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362
iTechSharp/srcbc/crypto/engines/RC6Engine.cs
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362
iTechSharp/srcbc/crypto/engines/RC6Engine.cs
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using System;
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using Org.BouncyCastle.Crypto.Parameters;
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namespace Org.BouncyCastle.Crypto.Engines
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{
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/**
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* An RC6 engine.
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*/
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public class RC6Engine
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: IBlockCipher
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{
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private static readonly int wordSize = 32;
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private static readonly int bytesPerWord = wordSize / 8;
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/*
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* the number of rounds to perform
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*/
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private static readonly int _noRounds = 20;
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/*
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* the expanded key array of size 2*(rounds + 1)
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*/
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private int [] _S;
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/*
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* our "magic constants" for wordSize 32
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*
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* Pw = Odd((e-2) * 2^wordsize)
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* Qw = Odd((o-2) * 2^wordsize)
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*
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* where e is the base of natural logarithms (2.718281828...)
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* and o is the golden ratio (1.61803398...)
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*/
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private static readonly int P32 = unchecked((int) 0xb7e15163);
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private static readonly int Q32 = unchecked((int) 0x9e3779b9);
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private static readonly int LGW = 5; // log2(32)
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private bool forEncryption;
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/**
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* Create an instance of the RC6 encryption algorithm
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* and set some defaults
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*/
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public RC6Engine()
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{
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// _S = null;
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}
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public string AlgorithmName
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{
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get { return "RC6"; }
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}
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public bool IsPartialBlockOkay
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{
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get { return false; }
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}
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public int GetBlockSize()
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{
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return 4 * bytesPerWord;
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}
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/**
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* initialise a RC5-32 cipher.
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*
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* @param forEncryption whether or not we are for encryption.
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* @param parameters the parameters required to set up the cipher.
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* @exception ArgumentException if the parameters argument is
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* inappropriate.
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*/
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public void Init(
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bool forEncryption,
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ICipherParameters parameters)
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{
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if (!(parameters is KeyParameter))
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throw new ArgumentException("invalid parameter passed to RC6 init - " + parameters.GetType().ToString());
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this.forEncryption = forEncryption;
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KeyParameter p = (KeyParameter)parameters;
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SetKey(p.GetKey());
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}
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public int ProcessBlock(
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byte[] input,
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int inOff,
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byte[] output,
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int outOff)
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{
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int blockSize = GetBlockSize();
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if (_S == null)
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throw new InvalidOperationException("RC6 engine not initialised");
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if ((inOff + blockSize) > input.Length)
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throw new DataLengthException("input buffer too short");
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if ((outOff + blockSize) > output.Length)
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throw new DataLengthException("output buffer too short");
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return (forEncryption)
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? EncryptBlock(input, inOff, output, outOff)
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: DecryptBlock(input, inOff, output, outOff);
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}
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public void Reset()
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{
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}
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/**
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* Re-key the cipher.
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*
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* @param inKey the key to be used
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*/
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private void SetKey(
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byte[] key)
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{
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//
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// KEY EXPANSION:
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//
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// There are 3 phases to the key expansion.
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//
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// Phase 1:
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// Copy the secret key K[0...b-1] into an array L[0..c-1] of
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// c = ceil(b/u), where u = wordSize/8 in little-endian order.
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// In other words, we fill up L using u consecutive key bytes
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// of K. Any unfilled byte positions in L are zeroed. In the
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// case that b = c = 0, set c = 1 and L[0] = 0.
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//
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// compute number of dwords
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int c = (key.Length + (bytesPerWord - 1)) / bytesPerWord;
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if (c == 0)
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{
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c = 1;
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}
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int[] L = new int[(key.Length + bytesPerWord - 1) / bytesPerWord];
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// load all key bytes into array of key dwords
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for (int i = key.Length - 1; i >= 0; i--)
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{
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L[i / bytesPerWord] = (L[i / bytesPerWord] << 8) + (key[i] & 0xff);
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}
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//
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// Phase 2:
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// Key schedule is placed in a array of 2+2*ROUNDS+2 = 44 dwords.
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// Initialize S to a particular fixed pseudo-random bit pattern
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// using an arithmetic progression modulo 2^wordsize determined
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// by the magic numbers, Pw & Qw.
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//
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_S = new int[2+2*_noRounds+2];
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_S[0] = P32;
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for (int i=1; i < _S.Length; i++)
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{
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_S[i] = (_S[i-1] + Q32);
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}
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//
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// Phase 3:
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// Mix in the user's secret key in 3 passes over the arrays S & L.
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// The max of the arrays sizes is used as the loop control
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//
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int iter;
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if (L.Length > _S.Length)
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{
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iter = 3 * L.Length;
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}
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else
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{
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iter = 3 * _S.Length;
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}
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int A = 0;
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int B = 0;
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int ii = 0, jj = 0;
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for (int k = 0; k < iter; k++)
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{
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A = _S[ii] = RotateLeft(_S[ii] + A + B, 3);
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B = L[jj] = RotateLeft( L[jj] + A + B, A+B);
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ii = (ii+1) % _S.Length;
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jj = (jj+1) % L.Length;
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}
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}
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private int EncryptBlock(
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byte[] input,
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int inOff,
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byte[] outBytes,
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int outOff)
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{
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// load A,B,C and D registers from in.
