diff --git a/cyassl/internal.h b/cyassl/internal.h
index ccd7c8138..3225f418c 100644
--- a/cyassl/internal.h
+++ b/cyassl/internal.h
@@ -1969,6 +1969,10 @@ struct CYASSL {
     byte            hsInfoOn;           /* track handshake info        */
     byte            toInfoOn;           /* track timeout   info        */
 #endif
+#ifdef HAVE_FUZZER
+    CallbackFuzzer  fuzzerCb;           /* for testing with using fuzzer */
+    void*           fuzzerCtx;          /* user defined pointer */
+#endif
 #ifdef KEEP_PEER_CERT
     CYASSL_X509     peerCert;           /* X509 peer cert */
 #endif
diff --git a/cyassl/ssl.h b/cyassl/ssl.h
index 7109b0726..f8976d0f5 100644
--- a/cyassl/ssl.h
+++ b/cyassl/ssl.h
@@ -930,6 +930,21 @@ CYASSL_API int CyaSSL_set_group_messages(CYASSL*);
 typedef int (*CallbackIORecv)(CYASSL *ssl, char *buf, int sz, void *ctx);
 typedef int (*CallbackIOSend)(CYASSL *ssl, char *buf, int sz, void *ctx);
 
+#ifdef HAVE_FUZZER
+enum fuzzer_type {
+    FUZZ_HMAC      = 0,
+    FUZZ_ENCRYPT   = 1,
+    FUZZ_SIGNATURE = 2,
+    FUZZ_HASH      = 3,
+    FUZZ_HEAD      = 4
+};
+
+typedef int (*CallbackFuzzer)(CYASSL* ssl, const unsigned char* buf, int sz,
+        int type, void* fuzzCtx);
+
+CYASSL_API void CyaSSL_SetFuzzerCb(CYASSL* ssl, CallbackFuzzer cbf, void* fCtx);
+#endif
+
 CYASSL_API void CyaSSL_SetIORecv(CYASSL_CTX*, CallbackIORecv);
 CYASSL_API void CyaSSL_SetIOSend(CYASSL_CTX*, CallbackIOSend);
 
diff --git a/src/internal.c b/src/internal.c
index fb7b42217..8fd2972b6 100644
--- a/src/internal.c
+++ b/src/internal.c
@@ -1752,6 +1752,10 @@ int InitSSL(CYASSL* ssl, CYASSL_CTX* ctx)
     ssl->MacEncryptCtx    = NULL;
     ssl->DecryptVerifyCtx = NULL;
 #endif
+#ifdef HAVE_FUZZER
+    ssl->fuzzerCb         = NULL;
+    ssl->fuzzerCtx        = NULL;
+#endif
 #ifdef HAVE_PK_CALLBACKS
     #ifdef HAVE_ECC
         ssl->EccSignCtx   = NULL;
@@ -2529,6 +2533,10 @@ static int HashOutput(CYASSL* ssl, const byte* output, int sz, int ivSz)
     const byte* adj = output + RECORD_HEADER_SZ + ivSz;
     sz -= RECORD_HEADER_SZ;
     
+#ifdef HAVE_FUZZER
+    if (ssl->fuzzerCb)
+        ssl->fuzzerCb(ssl, output, sz, FUZZ_HASH, ssl->fuzzerCtx);
+#endif
 #ifdef CYASSL_DTLS
     if (ssl->options.dtls) {
         adj += DTLS_RECORD_EXTRA;
@@ -2954,6 +2962,11 @@ static int GetRecordHeader(CYASSL* ssl, const byte* input, word32* inOutIdx,
                            RecordLayerHeader* rh, word16 *size)
 {
     if (!ssl->options.dtls) {
+#ifdef HAVE_FUZZER
+        if (ssl->fuzzerCb)
+            ssl->fuzzerCb(ssl, input + *inOutIdx, RECORD_HEADER_SZ, FUZZ_HEAD,
+                    ssl->fuzzerCtx);
+#endif
         XMEMCPY(rh, input + *inOutIdx, RECORD_HEADER_SZ);
         *inOutIdx += RECORD_HEADER_SZ;
         ato16(rh->length, size);
@@ -2969,6 +2982,12 @@ static int GetRecordHeader(CYASSL* ssl, const byte* input, word32* inOutIdx,
         *inOutIdx += 4;  /* advance past rest of seq */
         ato16(input + *inOutIdx, size);
         *inOutIdx += LENGTH_SZ;
+#ifdef HAVE_FUZZER
+        if (ssl->fuzzerCb)
+            ssl->fuzzerCb(ssl, input + *inOutIdx - LENGTH_SZ - 8 - ENUM_LEN -
+                           VERSION_SZ, ENUM_LEN + VERSION_SZ + 8 + LENGTH_SZ,
+                           FUZZ_HEAD, ssl->fuzzerCtx);
+#endif
 #endif
     }
 
