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Bombe: add trial decryption preview

This commit is contained in:
s2224834 2019-01-08 19:37:34 +00:00
parent ad6e30f3d4
commit e74c86842b
3 changed files with 79 additions and 16 deletions
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60
src/core/lib/Bombe.mjs
View File

@ -191,9 +191,6 @@ export class BombeMachine {
if (ciphertext.length < crib.length) {
throw new OperationError("Crib overruns supplied ciphertext");
}
if (ciphertext.length > crib.length) {
throw new OperationError("Ciphertext is longer than crib");
}
if (crib.length < 2) {
// This is the absolute bare minimum to be sane, and even then it's likely too short to
// be useful
@ -204,7 +201,7 @@ export class BombeMachine {
// A shorter crib is preferable to reduce this chance, of course
throw new OperationError("Crib is too long");
}
for (let i=0; i<ciphertext.length; i++) {
for (let i=0; i<crib.length; i++) {
if (ciphertext[i] === crib[i]) {
throw new OperationError(`Invalid crib: character ${ciphertext[i]} at pos ${i} in both ciphertext and crib`);
}
@ -396,6 +393,46 @@ export class BombeMachine {
}
}
/**
* Single-pair steckering. Used for trial decryption rather than building a whole plugboard
* object for one pair
* @param {number[2]} stecker - Known stecker pair.
* @param {number} x - Letter to transform.
* @result number
*/
singleStecker(stecker, x) {
if (x === stecker[0]) {
return stecker[1];
}
if (x === stecker[1]) {
return stecker[0];
}
return x;
}
/**
* Trial decryption at the current setting.
* Used after we get a stop.
* This applies the detected stecker pair if we have one. It does not handle the other
* steckering or stepping (which is why we limit it to 26 characters, since it's guaranteed to
* be wrong after that anyway).
* @param {number[2]} stecker - Known stecker pair.
* @returns {string}
*/
tryDecrypt(stecker) {
const fastRotor = this.indicator.rotors[0];
const initialPos = fastRotor.pos;
const res = [];
// The indicator scrambler starts in the right place for the beginning of the ciphertext.
for (let i=0; i<Math.min(26, this.ciphertext.length); i++) {
const t = this.indicator.transform(this.singleStecker(stecker, a2i(this.ciphertext[i])));
res.push(i2a(this.singleStecker(stecker, t)));
fastRotor.pos = Utils.mod(fastRotor.pos + 1, 26);
}
fastRotor.pos = initialPos;
return res.join("");
}
/**
* Having set up the Bombe, do the actual attack run. This tries every possible rotor setting
* and attempts to logically invalidate them. If it can't, it's added to the list of candidate
@ -433,19 +470,26 @@ export class BombeMachine {
// Our steckering hypothesis is wrong. Correct value is the un-energised wire.
for (let j=0; j<26; j++) {
if (!this.wires[26*this.testRegister + j]) {
stecker = `${i2a(this.testRegister)} <-> ${i2a(j)}`;
stecker = [this.testRegister, j];
break;
}
}
} else if (count === 1) {
// This means our hypothesis for the steckering is correct.
stecker = `${i2a(this.testRegister)} <-> ${i2a(this.testInput[1])}`;
stecker = [this.testRegister, this.testInput[1]];
} else {
// Unusual, probably indicative of a poor menu. I'm a little unclear on how
// this was really handled, but we'll return it for the moment.
stecker = `? (wire count: ${count})`;
stecker = undefined;
}
result.push([this.indicator.getPos(), stecker]);
const testDecrypt = this.tryDecrypt(stecker);
let steckerStr;
if (stecker !== undefined) {
steckerStr = `${i2a(stecker[0])}${i2a(stecker[1])}`;
} else {
steckerStr = `?? (wire count: ${count})`;
}
result.push([this.indicator.getPos(), steckerStr, testDecrypt]);
}
// Step all the scramblers
// This loop counts how many rotors have reached their starting position (meaning the

