mirror of https://github.com/gchq/CyberChef.git
106 lines
3.0 KiB
JavaScript
106 lines
3.0 KiB
JavaScript
/**
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* @author Matt C [matt@artemisbot.uk]
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* @copyright Crown Copyright 2018
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* @license Apache-2.0
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*/
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import Operation from "../Operation";
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import Utils from "../Utils";
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import OperationError from "../errors/OperationError";
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/**
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* Affine Cipher Decode operation
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*/
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class AffineCipherDecode extends Operation {
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/**
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* AffineCipherDecode constructor
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*/
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constructor() {
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super();
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this.name = "Affine Cipher Decode";
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this.module = "Ciphers";
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this.description = "The Affine cipher is a type of monoalphabetic substitution cipher. To decrypt, each letter in an alphabet is mapped to its numeric equivalent, decrypted by a mathematical function, and converted back to a letter.";
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this.inputType = "string";
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this.outputType = "string";
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this.args = [
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{
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"name": "a",
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"type": "number",
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"value": 1
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},
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{
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"name": "b",
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"type": "number",
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"value": 0
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}
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];
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}
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/**
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* @param {string} input
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* @param {Object[]} args
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* @returns {string}
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*
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* @throws {OperationError} if a or b values are invalid
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*/
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run(input, args) {
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const alphabet = "abcdefghijklmnopqrstuvwxyz",
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[a, b] = args,
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aModInv = Utils.modInv(a, 26); // Calculates modular inverse of a
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let output = "";
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if (!/^\+?(0|[1-9]\d*)$/.test(a) || !/^\+?(0|[1-9]\d*)$/.test(b)) {
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throw new OperationError("The values of a and b can only be integers.");
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}
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if (Utils.gcd(a, 26) !== 1) {
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throw new OperationError("The value of `a` must be coprime to 26.");
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}
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for (let i = 0; i < input.length; i++) {
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if (alphabet.indexOf(input[i]) >= 0) {
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// Uses the affine decode function (y-b * A') % m = x (where m is length of the alphabet and A' is modular inverse)
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output += alphabet[Utils.mod((alphabet.indexOf(input[i]) - b) * aModInv, 26)];
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} else if (alphabet.indexOf(input[i].toLowerCase()) >= 0) {
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// Same as above, accounting for uppercase
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output += alphabet[Utils.mod((alphabet.indexOf(input[i].toLowerCase()) - b) * aModInv, 26)].toUpperCase();
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} else {
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// Non-alphabetic characters
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output += input[i];
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}
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}
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return output;
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}
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/**
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* Highlight Affine Cipher Decode
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*
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* @param {Object[]} pos
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* @param {number} pos[].start
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* @param {number} pos[].end
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* @param {Object[]} args
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* @returns {Object[]} pos
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*/
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highlight(pos, args) {
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return pos;
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}
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/**
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* Highlight Affine Cipher Decode in reverse
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*
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* @param {Object[]} pos
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* @param {number} pos[].start
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* @param {number} pos[].end
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* @param {Object[]} args
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* @returns {Object[]} pos
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*/
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highlightReverse(pos, args) {
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return pos;
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}
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}
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export default AffineCipherDecode;
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