// ZipCrypto.cs
// ------------------------------------------------------------------
//
// Copyright (c) 2008, 2009 Dino Chiesa and Microsoft Corporation.
// All rights reserved.
//
// This code module is part of DotNetZip, a zipfile class library.
//
// ------------------------------------------------------------------
//
// This code is licensed under the Microsoft Public License.
// See the file License.txt for the license details.
// More info on: http://dotnetzip.codeplex.com
//
// ------------------------------------------------------------------
//
// last saved (in emacs):
// Time-stamp: <2009-September-11 20:46:18>
//
// ------------------------------------------------------------------
//
// This module provides the implementation for "traditional" Zip encryption.
//
// Created Tue Apr 15 17:39:56 2008
//
// ------------------------------------------------------------------
using System;
namespace Ionic.Zip{
/// <summary>
/// This class implements the "traditional" or "classic" PKZip encryption,
/// which today is considered to be weak. On the other hand it is
/// ubiquitous. This class is intended for use only by the DotNetZip library.
/// </summary>
/// <remarks>
/// Most uses of the DotNetZip library will not involve direct calls into the
/// ZipCrypto class. Instead, the ZipCrypto class is instantiated and used by
/// the ZipEntry() class when encryption or decryption on an entry is employed.
/// If for some reason you really wanted to use a weak encryption algorithm
/// in some other application, you might use this library. But you would be much
/// better off using one of the built-in strong encryption libraries in the
/// .NET Framework, like the AES algorithm or SHA.
/// </remarks>
internal class ZipCrypto
{
/// <summary>
/// The default constructor for ZipCrypto.
/// </summary>
///
/// <remarks>
/// This class is intended for internal use by the library only. It's probably not useful to you. Seriously.
/// Stop reading this documentation. It's a waste of your time. Go do something else.
/// Check the football scores. Go get an ice cream with a friend. Seriously.
/// </remarks>
///
private ZipCrypto() { }
public static ZipCrypto ForWrite(string password)
{
ZipCrypto z = new ZipCrypto();
if (password == null)
throw new BadPasswordException("This entry requires a password.");
z.InitCipher(password);
return z;
}
public static ZipCrypto ForRead(string password, ZipEntry e)
{
System.IO.Stream s = e._archiveStream;
e._WeakEncryptionHeader = new byte[12];
byte[] eh = e._WeakEncryptionHeader;
ZipCrypto z = new ZipCrypto();
if (password == null)
throw new BadPasswordException("This entry requires a password.");
z.InitCipher(password);
ZipEntry.ReadWeakEncryptionHeader(s, eh);
// Decrypt the header. This has a side effect of "further initializing the
// encryption keys" in the traditional zip encryption.
byte[] DecryptedHeader = z.DecryptMessage(eh, eh.Length);
// CRC check
// According to the pkzip spec, the final byte in the decrypted header
// is the highest-order byte in the CRC. We check it here.
if (DecryptedHeader[11] != (byte)((e._Crc32 >> 24) & 0xff))
{
// In the case that bit 3 of the general purpose bit flag is set to
// indicate the presence of an 'Extended File Header' or a 'data
// descriptor' (signature 0x08074b50), the last byte of the decrypted
// header is sometimes compared with the high-order byte of the
// lastmodified time, rather than the high-order byte of the CRC, to
// verify the password.
//
// This is not documented in the PKWare Appnote.txt.
// This was discovered this by analysis of the Crypt.c source file in the InfoZip library
// http://www.info-zip.org/pub/infozip/
if ((e._BitField & 0x0008) != 0x0008)
{
throw new BadPasswordException("The password did not match.");
}
else if (DecryptedHeader[11] != (byte)((e._TimeBlob >> 8) & 0xff))
{
throw new BadPasswordException("The password did not match.");
}
// We have a good password.
}
else
{
// A-OK
}
return z;
}
/// <summary>
/// From AppNote.txt:
/// unsigned char decrypt_byte()
/// local unsigned short temp
/// temp :=- Key(2) | 2
/// decrypt_byte := (temp * (temp ^ 1)) bitshift-right 8
/// end decrypt_byte
/// </summary>
private byte MagicByte
{
get
{
UInt16 t = (UInt16)((UInt16)(_Keys[2] & 0xFFFF) | 2);
return (byte)((t * (t ^ 1)) >> 8);
}
}
// Decrypting:
// From AppNote.txt:
// loop for i from 0 to 11
// C := buffer(i) ^ decrypt_byte()
// update_keys(C)
// buffer(i) := C
// end loop
/// <summary>
/// Call this method on a cipher text to render the plaintext. You must
/// first initialize the cipher with a call to InitCipher.
