456 lines
16 KiB
C#
456 lines
16 KiB
C#
// ZipCrypto.cs
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// ------------------------------------------------------------------
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//
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// Copyright (c) 2008, 2009, 2011 Dino Chiesa
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// All rights reserved.
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//
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// This code module is part of DotNetZip, a zipfile class library.
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//
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// ------------------------------------------------------------------
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//
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// This code is licensed under the Microsoft Public License.
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// See the file License.txt for the license details.
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// More info on: http://dotnetzip.codeplex.com
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//
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// ------------------------------------------------------------------
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//
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// last saved (in emacs):
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// Time-stamp: <2011-July-28 06:30:59>
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//
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// ------------------------------------------------------------------
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//
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// This module provides the implementation for "traditional" Zip encryption.
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//
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// Created Tue Apr 15 17:39:56 2008
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//
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// ------------------------------------------------------------------
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using System;
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namespace Ionic.Zip
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{
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/// <summary>
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/// This class implements the "traditional" or "classic" PKZip encryption,
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/// which today is considered to be weak. On the other hand it is
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/// ubiquitous. This class is intended for use only by the DotNetZip
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/// library.
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/// </summary>
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///
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/// <remarks>
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/// Most uses of the DotNetZip library will not involve direct calls into
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/// the ZipCrypto class. Instead, the ZipCrypto class is instantiated and
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/// used by the ZipEntry() class when encryption or decryption on an entry
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/// is employed. If for some reason you really wanted to use a weak
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/// encryption algorithm in some other application, you might use this
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/// library. But you would be much better off using one of the built-in
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/// strong encryption libraries in the .NET Framework, like the AES
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/// algorithm or SHA.
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/// </remarks>
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internal class ZipCrypto
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{
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/// <summary>
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/// The default constructor for ZipCrypto.
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/// </summary>
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///
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/// <remarks>
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/// This class is intended for internal use by the library only. It's
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/// probably not useful to you. Seriously. Stop reading this
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/// documentation. It's a waste of your time. Go do something else.
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/// Check the football scores. Go get an ice cream with a friend.
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/// Seriously.
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/// </remarks>
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///
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private ZipCrypto() { }
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public static ZipCrypto ForWrite(string password)
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{
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ZipCrypto z = new ZipCrypto();
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if (password == null)
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throw new BadPasswordException("This entry requires a password.");
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z.InitCipher(password);
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return z;
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}
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public static ZipCrypto ForRead(string password, ZipEntry e)
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{
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System.IO.Stream s = e._archiveStream;
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e._WeakEncryptionHeader = new byte[12];
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byte[] eh = e._WeakEncryptionHeader;
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ZipCrypto z = new ZipCrypto();
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if (password == null)
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throw new BadPasswordException("This entry requires a password.");
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z.InitCipher(password);
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ZipEntry.ReadWeakEncryptionHeader(s, eh);
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// Decrypt the header. This has a side effect of "further initializing the
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// encryption keys" in the traditional zip encryption.
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byte[] DecryptedHeader = z.DecryptMessage(eh, eh.Length);
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// CRC check
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// According to the pkzip spec, the final byte in the decrypted header
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// is the highest-order byte in the CRC. We check it here.
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if (DecryptedHeader[11] != (byte)((e._Crc32 >> 24) & 0xff))
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{
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// In the case that bit 3 of the general purpose bit flag is set to
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// indicate the presence of an 'Extended File Header' or a 'data
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// descriptor' (signature 0x08074b50), the last byte of the decrypted
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// header is sometimes compared with the high-order byte of the
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// lastmodified time, rather than the high-order byte of the CRC, to
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// verify the password.
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//
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// This is not documented in the PKWare Appnote.txt. It was
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// discovered this by analysis of the Crypt.c source file in the
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// InfoZip library http://www.info-zip.org/pub/infozip/
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//
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// The reason for this is that the CRC for a file cannot be known
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// until the entire contents of the file have been streamed. This
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// means a tool would have to read the file content TWICE in its
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// entirety in order to perform PKZIP encryption - once to compute
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// the CRC, and again to actually encrypt.
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//
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// This is so important for performance that using the timeblob as
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// the verification should be the standard practice for DotNetZip
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// when using PKZIP encryption. This implies that bit 3 must be
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// set. The downside is that some tools still cannot cope with ZIP
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// files that use bit 3. Therefore, DotNetZip DOES NOT force bit 3
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// when PKZIP encryption is in use, and instead, reads the stream
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// twice.
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//
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if ((e._BitField & 0x0008) != 0x0008)
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{
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throw new BadPasswordException("The password did not match.");
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}
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else if (DecryptedHeader[11] != (byte)((e._TimeBlob >> 8) & 0xff))
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{
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throw new BadPasswordException("The password did not match.");
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}
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// We have a good password.
