/*
* The PRF is defined as:
*
* PRF(secret, label, seed) = P_MD5(S1, label + seed) XOR
* P_SHA-1(S2, label + seed);
*
* P_hash is defined as:
*
* P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) +
* HMAC_hash(secret, A(2) + seed) +
* HMAC_hash(secret, A(3) + seed) + ...
*
* And A() is defined as:
*
* A(0) = seed
* A(i) = HMAC_hash(secret, A(i-1))
*
* For simplicity, we compute an 80-byte block on each call, which
* corresponds to five iterations of MD5, and four of SHA-1.
*/
private synchronized void fillBuffer() {
int len = hmac_md5.macSize();
for (int i = 0; i < buffer.length; i += len) {
hmac_md5.update(md5_a, 0, md5_a.length);
hmac_md5.update(seed, 0, seed.length);
byte[] b = hmac_md5.digest();
hmac_md5.reset();
System.arraycopy(b, 0, buffer, i, len);
hmac_md5.update(md5_a, 0, md5_a.length);
md5_a = hmac_md5.digest();
hmac_md5.reset();
}
len = hmac_sha.macSize();
for (int i = 0; i < buffer.length; i += len) {
hmac_sha.update(sha_a, 0, sha_a.length);
hmac_sha.update(seed, 0, seed.length);
byte[] b = hmac_sha.digest();
hmac_sha.reset();
for (int j = 0; j < len; j++) {
buffer[j + i] ^= b[j];
}
hmac_sha.update(sha_a, 0, sha_a.length);
sha_a = hmac_sha.digest();
hmac_sha.reset();
}
idx = 0;
}
public void init(Map attributes) {
HashMap sha_attr = new HashMap();
HashMap md5_attr = new HashMap();
byte[] secret = (byte[]) attributes.get(SECRET);
if (secret != null) {
int l = (secret.length >>> 1) + (secret.length & 1);
byte[] s1 = Util.trim(secret, 0, l);
byte[] s2 = Util.trim(secret, secret.length - l, l);
md5_attr.put(IMac.MAC_KEY_MATERIAL, s1);
sha_attr.put(IMac.MAC_KEY_MATERIAL, s2);
try {
hmac_md5.init(md5_attr);
hmac_sha.init(sha_attr);
} catch (InvalidKeyException ike) {
throw new Error(ike.toString());
}
} else if (!init) {
throw new IllegalArgumentException("no secret supplied");
}
// else re-use
byte[] seeed = (byte[]) attributes.get(SEED);
if (seeed != null) {
seed = (byte[]) seeed.clone();
} else if (!init) {
throw new IllegalArgumentException("no seed supplied");
}
// else re-use
// A(0) is the seed, A(1) = HMAC_hash(secret, A(0)).
hmac_md5.update(seed, 0, seed.length);
md5_a = hmac_md5.digest();
hmac_md5.reset();
hmac_sha.update(seed, 0, seed.length);
sha_a = hmac_sha.digest();
hmac_sha.reset();
fillBuffer();
init = true;
}
