Substitution ciphers are one of the simplest forms of encryption, where replacement rules are provided that map each letter of the alphabet onto a different letter.[more]
This tool will generate randomly chosen keys that map the 26 letters of the English alphabet onto themselves. It also generates snippets of sample text from a range of English sources.[less]
Ciphers are not "public key" encryption, as the decode key is a simple inversion of the encode key and so must be securely transmitted to the recipient of the message. Ciphers can also be broken by frequency analysis without the need for the key, as long as enough encrypted text is available.