Cryptool Review

By: Mirmo

_Introduction_

CrypTool is a powerful tool for learning cryptography. It can be used for apply and analyse cryptographic algorithms. It’s a freeware and an open source project. It’s available in the four languages English, German, Polish and Spanish.

CrypTool is very simple to use and has extensive documentation.

It can crypt and decrypt :
- classic symmetric algorithms like Casear cipher, ROT-13, Vigenere, Hill, Substitution, Playfair, ADFGVX,solitaire, XOR…
- modern symmetric algorithms like IDEA , RC2, RC4, DES, Rijndael AES…
- RSA, RSA-AES or ECC-AES
Or further algorithm like twofish, serpent, RC6…

Cryptool can calculate MD2, MD4, MD5 , SHA-1, SHA-256, SHA-512 and RIPEMD-160 checksums of a file or text.

It’s possible to find/test prime numbers with Miller-Rabin test, Fermat test, Solovay-Strassen test or AKS test. You can also make a factorisation of a number with many methods.

And you can view demonstration of algorithms with a java applet for learning how they work

All this thing is very useful but the power of this tool is in capacity to reverse crytographic algorithms even if you have only ciphertext, a part of plain text or with a manual analysis.

Analysis is possible with many tools like entropy, histogram, floating frequency, autoccorelation periodicity, diagram, trigram or N-gram…

All this means that this tool is essential for those who want to learn the mechanics of cryptography, but also for those who enjoys net’s challenges.

_Where download it ?_

http://www.cryptool.org/index.php/en/download-topmenu-63.html
The current version is CrypTool 1.4.21

_How installing Cryptool ?_

Double click on Setup CrypTool_1_4_21_en.exe. Clic on Next button, “I agree” button for the license agreement, choose the destination folder or just click on Install. And when installation is finished, click on Next button and finish.

_A short example of use_

If we take this text for example:
“cyberarmy stands for freedom of thought freedom of expression and freedom of information on the internet we support the free creation development and proliferation of ideas and knowledge through such forums as the open source community we recognize that in order for these ideas to flow freely people must also possess the right to their own privacy we further recognize that to preserve these freedoms and rights they must be exercised responsibly we seek to educate people about privacy and things that threaten it and we seek to promote the responsible use of the internet as a medium for the sharing of thoughts ideas and information we believe that the people best qualified to regulate the internet are its users and we seek to empower them to remove or mitigate influences which are subversive to these freedoms and rights”
All characters are lowercase and no punctuation.

We copy the text in the main window.
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It then selects the cryptographic process. Here Vigenere.
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We choose a secret key to this text here : cyberarmy
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We obtain a ciphertext, totally unreadable.
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Let’s see if we can reverse the process without knowing the key. For this we can analyze the text with the entropy or histogram to determine the number of characters and their frequencies.
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If we consider that we are dealing with a Vigenere cipher type. You can use the analysis with the ciphertext.
2010-01-26_182720.png
The program determines a key of length 9.
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And we found the original key.
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To then decrypt the ciphertext.
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_Online Documentation_ :
http://www.cryptool.org/download/CrypToolPresentation-en.pdf

_Some other information_ :
Setup : 37 700 772 bytes
Installation : 75 195 651 bytes
Portable software : Yes ( can be install on a USB key)

Best regards,
mirmo

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