OfbBlockCipher
using Org.BouncyCastle.Crypto.Parameters;
using System;
namespace Org.BouncyCastle.Crypto.Modes
{
public class OfbBlockCipher : IBlockCipherMode, IBlockCipher
{
private byte[] IV;
private byte[] ofbV;
private byte[] ofbOutV;
private readonly int blockSize;
private readonly IBlockCipher cipher;
public IBlockCipher UnderlyingCipher => cipher;
public string AlgorithmName => cipher.AlgorithmName + "/OFB" + (blockSize * 8).ToString();
public bool IsPartialBlockOkay => true;
public OfbBlockCipher(IBlockCipher cipher, int blockSize)
{
this.cipher = cipher;
this.blockSize = blockSize / 8;
IV = new byte[cipher.GetBlockSize()];
ofbV = new byte[cipher.GetBlockSize()];
ofbOutV = new byte[cipher.GetBlockSize()];
}
public void Init(bool forEncryption, ICipherParameters parameters)
{
ParametersWithIV parametersWithIV = parameters as ParametersWithIV;
if (parametersWithIV != null) {
byte[] iV = parametersWithIV.GetIV();
if (iV.Length < IV.Length) {
Array.Copy(iV, 0, IV, IV.Length - iV.Length, iV.Length);
for (int i = 0; i < IV.Length - iV.Length; i++) {
IV[i] = 0;
}
} else
Array.Copy(iV, 0, IV, 0, IV.Length);
parameters = parametersWithIV.Parameters;
}
Reset();
if (parameters != null)
cipher.Init(true, parameters);
}
public int GetBlockSize()
{
return blockSize;
}
public int ProcessBlock(byte[] input, int inOff, byte[] output, int outOff)
{
Check.DataLength(input, inOff, blockSize, "input buffer too short");
Check.OutputLength(output, outOff, blockSize, "output buffer too short");
cipher.ProcessBlock(ofbV, 0, ofbOutV, 0);
for (int i = 0; i < blockSize; i++) {
output[outOff + i] = (byte)(ofbOutV[i] ^ input[inOff + i]);
}
Array.Copy(ofbV, blockSize, ofbV, 0, ofbV.Length - blockSize);
Array.Copy(ofbOutV, 0, ofbV, ofbV.Length - blockSize, blockSize);
return blockSize;
}
public void Reset()
{
Array.Copy(IV, 0, ofbV, 0, IV.Length);
}
}
}