Iso9797Alg3 - Retail MAC Calculation in Java

Iso9797Alg3MacTest.java

package cz.monetplus.mac;

import static org.assertj.core.api.Assertions.assertThat;

import org.apache.commons.codec.binary.Hex;
import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.Mac;
import org.bouncycastle.crypto.engines.DESEngine;
import org.bouncycastle.crypto.macs.ISO9797Alg3Mac;
import org.bouncycastle.crypto.params.KeyParameter;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Iso9797Alg3MacTest {

	private static final Logger log = LoggerFactory.getLogger(Iso9797Alg3MacTest.class);
	
	private static final String baseMsg = "30323030723c54c128e88001164761739001010010000000000000000350050911511500219811511505091012456702030011000811012345678901344761739001010010d10122011143878089303030303031303032313938574552543031333241424344454631323334353637383943415244204143434550544f52204e414d45202020202020205a4c494e202020202020202020435a7642313233343536373839303132333434355e504144494c4c412f4c2e202020202020202020202020202020205e39393031313230303030303030303030303030302a2a5858582a2a2a2a2a2a0203";
	private static final String macKey = "7CA110454A1A6E57E1ED3BF85377FE55";
	
	@Test
	public void iso9797Alg3MacTest() throws Exception {
		
		final BlockCipher cipher = new DESEngine();
		final KeyParameter key = createKey(Hex.decodeHex(macKey.toCharArray()));
		final byte[] dataToMac = Hex.decodeHex(baseMsg.toCharArray());
		final byte[] genMac = generateIso9797Alg3Mac(key, cipher, dataToMac);
		
		assertThat(genMac).isEqualTo(Hex.decodeHex("0015da835ffd7293".toCharArray()));
	}

	private byte[] generateIso9797Alg3Mac(KeyParameter key, BlockCipher cipher, byte[] data) {
		final Mac mac = new ISO9797Alg3Mac(cipher);
		mac.init(key);
		mac.update(data, 0, data.length);
		final byte[] out = new byte[8];
		mac.doFinal(out, 0);
		log.trace("Generated MAC : {}",Hex.encodeHexString(out));
		return out;
	}
	
	private static KeyParameter createKey(byte[] key) {
		if (key.length != 16) {
			throw new RuntimeException("Unsupported key len " + key.length + " B for ISO9797Alg3Mac");
		}
		return new KeyParameter(key);
	}
}