/// </summary>
/// <example>
/// <code>
/// var cipher = new ZipCrypto();
/// cipher.InitCipher(Password);
/// // Decrypt the header. This has a side effect of "further initializing the
/// // encryption keys" in the traditional zip encryption.
/// byte[] DecryptedMessage = cipher.DecryptMessage(EncryptedMessage);
/// </code>
/// </example>
/// <param name="cipherText">The encrypted buffer.</param>
/// <param name="length">
/// The number of bytes to encrypt.
/// Should be less than or equal to CipherText.Length.
/// </param>
/// <returns>The plaintext.</returns>
public byte[] DecryptMessage(byte[] cipherText, int length)
{
if (cipherText == null)
throw new System.ArgumentException("Bad length during Decryption: cipherText must be non-null.", "cipherText");
if (length > cipherText.Length)
throw new System.ArgumentException("Bad length during Decryption: the length parameter must be smaller than or equal to the size of the destination array.", "length");
byte[] PlainText = new byte[length];
for (int i = 0; i < length; i++)
{
byte C = (byte)(cipherText[i] ^ MagicByte);
UpdateKeys(C);
PlainText[i] = C;
}
return PlainText;
}
/// <summary>
/// This is the converse of DecryptMessage. It encrypts the plaintext
/// and produces a ciphertext.
/// </summary>
/// <param name="plaintext">The plain text buffer.</param>
/// <param name="length">
/// The number of bytes to encrypt.
/// Should be less than or equal to PlainText.Length.
/// </param>
/// <returns>The ciphertext.</returns>
public byte[] EncryptMessage(byte[] plaintext, int length)
{
if (plaintext == null)
throw new System.ArgumentException("Bad length during Encryption: the plainText must be non-null.", "plaintext");
if (length > plaintext.Length)
throw new System.ArgumentException("Bad length during Encryption: The length parameter must be smaller than or equal to the size of the destination array.", "length");
byte[] CipherText = new byte[length];
for (int i = 0; i < length; i++)
{
byte C = plaintext[i];
CipherText[i] = (byte)(plaintext[i] ^ MagicByte);
UpdateKeys(C);
}
return CipherText;
}
/// <summary>
/// This initializes the cipher with the given password.
/// See AppNote.txt for details.
/// </summary>
/// <param name="passphrase">The passphrase for encrypting or decrypting with this cipher.
/// </param>
/// <remarks>
/// <code>
/// Step 1 - Initializing the encryption keys
/// -----------------------------------------
/// Start with these keys:
/// Key(0) := 305419896 (0x12345678)
/// Key(1) := 591751049 (0x23456789)
/// Key(2) := 878082192 (0x34567890)
///
/// Then, initialize the keys with a password:
///
/// loop for i from 0 to length(password)-1
/// update_keys(password(i))
/// end loop
///
/// Where update_keys() is defined as:
///
/// update_keys(char):
/// Key(0) := crc32(key(0),char)
/// Key(1) := Key(1) + (Key(0) bitwiseAND 000000ffH)
/// Key(1) := Key(1) * 134775813 + 1
/// Key(2) := crc32(key(2),key(1) rightshift 24)
/// end update_keys
///
/// Where crc32(old_crc,char) is a routine that given a CRC value and a
/// character, returns an updated CRC value after applying the CRC-32
/// algorithm described elsewhere in this document.
///
/// </code>
/// <para>
/// After the keys are initialized, then you can use the cipher to encrypt
/// the plaintext.
/// </para>
/// <para>
/// Essentially we encrypt the password with the keys, then discard the
/// ciphertext for the password. This initializes the keys for later use.
/// </para>
/// </remarks>
public void InitCipher(string passphrase)
{
byte[] p = SharedUtilities.StringToByteArray(passphrase);
for (int i = 0; i < passphrase.Length; i++)
UpdateKeys(p[i]);
}
private void UpdateKeys(byte byteValue)
{
_Keys[0] = (UInt32)crc32.ComputeCrc32((int)_Keys[0], byteValue);
_Keys[1] = _Keys[1] + (byte)_Keys[0];
_Keys[1] = _Keys[1] * 0x08088405 + 1;
_Keys[2] = (UInt32)crc32.ComputeCrc32((int)_Keys[2], (byte)(_Keys[1] >> 24));
}
///// <summary>
///// Generate random keys for this crypto effort. This is what you want
///// to do when you encrypt.
