mirror of https://github.com/gchq/CyberChef.git
42 lines
1.2 KiB
JavaScript
42 lines
1.2 KiB
JavaScript
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/**
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* Cipher functions.
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*
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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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*/
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/**
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* Affine Cipher Encode operation.
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*
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* @author Matt C [matt@artemisbot.uk]
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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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export function affineEncode(input, args) {
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const alphabet = "abcdefghijklmnopqrstuvwxyz",
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a = args[0],
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b = args[1];
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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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return "The values of a and b can only be integers.";
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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 function ax+b % m = y (where m is length of the alphabet)
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output += alphabet[((a * alphabet.indexOf(input[i])) + b) % 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[((a * alphabet.indexOf(input[i].toLowerCase())) + b) % 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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