Here you will find a summary of the most important features of the current release version of CrypTool (latest stable version). These features differ from the features of the successors which are currently under developement.

CrypTool is a freeware program which enables you to apply and analyze cryptographic mechanisms. It has the typical look-and-feel of a modern Windows application. CrypTool contains exhaustive online help, which can be understood without extensive knowledge of cryptography. CrypTool is available in English, German, Polish and Spanish. CrypTool has implemented almost all state-of-the-art crypto functions and allows you to learn about and use cryptography within the same environment.

• classic methods: e.g. the Caesar cipher, the ADFGVX cipher, the double-column transposition (permutation) and the Enigma encryption algorithm
• modern methods: e.g. the RSA and the AES algorithms, hybrid encryption and algorithms based on lattice reduction and elliptic curves

A summary of all the encryption algorithms implemented in CrypTool is available in the online help page for the Crypt/Decrypt menu. Many screenshots can be found on this website and in the included CrypTool presentation.

If you encrypt a document the result will be shown in a new sub-window: The title of the resulting window contains both the name of the original document and the encryption key used. The usage of keys is supported by two special icons: Clicking the icon Show key allows you to store a copy of the key used from a resulting window into an internal storage. If you then encrypt another document with the same encryption method the icon Insert key is active within the key entry dialog box. This is helpful, especially with more complex keys.

Automatic analysis tools for the classic encryption algorithms are provided for obtaining the key of the encrypted document or a card deck (eventually using any additional information like the unencrypted document or the language of the document). For additional information on automatic analysis, go within CrypTool to the help screen for the Analysis menu and choose the encryption algorithm to be analyzed there.

To support your manual analysis of documents, CrypTool can display a histogram of the document, determine the statistics for any N-gram and calculate entropy and autocorrelation.

The encryption functions within the menu Crypt/Decrypt are implemented in a way that they can be called upon and performed efficiently. On the other hand, the functions in the menu Indiv. Procedures are implemented in a way that they can be performed step by step and interactively. In this 2nd menu the main focus is on e-learning.

• calculate hash values and show their sensitivity
• create Message Authentication Codes (MACs)
• find out how strong keys can be generated from passwords according to the PKCS#5 standard
• compress and decompress documents. This enables the study of file compression prior to the actual encryption of a given document
• generate or analyze pseudo random numbers
• demonstrate protocols for authentication und key exchange (DH)
• step through some ciphers forward and backwards (using the animation software ANIMAL)
• apply common encodings like base64 and uuencode

Which menu items can be selected depends on the type of the active document. The menus and sub-menus of CrypTool are dynamically generated, depending on the opened document's type (binary or text). All menu items are visible all the time, but only the ones which fit to current document type can be selected. The remaining menu items are disabled. An overview of all menu items (menu tree) within CrypTool can be found in appendix A of the script.

Within CrypTool the modern algorithms are implemented according to international standards. The authors of CrypTool did not implement cryptographic functionality where good free programs were available on the internet: So e.g. dictionary attacks against password files (see John-the-Ripper) are not part of CrypTool yet. Nevertheless CrypTool contains a tool to check out the quality of your passwords.

The RSA Cryptosystem

The RSA cryptosystem (see menu Indiv. Procedures \ RSA Cryptosystem \ RSA demonstration) is covered comprehensively and implemented for different codings. The RSA key can be generated from prime numbers selected by the user. Key generation, encryption and decryption can be followed step-by-step.

Factorisation of numbers is also an important application for cryptography. Simple RSA cryptosystems can be easily cracked using the factorisation algorithms presented in CrypTool. Thus, you get an idea of the minimum length of keys necessary for secure systems.

