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I am new to iOS and Swift and I am using HMACSHA256 algorithm in Java as well as Swift. However, for same input values I am getting different result. I am not sure why.

This is my Java Code

 byte[] secret = new byte[] {0, 0, 0, 0, 38, 8, 117, -119};
 byte[] message = new byte[] {5, 96, 98, 37, 5, -110, 99, 2, -125, 
 88, 55};

 Mac sha256_HMAC = Mac.getInstance("HmacSHA256");
 SecretKeySpec secret_key = new SecretKeySpec(secret, 
"HmacSHA256");
 sha256_HMAC.init(secret_key);

 String hash = 
Base64.encodeBase64String(sha256_HMAC.doFinal(message));
 System.out.println(hash);

This is my Swift Code

func hmac(algorithm: CryptoAlgorithm, key: String) -> String {

        let str = self.cString(using: String.Encoding.utf8)
        let strLen = Int(self.lengthOfBytes(using: 
String.Encoding.utf8))
        let digestLen = algorithm.digestLength
        let result = 
UnsafeMutablePointer<CUnsignedChar>.allocate(capacity: digestLen)
        let keyStr = key.cString(using: String.Encoding.utf8)
        let keyLen = Int(key.lengthOfBytes(using: 
String.Encoding.utf8))


        CCHmac(algorithm.HMACAlgorithm, keyStr, keyLen, str, 
strLen, result)

        let digest = stringFromResult(result: result, length: 
digestLen)

        //result.deallocate(capacity: digestLen)
        result.deallocate()
        return digest

    }

     private func stringFromResult(result: 
UnsafeMutablePointer<CUnsignedChar>, length: Int) -> String {

        let hash = NSMutableString()

        for i in 0..<length {

            hash.appendFormat("%02x", result[i])

        }

    return String(hash).lowercased()

}

The input to both functions are same 

byte[] secret = new byte[] {0, 0, 0, 0, 38, 8, 117, -119};
byte[] message = new byte[] {5, 96, 98, 37, 5, -110, 99, 2, -125, 88, 55};

Below is the result I am expecting

Exact result in byte array [-18, -12, 79, 109, 84, 107, 37, 114, 80, 22, 83, 18, 126, -123, -73, -38, 120, -79, 49, 87, -109, -30, -103, -17, -87, 69, 117, 3, -89, 36, -46, 108]

Result in String - 7vRPbVRrJXJQFlMSfoW32nixMVeT4pnvqUV1A6ck0mw=
Ashish Kirpan
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    You're not doing any base64 encoding in your Swift variant, is that an oversight? – Gereon Aug 09 '19 at 08:47
  • I tried with below code, but still not working. – Ashish Kirpan Aug 09 '19 at 09:41
  • func base64Encoded() -> String? { return data(using: .utf8)?.base64EncodedString() } – Ashish Kirpan Aug 09 '19 at 09:51
  • I had some debugging and I think this issue is related to input to Hmac. In java the input to hmac algo is in byte array however, in swift input to hmac is in String format. I converted the above byte array input in hexString but still the final digest value in both the cases (java and swift) is different. I also tried to generate the hmac value [named https://www.freeformatter.com/hmac-generator.html#ad-output]here using that hex input but the output is still different. – Ashish Kirpan Aug 12 '19 at 05:42

0 Answers0