gchq/CyberChef · error · OperationError

Value ${Utils.bin(n, 4)} is not in the encoding scheme

Error message

Value ${Utils.bin(n, 4)} is not in the encoding scheme

What it means

Thrown by From BCD when a parsed nibble value is not present in the selected encoding scheme's lookup array (encoding.indexOf(n) < 0). Each BCD scheme (8 4 2 1, Excess-3, etc.) only accepts certain 4-bit patterns; a nibble outside that set is invalid for the scheme. The offending 4-bit value is shown in binary for diagnostics.

Source

Thrown at src/core/operations/FromBCD.mjs:114

            // Discard each high nibble
            for (let i = 0; i < nibbles.length; i++) {
                nibbles.splice(i, 1); // lgtm [js/loop-iteration-skipped-due-to-shifting]
            }
        }

        if (signed) {
            const sign = nibbles.pop();
            if (sign === 13 ||
                sign === 11) {
                // Negative
                output += "-";
            }
        }

        nibbles.forEach(n => {
            if (isNaN(n)) throw new OperationError("Invalid input");
            const val = encoding.indexOf(n);
            if (val < 0) throw new OperationError(`Value ${Utils.bin(n, 4)} is not in the encoding scheme`);
            output += val.toString();
        });

        return new BigNumber(output);
    }

}

export default FromBCD;

View on GitHub (pinned to 4290ea7539)

Solutions

1. Identify the correct BCD encoding scheme used by the source system and select it.
2. If the data may contain hex digits, verify it is actually BCD and not plain hex.
3. Try alternate schemes (8 4 2 1, 4 2 2 1, 5 4 2 1, Excess-3) to find the matching one.

Example fix

// before: wrong scheme for the data
fromBcd.run(input, ['8 4 2 1', true, false, 'Raw']) // nibble 0xA not in 8421
// after: use a scheme that accepts the pattern, or confirm data is BCD
fromBcd.run(input, ['Excess-3', true, false, 'Raw'])

// Check each nibble's 4-bit value is valid for the chosen scheme before decoding
const validSet = ENCODING_LOOKUP[scheme];
// after splitting into nibbles, ensure encoding.includes(n) for each
if (!nibbles.every(n => validSet.includes(n))) {
  // pick a different scheme or reject the data
}

function nibbleInScheme(n, scheme) {
  return ENCODING_LOOKUP[scheme].includes(n);
}

try {
  fromBcd.run(input, args);
} catch (e) {
  if (e.type === 'OperationError' && /is not in the encoding scheme/.test(e.message)) {
    // wrong scheme; try alternate schemes (8421, 4221, 5421, Excess-3)
  } else throw e;
}

When it happens

Trigger: Selecting the wrong BCD scheme for the data (e.g. feeding Excess-3 data as 8 4 2 1); data containing nibble values like 0xA-0xF which are invalid in plain BCD; unsigned data interpreted under a scheme that excludes the encountered patterns.

Common situations: Not knowing which BCD variant the source used; legacy mainframe/EBCDIC data with a different scheme; mixing packed/unpacked assumptions.

Related errors

• Invalid input
• Invalid value
• Human-Readable Part (HRP) cannot be empty.
• HRP contains invalid character at position ${i}. Only printa
• Encoded string exceeds maximum length of 90 characters (got

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/d542c8a20d3d8269. Report an issue: GitHub.