gchq/CyberChef · error · OperationError

${name} must be a whitespace-separated list of uppercase let

Error message

${name} must be a whitespace-separated list of uppercase letter pairs

What it means

Thrown by the PairMapBase constructor (parent of Plugboard and Reflector) when, after splitting the pairs string on whitespace, any token does not match /^[A-Z]{2}$/ — i.e. it is not exactly two uppercase letters. An empty pairs string is allowed (no connections); otherwise every whitespace-separated token must be a two-letter uppercase pair.

Source

Thrown at src/core/lib/Enigma.mjs:180

 */
class PairMapBase {
    /**
     * PairMapBase constructor.
     *
     * @param {string} pairs - A whitespace separated string of letter pairs to swap.
     * @param {string} [name='PairMapBase'] - For errors, the name of this object.
     */
    constructor(pairs, name="PairMapBase") {
        // I've chosen to make whitespace significant here to make a) code and
        // b) inputs easier to read
        this.pairs = pairs;
        this.map = {};
        if (pairs === "") {
            return;
        }
        pairs.split(/\s+/).forEach(pair => {
            if (!/^[A-Z]{2}$/.test(pair)) {
                throw new OperationError(name + " must be a whitespace-separated list of uppercase letter pairs");
            }
            const a = a2i(pair[0]), b = a2i(pair[1]);
            if (a === b) {
                // self-stecker
                return;
            }
            if (Object.prototype.hasOwnProperty.call(this.map, a)) {
                throw new OperationError(`${name} connects ${pair[0]} more than once`);
            }
            if (Object.prototype.hasOwnProperty.call(this.map, b)) {
                throw new OperationError(`${name} connects ${pair[1]} more than once`);
            }
            this.map[a] = b;
            this.map[b] = a;
        });
    }

    /**

View on GitHub (pinned to 4290ea7539)

Solutions

1. Format pairs as whitespace-separated two-uppercase-letter tokens (e.g. 'AY BR CU DH').
2. Uppercase the input and strip non-letter characters first.
3. Validate every token with /^[A-Z]{2}$/ before constructing.

Example fix

// before
new Plugboard('AYBRCUDH'); // no spaces -> one 8-char token

// after
new Plugboard('AY BR CU DH');

function normalisePairs(pairs) {
  return pairs.toUpperCase().trim().split(/\s+/).filter(Boolean);
}
const tokens = normalisePairs(pairs);
if (tokens.some(t => !/^[A-Z]{2}$/.test(t))) {
  throw new Error("All pairs must be two uppercase letters separated by whitespace.");
}

function isPairList(pairs) {
  if (pairs === "") return true;
  return pairs.split(/\s+/).every(t => /^[A-Z]{2}$/.test(t));
}

When it happens

Trigger: new Plugboard(pairs) or new Reflector(pairs) where pairs contains a single letter, a 3+ letter token, lowercase, digits, a symbol, or stray punctuation. Whitespace-splitting means any malformed token triggers it.

Common situations: Pasting a reflector/plugboard spec in the wrong format (e.g. concatenated 'AYBRCU' instead of space-separated 'AY BR CU'); lowercase input; trailing punctuation; a single dangling letter from a typo.

Related errors

• ${name} connects ${pair[0]} more than once
• Rotor wiring must be 26 unique uppercase letters
• Rotor steps must be 0-26 unique uppercase letters
• Rotor ring setting must be exactly one uppercase letter
• Rotor initial position must be exactly one uppercase letter

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/3bc3abd6f92ed358. Report an issue: GitHub.