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Require (a, 26) to be coprime in affine encode

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Ethan Harvey 2024-04-10 23:19:50 +00:00
parent b2e400f474
commit a09f8451fd
1 changed files with 6 additions and 0 deletions
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6
src/core/lib/Ciphers.mjs
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@ -3,6 +3,7 @@
* *
* @author Matt C [matt@artemisbot.uk] * @author Matt C [matt@artemisbot.uk]
* @author n1474335 [n1474335@gmail.com] * @author n1474335 [n1474335@gmail.com]
* @author Evie H [evie@evie.sh]
* *
* @copyright Crown Copyright 2018 * @copyright Crown Copyright 2018
* @license Apache-2.0 * @license Apache-2.0
@ -10,6 +11,7 @@
*/ */
import OperationError from "../errors/OperationError.mjs"; import OperationError from "../errors/OperationError.mjs";
import Utils from "../Utils.mjs";
import CryptoJS from "crypto-js"; import CryptoJS from "crypto-js";
/** /**
@ -30,6 +32,10 @@ export function affineEncode(input, args) {
throw new OperationError("The values of a and b can only be integers."); 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++) { for (let i = 0; i < input.length; i++) {
if (alphabet.indexOf(input[i]) >= 0) { if (alphabet.indexOf(input[i]) >= 0) {
// Uses the affine function ax+b % m = y (where m is length of the alphabet) // Uses the affine function ax+b % m = y (where m is length of the alphabet)