gchq/CyberChef · error · OperationError

Size must be greater than 0

Error message

Size must be greater than 0

What it means

Thrown by the Shake operation when the 'Size' argument (output length) is negative. SHAKE is an extendable-output function whose output size is user-controlled, and a negative size is meaningless. Note the guard checks size < 0, so a size of 0 passes this check but the message says 'greater than 0', a minor mismatch between message and guard.

Source

Thrown at src/core/operations/Shake.mjs:53

                "name": "Size",
                "type": "number",
                "value": 512
            }
        ];
    }

    /**
     * @param {ArrayBuffer} input
     * @param {Object[]} args
     * @returns {string}
     */
    run(input, args) {
        const capacity = parseInt(args[0], 10),
            size = args[1];
        let algo;

        if (size < 0)
            throw new OperationError("Size must be greater than 0");

        switch (capacity) {
            case 128:
                algo = JSSHA3.shake128;
                break;
            case 256:
                algo = JSSHA3.shake256;
                break;
            default:
                throw new OperationError("Invalid size");
        }

        return algo(input, size);
    }

}

export default Shake;

View on GitHub (pinned to 4290ea7539)

Solutions

1. Set the Size argument to a positive integer (default is 512).
2. If computing size dynamically, clamp it to a minimum of 1 before passing.
3. Be aware that 0 currently passes the guard but produces empty output - use a positive value.

Example fix

// before
run(input, ["256", -16])
// after
run(input, ["256", 512])

const capacity = parseInt(args[0], 10);
const size = args[1];
if (typeof size !== "number" || size < 0) {
  throw new Error("Shake size must be a non-negative integer.");
}
// safe to invoke Shake (note: 0 currently passes but yields empty output)

function isValidShakeSize(size) {
  return typeof size === "number" && Number.isFinite(size) && size > 0;
}

try {
  chef.shake(input, { capacity: "256", size: 512 });
} catch (e) {
  // e.message indicates the size or capacity problem.
}

When it happens

Trigger: The 'Size' number argument is set to a negative value in the recipe. Can occur when a UI field is edited to a negative number or when a recipe is constructed programmatically with a negative size.

Common situations: Manual entry error in the Size field; recipe imported with a corrupted/typo'd size value; arithmetic that computes size from another field producing a negative result.

Related errors

• Invalid size
• Invalid size
• Invalid size
• Invalid block cipher mode: ${mode}
• Invalid ciphertext length: ${originalLength} bytes. Must be

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/6e8af4bee89865f8. Report an issue: GitHub.