// EncryptionAlgorithm.cs
// ------------------------------------------------------------------
//
// Copyright (c) 2009 Dino Chiesa
// 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-October-21 17:24:45>
//
// ------------------------------------------------------------------
//
// This module defines the EncryptionAgorithm enum
//
//
// ------------------------------------------------------------------
namespace Ionic.Zip{
/// <summary>
/// An enum that provides the various encryption algorithms supported by this
/// library.
/// </summary>
///
/// <remarks>
///
/// <para>
/// <c>PkzipWeak</c> implies the use of Zip 2.0 encryption, which is known to be
/// weak and subvertible.
/// </para>
///
/// <para>
/// A note on interoperability: Values of <c>PkzipWeak</c> and <c>None</c> are
/// specified in <see
/// href="http://www.pkware.com/documents/casestudies/APPNOTE.TXT">PKWARE's zip
/// specification</see>, and are considered to be "standard". Zip archives
/// produced using these options will be interoperable with many other zip tools
/// and libraries, including Windows Explorer.
/// </para>
///
/// <para>
/// Values of <c>WinZipAes128</c> and <c>WinZipAes256</c> are not part of the Zip
/// specification, but rather imply the use of a vendor-specific extension from
/// WinZip. If you want to produce interoperable Zip archives, do not use these
/// values. For example, if you produce a zip archive using WinZipAes256, you
/// will be able to open it in Windows Explorer on Windows XP and Vista, but you
/// will not be able to extract entries; trying this will lead to an "unspecified
/// error". For this reason, some people have said that a zip archive that uses
/// WinZip's AES encryption is not actually a zip archive at all. A zip archive
/// produced this way will be readable with the WinZip tool (Version 11 and
/// beyond).
/// </para>
///
/// <para>
/// There are other third-party tools and libraries, both commercial and
/// otherwise, that support WinZip's AES encryption. These will be able to read
/// AES-encrypted zip archives produced by DotNetZip, and conversely applications
/// that use DotNetZip to read zip archives will be able to read AES-encrypted
/// archives produced by those tools or libraries. Consult the documentation for
/// those other tools and libraries to find out if WinZip's AES encryption is
/// supported.
/// </para>
///
/// <para>
/// In case you care: According to <see
/// href="http://www.winzip.com/aes_info.htm">the WinZip specification</see>, the
/// actual AES key used is derived from the <see cref="ZipEntry.Password"/> via an
/// algorithm that complies with <see
/// href="http://www.ietf.org/rfc/rfc2898.txt">RFC 2898</see>, using an iteration
/// count of 1000. The algorithm is sometimes referred to as PBKDF2, which stands
/// for "Password Based Key Derivation Function #2".
/// </para>
///
/// <para>
/// A word about password strength and length: The AES encryption technology is
/// very good, but any system is only as secure as the weakest link. If you want
/// to secure your data, be sure to use a password that is hard to guess. To make
/// it harder to guess (increase its "entropy"), you should make it longer. If
/// you use normal characters from an ASCII keyboard, a password of length 20 will
/// be strong enough that it will be impossible to guess. For more information on
/// that, I'd encourage you to read <see
/// href="http://www.redkestrel.co.uk/Articles/RandomPasswordStrength.html">this
/// article.</see>
/// </para>
///
/// <para>
/// The WinZip AES algorithms are not supported with the version of DotNetZip that
/// runs on the .NET Compact Framework. This is because .NET CF lacks the
/// HMACSHA1 class that is required for producing the archive.
/// </para>
/// </remarks>
public enum EncryptionAlgorithm
{
/// <summary>
/// No encryption at all.
/// </summary>
None = 0,
/// <summary>
/// Traditional or Classic pkzip encryption.
/// </summary>
PkzipWeak,
#if AESCRYPTO
/// <summary>
/// WinZip AES encryption (128 key bits).
/// </summary>
WinZipAes128,
/// <summary>
/// WinZip AES encryption (256 key bits).
/// </summary>
WinZipAes256,
#endif
/// <summary>
/// An encryption algorithm that is not supported by DotNetZip.
/// </summary>
Unsupported = 4,
// others... not implemented (yet?)
}
}
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