Net encryption generalized to support more algorithms

Lidgren.Network/Encryption/NetXteaEncryption.cs

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+/* Copyright (c) 2010 Michael Lidgren
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software
+and associated documentation files (the "Software"), to deal in the Software without
+restriction, including without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom
+the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or
+substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+using System;
+using System.Security.Cryptography;
+using System.Text;
+using System.Security;
+
+namespace Lidgren.Network
+{
+	/// <summary>
+	/// Methods to encrypt and decrypt data using the XTEA algorithm
+	/// </summary>
+	public sealed class NetXtea : NetBlockEncryptionBase
+	{
+		private const int c_blockSize = 8;
+		private const int c_keySize = 16;
+		private const int c_delta = unchecked((int)0x9E3779B9);
+
+		private readonly int m_numRounds;
+		private readonly uint[] m_sum0;
+		private readonly uint[] m_sum1;
+
+		public override int BlockSize { get { return c_blockSize; } }
+
+		/// <summary>
+		/// 16 byte key
+		/// </summary>
+		public NetXtea(byte[] key, int rounds)
+		{
+			if (key.Length < c_keySize)
+				throw new NetException("Key too short!");
+
+			m_numRounds = rounds;
+			m_sum0 = new uint[m_numRounds];
+			m_sum1 = new uint[m_numRounds];
+			uint[] tmp = new uint[8];
+
+			int num2;
+			int index = num2 = 0;
+			while (index < 4)
+			{
+				tmp[index] = BitConverter.ToUInt32(key, num2);
+				index++;
+				num2 += 4;
+			}
+			for (index = num2 = 0; index < 32; index++)
+			{
+				m_sum0[index] = ((uint)num2) + tmp[num2 & 3];
+				num2 += -1640531527;
+				m_sum1[index] = ((uint)num2) + tmp[(num2 >> 11) & 3];
+			}
+		}
+
+		/// <summary>
+		/// 16 byte key
+		/// </summary>
+		public NetXtea(byte[] key)
+			: this(key, 32)
+		{
+		}
+
+		/// <summary>
+		/// String to hash for key
+		/// </summary>
+		public NetXtea(string key)
+			: this(SHA1.Create().ComputeHash(Encoding.ASCII.GetBytes(key)), 32)
+		{
+		}
+
+		protected override void EncryptBlock(byte[] source, int sourceOffset, byte[] destination)
+		{
+			uint v0 = BytesToUInt(source, sourceOffset);
+			uint v1 = BytesToUInt(source, sourceOffset + 4);
+
+			for (int i = 0; i != m_numRounds; i++)
+			{
+				v0 += (((v1 << 4) ^ (v1 >> 5)) + v1) ^ m_sum0[i];
+				v1 += (((v0 << 4) ^ (v0 >> 5)) + v0) ^ m_sum1[i];
+			}
+
+			UIntToBytes(v0, destination, 0);
+			UIntToBytes(v1, destination, 0 + 4);
+
+			return;
+		}
+
+		protected override void DecryptBlock(byte[] source, int sourceOffset, byte[] destination)
+		{
+			// Pack bytes into integers
+			uint v0 = BytesToUInt(source, sourceOffset);
+			uint v1 = BytesToUInt(source, sourceOffset + 4);
+
+			for (int i = m_numRounds - 1; i >= 0; i--)
+			{
+				v1 -= (((v0 << 4) ^ (v0 >> 5)) + v0) ^ m_sum1[i];
+				v0 -= (((v1 << 4) ^ (v1 >> 5)) + v1) ^ m_sum0[i];
+			}
+
+			UIntToBytes(v0, destination, 0);
+			UIntToBytes(v1, destination, 0 + 4);
+
+			return;
+		}
+
+		private static uint BytesToUInt(byte[] bytes, int offset)
+		{
+			uint retval = (uint)(bytes[offset] << 24);
+			retval |= (uint)(bytes[++offset] << 16);
+			retval |= (uint)(bytes[++offset] << 8);
+			return (retval | bytes[++offset]);
+		}
+
+		private static void UIntToBytes(uint value, byte[] destination, int destinationOffset)
+		{
+			destination[destinationOffset++] = (byte)(value >> 24);
+			destination[destinationOffset++] = (byte)(value >> 16);
+			destination[destinationOffset++] = (byte)(value >> 8);
+			destination[destinationOffset++] = (byte)value;
+		}
+	}
+}