space-pew/Lidgren.Network/Encryption/NetBlockEncryptionBase.cs

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2015-12-04 10:23:49 +01:00
using System;
using System.Collections.Generic;
namespace Lidgren.Network
{
/// <summary>
/// Base for a non-threadsafe encryption class
/// </summary>
public abstract class NetBlockEncryptionBase : NetEncryption
{
// temporary space for one block to avoid reallocating every time
private byte[] m_tmp;
/// <summary>
/// Block size in bytes for this cipher
/// </summary>
public abstract int BlockSize { get; }
/// <summary>
/// NetBlockEncryptionBase constructor
/// </summary>
public NetBlockEncryptionBase(NetPeer peer)
: base(peer)
{
m_tmp = new byte[BlockSize];
}
/// <summary>
/// Encrypt am outgoing message with this algorithm; no writing can be done to the message after encryption, or message will be corrupted
/// </summary>
public override bool Encrypt(NetOutgoingMessage msg)
{
int payloadBitLength = msg.LengthBits;
int numBytes = msg.LengthBytes;
int blockSize = BlockSize;
int numBlocks = (int)Math.Ceiling((double)numBytes / (double)blockSize);
int dstSize = numBlocks * blockSize;
msg.EnsureBufferSize(dstSize * 8 + (4 * 8)); // add 4 bytes for payload length at end
msg.LengthBits = dstSize * 8; // length will automatically adjust +4 bytes when payload length is written
for(int i=0;i<numBlocks;i++)
{
EncryptBlock(msg.m_data, (i * blockSize), m_tmp);
Buffer.BlockCopy(m_tmp, 0, msg.m_data, (i * blockSize), m_tmp.Length);
}
// add true payload length last
msg.Write((UInt32)payloadBitLength);
return true;
}
/// <summary>
/// Decrypt an incoming message encrypted with corresponding Encrypt
/// </summary>
/// <param name="msg">message to decrypt</param>
/// <returns>true if successful; false if failed</returns>
public override bool Decrypt(NetIncomingMessage msg)
{
int numEncryptedBytes = msg.LengthBytes - 4; // last 4 bytes is true bit length
int blockSize = BlockSize;
int numBlocks = numEncryptedBytes / blockSize;
if (numBlocks * blockSize != numEncryptedBytes)
return false;
for (int i = 0; i < numBlocks; i++)
{
DecryptBlock(msg.m_data, (i * blockSize), m_tmp);
Buffer.BlockCopy(m_tmp, 0, msg.m_data, (i * blockSize), m_tmp.Length);
}
// read 32 bits of true payload length
uint realSize = NetBitWriter.ReadUInt32(msg.m_data, 32, (numEncryptedBytes * 8));
msg.m_bitLength = (int)realSize;
return true;
}
/// <summary>
/// Encrypt a block of bytes
/// </summary>
protected abstract void EncryptBlock(byte[] source, int sourceOffset, byte[] destination);
/// <summary>
/// Decrypt a block of bytes
/// </summary>
protected abstract void DecryptBlock(byte[] source, int sourceOffset, byte[] destination);
}
}