gchq/CyberChef · warning · OperationError

Invalid alphabet size, required to be between 2 and 9 (inclu

Error message

Invalid alphabet size, required to be between 2 and 9 (inclusive).

What it means

First validation in Generate De Bruijn Sequence: rejects alphabet size `k` outside 2..9 inclusive. The De Bruijn generator allocates an array of size k*n and branches over k symbols, so the bound keeps memory and runtime sane. Note the ordering quirk: this range check runs BEFORE the integer check, so a non-integer k that is also out of range (e.g. 1.5 or 10.5) hits this message rather than the integer one.

Source

Thrown at src/core/operations/GenerateDeBruijnSequence.mjs:50

            },
            {
                name: "Key length (n)",
                type: "number",
                value: 3
            }
        ];
    }

    /**
     * @param {string} input
     * @param {Object[]} args
     * @returns {string}
     */
    run(input, args) {
        const [k, n] = args;

        if (k < 2 || k > 9) {
            throw new OperationError("Invalid alphabet size, required to be between 2 and 9 (inclusive).");
        }

        if (!Number.isInteger(k)) {
            throw new OperationError("Invalid alphabet size, required to be integer.");
        }

        if (!Number.isInteger(n)) {
            throw new OperationError("Invalid key length, required to be integer.");
        }

        if (n < 2) {
            throw new OperationError("Invalid key length, required to be at least 2.");
        }

        if (Math.pow(k, n) > 50000) {
            throw new OperationError("Too many permutations, please reduce k^n to under 50,000.");
        }

View on GitHub (pinned to 4290ea7539)

Solutions

1. Set Alphabet size (k) to an integer between 2 and 9 inclusive.
2. If you need a larger alphabet, reduce n so k^n stays under 50,000, but k itself cannot exceed 9 in this op.
3. Enter whole numbers only in the k field.

Example fix

// before
args = [10, 3];
// after
args = [9, 3];

if (!Number.isInteger(k) || k < 2 || k > 9) throw new Error("Alphabet size k must be an integer in [2, 9]");

/** @param {number} k */
function isValidAlphabetSize(k){return Number.isInteger(k) && k >= 2 && k <= 9;}

When it happens

Trigger: Setting Alphabet size (k) to 1, 0, a negative, 10+, or any non-integer value that falls outside 2..9 (e.g. k=10 or k=1.5 both fail here).

Common situations: Mistaking k for key length; entering a large alphabet assuming the op supports arbitrary bases; passing a float because the number field accepted decimals.

Related errors

• Invalid key length, required to be at least 2.
• Invalid alphabet size, required to be integer.
• Invalid key length, required to be integer.
• Too many permutations, please reduce k^n to under 50,000.
• Invalid block cipher mode: ${mode}

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/f993f26f7781a18a. Report an issue: GitHub.