mirror of https://github.com/gchq/CyberChef.git
82 lines
2.0 KiB
JavaScript
82 lines
2.0 KiB
JavaScript
/**
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* @author Flavio Diez [flaviofdiez+cyberchef@gmail.com]
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* @copyright Crown Copyright 2020
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* @license Apache-2.0
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*/
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import Operation from "../Operation.mjs";
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import OperationError from "../errors/OperationError.mjs";
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/**
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* Rail Fence Cipher Decode operation
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*/
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class RailFenceCipherDecode extends Operation {
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/**
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* RailFenceCipherDecode constructor
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*/
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constructor() {
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super();
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this.name = "Rail Fence Cipher Decode";
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this.module = "Ciphers";
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this.description = "Decodes Strings that were created using the Rail fence Cipher provided a key and an offset";
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this.infoURL = "https://wikipedia.org/wiki/Rail_fence_cipher";
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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: "Key",
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type: "number",
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value: 2
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},
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{
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name: "Offset",
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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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run(input, args) {
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const [key, offset] = args;
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const cipher = input;
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if (key < 2) {
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throw new OperationError("Key has to be bigger than 2");
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} else if (key > cipher.length) {
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throw new OperationError("Key should be smaller than the cipher's length");
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}
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if (offset < 0) {
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throw new OperationError("Offset has to be a positive integer");
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}
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const cycle = (key - 1) * 2;
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const plaintext = new Array(cipher.length);
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let j = 0;
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let x, y;
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for (y = 0; y < key; y++) {
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for (x = 0; x < cipher.length; x++) {
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if ((y + x + offset) % cycle === 0 || (y - x - offset) % cycle === 0) {
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plaintext[x] = cipher[j++];
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}
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}
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}
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return plaintext.join("").trim();
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}
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}
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export default RailFenceCipherDecode;
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