CrypTool 1 (CT1) is an outdated, free Windows program for cryptography and cryptanalysis.
It is part of the CrypTool Project.
CT1 was available in 6 languages and one of our most popular software variants for learning cryptography.
The last release of the desktop version for Windows was CrypTool 1.4.42 (released December 21th, 2021). Since mid 2026, CT1 is depricated and will not be supported any more (even no bugfixes and 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 temporary bugfix for the failure in the CA certification step.
- wait for "CT1bro" to come: CT1 will be updated and ported to the browser till mid 2027. We are looking for testers. The first tests can start in December 2026.