feat: added/update MAC functions to sign or verify nip44 payload

3 files changed, 232 insertions, 50 deletions

diff --git a/src/noscrypt.c b/src/noscrypt.c
index 9ab1c6e..14f959b 100644
--- a/src/noscrypt.c
+++ b/src/noscrypt.c
@@ -27,6 +27,7 @@
 #include <mbedtls/platform_util.h>
 #include <mbedtls/md.h>
 #include <mbedtls/hkdf.h>
+#include <mbedtls/hmac_drbg.h>
 #include <mbedtls/chacha20.h>
 #include <mbedtls/sha256.h>
 
@@ -82,7 +83,7 @@
 struct nc_expand_keys {
 	uint8_t chacha_key[CHACHA_KEY_SIZE];
 	uint8_t chacha_nonce[CHACHA_NONCE_SIZE];
-	uint8_t hamc_key[NC_HMAC_KEY_SIZE];
+	uint8_t hmac_key[NC_HMAC_KEY_SIZE];
 };
 
 struct shared_secret {
@@ -286,7 +287,7 @@ static inline void _expandKeysFromHkdf(const struct message_key* hkdf, struct nc
 	hkdfBytes += CHACHA_NONCE_SIZE;	//Offset by nonce size
 
 	MEMMOV(
-		keys->hamc_key, 
+		keys->hmac_key, 
 		hkdfBytes,
 		NC_HMAC_KEY_SIZE
 	);
@@ -376,7 +377,7 @@ static inline NCResult _encryptEx(
 	_expandKeysFromHkdf(&messageKey, &cipherKeys);
 
 	//Copy the hmac key into the args
-	MEMMOV(hmacKey, cipherKeys.hamc_key, NC_HMAC_KEY_SIZE);
+	MEMMOV(hmacKey, cipherKeys.hmac_key, NC_HMAC_KEY_SIZE);
 
 	//CHACHA20
 	result = _chachaEncipher(&cipherKeys, args);
@@ -428,41 +429,6 @@ Cleanup:
 }
 
 /*
-* Compute the sha256 digest of the data. This function should always return 0
-* on success.
-*/
-static inline int _computeSha256Digest(const uint8_t* data, size_t length, uint8_t digest[32])
-{
-	int result;
-	mbedtls_sha256_context sha256;
-
-	DEBUG_ASSERT2(data != NULL, "Expected valid data buffer")
-	DEBUG_ASSERT2(digest != NULL, "Expected valid digest buffer")
-
-	//Init the sha256 context
-	mbedtls_sha256_init(&sha256);
-
-	//starting context should never fail
-	result = mbedtls_sha256_starts(&sha256, 0);
-	DEBUG_ASSERT2(result == 0, "Expected sha256 starts to return 0")
-
-	//may fail if the data is invalid
-	if ((result = mbedtls_sha256_update(&sha256, data, length)) != 0)
-	{
-		goto Cleanup;
-	}
-
-	//Finishing context should never fail
-	result = mbedtls_sha256_finish(&sha256, digest);
-
-Cleanup:
-	//Always free the context
-	mbedtls_sha256_free(&sha256);
-
-	return result;
-}
-
-/*
 * EXTERNAL API FUNCTIONS
 */
 NC_EXPORT uint32_t NC_CC NCGetContextStructSize(void) 
@@ -626,7 +592,7 @@ NC_EXPORT NCResult NC_CC NCSignData(
 	CHECK_NULL_ARG(sig64, 5)
 
 	//Compute sha256 of the data before signing
-	if(_computeSha256Digest(data, dataSize, digest) != 0)
+	if(mbedtls_sha256(data, dataSize, digest, 0) != 0)
 	{
 		return E_INVALID_ARG;
 	}
@@ -683,7 +649,7 @@ NC_EXPORT NCResult NC_CC NCVerifyData(
 	CHECK_NULL_ARG(sig64, 4)
 
 	//Compute sha256 of the data before verifying
-	if (_computeSha256Digest(data, dataSize, digest) != 0)
+	if (mbedtls_sha256(data, dataSize, digest, 0) != 0)
 	{
 		return E_INVALID_ARG;
 	}
@@ -922,3 +888,139 @@ Cleanup:
 	return result;
 }
 
