CHelix v1.07 A class to implement the "Helix" Encryption and Authentication cipher

CHelix is a C++ implementation for the Helix Encryption and Authentication algorithm as presented in a November 2003 Dr. Dobb's Journal article by Niels Ferguson and Bruce Schneier. For further information please refer to the article and / or the web site for it at http://www.macfergus.com/helix.

The enclosed zip file contains the CHelix source code and also includes a VC 6 workspace file to build a small test app and DLL version of Helix.

Copyright

• You are allowed to include the source code in any product (commercial, shareware, freeware or otherwise) when your product is released in binary form.
• You are allowed to modify the source code in any way you want except you cannot modify the copyright details at the top of each module.
• If you want to distribute source code with your application, then you are only allowed to distribute versions released by the author. This is to maintain a single distribution point for the source code.

Updates

v1.0 (29 November 2003)

• Initial public release.

V1.01 (30 November 2003)

• Following an email update from Niels Ferguson, the following changes were made:
• Removed the need for the doBlk function
• Made the Block function inline.
• Removed the unneeded code "m_i8 >> 31"
• Removed the unneeded local variable tag in the Finish method.
• Removed the switch statement in preference for a lookup array in Decrypt.
• plaintext is now not released from Decrypt if the MAC's do not match up.
• Optimized the key method CHelix::Block by using register local variables. This now gets the throughput on my machine up to 191 MB / second

V1.02 (1 December 2003)

• Optimized the for loop in Finish. Now it is only called 3 times instead of 4.

V1.03 (1 December 2003)

• Further optimizations as suggested by Serhiy Pavlov boost the speed to 208 MB / second on my home machine. This corresponds to a speed of 10.4 clock ticks per byte!,
• Also produced a DLL version of the algorithm, so that client applications which do not or cannot (e.g. Visual Basic) muck around with the C++ source code can use the code.

V1.04 (18 June 2004)

• Fixed a bug in the CHelix constructor. Thanks to Richard Gyger for reporting this problem.

V1.05 (17 September 2004)

• Fixed a number of warnings in the code when compiled in VC .Net 2003 with the "Force conformance in For Loop Scope" compiler option is set.

V1.06 (28 October 2004)

• Fixed a problem in the decryption where the Helix_Decrypt_Masks bit masks were incorrectly defined. Thanks to Dwain Skinner for reporting and providing a fix for this problem.
• Removed the declaration of #pragma intrinsic(_rotl) as recent Platform SDK's already have this defined.
• Sample app provided with download, now uses console I/O for reporting its results.

V1.07 (30 December 2006)

• Updated copyright details.
• Addition of a CHELIX_EXT_CLASS preprocessor macro to allow the classes to be more easily added to an extension dll
• Optimized CHelix constructor code.
• Code now uses newer C++ style casts instead of C style casts.
• Updated the code to clean compile on VC2005
• Reworked the layout of the CHelixMAC operator== method
• Replaced use of BOOL with bool in the class.
• Updated documentation to use the same style as the web site