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Macide Celik 2019-10-28 00:53:03 +03:00 • committed by GitHub
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src/core/operations/AffineCipherDecode.mjs
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/**
* @author Matt C [matt@artemisbot.uk]
* @copyright Crown Copyright 2018
* @license Apache-2.0
*/
import Operation from "../Operation.mjs";
import Utils from "../Utils.mjs";
import OperationError from "../errors/OperationError.mjs";
/**
* Affine Cipher Decode operation
*/
class AffineCipherDecode extends Operation {
/**
* AffineCipherDecode constructor
*/
constructor() {
super();
this.name = "Affine Cipher Decode";
this.module = "Ciphers";
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.";
this.infoURL = "https://wikipedia.org/wiki/Affine_cipher";
this.inputType = "string";
this.outputType = "string";
this.args = [
{
"name": "a",
"type": "number",
"value": 1
},
{
"name": "b",
"type": "number",
"value": 0
}
];
}
/**
* @param {string} input
* @param {Object[]} args
* @returns {string}
*
* @throws {OperationError} if a or b values are invalid
*/
run(input, args) {
const alphabet = "abcdefghijklmnopqrstuvwxyz",
[a, b] = args,
aModInv = Utils.modInv(a, 26); // Calculates modular inverse of a
let output = "";
if (!/^\+?(0|[1-9]\d*)$/.test(a) || !/^\+?(0|[1-9]\d*)$/.test(b)) {
throw new OperationError("The values of a and b can only be integers.");
}
if (Utils.gcd(a, 26) !== 1) {
throw new OperationError("The value of `a` must be coprime to 26.");
}
for (let i = 0; i < input.length; i++) {
if (alphabet.indexOf(input[i]) >= 0) {
// Uses the affine decode function (y-b * A') % m = x (where m is length of the alphabet and A' is modular inverse)
output += alphabet[Utils.mod((alphabet.indexOf(input[i]) - b) * aModInv, 26)];
} else if (alphabet.indexOf(input[i].toLowerCase()) >= 0) {
// Same as above, accounting for uppercase
output += alphabet[Utils.mod((alphabet.indexOf(input[i].toLowerCase()) - b) * aModInv, 26)].toUpperCase();
} else {
// Non-alphabetic characters
output += input[i];
}
}
return output;
}
/**
* Highlight Affine Cipher Decode
*
* @param {Object[]} pos
* @param {number} pos[].start
* @param {number} pos[].end
* @param {Object[]} args
* @returns {Object[]} pos
*/
highlight(pos, args) {
return pos;
}
/**
* Highlight Affine Cipher 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 AffineCipherDecode;