+NC_EXPORT NCResult NCComputeMac(
+	const NCContext* ctx,
+	const uint8_t hmacKey[NC_HMAC_KEY_SIZE],
+	const uint8_t* payload,
+	size_t payloadSize,
+	uint8_t hmacOut[NC_ENCRYPTION_MAC_SIZE]
+)
+{
+	CHECK_NULL_ARG(ctx, 0)
+	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_NULL_ARG(hmacKey, 1)
+	CHECK_NULL_ARG(payload, 2)
+	CHECK_ARG_RANGE(payloadSize, 1, UINT32_MAX, 3)
+	CHECK_NULL_ARG(hmacOut, 4)
+
+	/*
+	* Compute the hmac of the data using the supplied hmac key
+	*/
+	return mbedtls_md_hmac(
+		_getSha256MdInfo(), 
+		hmacKey, 
+		NC_HMAC_KEY_SIZE, 
+		payload, 
+		payloadSize, 
+		hmacOut
+	) == 0 ? NC_SUCCESS : E_OPERATION_FAILED;
+}
+
+NC_EXPORT NCResult NC_CC NCVerifyMacEx(
+	const NCContext* ctx,
+	const uint8_t conversationKey[NC_CONV_KEY_SIZE],
+	NCMacVerifyArgs* args
+)
+{
+	NCResult result;
+	const mbedtls_md_info_t* sha256Info;
+	struct message_key messageKey;
+	struct nc_expand_keys keys;
+	uint8_t hmacOut[NC_ENCRYPTION_MAC_SIZE];
+
+	CHECK_NULL_ARG(ctx, 0)
+	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_NULL_ARG(conversationKey, 1)
+	CHECK_NULL_ARG(args, 2)
+
+	CHECK_INVALID_ARG(args->mac, 2)
+	CHECK_INVALID_ARG(args->payload, 2)
+	CHECK_INVALID_ARG(args->nonce, 2)
+	CHECK_ARG_RANGE(args->payloadSize, NIP44_MIN_ENC_MESSAGE_SIZE, NIP44_MAX_ENC_MESSAGE_SIZE, 2)
+
+	sha256Info = _getSha256MdInfo();
+
+	/*
+	* We need to get the message key in order to 
+	* get the required hmac key
+	*/
+	result = _getMessageKey(
+		sha256Info,
+		(struct conversation_key*)conversationKey,
+		args->nonce,
+		NC_ENCRYPTION_NONCE_SIZE,
+		&messageKey
+	);
+
+	if(result != NC_SUCCESS)
+	{
+		goto Cleanup;
+	}
+
+	/* Expand keys to get the hmac-key */
+	_expandKeysFromHkdf(&messageKey, &keys);
+
+	/*
+	* Compute the hmac of the data using the computed hmac key
+	*/
+	if(mbedtls_md_hmac(sha256Info, keys.hmac_key, NC_HMAC_KEY_SIZE, args->payload, args->payloadSize, hmacOut) != 0)
+	{
+		result = E_OPERATION_FAILED;
+		goto Cleanup;
+	}
+
+	/* constant time compare the macs */
+
+	result = 0;
+
+	for (int i = 0; i < NC_ENCRYPTION_MAC_SIZE; i++)
+	{
+		result |= args->mac[i] - hmacOut[i];
+	}
+
+Cleanup:
+	/* Clean up sensitive data */
+	ZERO_FILL(&messageKey, sizeof(messageKey));
+	ZERO_FILL(&keys, sizeof(keys));
+	ZERO_FILL(hmacOut, NC_ENCRYPTION_MAC_SIZE);
+
+	return result;
+}
+
+NC_EXPORT NCResult NC_CC NCVerifyMac(
+	const NCContext* ctx,
+	const NCSecretKey* sk,
+	const NCPublicKey* pk,
+	NCMacVerifyArgs* args
+)
+{
+	CHECK_NULL_ARG(ctx, 0)
+	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_NULL_ARG(sk, 1)
+	CHECK_NULL_ARG(pk, 2)
+	CHECK_NULL_ARG(args, 3)
+
+	NCResult result;
+	struct shared_secret sharedSecret;
+	struct conversation_key conversationKey;
+
+	/* Computed the shared point so we can get the converstation key */
+	if ((result = _computeSharedSecret(ctx, sk, pk, &sharedSecret)) != NC_SUCCESS)
+	{
+		goto Cleanup;
+	}
+
+	if ((result = _computeConversationKey(ctx, _getSha256MdInfo(), &sharedSecret, &conversationKey)) != NC_SUCCESS)
+	{
+		goto Cleanup;
+	}
+
+	result = NCVerifyMacEx(ctx, (uint8_t*)&conversationKey, args);
+
+Cleanup:
+	/* Clean up sensitive data */
+	ZERO_FILL(&sharedSecret, sizeof(sharedSecret));
+	ZERO_FILL(&conversationKey, sizeof(conversationKey));
+
+	return result;
+}
\ No newline at end of file
diff --git a/src/noscrypt.h b/src/noscrypt.h
index 387d856..983206c 100644
--- a/src/noscrypt.h
+++ b/src/noscrypt.h
@@ -73,6 +73,7 @@
 #define NC_SHARED_SEC_SIZE 32
 #define NC_CONV_KEY_SIZE 32
 #define NC_HMAC_KEY_SIZE 32
+#define NC_ENCRYPTION_MAC_SIZE 32
 #define NC_MESSAGE_KEY_SIZE NIP44_MESSAGE_KEY_SIZE
 
