/**
* return true if the value r and s represent a DSA signature for the passed in message for
* standard DSA the message should be a SHA-1 hash of the real message to be verified.
*/
public boolean verifySignature(byte[] message, BigInteger r, BigInteger s) {
BigInteger m = new BigInteger(1, message);
DSAParameters params = key.getParameters();
BigInteger zero = BigInteger.valueOf(0);
if (zero.compareTo(r) >= 0 || params.getQ().compareTo(r) <= 0) {
return false;
}
if (zero.compareTo(s) >= 0 || params.getQ().compareTo(s) <= 0) {
return false;
}
BigInteger w = s.modInverse(params.getQ());
BigInteger u1 = m.multiply(w).mod(params.getQ());
BigInteger u2 = r.multiply(w).mod(params.getQ());
u1 = params.getG().modPow(u1, params.getP());
u2 = ((DSAPublicKeyParameters) key).getY().modPow(u2, params.getP());
BigInteger v = u1.multiply(u2).mod(params.getP()).mod(params.getQ());
return v.equals(r);
}
public boolean equals(Object obj) {
if (!(obj instanceof DSAParameters)) {
return false;
}
DSAParameters pm = (DSAParameters) obj;
return (pm.getP().equals(p) && pm.getQ().equals(q) && pm.getG().equals(g));
}
/**
* generate a signature for the given message using the key we were initialised with. For
* conventional DSA the message should be a SHA-1 hash of the message of interest.
*
* @param message the message that will be verified later.
*/
public BigInteger[] generateSignature(byte[] message) {
BigInteger m = new BigInteger(1, message);
DSAParameters params = key.getParameters();
BigInteger k;
do {
k = new BigInteger(params.getQ().bitLength(), random);
} while (k.compareTo(params.getQ()) >= 0);
BigInteger r = params.getG().modPow(k, params.getP()).mod(params.getQ());
k =
k.modInverse(params.getQ())
.multiply(m.add(((DSAPrivateKeyParameters) key).getX().multiply(r)));
BigInteger s = k.mod(params.getQ());
BigInteger[] res = new BigInteger[2];
res[0] = r;
res[1] = s;
return res;
}
