XCI-Explorer/XTSSharp/XtsCryptoTransform.cs

using System;
using System.Security.Cryptography;

namespace XTSSharp
{
	public class XtsCryptoTransform : IDisposable
	{
		private readonly byte[] _cc = new byte[16];

		private readonly bool _decrypting;

		private readonly ICryptoTransform _key1;

		private readonly ICryptoTransform _key2;

		private readonly byte[] _pp = new byte[16];

		private readonly byte[] _t = new byte[16];

		private readonly byte[] _tweak = new byte[16];

		public XtsCryptoTransform(ICryptoTransform key1, ICryptoTransform key2, bool decrypting)
		{
			if (key1 == null)
			{
				throw new ArgumentNullException("key1");
			}
			if (key2 == null)
			{
				throw new ArgumentNullException("key2");
			}
			_key1 = key1;
			_key2 = key2;
			_decrypting = decrypting;
		}

		public void Dispose()
		{
			_key1.Dispose();
			_key2.Dispose();
		}

		public int TransformBlock(byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset, ulong sector)
		{
			FillArrayFromSectorLittleEndian(_tweak, sector);
			int num = inputCount >> 4;
			int num2 = inputCount & 0xF;
			_key2.TransformBlock(_tweak, 0, _tweak.Length, _t, 0);
			int num3 = (num2 != 0) ? (num - 1) : num;
			for (int i = 0; i < num3; i++)
			{
				TweakCrypt(inputBuffer, inputOffset, outputBuffer, outputOffset, _t);
				inputOffset += 16;
				outputOffset += 16;
			}
			if (num2 > 0)
			{
				if (_decrypting)
				{
					Buffer.BlockCopy(_t, 0, _cc, 0, 16);
					MultiplyByX(_cc);
					TweakCrypt(inputBuffer, inputOffset, _pp, 0, _cc);
					int j;
					for (j = 0; j < num2; j++)
					{
						_cc[j] = inputBuffer[16 + j + inputOffset];
						outputBuffer[16 + j + outputOffset] = _pp[j];
					}
					for (; j < 16; j++)
					{
						_cc[j] = _pp[j];
					}
					TweakCrypt(_cc, 0, outputBuffer, outputOffset, _t);
				}
				else
				{
					TweakCrypt(inputBuffer, inputOffset, _cc, 0, _t);
					int k;
					for (k = 0; k < num2; k++)
					{
						_pp[k] = inputBuffer[16 + k + inputOffset];
						outputBuffer[16 + k + outputOffset] = _cc[k];
					}
					for (; k < 16; k++)
					{
						_pp[k] = _cc[k];
					}
					TweakCrypt(_pp, 0, outputBuffer, outputOffset, _t);
				}
			}
			return inputCount;
		}

		private static void FillArrayFromSectorBigEndian(byte[] value, ulong sector)
		{
			value[7] = (byte)((sector >> 56) & 0xFF);
			value[6] = (byte)((sector >> 48) & 0xFF);
			value[5] = (byte)((sector >> 40) & 0xFF);
			value[4] = (byte)((sector >> 32) & 0xFF);
			value[3] = (byte)((sector >> 24) & 0xFF);
			value[2] = (byte)((sector >> 16) & 0xFF);
			value[1] = (byte)((sector >> 8) & 0xFF);
			value[0] = (byte)(sector & 0xFF);
		}

		private static void FillArrayFromSectorLittleEndian(byte[] value, ulong sector)
		{
			value[8] = (byte)((sector >> 56) & 0xFF);
			value[9] = (byte)((sector >> 48) & 0xFF);
			value[10] = (byte)((sector >> 40) & 0xFF);
			value[11] = (byte)((sector >> 32) & 0xFF);
			value[12] = (byte)((sector >> 24) & 0xFF);
			value[13] = (byte)((sector >> 16) & 0xFF);
			value[14] = (byte)((sector >> 8) & 0xFF);
			value[15] = (byte)(sector & 0xFF);
		}

		private void TweakCrypt(byte[] inputBuffer, int inputOffset, byte[] outputBuffer, int outputOffset, byte[] t)
		{
			for (int i = 0; i < 16; i++)
			{
				outputBuffer[i + outputOffset] = (byte)(inputBuffer[i + inputOffset] ^ t[i]);
			}
			_key1.TransformBlock(outputBuffer, outputOffset, 16, outputBuffer, outputOffset);
			for (int j = 0; j < 16; j++)
			{
				outputBuffer[j + outputOffset] = (byte)(outputBuffer[j + outputOffset] ^ t[j]);
			}
			MultiplyByX(t);
		}

		private static void MultiplyByX(byte[] i)
		{
			byte b = 0;
			byte b2 = 0;
			for (int j = 0; j < 16; j++)
			{
				b2 = (byte)(i[j] >> 7);
				i[j] = (byte)(((i[j] << 1) | b) & 0xFF);
				b = b2;
			}
			if (b2 > 0)
			{
				i[0] ^= 135;
			}
		}
	}
}