HMAC-SHA256 Algorithm for signature calculation

If you're using Guava, its latest release now lets you use

 Hashing.hmacSha256()

One example of using this:

String hash = Hashing.hmacSha256("mykey".getBytes(StandardCharsets.UTF_8)).hashString("my_message", StandardCharsets.UTF_8).toString()

Further documentation here: https://guava.dev/releases/23.0/api/docs/com/google/common/hash/Hashing.html#hmacSha256-byte:A-

The 0x just denotes that the characters after it represent a hex string.

0x1A == 1Ah == 26 == 1A

So the 0x is just to clarify what format the output is in, no need to worry about it.

Here is my solution:

public static String encode(String key, String data) throws Exception {
  Mac sha256_HMAC = Mac.getInstance("HmacSHA256");
  SecretKeySpec secret_key = new SecretKeySpec(key.getBytes("UTF-8"), "HmacSHA256");
  sha256_HMAC.init(secret_key);

  return Hex.encodeHexString(sha256_HMAC.doFinal(data.getBytes("UTF-8")));
}

public static void main(String [] args) throws Exception {
  System.out.println(encode("key", "The quick brown fox jumps over the lazy dog"));
}

Or you can return the hash encoded in Base64:

Base64.encodeBase64String(sha256_HMAC.doFinal(data.getBytes("UTF-8")));

The output in hex is as expected:

f7bc83f430538424b13298e6aa6fb143ef4d59a14946175997479dbc2d1a3cd8