Interactive Demonstrations / Visualizations

These interactive demonstrations (visualizations) are helpful for improving the understanding of the following topics:

• creating an electronic signature (menu Digital Signatures/PKI \ Sign Message)
• processing hybrid encryption (menu Crypt/Decrypt \ Hybrid \ RSA-AES Encryption)
• how do modifications to a document change the hash value
  • sensitivity of hash algorithms (menu Indiv. Procedures \ Hash \ Hash Demonstration)
  • generation of hash value collisions (birthday paradox) (menu Analysis \ Hash \ Attack on the Hash Value of the Digital Signature)
• Diffie-Hellman key exchange (menu Indiv. Procedures \ Protocols \ Diffie-Hellman Demonstration)
• side-channel attack (menu Analysis \ Asymmetric Encryption \ Side-Channel Attack on Textbook RSA)
• authentication protocols (menu Indiv. Procedures \ Protocols \ Network Authentication)
• shared secrets using Chinese Remainder Theorem (menu Indiv. Procedures \ Chinese Remainder Theorem Applications \ Secret Sharing by CRT) and Shamir (menu Indiv. Procedures \ Secret Sharing Demonstration (Shamir))
• visualizations of some algorithms (e.g. Vigenère, AES, Enigma) (menu Indiv. Procedures \ Visualization of Algorithms)
• find out how an ancient number theoretic theorem (Chinese Remainder Theorem) can be applied (e.g. when are the planets of our solar system positioned in one straight line) (menu Indiv. Procedures \ Chinese Remainder Theorem Applications \ Astronomy and Planetary Motion)
• 3D visualization of big sets of random numbers (menu Analysis \ Analyse Randomness \ 3D Visualization)
• computer based training for number theory (menu Indiv. Procedures \ Number Theory - Interactive \ Learning Tool for Number Theory)
• point addition on elliptic curves (menu Indiv. Procedures \ Number Theory - Interactive \ Point Addition on Elliptic Curves)

Besides the interactive demonstrations the CrypTool package contains the educational game The Number Shark, which trains pupils to calculate factors of integer numbers.

Online help, documentation and tutorials

During the development of CrypTool, much care has been taken to ensure that context sensitive help is available at any point by pressing the F1 key. You can get a fast overview, if you move through the menu items: Just click F1 to see details about any menu item.

• explanation of all basic cryptographic terms
• a short list of references.
• a chronology of the development in cryptography
• examples (tutorials) for an easy kick off
• a well sorted index of cryptographic topics

• The readme file contains all important elements of the CrypTool package, new features of this version, a description of the project, and how to install and use CrypTool
• The CrypTool presentation, with about 100 slides, gives an overview of the CrypTool project and CrypTool's features
• In the script (provided as a PDF file with about 200 pages) you will find more, mathematically-oriented information about
  • cryptographic methods
  • prime numbers
  • elementary number theory with many examples
  • current results of the cryptanalytic research
  Additionally the appendix contains a list of movies and novels where cryptography plays a role.
• In the fantasy story The Dialogue of the Sisters by Dr. Carsten Elsner two sisters in a psychiatric hospital use a variant of the RSA cryptosystem
• Within the fantasy story The Chinese Labyrinth by Dr. Carsten Elsner, Marco Polo has to solve some number theoretic problems to become a chief advisor of the Great Khan

We are appreciative for the support of the following companies and projects:

• For the hash functions, symmetric and asymmetric ciphers, and key management, CrypTool 1.x uses the Secude Toolkit. That toolkit has been made available for us by the Secude IT Security GmbH. At the enclosed Secude toolkit the support for smart cards has been deactivated. However, if you hold a valid license for the Secude library, you can use your ticket file to activate smart card support in CrypTool 1.x.
• For the demonstration of ECC-AES hybrid encryption, we leverage the "cv act library" from cryptovision.
• For the demonstration of both the RSA crypto system, and the factorisation of numbers, CrypTool uses the ‘Miracl’ library for arbitrary precision arithmetic. The Miracl library is provided by Shamus Software Ltd.
• For the demonstration of hash collisions (birthday paradox), CrypTool uses the OpenSSL library libeay32.dll.
• For the attacks against RSA based on lattice basis reduction (LLL), we use the number theory library NTL from Victor Shoup.
• We also use the GMP library for primality tests.