// Copyright (c) 1999-2004 Brian Wellington (bwelling@xbill.org)
package org.xbill.DNS.utils;
import java.util.Arrays;
import java.security.*;
/**
* A pure java implementation of the HMAC-MD5 secure hash algorithm
*
* @author Brian Wellington
*/
public class HMAC {
MessageDigest digest;
private byte [] ipad, opad;
private static final byte IPAD = 0x36;
private static final byte OPAD = 0x5c;
private static final byte PADLEN = 64;
private void
init(byte [] key) {
int i;
if (key.length > PADLEN) {
key = digest.digest(key);
digest.reset();
}
ipad = new byte[PADLEN];
opad = new byte[PADLEN];
for (i = 0; i < key.length; i++) {
ipad[i] = (byte) (key[i] ^ IPAD);
opad[i] = (byte) (key[i] ^ OPAD);
}
for (; i < PADLEN; i++) {
ipad[i] = IPAD;
opad[i] = OPAD;
}
digest.update(ipad);
}
/**
* Creates a new HMAC instance
* @param digest The message digest object.
* @param key The secret key
*/
public
HMAC(MessageDigest digest, byte [] key) {
digest.reset();
this.digest = digest;
init(key);
}
/**
* Creates a new HMAC instance
* @param digestName The name of the message digest function.
* @param key The secret key.
*/
public
HMAC(String digestName, byte [] key) {
try {
digest = MessageDigest.getInstance(digestName);
} catch (NoSuchAlgorithmException e) {
throw new IllegalArgumentException("unknown digest algorithm "
+ digestName);
}
init(key);
}
/**
* Adds data to the current hash
* @param b The data
* @param offset The index at which to start adding to the hash
* @param length The number of bytes to hash
*/
public void
update(byte [] b, int offset, int length) {
digest.update(b, offset, length);
}
/**
* Adds data to the current hash
* @param b The data
*/
public void
update(byte [] b) {
digest.update(b);
}
/**
* Signs the data (computes the secure hash)
* @return An array with the signature
*/
public byte []
sign() {
byte [] output = digest.digest();
digest.reset();
digest.update(opad);
return digest.digest(output);
}
/**
* Verifies the data (computes the secure hash and compares it to the input)
* @param signature The signature to compare against
* @return true if the signature matched, false otherwise
*/
public boolean
verify(byte [] signature) {
return Arrays.equals(signature, sign());
}
/**
* Resets the HMAC object for further use
*/
public void
clear() {
digest.reset();
digest.update(ipad);
}
}
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