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}
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else
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{
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// A-OK
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}
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return z;
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}
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/// <summary>
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/// From AppNote.txt:
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/// unsigned char decrypt_byte()
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/// local unsigned short temp
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/// temp :=- Key(2) | 2
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/// decrypt_byte := (temp * (temp ^ 1)) bitshift-right 8
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/// end decrypt_byte
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/// </summary>
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private byte MagicByte
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{
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get
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{
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UInt16 t = (UInt16)((UInt16)(_Keys[2] & 0xFFFF) | 2);
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return (byte)((t * (t ^ 1)) >> 8);
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}
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}
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// Decrypting:
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// From AppNote.txt:
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// loop for i from 0 to 11
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// C := buffer(i) ^ decrypt_byte()
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// update_keys(C)
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// buffer(i) := C
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// end loop
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/// <summary>
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/// Call this method on a cipher text to render the plaintext. You must
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/// first initialize the cipher with a call to InitCipher.
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/// </summary>
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///
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/// <example>
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/// <code>
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/// var cipher = new ZipCrypto();
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/// cipher.InitCipher(Password);
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/// // Decrypt the header. This has a side effect of "further initializing the
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/// // encryption keys" in the traditional zip encryption.
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/// byte[] DecryptedMessage = cipher.DecryptMessage(EncryptedMessage);
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/// </code>
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/// </example>
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///
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/// <param name="cipherText">The encrypted buffer.</param>
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/// <param name="length">
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/// The number of bytes to encrypt.
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/// Should be less than or equal to CipherText.Length.
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/// </param>
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///
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/// <returns>The plaintext.</returns>
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public byte[] DecryptMessage(byte[] cipherText, int length)
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{
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if (cipherText == null)
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throw new ArgumentNullException("cipherText");
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if (length > cipherText.Length)
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throw new ArgumentOutOfRangeException("length",
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"Bad length during Decryption: the length parameter must be smaller than or equal to the size of the destination array.");
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byte[] plainText = new byte[length];
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for (int i = 0; i < length; i++)
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{
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byte C = (byte)(cipherText[i] ^ MagicByte);
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UpdateKeys(C);
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plainText[i] = C;
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}
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return plainText;
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}
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/// <summary>
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/// This is the converse of DecryptMessage. It encrypts the plaintext
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/// and produces a ciphertext.
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/// </summary>
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///
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/// <param name="plainText">The plain text buffer.</param>
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///
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/// <param name="length">
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/// The number of bytes to encrypt.
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/// Should be less than or equal to plainText.Length.
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/// </param>
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///
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/// <returns>The ciphertext.</returns>
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public byte[] EncryptMessage(byte[] plainText, int length)
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{
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if (plainText == null)
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throw new ArgumentNullException("plaintext");
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if (length > plainText.Length)
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throw new ArgumentOutOfRangeException("length",
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"Bad length during Encryption: The length parameter must be smaller than or equal to the size of the destination array.");
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byte[] cipherText = new byte[length];
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for (int i = 0; i < length; i++)
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{
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byte C = plainText[i];
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cipherText[i] = (byte)(plainText[i] ^ MagicByte);
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UpdateKeys(C);
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}
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return cipherText;
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}
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/// <summary>
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/// This initializes the cipher with the given password.
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/// See AppNote.txt for details.
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/// </summary>
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///
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/// <param name="passphrase">
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/// The passphrase for encrypting or decrypting with this cipher.
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/// </param>
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///
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/// <remarks>
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/// <code>
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/// Step 1 - Initializing the encryption keys
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/// -----------------------------------------
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/// Start with these keys:
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/// Key(0) := 305419896 (0x12345678)
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/// Key(1) := 591751049 (0x23456789)
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/// Key(2) := 878082192 (0x34567890)
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///
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/// Then, initialize the keys with a password:
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///
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/// loop for i from 0 to length(password)-1
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/// update_keys(password(i))
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/// end loop
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///
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/// Where update_keys() is defined as:
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///
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/// update_keys(char):
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/// Key(0) := crc32(key(0),char)
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/// Key(1) := Key(1) + (Key(0) bitwiseAND 000000ffH)
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/// Key(1) := Key(1) * 134775813 + 1
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/// Key(2) := crc32(key(2),key(1) rightshift 24)
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/// end update_keys
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///
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/// Where crc32(old_crc,char) is a routine that given a CRC value and a
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/// character, returns an updated CRC value after applying the CRC-32
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/// algorithm described elsewhere in this document.
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///
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/// </code>
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///
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/// <para>
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/// After the keys are initialized, then you can use the cipher to
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/// encrypt the plaintext.
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/// </para>
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///
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/// <para>
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/// Essentially we encrypt the password with the keys, then discard the
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/// ciphertext for the password. This initializes the keys for later use.
