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