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using System;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Security;
using Org.BouncyCastle.Utilities;
namespace Org.BouncyCastle.Crypto.Engines
{
/**
* this does your basic RSA algorithm with blinding
*/
public class RsaBlindedEngine
: IAsymmetricBlockCipher
{
private readonly RsaCoreEngine core = new RsaCoreEngine();
private RsaKeyParameters key;
private SecureRandom random;
public string AlgorithmName
{
get { return "RSA"; }
}
/**
* initialise the RSA engine.
*
* @param forEncryption true if we are encrypting, false otherwise.
* @param param the necessary RSA key parameters.
*/
public void Init(
bool forEncryption,
ICipherParameters param)
{
core.Init(forEncryption, param);
if (param is ParametersWithRandom)
{
ParametersWithRandom rParam = (ParametersWithRandom)param;
key = (RsaKeyParameters)rParam.Parameters;
random = rParam.Random;
}
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 inBuf 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[] inBuf,
int inOff,
int inLen)
{
if (key == null)
throw new InvalidOperationException("RSA engine not initialised");
BigInteger input = core.ConvertInput(inBuf, inOff, inLen);
BigInteger result;
if (key is RsaPrivateCrtKeyParameters)
{
RsaPrivateCrtKeyParameters k = (RsaPrivateCrtKeyParameters)key;
BigInteger e = k.PublicExponent;
if (e != null) // can't do blinding without a public exponent
{
BigInteger m = k.Modulus;
BigInteger r = BigIntegers.CreateRandomInRange(
BigInteger.One, m.Subtract(BigInteger.One), random);
BigInteger blindedInput = r.ModPow(e, m).Multiply(input).Mod(m);
BigInteger blindedResult = core.ProcessBlock(blindedInput);
BigInteger rInv = r.ModInverse(m);
result = blindedResult.Multiply(rInv).Mod(m);
}
else
{
result = core.ProcessBlock(input);
}
}
else
{
result = core.ProcessBlock(input);
}
return core.ConvertOutput(result);
}
}
}
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