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Typex: input wiring is reversed

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s2224834 2019-02-08 18:08:13 +00:00
parent 220053c044
commit 5a2a8b4c8e
1 changed files with 39 additions and 1 deletions
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40
src/core/lib/Typex.mjs
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@ -2,6 +2,7 @@
* Emulation of the Typex machine.
*
* @author s2224834
* @author The National Museum of Computing - Bombe Rebuild Project
* @copyright Crown Copyright 2019
* @license Apache-2.0
*/
@ -28,7 +29,7 @@ export const ROTORS = [
* An example Typex reflector. Again, randomised.
*/
export const REFLECTORS = [
{name: "Standard", value: "AN BC FG IE KD LU MH OR TS VZ WQ XJ YP"},
{name: "Example", value: "AN BC FG IE KD LU MH OR TS VZ WQ XJ YP"},
];
// Special character handling on Typex keyboard
@ -172,6 +173,8 @@ export class Rotor extends Enigma.Rotor {
* Typex input plugboard. Based on a Rotor, because it allows arbitrary maps, not just switches
* like the Enigma plugboard.
* Not to be confused with the reflector plugboard.
* This is also where the Typex's backwards input wiring is implemented - it's a bit of a hack, but
* it means everything else continues to work like in the Enigma.
*/
export class Plugboard extends Enigma.Rotor {
/**
@ -180,10 +183,45 @@ export class Plugboard extends Enigma.Rotor {
* @param {string} wiring - 26 character string of mappings from A-Z, as per rotors, or "".
*/
constructor(wiring) {
// Typex input wiring is backwards vs Enigma: that is, letters enter the rotors in a
// clockwise order, vs. Enigma's anticlockwise (or vice versa depending on which side
// you're looking at it from). I'm doing the transform here to avoid having to rewrite
// the Engima crypt() method in Typex as well.
// Note that the wiring for the reflector is the same way around as Enigma, so no
// transformation is necessary on that side.
// We're going to achieve this by mapping the plugboard settings through an additional
// transform that mirrors the alphabet before we pass it to the superclass.
if (!/^[A-Z]{26}$/.test(wiring)) {
throw new OperationError("Plugboard wiring must be 26 unique uppercase letters");
}
const reversed = "AZYXWVUTSRQPONMLKJIHGFEDCB";
wiring = wiring.replace(/./g, x => {
return reversed[Enigma.a2i(x)];
});
try {
super(wiring, "", "A", "A");
} catch (err) {
throw new OperationError(err.message.replace("Rotor", "Plugboard"));
}
}
/**
* Transform a character through this rotor forwards.
*
* @param {number} c - The character.
* @returns {number}
*/
transform(c) {
return Utils.mod(this.map[Utils.mod(c + this.pos, 26)] - this.pos, 26);
}
/**
* Transform a character through this rotor backwards.
*
* @param {number} c - The character.
* @returns {number}
*/
revTransform(c) {
return Utils.mod(this.revMap[Utils.mod(c + this.pos, 26)] - this.pos, 26);
}
}