CyberChef/src/core/operations/VigenèreDecode.mjs

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/**
* @author Matt C [matt@artemisbot.uk]
* @copyright Crown Copyright 2018
* @license Apache-2.0
*/
import Operation from "../Operation";
/**
* Vigenère Decode operation
*/
class VigenèreDecode extends Operation {
/**
* VigenèreDecode constructor
*/
constructor() {
super();
this.name = "Vigenère Decode";
this.module = "Ciphers";
this.description = "The Vigenere cipher is a method of encrypting alphabetic text by using a series of different Caesar ciphers based on the letters of a keyword. It is a simple form of polyalphabetic substitution.";
this.inputType = "string";
this.outputType = "string";
this.args = [
{
"name": "Key",
"type": "string",
"value": ""
}
];
}
/**
* @param {string} input
* @param {Object[]} args
* @returns {string}
*/
run(input, args) {
const alphabet = "abcdefghijklmnopqrstuvwxyz",
key = args[0].toLowerCase();
let output = "",
fail = 0,
keyIndex,
msgIndex,
chr;
if (!key) return "No key entered";
if (!/^[a-zA-Z]+$/.test(key)) return "The key must consist only of letters";
for (let i = 0; i < input.length; i++) {
if (alphabet.indexOf(input[i]) >= 0) {
chr = key[(i - fail) % key.length];
keyIndex = alphabet.indexOf(chr);
msgIndex = alphabet.indexOf(input[i]);
// Subtract indexes from each other, add 26 just in case the value is negative,
// modulo to remove if neccessary
output += alphabet[(msgIndex - keyIndex + alphabet.length) % 26];
} else if (alphabet.indexOf(input[i].toLowerCase()) >= 0) {
chr = key[(i - fail) % key.length].toLowerCase();
keyIndex = alphabet.indexOf(chr);
msgIndex = alphabet.indexOf(input[i].toLowerCase());
output += alphabet[(msgIndex + alphabet.length - keyIndex) % 26].toUpperCase();
} else {
output += input[i];
fail++;
}
}
return output;
}
/**
* Highlight Vigenère Decode
*
* @param {Object[]} pos
* @param {number} pos[].start
* @param {number} pos[].end
* @param {Object[]} args
* @returns {Object[]} pos
*/
highlight(pos, args) {
return pos;
}
/**
* Highlight Vigenère Decode in reverse
*
* @param {Object[]} pos
* @param {number} pos[].start
* @param {number} pos[].end
* @param {Object[]} args
* @returns {Object[]} pos
*/
highlightReverse(pos, args) {
return pos;
}
}
export default VigenèreDecode;