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/// </para>
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///
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/// </remarks>
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public void InitCipher(string passphrase)
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{
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byte[] p = SharedUtilities.StringToByteArray(passphrase);
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for (int i = 0; i < passphrase.Length; i++)
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UpdateKeys(p[i]);
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}
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private void UpdateKeys(byte byteValue)
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{
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_Keys[0] = (UInt32)crc32.ComputeCrc32((int)_Keys[0], byteValue);
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_Keys[1] = _Keys[1] + (byte)_Keys[0];
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_Keys[1] = _Keys[1] * 0x08088405 + 1;
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_Keys[2] = (UInt32)crc32.ComputeCrc32((int)_Keys[2], (byte)(_Keys[1] >> 24));
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}
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///// <summary>
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///// The byte array representing the seed keys used.
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///// Get this after calling InitCipher. The 12 bytes represents
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///// what the zip spec calls the "EncryptionHeader".
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///// </summary>
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//public byte[] KeyHeader
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//{
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// get
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// {
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// byte[] result = new byte[12];
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// result[0] = (byte)(_Keys[0] & 0xff);
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// result[1] = (byte)((_Keys[0] >> 8) & 0xff);
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// result[2] = (byte)((_Keys[0] >> 16) & 0xff);
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// result[3] = (byte)((_Keys[0] >> 24) & 0xff);
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// result[4] = (byte)(_Keys[1] & 0xff);
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// result[5] = (byte)((_Keys[1] >> 8) & 0xff);
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// result[6] = (byte)((_Keys[1] >> 16) & 0xff);
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// result[7] = (byte)((_Keys[1] >> 24) & 0xff);
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// result[8] = (byte)(_Keys[2] & 0xff);
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// result[9] = (byte)((_Keys[2] >> 8) & 0xff);
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// result[10] = (byte)((_Keys[2] >> 16) & 0xff);
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// result[11] = (byte)((_Keys[2] >> 24) & 0xff);
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// return result;
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// }
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//}
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// private fields for the crypto stuff:
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private UInt32[] _Keys = { 0x12345678, 0x23456789, 0x34567890 };
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private Ionic.Crc.CRC32 crc32 = new Ionic.Crc.CRC32();
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}
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internal enum CryptoMode
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{
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Encrypt,
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Decrypt
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}
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/// <summary>
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/// A Stream for reading and concurrently decrypting data from a zip file,
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/// or for writing and concurrently encrypting data to a zip file.
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/// </summary>
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internal class ZipCipherStream : System.IO.Stream
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{
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private ZipCrypto _cipher;
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private System.IO.Stream _s;
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private CryptoMode _mode;
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/// <summary> The constructor. </summary>
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/// <param name="s">The underlying stream</param>
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/// <param name="mode">To either encrypt or decrypt.</param>
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/// <param name="cipher">The pre-initialized ZipCrypto object.</param>
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public ZipCipherStream(System.IO.Stream s, ZipCrypto cipher, CryptoMode mode)
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: base()
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{
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_cipher = cipher;
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_s = s;
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_mode = mode;
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}
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public override int Read(byte[] buffer, int offset, int count)
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{
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if (_mode == CryptoMode.Encrypt)
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throw new NotSupportedException("This stream does not encrypt via Read()");
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if (buffer == null)
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throw new ArgumentNullException("buffer");
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byte[] db = new byte[count];
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int n = _s.Read(db, 0, count);
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byte[] decrypted = _cipher.DecryptMessage(db, n);
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for (int i = 0; i < n; i++)
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{
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buffer[offset + i] = decrypted[i];
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}
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return n;
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}
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public override void Write(byte[] buffer, int offset, int count)
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{
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if (_mode == CryptoMode.Decrypt)
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throw new NotSupportedException("This stream does not Decrypt via Write()");
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if (buffer == null)
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throw new ArgumentNullException("buffer");
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// workitem 7696
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if (count == 0) return;
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byte[] plaintext = null;
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if (offset != 0)
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{
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plaintext = new byte[count];
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for (int i = 0; i < count; i++)
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{
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plaintext[i] = buffer[offset + i];
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}
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}
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else plaintext = buffer;
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byte[] encrypted = _cipher.EncryptMessage(plaintext, count);
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_s.Write(encrypted, 0, encrypted.Length);
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}
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public override bool CanRead
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{
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get { return (_mode == CryptoMode.Decrypt); }
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}
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public override bool CanSeek
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{
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get { return false; }
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}
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public override bool CanWrite
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{
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get { return (_mode == CryptoMode.Encrypt); }
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}
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public override void Flush()
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{
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//throw new NotSupportedException();
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}
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public override long Length
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{
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get { throw new NotSupportedException(); }
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}
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public override long Position
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{
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get { throw new NotSupportedException(); }
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set { throw new NotSupportedException(); }
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}
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public override long Seek(long offset, System.IO.SeekOrigin origin)
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{
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throw new NotSupportedException();
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}
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public override void SetLength(long value)
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{
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throw new NotSupportedException();
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}
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}
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}
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