Tero DES C# Test

Author: Dave
Date: 01.04.13 - 6:10pm

Ok this one was a little painful to create, but i got it working.

There is a nice free DES/Triple DES Javascript library that can found at: tero.co.uk. The code has even been ported into PHP and Perl.

The author was very kind to even write an in depth description of how it works and what its default modes are (i would have been lost with out it!) He also states that it si tested as compatible with .NET which is awesome.

A while back I used the PHP version of the code in a web app. Now came the time I wanted to access the data from a .NET backend application. My initial attempts at using the .NET library for it failed because I didnt understand the key padding or when to use DES over Triple DES etc. Crypto can suck to debug :( so anyway..my first stab just to get something running and usable, was to use Phalanger to run a .NET compiled version of the php script. This worked, but it added 3mb of dependencies to the install and a 1mb file took almost 1 minute to decrypt.

This could be acceptable, because i know the compatibility is perfect, and in all my testing, I never encountered a decryption error with the original PHP script running through Phalanger (kudos to the author!).

Anyway, I still wanted to see if I could get the native .NET DES/3DES implementation working in a way that was compatible with the tero module. After a day of reading and experimentation I think I have it working and all debugged. You can download the test app here

In testing I also stumbled across a stupid decision MS made in their .NET library namely the CryptographicException - "Specified key is a known weak key for DES and cannot be used." Sure thats a nice warning, but what if I need to decrypt data that was encrypted to a known weak key? Who are you to say I cant! Luckily after some googling, a workaround was found that directly accesses an internal member of the class via reflection. Thanks Ray_M !

Note: This seems to be compatiable with text strings, I dont think its binary safe yet, I am still hosing with some more testing..did i mention debugging this stuff sucks...and .NET streams are a pita..

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