8
src/core/operations/Bombe.mjs
View File

@ -112,7 +112,7 @@ class Bombe extends Operation {
// For symmetry with the Enigma op, for the input we'll just remove all invalid characters
input = input.replace(/[^A-Za-z]/g, "").toUpperCase();
crib = crib.replace(/[^A-Za-z]/g, "").toUpperCase();
const ciphertext = input.slice(offset, offset+crib.length);
const ciphertext = input.slice(offset);
const reflector = new Reflector(reflectorstr);
let update;
if (ENVIRONMENT_IS_WORKER()) {
@ -122,9 +122,9 @@ class Bombe extends Operation {
}
const bombe = new BombeMachine(rotors, reflector, ciphertext, crib, update);
const result = bombe.run();
let msg = `Bombe run on menu with ${bombe.nLoops} loops (2+ desirable). Note: Rotor positions are listed left to right and start at the beginning of the crib, and ignore stepping and the ring setting. One stecker pair is determined. Results:\n`;
for (const [setting, wires] of result) {
msg += `Stop: ${setting} (${wires})\n`;
let msg = `Bombe run on menu with ${bombe.nLoops} loops (2+ desirable). Note: Rotor positions are listed left to right and start at the beginning of the crib, and ignore stepping and the ring setting. One stecker pair is determined. A decryption preview starting at the beginning of the crib and ignoring stepping is also provided. Results:\n`;
for (const [setting, stecker, decrypt] of result) {
msg += `Stop: ${setting} (plugboard: ${stecker}): ${decrypt}\n`;
}
return msg;
}

27
tests/operations/tests/Bombe.mjs
View File

@ -8,9 +8,10 @@ import TestRegister from "../TestRegister";
TestRegister.addTests([
{
// Plugboard for this test is BO LC KE GA
name: "Bombe: 3 rotor (self-stecker)",
input: "BBYFLTHHYIJQAYBBYS",
expectedMatch: /LGA \(S <-> S\)/,
expectedMatch: /LGA \(plugboard: SS\): VFISUSGTKSTMPSUNAK/,
recipeConfig: [
{
"op": "Bombe",
@ -28,7 +29,7 @@ TestRegister.addTests([
{
name: "Bombe: 3 rotor (other stecker)",
input: "JBYALIHDYNUAAVKBYM",
expectedMatch: /LGA \(A <-> G\)/,
expectedMatch: /LGA \(plugboard: AG\): QFIMUMAFKMQSKMYNGW/,
recipeConfig: [
{
"op": "Bombe",
@ -46,7 +47,7 @@ TestRegister.addTests([
{
name: "Bombe: crib offset",
input: "AAABBYFLTHHYIJQAYBBYS", // first three chars here are faked
expectedMatch: /LGA \(S <-> S\)/,
expectedMatch: /LGA \(plugboard: SS\): VFISUSGTKSTMPSUNAK/,
recipeConfig: [
{
"op": "Bombe",
@ -61,12 +62,30 @@ TestRegister.addTests([
}
]
},
{
name: "Bombe: multiple stops",
input: "BBYFLTHHYIJQAYBBYS",
expectedMatch: /LGA \(plugboard: TT\): VFISUSGTKSTMPSUNAK/,
recipeConfig: [
{
"op": "Bombe",
"args": [
"BDFHJLCPRTXVZNYEIWGAKMUSQO<W", // III
"AJDKSIRUXBLHWTMCQGZNPYFVOE<F", // II
"EKMFLGDQVZNTOWYHXUSPAIBRCJ<R", // I
"",
"AY BR CU DH EQ FS GL IP JX KN MO TZ VW", // B
"THISISATESTM", 0,
]
}
]
},
/*
* Long test is long
{
name: "Bombe: 4 rotor",
input: "LUOXGJSHGEDSRDOQQX",
expectedMatch: /LHSC \(S <-> S\)/,
expectedMatch: /LHSC \(plugboard: SS\)/,
recipeConfig: [
{
"op": "Bombe",