/** * 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); }