Autokey

A Javascript implementation of the simple Autokey cipher. Autokey has some useful characteristics: the output is the same length as the input and looks like the input was merely jumbled as it uses the same alphabet as the input:

• Input: all our words from loose using have lost their edge.
• Output: kbu cjd hprjy qmud ilujd xpxkq xxsw hvng zgksj nqwa.

This is similar to and based on the stream cipher implementation at https://github.com/hex7c0/autokey but restricts the input and output to a given alphabet. This means you can let spaces, punctuation, and other characters go through the algorithm with no change.

How it works

To install:

npm install node-autokey

Example script

var Autokey = require('node-autokey');
var assert = require('assert')

var alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

// The key does not have to be chosen from the alphabet.
var akey = new Autokey("My Key Is This@)(#*$", alphabet);

var input = "Something very important!";
var ciphertext = akey.encode(input);
console.log(ciphertext);
var recoveredtext = akey.decode(ciphertext);
assert.equal(recoveredtext, input);

Caveat

Autokey is a very old cipher with known vulnerabilities and is not as secure as modern encryption systems. You should consider this algorithm as a slightly better alternative to ROT13 or base64 for obfuscating text.