Matching Java SHA2 Output vs MySQL SHA2 Output

Question

When I reproduce a SHA2 hash via the following code:

MessageDigest digest = MessageDigest.getInstance(\"SHA-256\");
digest.digest(\"A\".getBytes(\"UTF-8\"));


        

Answer 1

First check out your DB result it looks like your initial hash is actually a SHA-224 not SHA-256:

mysql> SELECT SHA2("A", 224);
+----------------------------------------------------------+
| SHA2("A", 224)                                           |
+----------------------------------------------------------+
| 5cfe2cddbb9940fb4d8505e25ea77e763a0077693dbb01b1a6aa94f2 |
+----------------------------------------------------------+
1 row in set (0.00 sec)

Instead of:

mysql> SELECT SHA2("A", 256);
+------------------------------------------------------------------+
| SHA2("A", 256)                                                   |
+------------------------------------------------------------------+
| 559aead08264d5795d3909718cdd05abd49572e84fe55590eef31a88a08fdffd |
+------------------------------------------------------------------+
1 row in set (0.06 sec)

From there you're on the right track you just need to convert the byte[] output to a hex string.

import java.security.MessageDigest;

public class TestSHA256 {

    public static void main(String[] args) {
        try {
            MessageDigest digest = MessageDigest.getInstance("SHA-256");
            byte[] hash = digest.digest("A".getBytes("UTF-8"));

            StringBuilder hexString = new StringBuilder();
            for (int i: hash) {
                hexString.append(Integer.toHexString(0XFF & i));
            }
            System.out.println(hexString);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Output:

559aead08264d5795d399718cdd5abd49572e84fe55590eef31a88a08fdffd

Answer 2

Integer.toHexString(0XFF & i) must be replaced with String.format("%02x", 0XFF & i), otherwise it only produces a 1 character output, while 2 characters are expected.