gchq/CyberChef · error · OperationError

Base must be defined

Error message

Base must be defined

What it means

Thrown by the Modular Exponentiation operation in 'Case 2': the Base argument is blank, the Exponent argument is supplied, and the Input field is also blank — so there is no value to use as the base. The operation resolves a missing Base from the Input; if both are empty it cannot proceed and throws at ModularExponentiation.mjs:83.

Source

Thrown at src/core/operations/ModularExponentiation.mjs:83

        const mod = modParam;
        if (!mod) {
            throw new OperationError("Modulus must be defined");
        }

        // Base *or* Exponent (but not both) are taken from the Input
        // if their boxes are empty.
        let base, exp;
        if (baseParam && expParam) {
            // Case 1: base and exponent both given as parameters
            base = baseParam;
            exp  = expParam;
        } else if (!baseParam && expParam) {
            // Case 2: base missing - take from input
            base = inputVal;
            exp  = expParam;
            if (!base) {
                throw new OperationError("Base must be defined");
            }
        } else if (baseParam && !expParam) {
            // Case 3: exponent missing - take from input
            base = baseParam;
            exp  = inputVal;
            if (!exp) {
                throw new OperationError("Exponent must be defined");
            }
        } else if (!inputVal) {
            // Case 4: base and exponent both missing
            throw new OperationError("Base and Exponent must be defined");
        } else throw new OperationError("Ambiguous input: specify either Base or Exponent when using Input");

        // Parse numbers
        const baseBI = parseBigInt(base, "Base");
        const expBI  = parseBigInt(exp, "Exponent");
        const modBI  = parseBigInt(mod, "Modulus");

View on GitHub (pinned to 4290ea7539)

Solutions

1. Provide a Base value either in the Base argument or in the Input field (whichever you left empty).
2. If using Input as the base, ensure the upstream recipe step actually emits a value.
3. Validate that at least one of Base-arg / Input is non-empty when Exponent is set.

Example fix

// before — base missing both as arg and input
modExp.run('', ['', '15', '6']);   // base blank, input blank

// after — supply base via input
modExp.run('2', ['', '15', '6']);  // 2^6 mod 15

// Case 2: Base blank, Exponent set -> Base must come from Input.
function resolveBaseCase2(baseArg, input) {
  const base = (baseArg ?? '').trim() || (input ?? '').trim();
  if (!base) throw new Error('Base must be defined (fill Base arg or Input)');
  return base;
}

function hasBaseForCase2(baseArg: unknown, input: unknown): boolean {
  const b = (typeof baseArg === 'string' ? baseArg.trim() : '') || (typeof input === 'string' ? input.trim() : '');
  return b.length > 0;
}

When it happens

Trigger: args: Base='', Exponent=<set>, and input='' (or whitespace). The code path at ModularExponentiation.mjs:78-84 takes base from inputVal, then rejects an empty base. Triggered whenever the user supplies only an exponent and forgets the input.

Common situations: User filled the Exponent field, left Base empty intending to use Input, but also left Input empty; a recipe where the upstream operation produced no output; whitespace-only input that trims to empty.

Related errors

• Modulus must be defined
• Exponent must be defined
• Base and Exponent must be defined
• Letter ${letter} is not included in LS47
• Unknown padding type: ${padding}

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/7d096e1874f0ddb4. Report an issue: GitHub.