diff --git a/cyassl/internal.h b/cyassl/internal.h
index ccd7c8138..6f53ba0b0 100644
--- a/cyassl/internal.h
+++ b/cyassl/internal.h
@@ -1969,6 +1969,9 @@ struct CYASSL {
     byte            hsInfoOn;           /* track handshake info        */
     byte            toInfoOn;           /* track timeout   info        */
 #endif
+#ifdef HAVE_FUZZER
+    CallbackFuzzer  fuzzerCb;           /* for testing with using fuzzer */
+#endif
 #ifdef KEEP_PEER_CERT
     CYASSL_X509     peerCert;           /* X509 peer cert */
 #endif
diff --git a/cyassl/ssl.h b/cyassl/ssl.h
index 7109b0726..33f7a3f71 100644
--- a/cyassl/ssl.h
+++ b/cyassl/ssl.h
@@ -930,6 +930,20 @@ 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
+};
+
+typedef int (*CallbackFuzzer)(const unsigned char* buf, int sz, int type,
+        void* ctx);
+
+CYASSL_API void CyaSSL_SetFuzzerCb(CYASSL* ssl, CallbackFuzzer cbf);
+#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 eb7baccb5..1819b4e0e 100644
--- a/src/internal.c
+++ b/src/internal.c
@@ -1752,6 +1752,9 @@ int InitSSL(CYASSL* ssl, CYASSL_CTX* ctx)
     ssl->MacEncryptCtx    = NULL;
     ssl->DecryptVerifyCtx = NULL;
 #endif
+#ifdef HAVE_FUZZER
+    ssl->fuzzerCb         = NULL;
+#endif
 #ifdef HAVE_PK_CALLBACKS
     #ifdef HAVE_ECC
         ssl->EccSignCtx   = NULL;
@@ -2527,6 +2530,10 @@ 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(output, sz, FUZZ_HASH, ssl->ctx);
+#endif
 #ifdef CYASSL_DTLS
     if (ssl->options.dtls) {
         adj += DTLS_RECORD_EXTRA;
@@ -5113,6 +5120,11 @@ static INLINE int Encrypt(CYASSL* ssl, byte* out, const byte* input, word16 sz)
         return ENCRYPT_ERROR;
     }
 
+#ifdef HAVE_FUZZER
+    if (ssl->fuzzerCb)
+        ssl->fuzzerCb(input, sz, FUZZ_ENCRYPT, ssl->ctx);
+#endif
+
     switch (ssl->specs.bulk_cipher_algorithm) {
         #ifdef BUILD_ARC4
             case cyassl_rc4:
@@ -6390,6 +6402,11 @@ 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(in, sz, FUZZ_HMAC, ssl->ctx);
+#endif
+
     XMEMSET(seq, 0, SEQ_SZ);
     conLen[0] = (byte)content;
     c16toa((word16)sz, &conLen[ENUM_LEN]);
@@ -10543,6 +10560,11 @@ 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(output + preSigIdx, preSigSz, FUZZ_SIGNATURE, ssl->ctx);
+#endif
+
             /* do signature */
             {
 #ifndef NO_OLD_TLS
@@ -10895,6 +10917,11 @@ static void PickHashSigAlgo(CYASSL* ssl,
             c16toa((word16)sigSz, output + idx);
             idx += LENGTH_SZ;
 
+#ifdef HAVE_FUZZER
+    if (ssl->fuzzerCb)
+        ssl->fuzzerCb(output + preSigIdx, preSigSz, FUZZ_SIGNATURE, ssl->ctx);
+#endif
+
             /* do signature */
             {
 #ifndef NO_OLD_TLS
diff --git a/src/ssl.c b/src/ssl.c
index 1b99e98fd..93d52c8d3 100644
--- a/src/ssl.c
+++ b/src/ssl.c
@@ -11501,6 +11501,13 @@ const byte* CyaSSL_get_sessionID(const CYASSL_SESSION* session)
 
 #endif /* SESSION_CERTS */
 
+#ifdef HAVE_FUZZER
+void CyaSSL_SetFuzzerCb(CYASSL* ssl, CallbackFuzzer cbf)
+{
+    if (ssl)
+        ssl->fuzzerCb = cbf;
+}
+#endif
 
 #ifndef NO_CERTS
 #ifdef  HAVE_PK_CALLBACKS
diff --git a/src/tls.c b/src/tls.c
index a569f064e..f52160df6 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(in, sz, FUZZ_HMAC, ssl->ctx);
+#endif
+
     CyaSSL_SetTlsHmacInner(ssl, myInner, sz, content, verify);
 
     ret = HmacSetKey(&hmac, CyaSSL_GetHmacType(ssl),