HMAC-SHA256 Algorithm for signature calculation

Question

I am trying to create a signature using the HMAC-SHA256 algorithm and this is my code. I am using US ASCII encoding.

final Charset asciiCs = Charset.forName("US-ASCII"); final Mac sha256_HMAC = Mac.getInstance("HmacSHA256"); final SecretKeySpec secret_key = new javax.crypto.spec.SecretKeySpec(asciiCs.encode("key").array(), "HmacSHA256"); sha256_HMAC.init(secret_key); final byte[] mac_data = sha256_HMAC.doFinal(asciiCs.encode("The quick brown fox jumps over the lazy dog").array()); String result = ""; for (final byte element : mac_data) {     result += Integer.toString((element & 0xff) + 0x100, 16).substring(1); } System.out.println("Result:[" + result + "]"); 

The result that I am getting from the above code is:

f7bc83f430538424b13298e6aa6fb143ef4d59a14946175997479dbc2d1a3cd8 

This is same as to that of shown in the wiki

HMAC_SHA256("key", "The quick brown fox jumps over the lazy dog") = 0x f7bc83f430538424b13298e6aa6fb143ef4d59a14946175997479dbc2d1a3cd8 

except for the 0x.

I am looking for ideas/comments if I am doing everything right or may be I can improve my code.

Answer 1

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 

Answer 2

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.