///// </summary>
//public void GenerateRandomKeys()
//{
// var rnd = new System.Random();
// _Keys[0] = (uint)rnd.Next();
// _Keys[1] = (uint)rnd.Next();
// _Keys[2] = (uint)rnd.Next();
//}
///// <summary>
///// The byte array representing the seed keys used.
///// Get this after calling InitCipher. The 12 bytes represents
///// what the zip spec calls the "EncryptionHeader".
///// </summary>
//public byte[] KeyHeader
//{
// get
// {
// byte[] result = new byte[12];
// result[0] = (byte)(_Keys[0] & 0xff);
// result[1] = (byte)((_Keys[0] >> 8) & 0xff);
// result[2] = (byte)((_Keys[0] >> 16) & 0xff);
// result[3] = (byte)((_Keys[0] >> 24) & 0xff);
// result[4] = (byte)(_Keys[1] & 0xff);
// result[5] = (byte)((_Keys[1] >> 8) & 0xff);
// result[6] = (byte)((_Keys[1] >> 16) & 0xff);
// result[7] = (byte)((_Keys[1] >> 24) & 0xff);
// result[8] = (byte)(_Keys[2] & 0xff);
// result[9] = (byte)((_Keys[2] >> 8) & 0xff);
// result[10] = (byte)((_Keys[2] >> 16) & 0xff);
// result[11] = (byte)((_Keys[2] >> 24) & 0xff);
// return result;
// }
//}
// private fields for the crypto stuff:
private UInt32[] _Keys = { 0x12345678, 0x23456789, 0x34567890 };
private Ionic.Zlib.CRC32 crc32 = new Ionic.Zlib.CRC32();
}
internal enum CryptoMode
{
Encrypt,
Decrypt
}
/// <summary>
/// A Stream for reading and concurrently decrypting data from a zip file,
/// or for writing and concurrently encrypting data to a zip file.
/// </summary>
internal class ZipCipherStream : System.IO.Stream
{
private ZipCrypto _cipher;
private System.IO.Stream _s;
private CryptoMode _mode;
/// <summary>
/// The constructor.
/// </summary>
/// <param name="s">The underlying stream</param>
/// <param name="mode">To either encrypt or decrypt.</param>
/// <param name="cipher">The pre-initialized ZipCrypto object.</param>
public ZipCipherStream(System.IO.Stream s, ZipCrypto cipher, CryptoMode mode)
: base()
{
_cipher = cipher;
_s = s;
_mode = mode;
}
public override int Read(byte[] buffer, int offset, int count)
{
if (_mode == CryptoMode.Encrypt)
throw new NotImplementedException();
byte[] db = new byte[count];
int n = _s.Read(db, 0, count);
byte[] decrypted = _cipher.DecryptMessage(db, n);
for (int i = 0; i < n; i++)
{
buffer[offset + i] = decrypted[i];
}
return n;
}
public override void Write(byte[] buffer, int offset, int count)
{
if (_mode == CryptoMode.Decrypt)
throw new NotImplementedException();
// workitem 7696
if (count == 0) return;
byte[] plaintext = null;
if (offset != 0)
{
plaintext = new byte[count];
for (int i = 0; i < count; i++)
{
plaintext[i] = buffer[offset + i];
}
}
else plaintext = buffer;
byte[] encrypted = _cipher.EncryptMessage(plaintext, count);
_s.Write(encrypted, 0, encrypted.Length);
}
public override bool CanRead
{
get { return (_mode == CryptoMode.Decrypt); }
}
public override bool CanSeek
{
get { return false; }
}
public override bool CanWrite
{
get { return (_mode == CryptoMode.Encrypt); }
}
public override void Flush()
{
//throw new NotImplementedException();
}
public override long Length
{
get { throw new NotImplementedException(); }
}
public override long Position
{
get { throw new NotImplementedException(); }
set { throw new NotImplementedException(); }
}
public override long Seek(long offset, System.IO.SeekOrigin origin)
{
throw new NotImplementedException();
}
public override void SetLength(long value)
{
throw new NotImplementedException();
}
}
}
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