## self implement

package PRLab ;

import javacard.framework.*;
import javacard.security.*;

public class HMAC  
{
	private final short BLOCK_SIZE = (short)64;
	private byte[] prk;
	private byte[] msg;
	private MessageDigest sha256 = MessageDigest.getInstance(MessageDigest.ALG_SHA_256, false);
	private byte[] ikeypad = new byte[BLOCK_SIZE];
	private byte[] okeypad = new byte[BLOCK_SIZE];
	HMAC(byte[] input_key){
		if(input_key.length <= BLOCK_SIZE){
			prk = new byte[input_key.length];
			Util.arrayCopy(input_key, (short)0, prk, (short)0, (short)input_key.length);
		}else{
			prk = new byte[32];
			sha256.doFinal(input_key, (short)0, (short)input_key.length, prk, (short)0);
		}
		for(short i = 0; i<prk.length; i++){
			ikeypad[i] = (byte)(prk[i]^0x36);
			okeypad[i] = (byte)(prk[i]^0x5c);
		}
		// The Util.arrayFill() have a strange bug that will left some bytes would not be filled. 
		Util.arrayFillNonAtomic(ikeypad, (short)prk.length, (short)(ikeypad.length-prk.length), (byte)0x36);
		Util.arrayFillNonAtomic(okeypad, (short)prk.length, (short)(okeypad.length-prk.length), (byte)0x5c);
	}
	public void update(byte[] newMsg){
		if(msg == null){
			msg = new byte[newMsg.length]; 
			Util.arrayCopy(newMsg, (short)0, msg, (short)0, (short)newMsg.length);
			return;
		}
		byte[] temp = new byte[msg.length + newMsg.length];
		concat(msg, newMsg, temp);
		msg = temp;
		JCSystem.requestObjectDeletion();
	}
	public void doFinal(byte[] output, short offset){
		sha256.update(ikeypad, (short)0, (short)ikeypad.length);
		sha256.doFinal(msg, (short)0, (short)msg.length, output, (short)0);
		
		sha256.update(okeypad, (short)0, (short)okeypad.length);
		sha256.doFinal(output, (short)0, (short)32, output, (short)0);
		
	}
	private void concat(byte[] a, byte[] b, byte[] output){
		Util.arrayCopy(a, (short)0, output, (short)0, (short)a.length);
		Util.arrayCopy(b, (short)0, output, (short)a.length, (short)b.length);
	}
}

## javacard api
J3R180 not support..... orz

HMACKey hmacKey = (HMACKey)KeyBuilder.buildKey(
                        KeyBuilder.ALG_TYPE_HMAC, 
                        JCSystem.MEMORY_TYPE_TRANSIENT_DESELECT, 
                        KeyBuilder.LENGTH_HMAC_SHA_256_BLOCK_64, 
                        false
                    );
hmacKey.setKey(new byte[]{'P','A','S','S','W','O','R','D',}, (short)0, (short)8);
Signature hmac = Signature.getInstance(Signature.ALG_HMAC_SHA_256, false);
hmac.init(hmacKey, Signature.MODE_SIGN);
hmac.sign(new byte[]{'j','o','s','h',}, (short)0, (short)4, apdu.getBuffer(), (short)0);
apdu.setOutgoingAndSend((short)0, (short)32);
// 3A 91 62 FE EF 7B 24 F0 92 07 DC 8E CA 56 4B 7E 69 8D E3 18 94 C9 84 5A 86 EA 52 86 95 75 03 9B