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using System;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Utilities;
namespace Org.BouncyCastle.Crypto.Modes
{
/**
* implements Cipher-Block-Chaining (CBC) mode on top of a simple cipher.
*/
public sealed class CbcBlockCipher
: IBlockCipherMode
{
private byte[] IV, cbcV, cbcNextV;
private int blockSize;
private IBlockCipher cipher;
private bool encrypting;
/**
* Basic constructor.
*
* @param cipher the block cipher to be used as the basis of chaining.
*/
public CbcBlockCipher(
IBlockCipher cipher)
{
this.cipher = cipher;
this.blockSize = cipher.GetBlockSize();
this.IV = new byte[blockSize];
this.cbcV = new byte[blockSize];
this.cbcNextV = new byte[blockSize];
}
/**
* return the underlying block cipher that we are wrapping.
*
* @return the underlying block cipher that we are wrapping.
*/
public IBlockCipher UnderlyingCipher => cipher;
/**
* Initialise the cipher and, possibly, the initialisation vector (IV).
* If an IV isn't passed as part of the parameter, the IV will be all zeros.
*
* @param forEncryption if true the cipher is initialised for
* encryption, if false for decryption.
* @param param the key and other data required by the cipher.
* @exception ArgumentException if the parameters argument is
* inappropriate.
*/
public void Init(bool forEncryption, ICipherParameters parameters)
{
bool oldEncrypting = this.encrypting;
this.encrypting = forEncryption;
if (parameters is ParametersWithIV ivParam)
{
if (ivParam.IVLength != blockSize)
throw new ArgumentException("initialisation vector must be the same length as block size");
ivParam.CopyIVTo(IV, 0, blockSize);
parameters = ivParam.Parameters;
}
else
{
Arrays.Fill(IV, 0x00);
}
Reset();
// if null it's an IV changed only (key is to be reused).
if (parameters != null)
{
cipher.Init(encrypting, parameters);
}
else if (oldEncrypting != encrypting)
{
throw new ArgumentException("cannot change encrypting state without providing key.");
}
}
/**
* return the algorithm name and mode.
*
* @return the name of the underlying algorithm followed by "/CBC".
*/
public string AlgorithmName
{
get { return cipher.AlgorithmName + "/CBC"; }
}
public bool IsPartialBlockOkay
{
get { return false; }
}
/**
* return the block size of the underlying cipher.
*
* @return the block size of the underlying cipher.
*/
public int GetBlockSize()
{
return cipher.GetBlockSize();
}
public int ProcessBlock(byte[] input, int inOff, byte[] output, int outOff)
{
#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
return encrypting
? EncryptBlock(input.AsSpan(inOff), output.AsSpan(outOff))
: DecryptBlock(input.AsSpan(inOff), output.AsSpan(outOff));
#else
return encrypting
? EncryptBlock(input, inOff, output, outOff)
: DecryptBlock(input, inOff, output, outOff);
#endif
}
#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
public int ProcessBlock(ReadOnlySpan<byte> input, Span<byte> output)
{
return encrypting
? EncryptBlock(input, output)
: DecryptBlock(input, output);
}
#endif
/**
* reset the chaining vector back to the IV and reset the underlying
* cipher.
*/
public void Reset()
{
Array.Copy(IV, 0, cbcV, 0, IV.Length);
Array.Clear(cbcNextV, 0, cbcNextV.Length);
}
#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
private int EncryptBlock(ReadOnlySpan<byte> input, Span<byte> output)
{
Check.DataLength(input, blockSize, "input buffer too short");
Check.OutputLength(output, blockSize, "output buffer too short");
for (int i = 0; i < blockSize; i++)
{
cbcV[i] ^= input[i];
}
int length = cipher.ProcessBlock(cbcV, output);
output[..blockSize].CopyTo(cbcV);
return length;
}
private int DecryptBlock(ReadOnlySpan<byte> input, Span<byte> output)
{
Check.DataLength(input, blockSize, "input buffer too short");
Check.OutputLength(output, blockSize, "output buffer too short");
input[..blockSize].CopyTo(cbcNextV);
int length = cipher.ProcessBlock(input, output);
for (int i = 0; i < blockSize; i++)
{
output[i] ^= cbcV[i];
}
byte[] tmp = cbcV;
cbcV = cbcNextV;
cbcNextV = tmp;
return length;
}
#else
private int EncryptBlock(byte[] input, int inOff, byte[] outBytes, int outOff)
{
Check.DataLength(input, inOff, blockSize, "input buffer too short");
Check.OutputLength(outBytes, outOff, blockSize, "output buffer too short");
for (int i = 0; i < blockSize; i++)
{
cbcV[i] ^= input[inOff + i];
}
int length = cipher.ProcessBlock(cbcV, 0, outBytes, outOff);
Array.Copy(outBytes, outOff, cbcV, 0, cbcV.Length);
return length;
}
private int DecryptBlock(byte[] input, int inOff, byte[] outBytes, int outOff)
{
Check.DataLength(input, inOff, blockSize, "input buffer too short");
Check.OutputLength(outBytes, outOff, blockSize, "output buffer too short");
Array.Copy(input, inOff, cbcNextV, 0, blockSize);
int length = cipher.ProcessBlock(input, inOff, outBytes, outOff);
for (int i = 0; i < blockSize; i++)
{
outBytes[outOff + i] ^= cbcV[i];
}
byte[] tmp = cbcV;
cbcV = cbcNextV;
cbcNextV = tmp;
return length;
}
#endif
}
}
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