Welcome to CrypTool-Online!

CrypTool-Online (CTO) is a website to explore, play around with, and learn about ancient and modern cryptography. The aim is to attract students, lecturers, and interested individuals.

Highlights 1

OpenSSL

OpenSSL v3 running locally in your browser

Modern encryption 2

RSA (explained step by step)

The most widespread asymmetric method for encryption and signing

Private polls (demo)

Conduct a private poll with homomorphic encryption

Historical encryption 7

Atbash

Simple monoalphabetic substitution cipher originally used on the Hebrew alphabet

Caesar / ROT13

Famous shifting cipher used by Julius Caesar

Monoalphabetic Substitution

Cipher that replaces letters with letters/characters

Multiplicative

Simple example for affine ciphers

Kamasutra

Substitution cipher described in the Kamasutra (400 BC)

Vigenère and variants

First strong polyalphabetic cipher that inspired many other ciphers

XOR

Single bits are XORed (typical component of more complex ciphers)

Checksums (hashing) 1

Certificate verification

Experiment with certificate validity periods, signature creation and verification dates. For this example files are already loaded.

Encoding/Decoding 2

ASCII

Letters are replaced by numbers of the ASCII code

Bacon

Coding that hides letters in sentences

Cryptanalysis 1

Neural Cipher Identifier

Identifies the cipher type, with only a short given ciphertext