diff options
Diffstat (limited to 'core/src/main/java/org/bouncycastle/crypto/engines/ElGamalEngine.java')
| -rw-r--r-- | core/src/main/java/org/bouncycastle/crypto/engines/ElGamalEngine.java | 217 |
1 files changed, 0 insertions, 217 deletions
diff --git a/core/src/main/java/org/bouncycastle/crypto/engines/ElGamalEngine.java b/core/src/main/java/org/bouncycastle/crypto/engines/ElGamalEngine.java deleted file mode 100644 index ef8e799d..00000000 --- a/core/src/main/java/org/bouncycastle/crypto/engines/ElGamalEngine.java +++ /dev/null @@ -1,217 +0,0 @@ -package org.bouncycastle.crypto.engines; - -import java.math.BigInteger; -import java.security.SecureRandom; - -import org.bouncycastle.crypto.AsymmetricBlockCipher; -import org.bouncycastle.crypto.CipherParameters; -import org.bouncycastle.crypto.DataLengthException; -import org.bouncycastle.crypto.params.ElGamalKeyParameters; -import org.bouncycastle.crypto.params.ElGamalPrivateKeyParameters; -import org.bouncycastle.crypto.params.ElGamalPublicKeyParameters; -import org.bouncycastle.crypto.params.ParametersWithRandom; -import org.bouncycastle.util.BigIntegers; - -/** - * this does your basic ElGamal algorithm. - */ -public class ElGamalEngine - implements AsymmetricBlockCipher -{ - private ElGamalKeyParameters key; - private SecureRandom random; - private boolean forEncryption; - private int bitSize; - - private static final BigInteger ZERO = BigInteger.valueOf(0); - private static final BigInteger ONE = BigInteger.valueOf(1); - private static final BigInteger TWO = BigInteger.valueOf(2); - - /** - * initialise the ElGamal engine. - * - * @param forEncryption true if we are encrypting, false otherwise. - * @param param the necessary ElGamal key parameters. - */ - public void init( - boolean forEncryption, - CipherParameters param) - { - if (param instanceof ParametersWithRandom) - { - ParametersWithRandom p = (ParametersWithRandom)param; - - this.key = (ElGamalKeyParameters)p.getParameters(); - this.random = p.getRandom(); - } - else - { - this.key = (ElGamalKeyParameters)param; - this.random = new SecureRandom(); - } - - this.forEncryption = forEncryption; - - BigInteger p = key.getParameters().getP(); - - bitSize = p.bitLength(); - - if (forEncryption) - { - if (!(key instanceof ElGamalPublicKeyParameters)) - { - throw new IllegalArgumentException("ElGamalPublicKeyParameters are required for encryption."); - } - } - else - { - if (!(key instanceof ElGamalPrivateKeyParameters)) - { - throw new IllegalArgumentException("ElGamalPrivateKeyParameters are required for decryption."); - } - } - } - - /** - * Return the maximum size for an input block to this engine. - * For ElGamal this is always one byte less than the size of P on - * encryption, and twice the length as the size of P on decryption. - * - * @return maximum size for an input block. - */ - public int getInputBlockSize() - { - if (forEncryption) - { - return (bitSize - 1) / 8; - } - - return 2 * ((bitSize + 7) / 8); - } - - /** - * Return the maximum size for an output block to this engine. - * For ElGamal this is always one byte less than the size of P on - * decryption, and twice the length as the size of P on encryption. - * - * @return maximum size for an output block. - */ - public int getOutputBlockSize() - { - if (forEncryption) - { - return 2 * ((bitSize + 7) / 8); - } - - return (bitSize - 1) / 8; - } - - /** - * Process a single block using the basic ElGamal algorithm. - * - * @param in the input array. - * @param inOff the offset into the input buffer where the data starts. - * @param inLen the length of the data to be processed. - * @return the result of the ElGamal process. - * @exception DataLengthException the input block is too large. - */ - public byte[] processBlock( - byte[] in, - int inOff, - int inLen) - { - if (key == null) - { - throw new IllegalStateException("ElGamal engine not initialised"); - } - - int maxLength = forEncryption - ? (bitSize - 1 + 7) / 8 - : getInputBlockSize(); - - if (inLen > maxLength) - { - throw new DataLengthException("input too large for ElGamal cipher.\n"); - } - - BigInteger p = key.getParameters().getP(); - - if (key instanceof ElGamalPrivateKeyParameters) // decryption - { - byte[] in1 = new byte[inLen / 2]; - byte[] in2 = new byte[inLen / 2]; - - System.arraycopy(in, inOff, in1, 0, in1.length); - System.arraycopy(in, inOff + in1.length, in2, 0, in2.length); - - BigInteger gamma = new BigInteger(1, in1); - BigInteger phi = new BigInteger(1, in2); - - ElGamalPrivateKeyParameters priv = (ElGamalPrivateKeyParameters)key; - // a shortcut, which generally relies on p being prime amongst other things. - // if a problem with this shows up, check the p and g values! - BigInteger m = gamma.modPow(p.subtract(ONE).subtract(priv.getX()), p).multiply(phi).mod(p); - - return BigIntegers.asUnsignedByteArray(m); - } - else // encryption - { - byte[] block; - if (inOff != 0 || inLen != in.length) - { - block = new byte[inLen]; - - System.arraycopy(in, inOff, block, 0, inLen); - } - else - { - block = in; - } - - BigInteger input = new BigInteger(1, block); - - if (input.compareTo(p) >= 0) - { - throw new DataLengthException("input too large for ElGamal cipher.\n"); - } - - ElGamalPublicKeyParameters pub = (ElGamalPublicKeyParameters)key; - - int pBitLength = p.bitLength(); - BigInteger k = new BigInteger(pBitLength, random); - - while (k.equals(ZERO) || (k.compareTo(p.subtract(TWO)) > 0)) - { - k = new BigInteger(pBitLength, random); - } - - BigInteger g = key.getParameters().getG(); - BigInteger gamma = g.modPow(k, p); - BigInteger phi = input.multiply(pub.getY().modPow(k, p)).mod(p); - - byte[] out1 = gamma.toByteArray(); - byte[] out2 = phi.toByteArray(); - byte[] output = new byte[this.getOutputBlockSize()]; - - if (out1.length > output.length / 2) - { - System.arraycopy(out1, 1, output, output.length / 2 - (out1.length - 1), out1.length - 1); - } - else - { - System.arraycopy(out1, 0, output, output.length / 2 - out1.length, out1.length); - } - - if (out2.length > output.length / 2) - { - System.arraycopy(out2, 1, output, output.length - (out2.length - 1), out2.length - 1); - } - else - { - System.arraycopy(out2, 0, output, output.length - out2.length, out2.length); - } - - return output; - } - } -} |