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//
// ZipAESStream.cs
//
// Copyright 2009 David Pierson
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library. Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
//
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module. An independent module is a module which is not derived from
// or based on this library. If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so. If you do not wish to do so, delete this
// exception statement from your version.
//
#if !NET_1_1 && !NETCF_2_0
using System;
using System.IO;
using System.Security.Cryptography;
namespace ICSharpCode.SharpZipLib.Encryption {
// Based on information from http://www.winzip.com/aes_info.htm
// and http://www.gladman.me.uk/cryptography_technology/fileencrypt/
/// <summary>
/// Encrypts and decrypts AES ZIP
/// </summary>
internal class ZipAESStream : CryptoStream {
/// <summary>
/// Constructor
/// </summary>
/// <param name="stream">The stream on which to perform the cryptographic transformation.</param>
/// <param name="transform">Instance of ZipAESTransform</param>
/// <param name="mode">Read or Write</param>
public ZipAESStream(Stream stream, ZipAESTransform transform, CryptoStreamMode mode)
: base(stream, transform, mode) {
_stream = stream;
_transform = transform;
_slideBuffer = new byte[1024];
_blockAndAuth = CRYPTO_BLOCK_SIZE + AUTH_CODE_LENGTH;
// mode:
// CryptoStreamMode.Read means we read from "stream" and pass decrypted to our Read() method.
// Write bypasses this stream and uses the Transform directly.
if (mode != CryptoStreamMode.Read) {
throw new Exception("ZipAESStream only for read");
}
}
// The final n bytes of the AES stream contain the Auth Code.
private const int AUTH_CODE_LENGTH = 10;
private Stream _stream;
private ZipAESTransform _transform;
private byte[] _slideBuffer;
private int _slideBufStartPos;
private int _slideBufFreePos;
// Blocksize is always 16 here, even for AES-256 which has transform.InputBlockSize of 32.
private const int CRYPTO_BLOCK_SIZE = 16;
private int _blockAndAuth;
/// <summary>
/// Reads a sequence of bytes from the current CryptoStream into buffer,
/// and advances the position within the stream by the number of bytes read.
/// </summary>
public override int Read(byte[] outBuffer, int offset, int count) {
int nBytes = 0;
while (nBytes < count) {
// Calculate buffer quantities vs read-ahead size, and check for sufficient free space
int byteCount = _slideBufFreePos - _slideBufStartPos;
// Need to handle final block and Auth Code specially, but don't know total data length.
// Maintain a read-ahead equal to the length of (crypto block + Auth Code).
// When that runs out we can detect these final sections.
int lengthToRead = _blockAndAuth - byteCount;
if (_slideBuffer.Length - _slideBufFreePos < lengthToRead) {
// Shift the data to the beginning of the buffer
int iTo = 0;
for (int iFrom = _slideBufStartPos; iFrom < _slideBufFreePos; iFrom++, iTo++) {
_slideBuffer[iTo] = _slideBuffer[iFrom];
}
_slideBufFreePos -= _slideBufStartPos; // Note the -=
_slideBufStartPos = 0;
}
int obtained = _stream.Read(_slideBuffer, _slideBufFreePos, lengthToRead);
_slideBufFreePos += obtained;
// Recalculate how much data we now have
byteCount = _slideBufFreePos - _slideBufStartPos;
if (byteCount >= _blockAndAuth) {
// At least a 16 byte block and an auth code remains.
_transform.TransformBlock(_slideBuffer,
_slideBufStartPos,
CRYPTO_BLOCK_SIZE,
outBuffer,
offset);
nBytes += CRYPTO_BLOCK_SIZE;
offset += CRYPTO_BLOCK_SIZE;
_slideBufStartPos += CRYPTO_BLOCK_SIZE;
} else {
// Last round.
if (byteCount > AUTH_CODE_LENGTH) {
// At least one byte of data plus auth code
int finalBlock = byteCount - AUTH_CODE_LENGTH;
_transform.TransformBlock(_slideBuffer,
_slideBufStartPos,
finalBlock,
outBuffer,
offset);
nBytes += finalBlock;
_slideBufStartPos += finalBlock;
}
else if (byteCount < AUTH_CODE_LENGTH)
throw new Exception("Internal error missed auth code"); // Coding bug
// Final block done. Check Auth code.
byte[] calcAuthCode = _transform.GetAuthCode();
for (int i = 0; i < AUTH_CODE_LENGTH; i++) {
if (calcAuthCode[i] != _slideBuffer[_slideBufStartPos + i]) {
throw new Exception("AES Authentication Code does not match. This is a super-CRC check on the data in the file after compression and encryption. \r\n"
+ "The file may be damaged.");
}
}
break; // Reached the auth code
}
}
return nBytes;
}
/// <summary>
/// Writes a sequence of bytes to the current stream and advances the current position within this stream by the number of bytes written.
/// </summary>
/// <param name="buffer">An array of bytes. This method copies count bytes from buffer to the current stream. </param>
/// <param name="offset">The byte offset in buffer at which to begin copying bytes to the current stream. </param>
/// <param name="count">The number of bytes to be written to the current stream. </param>
public override void Write(byte[] buffer, int offset, int count) {
// ZipAESStream is used for reading but not for writing. Writing uses the ZipAESTransform directly.
throw new NotImplementedException();
}
}
}
#endif
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