 /*
@@ -168,6 +169,27 @@ typedef struct nc_encryption_struct {
 } NCCryptoData;
 
 /*
+* A structure for Nip44 message authentication code verification. This structure
+* is used to pass arguments to the NCVerifyMac and NCVerifyMacEx functions. 
+*/
+typedef struct nc_mac_verify {
+
+	/* The message authentication code certifying the Nip44 payload */
+	const uint8_t mac[NC_ENCRYPTION_MAC_SIZE];
+
+	/* The nonce used for the original message encryption */
+	const uint8_t nonce[NC_ENCRYPTION_NONCE_SIZE];
+
+	/* The message payload data */
+	const uint8_t* payload;
+
+	/* The size of the payload data */
+	size_t payloadSize;
+
+} NCMacVerifyArgs;
+
+
+/*
 	API FUNCTIONS
 */
 
@@ -397,6 +419,22 @@ NC_EXPORT NCResult NC_CC NCDecrypt(
 	NCCryptoData* args
 );
 
+/*
+* High level api for verifying a Nip44 message authentication code using a secret key 
+and a public key. Use the NCVerifyMacEx functions for extended verification functionality.
+* @param ctx A pointer to an existing library context
+* @param sk A pointer to the secret key
+* @param pk A pointer to the 32byte compressed public key (x-only serialized public key)
+* @param args A pointer to the mac verification arguments
+* @return NC_SUCCESS if the operation was successful, otherwise an error code. Use NCParseErrorCode to
+* the error code and positional argument that caused the error
+*/
+NC_EXPORT NCResult NC_CC NCVerifyMac(
+	const NCContext* ctx,
+	const NCSecretKey* sk,
+	const NCPublicKey* pk,
+	NCMacVerifyArgs* args
+);
 
 /*--------------------------------------
 *		EXTENDED ENCRYPTION API
@@ -481,4 +519,37 @@ NC_EXPORT NCResult NC_CC NCDecryptEx(
 	NCCryptoData* args
 );
 
+/*
+* Verifies a Nip44 message authentication code using the given conversation key.
+* @param ctx A pointer to the existing library context
+* @param conversationKey A pointer to the 32byte conversation key
+* @param args A pointer to the mac verification arguments
+* @return NC_SUCCESS if the operation was successful, otherwise an error code. Use NCParseErrorCode to
+* the error code and positional argument that caused the error.
+*/
+NC_EXPORT NCResult NC_CC NCVerifyMacEx(
+	const NCContext* ctx,
+	const uint8_t conversationKey[NC_CONV_KEY_SIZE],
+	NCMacVerifyArgs* args
+);
+
+/*
+* Computes a message authentication code for a given payload using the given hmacKey and writes the
+* mac to the hmacOut buffer.
+* @param ctx A pointer to the existing library context
+* @param hmacKey A pointer to the 32byte hmac key
+* @param payload A pointer to the payload data buffer
+* @param payloadSize The size of the payload data buffer
+* @param hmacOut A pointer to the 32byte buffer to write the mac to
+* @return NC_SUCCESS if the operation was successful, otherwise an error code. Use NCParseErrorCode to
+* the error code and positional argument that caused the error.
+*/
+NC_EXPORT NCResult NCComputeMac(
+	const NCContext* ctx,
+	const uint8_t hmacKey[NC_HMAC_KEY_SIZE],
+	const uint8_t* payload,
+	size_t payloadSize,
+	uint8_t hmacOut[NC_ENCRYPTION_MAC_SIZE]
+);
+
 #endif // !NOSCRYPT_H
diff --git a/tests/test.c b/tests/test.c
index 6c73466..0c35c21 100644
--- a/tests/test.c
+++ b/tests/test.c
@@ -243,7 +243,7 @@ static int TestPublicApiArgumentValidation(void)
     NCSecretKey secKey;
     NCPublicKey pubKey;
     NCCryptoData cryptoData;
-    uint8_t hmacOut[NC_HMAC_KEY_SIZE];
+    uint8_t hmacKeyOut[NC_HMAC_KEY_SIZE];
 
