HMAC produces different strings in Python3 vs Golang

Question

I have a Golang function that calculates hmac for a given key and challenge. The go code is

func get_hmac64(psk string, challenge string) string {
    mac := hmac.New(sha3.New256, []byte(psk))
    mac.Write([]byte(challenge))
    macSum := mac.Sum(nil)
    var macSumB64 = make([]byte, (len(macSum)*8+5)/6)
    base64.URLEncoding.Encode(macSumB64, macSum)
    return string(macSumB64)
}

I translated this to Python3 as below.

    def get_hmac64(self, psk: str, challenge: str) ->str:
        """
        This generates a different string for same psk and challenge between Golang and Python3
        """
        psk_bytes = bytes(psk, "utf-8")
        challenge_bytes = bytes(challenge, "utf-8")
        mac = hmac.new(psk_bytes, challenge_bytes, hashlib.sha3_256)
        mac_digest = mac.digest()
        b64_encoded = base64.b64decode(mac_digest)
        return b64_encoded.decode("utf-8")
  
    print(get_hmac("abc", "def"))

For the python implementation the string returned is M1P63mj5ytdYUaJJ4m2UMtEKBgRG/K3AzHCW/TjIS1k= whereas for the Go code the generated input for the same key and string is qWISO-QliNl_dwhDBhkd3MaT

Shouldnt the value be same if the key, challenge and the hash remains same for the hmac implementation across languages? If so, what is the step that I missed in the Python translation?

Answer 1

The following code gives the same results as the one you report for your Python code:

func get_hmac64(psk string, challenge string) string {
    mac := hmac.New(sha3.New256, []byte(psk))
    mac.Write([]byte(challenge))
    macSum := mac.Sum(nil)
    return base64.StdEncoding.EncodeToString(macSum)
}

(Full code at https://go.dev/play/p/5lWG-jMfELz). The two differences are that I used sha3.New256 instead of the strange NewDragonHash, and that I fixed the base64 encoding by simply using the .EncodeToString() method.