Merge pull request #1788 from EvieHarv/master

Author: a3957273

src/core/lib/Ciphers.mjs

@@ -3,13 +3,15 @@
  *
  * @author Matt C [[email protected]]
  * @author n1474335 [[email protected]]
+ * @author Evie H [[email protected]]
  *
  * @copyright Crown Copyright 2018
  * @license Apache-2.0
  *
  */
 
 import OperationError from "../errors/OperationError.mjs";
+import Utils from "../Utils.mjs";
 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.");
     }
 
+    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 function ax+b % m = y (where m is length of the alphabet)

tests/browser/02_ops.js

@@ -37,7 +37,7 @@ module.exports = {
         testOp(browser, ["From Hex", "Add Text To Image", "To Base64"], Images.PNG_HEX, Images.PNG_CHEF_B64, [[], ["Chef", "Center", "Middle", 0, 0, 16], []]);
         testOp(browser, "Adler-32 Checksum", "test input", "16160411");
         testOp(browser, "Affine Cipher Decode", "test input", "rcqr glnsr", [1, 2]);
-        testOp(browser, "Affine Cipher Encode", "test input", "njln rbfpn", [2, 1]);
+        testOp(browser, "Affine Cipher Encode", "test input", "gndg zoujg", [3, 1]);
         testOp(browser, "AMF Decode", "\u000A\u0013\u0001\u0003a\u0006\u0009test", /"\$value": "test"/);
         testOp(browser, "AMF Encode", '{"a": "test"}', "\u000A\u0013\u0001\u0003a\u0006\u0009test");
         testOp(browser, "Analyse hash", "0123456789abcdef", /CRC-64/);