ElGamalSignaturepublic class ElGamalSignature extends SignatureSpi
| Fields Summary |
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| protected ElGamalKey | mKey | | protected ByteArrayOutputStream | mOut | | protected static BigInteger | kOne |
| Methods Summary |
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| protected java.lang.Object | engineGetParameter(java.lang.String param) return null;
| | protected void | engineInitSign(java.security.PrivateKey key)
if (!(key instanceof ElGamalPrivateKey))
throw new InvalidKeyException("I didn't get an ElGamalPrivateKey.");
mKey = (ElGamalKey)key;
mOut = new ByteArrayOutputStream();
| | protected void | engineInitVerify(java.security.PublicKey key)
if (!(key instanceof ElGamalPublicKey))
throw new InvalidKeyException("I didn't get an ElGamalPublicKey.");
mKey = (ElGamalKey)key;
mOut = new ByteArrayOutputStream();
| | protected void | engineSetParameter(java.lang.String param, java.lang.Object value)
| | protected byte[] | engineSign()
BigInteger x = ((ElGamalPrivateKey)mKey).getX();
BigInteger g = mKey.getG();
BigInteger p = mKey.getP();
BigInteger pminusone = p.subtract(kOne);
BigInteger k;
do {
k = new BigInteger(p.bitLength() - 1, new SecureRandom());
} while (k.gcd(pminusone).equals(kOne) == false);
BigInteger m = new BigInteger(1, mOut.toByteArray());
BigInteger a = g.modPow(k, p);
BigInteger top = m.subtract(x.multiply(a)).mod(pminusone);
BigInteger b = top.multiply(
k.modPow(kOne.negate(), pminusone)).mod(pminusone);
int modulusLength = (p.bitLength() + 7) / 8;
byte[] signature = new byte[modulusLength * 2];
byte[] aBytes = getBytes(a);
int aLength = aBytes.length;
byte[] bBytes = getBytes(b);
int bLength = bBytes.length;
System.arraycopy(aBytes, 0,
signature, modulusLength - aLength, aLength);
System.arraycopy(bBytes, 0,
signature, modulusLength * 2 - bLength, bLength);
return signature;
| | protected void | engineUpdate(byte b)
mOut.write(b);
| | protected void | engineUpdate(byte[] b, int off, int len)
mOut.write(b, off, len);
| | protected boolean | engineVerify(byte[] sigBytes)
BigInteger y = ((ElGamalPublicKey)mKey).getY();
BigInteger g = mKey.getG();
BigInteger p = mKey.getP();
int modulusLength = (p.bitLength() + 7) / 8;
byte[] aBytes = new byte[modulusLength];
byte[] bBytes = new byte[modulusLength];
System.arraycopy(sigBytes, 0, aBytes, 0, modulusLength);
System.arraycopy(sigBytes, modulusLength, bBytes, 0, modulusLength);
BigInteger a = new BigInteger(1, aBytes);
BigInteger b = new BigInteger(1, bBytes);
BigInteger first = y.modPow(a, p).multiply(a.modPow(b, p)).mod(p);
BigInteger m = new BigInteger(1, mOut.toByteArray());
BigInteger second = g.modPow(m,p);
return first.equals(second);
| | protected byte[] | getBytes(java.math.BigInteger big)
byte[] bigBytes = big.toByteArray();
if ((big.bitLength() % 8) != 0) {
return bigBytes;
}
else {
byte[] smallerBytes = new byte[big.bitLength() / 8];
System.arraycopy(bigBytes, 1, smallerBytes, 0, smallerBytes.length);
return smallerBytes;
}
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