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using System;
using Org.BouncyCastle.Crypto.Utilities;
namespace Org.BouncyCastle.Crypto.Engines
{
/// <summary>
/// Implementation of Daniel J. Bernstein's ChaCha stream cipher.
/// </summary>
public class ChaChaEngine
: Salsa20Engine
{
/// <summary>
/// Creates a 20 rounds ChaCha engine.
/// </summary>
public ChaChaEngine()
{
}
/// <summary>
/// Creates a ChaCha engine with a specific number of rounds.
/// </summary>
/// <param name="rounds">the number of rounds (must be an even number).</param>
public ChaChaEngine(int rounds)
: base(rounds)
{
}
public override string AlgorithmName
{
get { return "ChaCha" + rounds; }
}
protected override void AdvanceCounter()
{
if (++engineState[12] == 0)
{
++engineState[13];
}
}
protected override void ResetCounter()
{
engineState[12] = engineState[13] = 0;
}
protected override void SetKey(byte[] keyBytes, byte[] ivBytes)
{
if (keyBytes != null)
{
if ((keyBytes.Length != 16) && (keyBytes.Length != 32))
throw new ArgumentException(AlgorithmName + " requires 128 bit or 256 bit key");
PackTauOrSigma(keyBytes.Length, engineState, 0);
// Key
Pack.LE_To_UInt32(keyBytes, 0, engineState, 4, 4);
Pack.LE_To_UInt32(keyBytes, keyBytes.Length - 16, engineState, 8, 4);
}
// IV
Pack.LE_To_UInt32(ivBytes, 0, engineState, 14, 2);
}
protected override void GenerateKeyStream(byte[] output)
{
ChachaCore(rounds, engineState, x);
Pack.UInt32_To_LE(x, output, 0);
}
/// <summary>
/// ChaCha function.
/// </summary>
/// <param name="rounds">The number of ChaCha rounds to execute</param>
/// <param name="input">The input words.</param>
/// <param name="x">The ChaCha state to modify.</param>
internal static void ChachaCore(int rounds, uint[] input, uint[] x)
{
if (input.Length != 16)
throw new ArgumentException();
if (x.Length != 16)
throw new ArgumentException();
if (rounds % 2 != 0)
throw new ArgumentException("Number of rounds must be even");
uint x00 = input[ 0];
uint x01 = input[ 1];
uint x02 = input[ 2];
uint x03 = input[ 3];
uint x04 = input[ 4];
uint x05 = input[ 5];
uint x06 = input[ 6];
uint x07 = input[ 7];
uint x08 = input[ 8];
uint x09 = input[ 9];
uint x10 = input[10];
uint x11 = input[11];
uint x12 = input[12];
uint x13 = input[13];
uint x14 = input[14];
uint x15 = input[15];
for (int i = rounds; i > 0; i -= 2)
{
x00 += x04; x12 = R(x12 ^ x00, 16);
x08 += x12; x04 = R(x04 ^ x08, 12);
x00 += x04; x12 = R(x12 ^ x00, 8);
x08 += x12; x04 = R(x04 ^ x08, 7);
x01 += x05; x13 = R(x13 ^ x01, 16);
x09 += x13; x05 = R(x05 ^ x09, 12);
x01 += x05; x13 = R(x13 ^ x01, 8);
x09 += x13; x05 = R(x05 ^ x09, 7);
x02 += x06; x14 = R(x14 ^ x02, 16);
x10 += x14; x06 = R(x06 ^ x10, 12);
x02 += x06; x14 = R(x14 ^ x02, 8);
x10 += x14; x06 = R(x06 ^ x10, 7);
x03 += x07; x15 = R(x15 ^ x03, 16);
x11 += x15; x07 = R(x07 ^ x11, 12);
x03 += x07; x15 = R(x15 ^ x03, 8);
x11 += x15; x07 = R(x07 ^ x11, 7);
x00 += x05; x15 = R(x15 ^ x00, 16);
x10 += x15; x05 = R(x05 ^ x10, 12);
x00 += x05; x15 = R(x15 ^ x00, 8);
x10 += x15; x05 = R(x05 ^ x10, 7);
x01 += x06; x12 = R(x12 ^ x01, 16);
x11 += x12; x06 = R(x06 ^ x11, 12);
x01 += x06; x12 = R(x12 ^ x01, 8);
x11 += x12; x06 = R(x06 ^ x11, 7);
x02 += x07; x13 = R(x13 ^ x02, 16);
x08 += x13; x07 = R(x07 ^ x08, 12);
x02 += x07; x13 = R(x13 ^ x02, 8);
x08 += x13; x07 = R(x07 ^ x08, 7);
x03 += x04; x14 = R(x14 ^ x03, 16);
x09 += x14; x04 = R(x04 ^ x09, 12);
x03 += x04; x14 = R(x14 ^ x03, 8);
x09 += x14; x04 = R(x04 ^ x09, 7);
}
x[ 0] = x00 + input[ 0];
x[ 1] = x01 + input[ 1];
x[ 2] = x02 + input[ 2];
x[ 3] = x03 + input[ 3];
x[ 4] = x04 + input[ 4];
x[ 5] = x05 + input[ 5];
x[ 6] = x06 + input[ 6];
x[ 7] = x07 + input[ 7];
x[ 8] = x08 + input[ 8];
x[ 9] = x09 + input[ 9];
x[10] = x10 + input[10];
x[11] = x11 + input[11];
x[12] = x12 + input[12];
x[13] = x13 + input[13];
x[14] = x14 + input[14];
x[15] = x15 + input[15];
}
}
}
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