package org.bouncycastle.crypto.engines;
import org.bouncycastle.crypto.AsymmetricBlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.params.ParametersWithRandom;
import org.bouncycastle.crypto.params.RSAKeyParameters;
import org.bouncycastle.crypto.params.RSAPrivateCrtKeyParameters;
import java.math.BigInteger;
import java.security.SecureRandom;
/**
* this does your basic RSA algorithm with blinding
*/
public class RSABlindedEngine
implements AsymmetricBlockCipher
{
private static BigInteger ZERO = BigInteger.valueOf(0);
private RSACoreEngine core = new RSACoreEngine();
private RSAKeyParameters key;
private SecureRandom random;
/**
* initialise the RSA engine.
*
* @param forEncryption true if we are encrypting, false otherwise.
* @param param the necessary RSA key parameters.
*/
public void init(
boolean forEncryption,
CipherParameters param)
{
core.init(forEncryption, param);
if (param instanceof ParametersWithRandom)
{
ParametersWithRandom rParam = (ParametersWithRandom)param;
key = (RSAKeyParameters)rParam.getParameters();
random = rParam.getRandom();
}
else
{
key = (RSAKeyParameters)param;
random = new SecureRandom();
}
}
/**
* Return the maximum size for an input block to this engine.
* For RSA this is always one byte less than the key size on
* encryption, and the same length as the key size on decryption.
*
* @return maximum size for an input block.
*/
public int getInputBlockSize()
{
return core.getInputBlockSize();
}
/**
* Return the maximum size for an output block to this engine.
* For RSA this is always one byte less than the key size on
* decryption, and the same length as the key size on encryption.
*
* @return maximum size for an output block.
*/
public int getOutputBlockSize()
{
return core.getOutputBlockSize();
}
/**
* Process a single block using the basic RSA 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 RSA process.
* @exception DataLengthException the input block is too large.
*/
public byte[] processBlock(
byte[] in,
int inOff,
int inLen)
{
if (key == null)
{
throw new IllegalStateException("RSA engine not initialised");
}
if (key instanceof RSAPrivateCrtKeyParameters)
{
RSAPrivateCrtKeyParameters k = (RSAPrivateCrtKeyParameters)key;
BigInteger input = core.convertInput(in, inOff, inLen);
BigInteger m = k.getModulus();
BigInteger r = calculateR(m);
BigInteger result = core.processBlock(r.modPow(k.getPublicExponent(), m).multiply(input).mod(m));
return core.convertOutput(result.multiply(r.modInverse(m)).mod(m));
}
else
{
return core.convertOutput(core.processBlock(core.convertInput(in, inOff, inLen)));
}
}
/*
* calculate a random mess-with-their-heads value.
*/
private BigInteger calculateR(
BigInteger m)
{
int max = m.bitLength() - 1; // must be less than m.bitLength()
int min = max / 2;
int length = ((random.nextInt() & 0xff) * ((max - min) / 0xff)) + min;
BigInteger factor = new BigInteger(length, random);
while (factor.equals(ZERO))
{
factor = new BigInteger(length, random);
}
return factor;
}
}