hmacSha512 function
Implementation
Uint8List hmacSha512(Uint8List key, Uint8List input) {
HMac hMac = HMac.withDigest(SHA512Digest());
hMac.init(KeyParameter(key));
hMac.update(input, 0, input.length);
Uint8List out = Uint8List(64);
hMac.doFinal(out, 0);
return out;
}