gchq/CyberChef · error · OperationError

Error: Radix argument must be divisible by 2

Error message

Error: Radix argument must be divisible by 2

What it means

Thrown by the Luhn Checksum operation when the 'Radix' argument (args[0]) is within 2–36 but not divisible by 2. The Luhn mod-N algorithm requires an even base (the 'double and sum digits' step assumes base N splits cleanly), so run() rejects odd radices at LuhnChecksum.mjs:81 with an OperationError. This check runs after the range check (line 76), so odd values like 3, 5, …, 35 are the only ones that reach it.

Source

Thrown at src/core/operations/LuhnChecksum.mjs:81

        }, 0) % radix; // Use radix as the modulus base
    }

    /**
     * @param {string} input
     * @param {Object[]} args
     * @returns {string}
     */
    run(input, args) {
        if (!input) return "";

        const radix = args[0];

        if (radix < 2 || radix > 36) {
            throw new OperationError("Error: Radix argument must be between 2 and 36");
        }

        if (radix % 2 !== 0) {
            throw new OperationError("Error: Radix argument must be divisible by 2");
        }

        const checkSum = this.checksum(input, radix).toString(radix);
        let checkDigit = this.checksum(input + "0", radix);
        checkDigit = checkDigit === 0 ? 0 : (radix - checkDigit);
        checkDigit = checkDigit.toString(radix);

        return `Checksum: ${checkSum}
Checkdigit: ${checkDigit}
Luhn Validated String: ${input + "" + checkDigit}`;
    }

}

export default LuhnChecksum;

View on GitHub (pinned to 4290ea7539)

Solutions

1. Set Radix to an even integer between 2 and 36 (2, 4, 6, …, 36). 10 is the classic Luhn base.
2. Validate that radix % 2 === 0 before running.
3. If you genuinely need an odd base, Luhn mod-N is the wrong algorithm — pick a different checksum operation.

Example fix

// before
luhn.run(input, [11]);   // odd -> rejected

// after
luhn.run(input, [10]);   // even, classic Luhn

function evenRadix(r) {
  return Number.isInteger(r) && r >= 2 && r <= 36 && r % 2 === 0;
}
if (!evenRadix(radix)) throw new Error('Radix must be even, 2..36');

function isEvenRadix(v: unknown): v is number {
  return typeof v === 'number' && Number.isInteger(v) && v >= 2 && v <= 36 && v % 2 === 0;
}

When it happens

Trigger: Setting Radix to an odd integer between 3 and 35 inclusive — e.g. 3, 5, 7, 10 is fine, but 11 or 13 triggers it. Raised at LuhnChecksum.mjs:80-82.

Common situations: Choosing radix=10 (valid) but accidentally typing an odd value like 11; assuming any base 2–36 works; copying a recipe that used an odd base for a non-Luhn checksum.

Related errors

• Character: ${elem} is not valid in radix ${radix}.
• Error: Radix argument must be between 2 and 36
• Invalid custom CRC arguments
• Unknown checksum algorithm
• Error: Base argument must be between 2 and 36

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/6e32d0d232c359ed. Report an issue: GitHub.