/**
* Generate a signature for the message we've been loaded with using the key we were initialised
* with.
*/
public byte[] generateSignature() throws CryptoException, DataLengthException {
if (!forSigning) {
throw new IllegalStateException("RSADigestSigner not initialised for signature generation.");
}
byte[] hash = new byte[digest.getDigestSize()];
digest.doFinal(hash, 0);
try {
byte[] data = derEncode(hash);
return rsaEngine.processBlock(data, 0, data.length);
} catch (IOException e) {
throw new CryptoException("unable to encode signature: " + e.getMessage(), e);
}
}
/**
* return true if the internal state represents the signature described in the passed in array.
*/
public boolean verifySignature(byte[] signature) {
if (forSigning) {
throw new IllegalStateException("RSADigestSigner not initialised for verification");
}
byte[] hash = new byte[digest.getDigestSize()];
digest.doFinal(hash, 0);
byte[] sig;
byte[] expected;
try {
sig = rsaEngine.processBlock(signature, 0, signature.length);
expected = derEncode(hash);
} catch (Exception e) {
return false;
}
if (sig.length == expected.length) {
return Arrays.constantTimeAreEqual(sig, expected);
} else if (sig.length == expected.length - 2) // NULL left out
{
int sigOffset = sig.length - hash.length - 2;
int expectedOffset = expected.length - hash.length - 2;
expected[1] -= 2; // adjust lengths
expected[3] -= 2;
int nonEqual = 0;
for (int i = 0; i < hash.length; i++) {
nonEqual |= (sig[sigOffset + i] ^ expected[expectedOffset + i]);
}
for (int i = 0; i < sigOffset; i++) {
nonEqual |= (sig[i] ^ expected[i]); // check header less NULL
}
return nonEqual == 0;
} else {
return false;
}
}
/**
* initialise the signer for signing or verification.
*
* @param forSigning true if for signing, false otherwise
* @param parameters necessary parameters.
*/
public void init(boolean forSigning, CipherParameters parameters) {
this.forSigning = forSigning;
AsymmetricKeyParameter k;
if (parameters instanceof ParametersWithRandom) {
k = (AsymmetricKeyParameter) ((ParametersWithRandom) parameters).getParameters();
} else {
k = (AsymmetricKeyParameter) parameters;
}
if (forSigning && !k.isPrivate()) {
throw new IllegalArgumentException("signing requires private key");
}
if (!forSigning && k.isPrivate()) {
throw new IllegalArgumentException("verification requires public key");
}
reset();
rsaEngine.init(forSigning, parameters);
}