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 

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CryptoBrief

Simple and compact language for cryptographic algorithms

OpenSSL

Toolkit for general-purpose cryptography with graphical controls in your browser

Modern encryption 

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Private polls (demo)

Conduct a private poll with homomorphic encryption

RSA (explained step by step)

The most widespread asymmetric method for encryption and signing

Historical encryption 

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Atbash

Simple monoalphabetic substitution cipher originally used on the Hebrew alphabet

BitShift

Shifts the characters of a text bit by bit

Caesar / ROT13

Famous shifting cipher used by Julius Caesar

Enigma

World War 2 rotor encryption machine

Kamasutra

Involutory substitution cipher described in the Kamasutra (400 BC)

Monoalphabetic Substitution

Cipher that replaces letters with letters/characters

Multiplicative

Simple example for affine ciphers

Railfence / Redefence

Transposition cipher that uses a rail fence pattern

Vernam

Using XOR for implementing a one-time pad (OTP)

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) 

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Certificate verification

Experiment with certificate validity periods, signature creation and verification dates

Encoding/Decoding 

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ASCII

Letters are replaced by numbers of the ASCII code

Bacon

Coding that hides letters in sentences

Base64

Encodes binary data as a string of 64 distinct printable characters

Cryptanalysis 

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Homophonic Substitution Analyzer

Manual analysis of homophonic substitution ciphers. Among other things for use within the DECRYPT project.

Neural Cipher Identifier

Identifies the cipher type with AI – from just a short given ciphertext