About CrypTool 1
CrypTool 1 (CT1) was a free Windows program for cryptography and cryptanalysis. It was available in 6 languages and one of our most popular software variants for learning cryptography. Since mid 2026, CT1 is deprecated and no longer supported.
CT1 supported both contemporary teaching methods at schools and universities as well as awareness training for employees and civil servants. The program can still be downloaded here.
Originally designed as an internal business application for information security training, CrypTool 1 became an important open-source project in the field of cryptology and IT security awareness.
The last version of CrypTool 1 (1.4.42) offered among other things:
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Numerous classic and modern cryptographic algorithms (encryption and decryption, key generation, secure passwords, authentication, secure protocols, etc.)
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Visualization of several algorithms (Caesar, Enigma, RSA, Diffie-Hellman, digital signatures, AES, etc.)
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Cryptanalysis of several algorithms (Vigenère, RSA, AES, etc.)
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Cryptanalytical measurement methods (entropy, n-grams, autocorrelation, etc.)
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Related auxiliary methods (primality tests, factorization, base64 encoding, etc.)
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Number theory tutorial
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Comprehensive online help
The last release of the desktop version for Windows was CrypTool 1.4.42 (released December 21, 2021). Since mid 2026, CT1 is no longer supported — there will be no bugfixes or maintenance. If you really need to use CT1, consider these three options:
- Use the successors CrypTool 2 and CrypTool-Online, which are actively developed.
- Send an email to esslinger@cryptool.org to get a makeshift workaround for the failure in the CA certification step.
- Wait for "CT1bro" to come: CT1 will be updated and ported to the browser by mid 2027. The first tests can start in December 2026 — we are looking for testers.