CrypTool 1 (CT1) is an open-source Windows program for cryptography and cryptanalysis. It’s the most wide-spreaded e-learning software of its kind.
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"Installing CrypTool only requires a few clicks of the mouse, and learning how to use the application is equally straightforward. There is also an extensive amount of help available in each tutorial. In addition, new crypto algorithms and attacks are constantly being added to the (already impressive) CrypTool suite, making it ever more comprehensive in its scope."