@@ -5115,6 +5134,11 @@ static INLINE int Encrypt(CYASSL* ssl, byte* out, const byte* input, word16 sz)
         return ENCRYPT_ERROR;
     }
 
+#ifdef HAVE_FUZZER
+    if (ssl->fuzzerCb)
+        ssl->fuzzerCb(ssl, input, sz, FUZZ_ENCRYPT, ssl->fuzzerCtx);
+#endif
+
     switch (ssl->specs.bulk_cipher_algorithm) {
         #ifdef BUILD_ARC4
             case cyassl_rc4:
@@ -6392,6 +6416,11 @@ static int SSL_hmac(CYASSL* ssl, byte* digest, const byte* in, word32 sz,
     byte conLen[ENUM_LEN + LENGTH_SZ];     /* content & length */
     const byte* macSecret = CyaSSL_GetMacSecret(ssl, verify);
     
+#ifdef HAVE_FUZZER
+    if (ssl->fuzzerCb)
+        ssl->fuzzerCb(ssl, in, sz, FUZZ_HMAC, ssl->fuzzerCtx);
+#endif
+
     XMEMSET(seq, 0, SEQ_SZ);
     conLen[0] = (byte)content;
     c16toa((word16)sz, &conLen[ENUM_LEN]);
@@ -10545,6 +10574,12 @@ static void PickHashSigAlgo(CYASSL* ssl,
             /* Signtaure length will be written later, when we're sure what it
                is */
 
+#ifdef HAVE_FUZZER
+    if (ssl->fuzzerCb)
+        ssl->fuzzerCb(ssl, output + preSigIdx, preSigSz, FUZZ_SIGNATURE,
+                ssl->fuzzerCtx);
+#endif
+
             /* do signature */
             {
 #ifndef NO_OLD_TLS
@@ -10897,6 +10932,12 @@ static void PickHashSigAlgo(CYASSL* ssl,
             c16toa((word16)sigSz, output + idx);
             idx += LENGTH_SZ;
 
+#ifdef HAVE_FUZZER
+    if (ssl->fuzzerCb)
+        ssl->fuzzerCb(ssl, output + preSigIdx, preSigSz, FUZZ_SIGNATURE,
+                ssl->fuzzerCtx);
+#endif
+
             /* do signature */
             {
 #ifndef NO_OLD_TLS
diff --git a/src/ssl.c b/src/ssl.c
index 1b99e98fd..e630a847a 100644
--- a/src/ssl.c
+++ b/src/ssl.c
@@ -11501,6 +11501,15 @@ const byte* CyaSSL_get_sessionID(const CYASSL_SESSION* session)
 
 #endif /* SESSION_CERTS */
 
+#ifdef HAVE_FUZZER
+void CyaSSL_SetFuzzerCb(CYASSL* ssl, CallbackFuzzer cbf, void* fCtx)
+{
+    if (ssl) {
+        ssl->fuzzerCb  = cbf;
+        ssl->fuzzerCtx = fCtx;
+    }
+}
+#endif
 
 #ifndef NO_CERTS
 #ifdef  HAVE_PK_CALLBACKS
diff --git a/src/tls.c b/src/tls.c
index a569f064e..30feb6129 100644
--- a/src/tls.c
+++ b/src/tls.c
@@ -677,6 +677,11 @@ int TLS_hmac(CYASSL* ssl, byte* digest, const byte* in, word32 sz,
     if (ssl == NULL)
         return BAD_FUNC_ARG;
     
+#ifdef HAVE_FUZZER
+    if (ssl->fuzzerCb)
+        ssl->fuzzerCb(ssl, in, sz, FUZZ_HMAC, ssl->fuzzerCtx);
+#endif
+
     CyaSSL_SetTlsHmacInner(ssl, myInner, sz, content, verify);
 
     ret = HmacSetKey(&hmac, CyaSSL_GetHmacType(ssl),