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int A = BytesToWord(input, inOff);
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int B = BytesToWord(input, inOff + bytesPerWord);
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int C = BytesToWord(input, inOff + bytesPerWord*2);
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int D = BytesToWord(input, inOff + bytesPerWord*3);
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// Do pseudo-round #0: pre-whitening of B and D
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B += _S[0];
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D += _S[1];
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// perform round #1,#2 ... #ROUNDS of encryption
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for (int i = 1; i <= _noRounds; i++)
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{
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int t = 0,u = 0;
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t = B*(2*B+1);
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t = RotateLeft(t,5);
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u = D*(2*D+1);
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u = RotateLeft(u,5);
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A ^= t;
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A = RotateLeft(A,u);
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A += _S[2*i];
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C ^= u;
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C = RotateLeft(C,t);
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C += _S[2*i+1];
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int temp = A;
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A = B;
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B = C;
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C = D;
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D = temp;
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}
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// do pseudo-round #(ROUNDS+1) : post-whitening of A and C
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A += _S[2*_noRounds+2];
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C += _S[2*_noRounds+3];
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// store A, B, C and D registers to out
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WordToBytes(A, outBytes, outOff);
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WordToBytes(B, outBytes, outOff + bytesPerWord);
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WordToBytes(C, outBytes, outOff + bytesPerWord*2);
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WordToBytes(D, outBytes, outOff + bytesPerWord*3);
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return 4 * bytesPerWord;
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}
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private int DecryptBlock(
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byte[] input,
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int inOff,
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byte[] outBytes,
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int outOff)
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{
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// load A,B,C and D registers from out.
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int A = BytesToWord(input, inOff);
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int B = BytesToWord(input, inOff + bytesPerWord);
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int C = BytesToWord(input, inOff + bytesPerWord*2);
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int D = BytesToWord(input, inOff + bytesPerWord*3);
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// Undo pseudo-round #(ROUNDS+1) : post whitening of A and C
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C -= _S[2*_noRounds+3];
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A -= _S[2*_noRounds+2];
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// Undo round #ROUNDS, .., #2,#1 of encryption
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for (int i = _noRounds; i >= 1; i--)
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{
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int t=0,u = 0;
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int temp = D;
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D = C;
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C = B;
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B = A;
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A = temp;
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t = B*(2*B+1);
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t = RotateLeft(t, LGW);
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u = D*(2*D+1);
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u = RotateLeft(u, LGW);
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C -= _S[2*i+1];
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C = RotateRight(C,t);
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C ^= u;
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A -= _S[2*i];
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A = RotateRight(A,u);
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A ^= t;
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}
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// Undo pseudo-round #0: pre-whitening of B and D
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D -= _S[1];
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B -= _S[0];
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WordToBytes(A, outBytes, outOff);
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WordToBytes(B, outBytes, outOff + bytesPerWord);
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WordToBytes(C, outBytes, outOff + bytesPerWord*2);
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WordToBytes(D, outBytes, outOff + bytesPerWord*3);
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return 4 * bytesPerWord;
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}
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//////////////////////////////////////////////////////////////
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//
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// PRIVATE Helper Methods
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//
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//////////////////////////////////////////////////////////////
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/**
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* Perform a left "spin" of the word. The rotation of the given
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* word <em>x</em> is rotated left by <em>y</em> bits.
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* Only the <em>lg(wordSize)</em> low-order bits of <em>y</em>
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* are used to determine the rotation amount. Here it is
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* assumed that the wordsize used is a power of 2.
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*
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* @param x word to rotate
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* @param y number of bits to rotate % wordSize
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*/
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private int RotateLeft(int x, int y)
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{
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return ((int)((uint)(x << (y & (wordSize-1)))
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| ((uint) x >> (wordSize - (y & (wordSize-1))))));
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}
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/**
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* Perform a right "spin" of the word. The rotation of the given
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* word <em>x</em> is rotated left by <em>y</em> bits.
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* Only the <em>lg(wordSize)</em> low-order bits of <em>y</em>
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* are used to determine the rotation amount. Here it is
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* assumed that the wordsize used is a power of 2.
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*
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* @param x word to rotate
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* @param y number of bits to rotate % wordSize
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*/
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private int RotateRight(int x, int y)
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{
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return ((int)(((uint) x >> (y & (wordSize-1)))
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| (uint)(x << (wordSize - (y & (wordSize-1))))));
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}
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private int BytesToWord(
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byte[] src,
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int srcOff)
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{
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int word = 0;
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for (int i = bytesPerWord - 1; i >= 0; i--)
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{
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word = (word << 8) + (src[i + srcOff] & 0xff);
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}
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return word;
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}
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private void WordToBytes(
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int word,
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byte[] dst,
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int dstOff)
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{
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for (int i = 0; i < bytesPerWord; i++)
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{
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dst[i + dstOff] = (byte)word;
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word = (int) ((uint) word >> 8);
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}
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}
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}
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}
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