Welcome to CrypTool-Online!

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.

Highlights 1

OpenSSL

OpenSSL v3 running locally in your browser

Modern encryption 1

RSA (explained step by step)

The most widespread asymmetric method for encryption and signing

Historical encryption 4

Atbash

Simple monoalphabetic substitution cipher originally used on the Hebrew alphabet

Caesar / Rot13

Famous shifting cipher used by Julius Caesar

Multiplicative

Simple example for affine chiphers

Kamasutra

Substitution cipher described in the Kama Sutra (400 BC)

Vigenère ciphers 6

Vigenère

First strong polyalphabetic cipher that inspired many other ciphers

Autokey

Variant of Vigenère, extends key with plaintext instead of repeating the key

Beaufort

Variant of Vigenère, which reverses the alphabet

Gronsfeld

Variant of Vigenère, using a number as its key

Trithemius

Predessesor of Vigenère, with a fixed key

Porta

Variant of Vigenère, with half the key space

Checksums (hashing) 1

Certificate verification

Experiment with certificate validity periods, signature creation and verification dates

Encoding/Decoding 2

ASCII

Letters are replaced by numbers of the ASCII code

Bacon

Coding that hides letters in sentences