OpenPgpCfbBlockCipher
using Org.BouncyCastle.Crypto.Parameters;
using System;
namespace Org.BouncyCastle.Crypto.Modes
{
public class OpenPgpCfbBlockCipher : IBlockCipherMode, IBlockCipher
{
private byte[] IV;
private byte[] FR;
private byte[] FRE;
private readonly IBlockCipher cipher;
private readonly int blockSize;
private int count;
private bool forEncryption;
public IBlockCipher UnderlyingCipher => cipher;
public string AlgorithmName => cipher.AlgorithmName + "/OpenPGPCFB";
public bool IsPartialBlockOkay => true;
public OpenPgpCfbBlockCipher(IBlockCipher cipher)
{
this.cipher = cipher;
blockSize = cipher.GetBlockSize();
IV = new byte[blockSize];
FR = new byte[blockSize];
FRE = new byte[blockSize];
}
public int GetBlockSize()
{
return cipher.GetBlockSize();
}
public int ProcessBlock(byte[] input, int inOff, byte[] output, int outOff)
{
if (!forEncryption)
return DecryptBlock(input.AsSpan(inOff), output.AsSpan(outOff));
return EncryptBlock(input.AsSpan(inOff), output.AsSpan(outOff));
}
public int ProcessBlock(ReadOnlySpan<byte> input, Span<byte> output)
{
if (!forEncryption)
return DecryptBlock(input, output);
return EncryptBlock(input, output);
}
public void Reset()
{
count = 0;
Array.Copy(IV, 0, FR, 0, FR.Length);
}
public void Init(bool forEncryption, ICipherParameters parameters)
{
this.forEncryption = forEncryption;
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();
cipher.Init(true, parameters);
}
private byte EncryptByte(byte data, int blockOff)
{
return (byte)(FRE[blockOff] ^ data);
}
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");
if (count > blockSize) {
FR[blockSize - 2] = (output[0] = EncryptByte(input[0], blockSize - 2));
FR[blockSize - 1] = (output[1] = EncryptByte(input[1], blockSize - 1));
cipher.ProcessBlock(FR, FRE);
for (int i = 2; i < blockSize; i++) {
FR[i - 2] = (output[i] = EncryptByte(input[i], i - 2));
}
} else if (count == 0) {
cipher.ProcessBlock(FR, FRE);
for (int j = 0; j < blockSize; j++) {
FR[j] = (output[j] = EncryptByte(input[j], j));
}
count += blockSize;
} else if (count == blockSize) {
cipher.ProcessBlock(FR, FRE);
output[0] = EncryptByte(input[0], 0);
output[1] = EncryptByte(input[1], 1);
Array.Copy(FR, 2, FR, 0, blockSize - 2);
output.Slice(0, 2).CopyTo(FR.AsSpan(blockSize - 2));
cipher.ProcessBlock(FR, FRE);
for (int k = 2; k < blockSize; k++) {
FR[k - 2] = (output[k] = EncryptByte(input[k], k - 2));
}
count += blockSize;
}
return blockSize;
}
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");
if (count > blockSize) {
byte b = input[0];
FR[blockSize - 2] = b;
output[0] = EncryptByte(b, blockSize - 2);
b = input[1];
FR[blockSize - 1] = b;
output[1] = EncryptByte(b, blockSize - 1);
cipher.ProcessBlock(FR, FRE);
for (int i = 2; i < blockSize; i++) {
b = input[i];
FR[i - 2] = b;
output[i] = EncryptByte(b, i - 2);
}
} else if (count == 0) {
cipher.ProcessBlock(FR, FRE);
for (int j = 0; j < blockSize; j++) {
FR[j] = input[j];
output[j] = EncryptByte(input[j], j);
}
count += blockSize;
} else if (count == blockSize) {
cipher.ProcessBlock(FR, 0, FRE, 0);
byte b2 = input[0];
byte b3 = input[1];
output[0] = EncryptByte(b2, 0);
output[1] = EncryptByte(b3, 1);
Array.Copy(FR, 2, FR, 0, blockSize - 2);
FR[blockSize - 2] = b2;
FR[blockSize - 1] = b3;
cipher.ProcessBlock(FR, 0, FRE, 0);
for (int k = 2; k < blockSize; k++) {
byte b4 = input[k];
FR[k - 2] = b4;
output[k] = EncryptByte(b4, k - 2);
}
count += blockSize;
}
return blockSize;
}
}
}