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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 IRsa core;
private RsaKeyParameters key;
private SecureRandom random;
public RsaBlindedEngine()
: this(new RsaCoreEngine())
{
}
public RsaBlindedEngine(IRsa rsa)
{
this.core = rsa;
}
public virtual 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 virtual void Init(bool forEncryption, ICipherParameters param)
{
SecureRandom providedRandom = null;
if (param is ParametersWithRandom withRandom)
{
providedRandom = withRandom.Random;
param = withRandom.Parameters;
}
core.Init(forEncryption, param);
this.key = (RsaKeyParameters)param;
this.random = InitSecureRandom(needed: key is RsaPrivateCrtKeyParameters, providedRandom);
}
/**
* 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 virtual 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 virtual 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 virtual 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 = ProcessInput(input);
return core.ConvertOutput(result);
}
protected virtual SecureRandom InitSecureRandom(bool needed, SecureRandom provided)
{
return needed ? CryptoServicesRegistrar.GetSecureRandom(provided) : null;
}
private BigInteger ProcessInput(BigInteger input)
{
if (!(key is RsaPrivateCrtKeyParameters crt))
return core.ProcessBlock(input);
BigInteger e = crt.PublicExponent;
BigInteger m = crt.Modulus;
BigInteger r = BigIntegers.CreateRandomInRange(BigInteger.One, m.Subtract(BigInteger.One), random);
BigInteger blind = r.ModPow(e, m);
BigInteger unblind = BigIntegers.ModOddInverse(m, r);
BigInteger blindedInput = blind.Multiply(input).Mod(m);
BigInteger blindedResult = core.ProcessBlock(blindedInput);
return unblind.Multiply(blindedResult).Mod(m);
}
}
}
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