Message Authentication Code
A message authentication code is calculated based with a private key. Only
owners of the corresponding private key can calculate and verify the
authentication code. Because the private key cannot be derived from the
generated hash this is a secure method to e.g. sign API calls which are
transmitted over unsafe transport channels. For example verification links
send via email.
Since Java 1.4
import java.nio.charset.StandardCharsets;
import java.util.HexFormat;
import javax.crypto.KeyGenerator;
import javax.crypto.Mac;
import javax.crypto.SecretKey;
public class MessageAuthenticationCode {
static void addSignature(Mac mac, String msg) {
mac.reset();
byte[] signature = mac.doFinal(msg.getBytes(StandardCharsets.UTF_8));
System.out.printf("%s&hmac=%s%n", msg, HexFormat.of().formatHex(signature));
}
public static void main(String[] args) throws Exception {
SecretKey key = KeyGenerator.getInstance("HmacSHA3-256").generateKey();
Mac mac = Mac.getInstance("HmacSHA3-256");
mac.init(key);
// Same content will create the same signature
addSignature(mac, "confirm=alice@example.com&date=20210917");
addSignature(mac, "confirm=alice@example.com&date=20210917");
// Different content will result in a different signature
addSignature(mac, "confirm=marvin@example.com&date=20210917");
}
}
This snippet at GitHub
