {
 
-    chdir '..' or die;
-
-    # Confirm this is the project root directory and try again
-    if ( !(-d 'scripts' && -d 'include' && -d 'library' && -f $config_file) ) {
-        die "If no file specified, must be run from the project root or scripts directory.\n";
+    if ( -d 'importer' && -d 'inc' && -d 'src') {
+        $config_file = "inc/mbedtls/config.h";
+    }
+    else {
+        chdir '..' or die;
+        # Confirm this is the project root directory and try again
+        if ( !(-d 'scripts' && -d 'include' && -d 'library' && -f $config_file) ) {
+            die "If no file specified, must be run from the project root or scripts directory.\n";
+        }
     }
 }
 
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 02f96a9..42ef32d 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -1491,7 +1491,7 @@
     msg "build: arm-none-eabi-gcc MBEDTLS_NO_64BIT_MULTIPLICATION, make" # ~ 10s
     scripts/config.pl baremetal
     scripts/config.pl set MBEDTLS_NO_64BIT_MULTIPLICATION
-    make CC=arm-none-eabi-gcc AR=arm-none-eabi-ar LD=arm-none-eabi-ld CFLAGS='-Werror -O1 -march=armv6-m -mthumb' lib
+    make TINYCRYPT_BUILD=0 CC=arm-none-eabi-gcc AR=arm-none-eabi-ar LD=arm-none-eabi-ld CFLAGS='-Werror -O1 -march=armv6-m -mthumb' lib
     echo "Checking that software 64-bit multiplication is not required"
     if_build_succeeded not grep __aeabi_lmul library/*.o
 }
diff --git a/tests/scripts/basic-build-test.sh b/tests/scripts/basic-build-test.sh
index 8990dfb..d559fa5 100755
--- a/tests/scripts/basic-build-test.sh
+++ b/tests/scripts/basic-build-test.sh
@@ -25,13 +25,37 @@
 #
 # This script has been written to be generic and should work on any shell.
 #
-# Usage: basic-build-tests.sh
+# Usage: basic-build-tests.sh               to run all tests
+#        basic-build-tests.sh unit_test     to run only unit tests
 #
 
 # Abort on errors (and uninitiliased variables)
 set -eu
 
-if [ -d library -a -d include -a -d tests ]; then :; else
+CONFIG_H='include/mbedtls/config.h'
+CONFIG_BAK="$CONFIG_H.bak"
+
+UNIT_TESTS_ONLY=0
+
+echo
+if [ -z ${1+x} ]
+then
+    echo "Running all tests"
+else
+    if [ "$1" = "unit_test" ]
+    then
+        echo "Running only unit tests"
+        UNIT_TESTS_ONLY=1
+    fi
+fi
+echo
+
+# Check test environment. If importer, src and inc folders are present then
+# there is a different directory structure and we need to adapt to it.
+if [ -d importer -a -d inc -a -d src ]; then
+    CONFIG_H='inc/mbedtls/config.h'
+    CONFIG_BAK="$CONFIG_H.bak"
+elif [ -d library -a -d include -a -d tests ]; then :; else
     echo "Must be run from mbed TLS root" >&2
     exit 1
 fi
@@ -49,9 +73,6 @@
 export GNUTLS_CLI="$GNUTLS_CLI"
 export GNUTLS_SERV="$GNUTLS_SERV"
 
-CONFIG_H='include/mbedtls/config.h'
-CONFIG_BAK="$CONFIG_H.bak"
-
 # Step 0 - print build environment info
 OPENSSL="$OPENSSL"                           \
     OPENSSL_LEGACY="$OPENSSL_LEGACY"         \
@@ -79,6 +100,12 @@
 perl scripts/run-test-suites.pl -v 2 |tee unit-test-$TEST_OUTPUT
 echo
 
+# only unit test are run?
+if [ $UNIT_TESTS_ONLY -eq 1 ]
+then
+    exit 0
+fi
+
 # Step 2b - System Tests
 sh ssl-opt.sh |tee sys-test-$TEST_OUTPUT
 echo
diff --git a/tests/scripts/list-symbols.sh b/tests/scripts/list-symbols.sh
index 930722c..12b3281 100755
--- a/tests/scripts/list-symbols.sh
+++ b/tests/scripts/list-symbols.sh
@@ -16,7 +16,7 @@
 scripts/config.pl full
 make clean
 make_ret=
-CFLAGS=-fno-asynchronous-unwind-tables make lib \
+CFLAGS=-fno-asynchronous-unwind-tables TINYCRYPT_BUILD=0 make lib \
       >list-symbols.make.log 2>&1 ||
   {
     make_ret=$?
diff --git a/tinycrypt/ecc.c b/tinycrypt/ecc.c
index 086555a..a0333b0 100644
--- a/tinycrypt/ecc.c
+++ b/tinycrypt/ecc.c
@@ -63,7 +63,6 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
-#if defined(MBEDTLS_USE_TINYCRYPT)
 #include <tinycrypt/ecc.h>
 #include "mbedtls/platform_util.h"
 #include "mbedtls/sha256.h"
@@ -1258,7 +1257,4 @@
 	NUM_ECC_BYTES, NUM_ECC_BYTES, _public + NUM_ECC_WORDS);
 	return UECC_SUCCESS;
 }
-#else
-typedef int mbedtls_dummy_tinycrypt_def;
-#endif /* MBEDTLS_USE_TINYCRYPT */
 
diff --git a/tinycrypt/ecc_dh.c b/tinycrypt/ecc_dh.c
index 3070ecf..1b1ff3f 100644
--- a/tinycrypt/ecc_dh.c
+++ b/tinycrypt/ecc_dh.c
@@ -66,7 +66,6 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
-#if defined(MBEDTLS_USE_TINYCRYPT)
 #include <tinycrypt/ecc.h>
 #include <tinycrypt/ecc_dh.h>
 #include <string.h>
@@ -184,6 +183,3 @@
 
 	return r;
 }
-#else
-typedef int mbedtls_dummy_tinycrypt_def;
-#endif /* MBEDTLS_USE_TINYCRYPT */
diff --git a/tinycrypt/ecc_dsa.c b/tinycrypt/ecc_dsa.c
index 3b5560c..8c6bb19 100644
--- a/tinycrypt/ecc_dsa.c
+++ b/tinycrypt/ecc_dsa.c
@@ -64,7 +64,6 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
-#if defined(MBEDTLS_USE_TINYCRYPT)
 #include <tinycrypt/ecc.h>
 #include <tinycrypt/ecc_dsa.h>
 #include "mbedtls/platform_util.h"
@@ -317,6 +316,3 @@
 
 	return UECC_FAILURE;
 }
-#else
-typedef int mbedtls_dummy_tinycrypt_def;
-#endif /* MBEDTLS_USE_TINYCRYPT */