CrypTool-Online (CTO) is a website to explore, play around with, and learn about ancient and modern cryptography. All tools are open source and mostly developed by students.
OpenSSL v3 running locally in your browser
The most widespread asymmetric method for encryption and signing
Simple monoalphabetic substitution cipher originally used on the Hebrew alphabet
Famous shifting cipher used by Julius Caesar
Simple example for affine chiphers
Substitution cipher described in the Kama Sutra (400 BC)
First strong polyalphabetic cipher that inspired many other ciphers
Variant of Vigenère, extends key with plaintext instead of repeating the key
Variant of Vigenère, which reverses the alphabet
Variant of Vigenère, using a number as its key
Predessesor of Vigenère, with a fixed key
Variant of Vigenère, with half the key space
Experiment with certificate validity periods, signature creation and verification dates
Letters are replaced by numbers of the ASCII code
Coding that hides letters in sentences