     PRINTL("TEST: Public API argument validation tests\n")
 
@@ -303,25 +303,25 @@ static int TestPublicApiArgumentValidation(void)
     cryptoData.outputData = sig64;
     FillRandomData(&cryptoData.nonce, 32);
 
-    TEST(NCEncrypt(NULL, &secKey, &pubKey, hmacOut, &cryptoData), ARG_ERROR_POS_0)
-    TEST(NCEncrypt(&ctx, NULL, &pubKey, hmacOut, &cryptoData), ARG_ERROR_POS_1)
-	TEST(NCEncrypt(&ctx, &secKey, NULL, hmacOut, &cryptoData), ARG_ERROR_POS_2)
+    TEST(NCEncrypt(NULL, &secKey, &pubKey, hmacKeyOut, &cryptoData), ARG_ERROR_POS_0)
+    TEST(NCEncrypt(&ctx, NULL, &pubKey, hmacKeyOut, &cryptoData), ARG_ERROR_POS_1)
+	TEST(NCEncrypt(&ctx, &secKey, NULL, hmacKeyOut, &cryptoData), ARG_ERROR_POS_2)
     TEST(NCEncrypt(&ctx, &secKey, &pubKey, NULL, &cryptoData), ARG_ERROR_POS_3)
-    TEST(NCEncrypt(&ctx, &secKey, &pubKey, hmacOut, NULL), ARG_ERROR_POS_4)
+    TEST(NCEncrypt(&ctx, &secKey, &pubKey, hmacKeyOut, NULL), ARG_ERROR_POS_4)
 
     //Test invalid data size
     cryptoData.dataSize = 0;
-    TEST(NCEncrypt(&ctx, &secKey, &pubKey, hmacOut, &cryptoData), ARG_RAMGE_ERROR_POS_4)
+    TEST(NCEncrypt(&ctx, &secKey, &pubKey, hmacKeyOut, &cryptoData), ARG_RAMGE_ERROR_POS_4)
     
     //Test null input data
     cryptoData.dataSize = 32;
     cryptoData.inputData = NULL;
-	TEST(NCEncrypt(&ctx, &secKey, &pubKey, hmacOut, &cryptoData), ARG_INVALID_ERROR_POS_4)
+	TEST(NCEncrypt(&ctx, &secKey, &pubKey, hmacKeyOut, &cryptoData), ARG_INVALID_ERROR_POS_4)
 
     //Test null output data
 	cryptoData.inputData = zero32;
     cryptoData.outputData = NULL;
-	TEST(NCEncrypt(&ctx, &secKey, &pubKey, hmacOut, &cryptoData), ARG_INVALID_ERROR_POS_4)
+	TEST(NCEncrypt(&ctx, &secKey, &pubKey, hmacKeyOut, &cryptoData), ARG_INVALID_ERROR_POS_4)
 
     //Decrypt
     cryptoData.dataSize = 32;
@@ -345,8 +345,17 @@ static int TestPublicApiArgumentValidation(void)
     //Test null output data
     cryptoData.inputData = zero32;
     cryptoData.outputData = NULL;
-	TEST(NCDecrypt(&ctx, &secKey, &pubKey, &cryptoData), ARG_INVALID_ERROR_POS_3)
-
+    TEST(NCDecrypt(&ctx, &secKey, &pubKey, &cryptoData), ARG_INVALID_ERROR_POS_3)
+    
+    {
+        uint8_t hmacDataOut[NC_ENCRYPTION_MAC_SIZE];
+        TEST(NCComputeMac(NULL, hmacKeyOut, zero32, 32, hmacDataOut), ARG_ERROR_POS_0)
+        TEST(NCComputeMac(&ctx, NULL, zero32, 32, hmacDataOut), ARG_ERROR_POS_1)
+        TEST(NCComputeMac(&ctx, hmacKeyOut, NULL, 32, hmacDataOut), ARG_ERROR_POS_2)
+        TEST(NCComputeMac(&ctx, hmacKeyOut, zero32, 0, hmacDataOut), ARG_RAMGE_ERROR_POS_3)
+        TEST(NCComputeMac(&ctx, hmacKeyOut, zero32, 32, NULL), ARG_ERROR_POS_4)
+    }
+    
     PRINTL("\nPASSED: Public API argument validation tests completed\n")
 
     return 0;