using System;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Parameters;
namespace Org.BouncyCastle.Crypto.Encodings{
/**
* ISO 9796-1 padding. Note in the light of recent results you should
* only use this with RSA (rather than the "simpler" Rabin keys) and you
* should never use it with anything other than a hash (ie. even if the
* message is small don't sign the message, sign it's hash) or some "random"
* value. See your favorite search engine for details.
*/
public class ISO9796d1Encoding
: IAsymmetricBlockCipher
{
private static readonly byte[] shadows = { 0xe, 0x3, 0x5, 0x8, 0x9, 0x4, 0x2, 0xf,
0x0, 0xd, 0xb, 0x6, 0x7, 0xa, 0xc, 0x1 };
private static readonly byte[] inverse = { 0x8, 0xf, 0x6, 0x1, 0x5, 0x2, 0xb, 0xc,
0x3, 0x4, 0xd, 0xa, 0xe, 0x9, 0x0, 0x7 };
private readonly IAsymmetricBlockCipher engine;
private bool forEncryption;
private int bitSize;
private int padBits = 0;
public ISO9796d1Encoding(
IAsymmetricBlockCipher cipher)
{
this.engine = cipher;
}
public string AlgorithmName
{
get { return engine.AlgorithmName + "/ISO9796-1Padding"; }
}
public IAsymmetricBlockCipher GetUnderlyingCipher()
{
return engine;
}
public void Init(
bool forEncryption,
ICipherParameters parameters)
{
RsaKeyParameters kParam;
if (parameters is ParametersWithRandom)
{
ParametersWithRandom rParam = (ParametersWithRandom)parameters;
kParam = (RsaKeyParameters)rParam.Parameters;
}
else
{
kParam = (RsaKeyParameters)parameters;
}
engine.Init(forEncryption, parameters);
bitSize = kParam.Modulus.BitLength;
this.forEncryption = forEncryption;
}
/**
* return the input block size. The largest message we can process
* is (key_size_in_bits + 3)/16, which in our world comes to
* key_size_in_bytes / 2.
*/
public int GetInputBlockSize()
{
int baseBlockSize = engine.GetInputBlockSize();
if (forEncryption)
{
return (baseBlockSize + 1) / 2;
}
else
{
return baseBlockSize;
}
}
/**
* return the maximum possible size for the output.
*/
public int GetOutputBlockSize()
{
int baseBlockSize = engine.GetOutputBlockSize();
if (forEncryption)
{
return baseBlockSize;
}
else
{
return (baseBlockSize + 1) / 2;
}
}
/**
* set the number of bits in the next message to be treated as
* pad bits.
*/
public void SetPadBits(
int padBits)
{
if (padBits > 7)
{
throw new ArgumentException("padBits > 7");
}
this.padBits = padBits;
}
/**
* retrieve the number of pad bits in the last decoded message.
*/
public int GetPadBits()
{
return padBits;
}
public byte[] ProcessBlock(
byte[] input,
int inOff,
int length)
{
if (forEncryption)
{
return EncodeBlock(input, inOff, length);
}
else
{
return DecodeBlock(input, inOff, length);
}
}
private byte[] EncodeBlock(
byte[] input,
int inOff,
int inLen)
{
byte[] block = new byte[(bitSize + 7) / 8];
int r = padBits + 1;
int z = inLen;
int t = (bitSize + 13) / 16;
for (int i = 0; i < t; i += z)
{
if (i > t - z)
{
Array.Copy(input, inOff + inLen - (t - i),
block, block.Length - t, t - i);
}
else
{
Array.Copy(input, inOff, block, block.Length - (i + z), z);
}
}
for (int i = block.Length - 2 * t; i != block.Length; i += 2)
{
byte val = block[block.Length - t + i / 2];
block[i] = (byte)((shadows[(uint) (val & 0xff) >> 4] << 4)
| shadows[val & 0x0f]);
block[i + 1] = val;
}
block[block.Length - 2 * z] ^= (byte) r;
block[block.Length - 1] = (byte)((block[block.Length - 1] << 4) | 0x06);
int maxBit = (8 - (bitSize - 1) % 8);
int offSet = 0;
if (maxBit != 8)
{
block[0] &= (byte) ((ushort) 0xff >> maxBit);
block[0] |= (byte) ((ushort) 0x80 >> maxBit);
}
else
{
block[0] = 0x00;
block[1] |= 0x80;
offSet = 1;
}
return engine.ProcessBlock(block, offSet, block.Length - offSet);
}
/**
* @exception InvalidCipherTextException if the decrypted block is not a valid ISO 9796 bit string
*/
private byte[] DecodeBlock(
byte[] input,
int inOff,
int inLen)
{
byte[] block = engine.ProcessBlock(input, inOff, inLen);
int r = 1;
int t = (bitSize + 13) / 16;
if ((block[block.Length - 1] & 0x0f) != 0x6)
{
throw new InvalidCipherTextException("invalid forcing byte in block");
}
block[block.Length - 1] =
(byte)(((ushort)(block[block.Length - 1] & 0xff) >> 4)
| ((inverse[(block[block.Length - 2] & 0xff) >> 4]) << 4));
block[0] = (byte)((shadows[(uint) (block[1] & 0xff) >> 4] << 4)
| shadows[block[1] & 0x0f]);
bool boundaryFound = false;
int boundary = 0;
for (int i = block.Length - 1; i >= block.Length - 2 * t; i -= 2)
{
int val = ((shadows[(uint) (block[i] & 0xff) >> 4] << 4)
| shadows[block[i] & 0x0f]);
if (((block[i - 1] ^ val) & 0xff) != 0)
{
if (!boundaryFound)
{
boundaryFound = true;
r = (block[i - 1] ^ val) & 0xff;
boundary = i - 1;
}
else
{
throw new InvalidCipherTextException("invalid tsums in block");
}
}
}
block[boundary] = 0;
byte[] nblock = new byte[(block.Length - boundary) / 2];
for (int i = 0; i < nblock.Length; i++)
{
nblock[i] = block[2 * i + boundary + 1];
}
padBits = r - 1;
return nblock;
}
}
}
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