using System;
using Org.BouncyCastle.Crypto.Parameters;
namespace Org.BouncyCastle.Crypto.Engines{
/**
* The specification for RC5 came from the <code>RC5 Encryption Algorithm</code>
* publication in RSA CryptoBytes, Spring of 1995.
* <em>http://www.rsasecurity.com/rsalabs/cryptobytes</em>.
* <p>
* This implementation is set to work with a 64 bit word size.</p>
*/
public class RC564Engine
: IBlockCipher
{
private static readonly int wordSize = 64;
private static readonly int bytesPerWord = wordSize / 8;
/*
* the number of rounds to perform
*/
private int _noRounds;
/*
* the expanded key array of size 2*(rounds + 1)
*/
private long [] _S;
/*
* our "magic constants" for wordSize 62
*
* Pw = Odd((e-2) * 2^wordsize)
* Qw = Odd((o-2) * 2^wordsize)
*
* where e is the base of natural logarithms (2.718281828...)
* and o is the golden ratio (1.61803398...)
*/
private static readonly long P64 = unchecked( (long) 0xb7e151628aed2a6bL);
private static readonly long Q64 = unchecked( (long) 0x9e3779b97f4a7c15L);
private bool forEncryption;
/**
* Create an instance of the RC5 encryption algorithm
* and set some defaults
*/
public RC564Engine()
{
_noRounds = 12;
// _S = null;
}
public string AlgorithmName
{
get { return "RC5-64"; }
}
public bool IsPartialBlockOkay
{
get { return false; }
}
public int GetBlockSize()
{
return 2 * bytesPerWord;
}
/**
* initialise a RC5-64 cipher.
*
* @param forEncryption whether or not we are for encryption.
* @param parameters the parameters required to set up the cipher.
* @exception ArgumentException if the parameters argument is
* inappropriate.
*/
public void Init(
bool forEncryption,
ICipherParameters parameters)
{
if (!(typeof(RC5Parameters).IsInstanceOfType(parameters)))
{
throw new ArgumentException("invalid parameter passed to RC564 init - " + parameters.GetType().ToString());
}
RC5Parameters p = (RC5Parameters)parameters;
this.forEncryption = forEncryption;
_noRounds = p.Rounds;
SetKey(p.GetKey());
}
public int ProcessBlock(
byte[] input,
int inOff,
byte[] output,
int outOff)
{
return (forEncryption) ? EncryptBlock(input, inOff, output, outOff)
: DecryptBlock(input, inOff, output, outOff);
}
public void Reset()
{
}
/**
* Re-key the cipher.
*
* @param key the key to be used
*/
private void SetKey(
byte[] key)
{
//
// KEY EXPANSION:
//
// There are 3 phases to the key expansion.
//
// Phase 1:
// Copy the secret key K[0...b-1] into an array L[0..c-1] of
// c = ceil(b/u), where u = wordSize/8 in little-endian order.
// In other words, we fill up L using u consecutive key bytes
// of K. Any unfilled byte positions in L are zeroed. In the
// case that b = c = 0, set c = 1 and L[0] = 0.
//
long[] L = new long[(key.Length + (bytesPerWord - 1)) / bytesPerWord];
for (int i = 0; i != key.Length; i++)
{
L[i / bytesPerWord] += (long)(key[i] & 0xff) << (8 * (i % bytesPerWord));
}
//
// Phase 2:
// Initialize S to a particular fixed pseudo-random bit pattern
// using an arithmetic progression modulo 2^wordsize determined
// by the magic numbers, Pw & Qw.
//
_S = new long[2*(_noRounds + 1)];
_S[0] = P64;
for (int i=1; i < _S.Length; i++)
{
_S[i] = (_S[i-1] + Q64);
}
//
// Phase 3:
// Mix in the user's secret key in 3 passes over the arrays S & L.
// The max of the arrays sizes is used as the loop control
//
int iter;
if (L.Length > _S.Length)
{
iter = 3 * L.Length;
}
else
{
iter = 3 * _S.Length;
}
long A = 0, B = 0;
int ii = 0, jj = 0;
for (int k = 0; k < iter; k++)
{
A = _S[ii] = RotateLeft(_S[ii] + A + B, 3);
B = L[jj] = RotateLeft( L[jj] + A + B, A+B);
ii = (ii+1) % _S.Length;
jj = (jj+1) % L.Length;
}
}
/**
* Encrypt the given block starting at the given offset and place
* the result in the provided buffer starting at the given offset.
*
* @param in in byte buffer containing data to encrypt
* @param inOff offset into src buffer
* @param out out buffer where encrypted data is written
* @param outOff offset into out buffer
*/
private int EncryptBlock(
byte[] input,
int inOff,
byte[] outBytes,
int outOff)
{
long A = BytesToWord(input, inOff) + _S[0];
long B = BytesToWord(input, inOff + bytesPerWord) + _S[1];
for (int i = 1; i <= _noRounds; i++)
{
A = RotateLeft(A ^ B, B) + _S[2*i];
B = RotateLeft(B ^ A, A) + _S[2*i+1];
}
WordToBytes(A, outBytes, outOff);
WordToBytes(B, outBytes, outOff + bytesPerWord);
return 2 * bytesPerWord;
}
private int DecryptBlock(
byte[] input,
int inOff,
byte[] outBytes,
int outOff)
{
long A = BytesToWord(input, inOff);
long B = BytesToWord(input, inOff + bytesPerWord);
for (int i = _noRounds; i >= 1; i--)
{
B = RotateRight(B - _S[2*i+1], A) ^ A;
A = RotateRight(A - _S[2*i], B) ^ B;
}
WordToBytes(A - _S[0], outBytes, outOff);
WordToBytes(B - _S[1], outBytes, outOff + bytesPerWord);
return 2 * bytesPerWord;
}
//////////////////////////////////////////////////////////////
//
// PRIVATE Helper Methods
//
//////////////////////////////////////////////////////////////
/**
* Perform a left "spin" of the word. The rotation of the given
* word <em>x</em> is rotated left by <em>y</em> bits.
* Only the <em>lg(wordSize)</em> low-order bits of <em>y</em>
* are used to determine the rotation amount. Here it is
* assumed that the wordsize used is a power of 2.
*
* @param x word to rotate
* @param y number of bits to rotate % wordSize
*/
private long RotateLeft(long x, long y) {
return ((long) ( (ulong) (x << (int) (y & (wordSize-1))) |
((ulong) x >> (int) (wordSize - (y & (wordSize-1)))))
);
}
/**
* Perform a right "spin" of the word. The rotation of the given
* word <em>x</em> is rotated left by <em>y</em> bits.
* Only the <em>lg(wordSize)</em> low-order bits of <em>y</em>
* are used to determine the rotation amount. Here it is
* assumed that the wordsize used is a power of 2.
*
* @param x word to rotate
* @param y number of bits to rotate % wordSize
*/
private long RotateRight(long x, long y) {
return ((long) ( ((ulong) x >> (int) (y & (wordSize-1))) |
(ulong) (x << (int) (wordSize - (y & (wordSize-1)))))
);
}
private long BytesToWord(
byte[] src,
int srcOff)
{
long word = 0;
for (int i = bytesPerWord - 1; i >= 0; i--)
{
word = (word << 8) + (src[i + srcOff] & 0xff);
}
return word;
}
private void WordToBytes(
long word,
byte[] dst,
int dstOff)
{
for (int i = 0; i < bytesPerWord; i++)
{
dst[i + dstOff] = (byte)word;
word = (long) ((ulong) word >> 8);
}
}
}
}
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