gchq/CyberChef · error · OperationError

Crib cannot be empty

Error message

Crib cannot be empty

What it means

Thrown by MultipleBombe.run when the crib (args[4]) is an empty string. The Bombe attack requires a known plaintext fragment (the 'crib') to build its menu; without one there is nothing to test rotor settings against.

Source

Thrown at src/core/operations/MultipleBombe.mjs:217

        }
        if (fourthRotorsStr !== "") {
            for (let rstr of fourthRotorsStr.split("\n")) {
                rstr = this.validateRotor(rstr);
                fourthRotors.push(rstr);
            }
        }
        if (fourthRotors.length === 0) {
            fourthRotors.push("");
        }
        for (const rstr of reflectorsStr.split("\n")) {
            const reflector = new Reflector(rstr);
            reflectors.push(reflector);
        }
        if (reflectors.length === 0) {
            throw new OperationError("A minimum of one reflector must be supplied");
        }
        if (crib.length === 0) {
            throw new OperationError("Crib cannot be empty");
        }
        if (offset < 0) {
            throw new OperationError("Offset cannot be negative");
        }
        // 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);
        let update;
        if (isWorkerEnvironment()) {
            update = this.updateStatus;
        } else {
            update = undefined;
        }
        let bombe = undefined;
        const output = {bombeRuns: []};
        // I could use a proper combinatorics algorithm here... but it would be more code to
        // write one, and we don't seem to have one in our existing libraries, so massively nested

View on GitHub (pinned to 4290ea7539)

Solutions

1. Enter a known-plaintext fragment in the Crib field (e.g. 'WETTER').
2. Ensure the crib actually appears in the ciphertext at the given offset.
3. Double-check the crib is not just whitespace — although note the check uses raw length, so whitespace passes but will be stripped later leaving an empty effective crib.

Example fix

// before
chef.bake("Multiple Bombe", [..., "", 0, true]);
// after
chef.bake("Multiple Bombe", [..., "WETTER", 0, true]);

const crib = args[4];
if (typeof crib !== "string" || crib.length === 0) {
  // enter a known-plaintext fragment
}

const hasCrib = (c) => typeof c === "string" && c.replace(/[^A-Za-z]/g, "").length > 0;

try { chef.bake("Multiple Bombe", args); }
catch (e) { if (e.message === "Crib cannot be empty") enterCrib(); else throw e; }

When it happens

Trigger: run(input, args) where args[4] === '' (the Crib field). Checked before the crib is uppercased/filtered, so any zero-length string trips it.

Common situations: User forgot to enter a crib; crib was in a different field; recipe loaded with the crib field blanked; crib consisted only of characters that were intended but never typed.

Related errors

• Rotor wiring must be 26 unique uppercase letters
• A minimum of three rotors must be supplied
• A minimum of one reflector must be supplied
• Offset cannot be negative
• ${name} connects ${pair[1]} more than once

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/b191c7ce6bfa8036. Report an issue: GitHub.