gchq/CyberChef · error · OperationError

Invalid key length: ${key.length} bytes SM4 uses a key leng

Error message

Invalid key length: ${key.length} bytes

SM4 uses a key length of 16 bytes (128 bits).

What it means

Thrown by SM4 Encrypt when the key, decoded via Utils.convertToByteArray, is not exactly 16 bytes. SM4 requires a 128-bit key. The key toggle (Hex/UTF8/Latin1/Base64) determines how the key string is decoded before the length is checked.

Source

Thrown at src/core/operations/SM4Encrypt.mjs:72

                "name": "Output",
                "type": "option",
                "value": ["Hex", "Raw"]
            }
        ];
    }

    /**
     * @param {string} input
     * @param {Object[]} args
     * @returns {string}
     */
    run(input, args) {
        const key = Utils.convertToByteArray(args[0].string, args[0].option),
            iv = Utils.convertToByteArray(args[1].string, args[1].option),
            [,, mode, inputType, outputType] = args;

        if (key.length !== 16)
            throw new OperationError(`Invalid key length: ${key.length} bytes

SM4 uses a key length of 16 bytes (128 bits).`);
        if (iv.length !== 16 && !mode.startsWith("ECB"))
            throw new OperationError(`Invalid IV length: ${iv.length} bytes

SM4 uses an IV length of 16 bytes (128 bits).
Make sure you have specified the type correctly (e.g. Hex vs UTF8).`);

        input = Utils.convertToByteArray(input, inputType);
        const output = encryptSM4(input, key, iv, mode.substring(0, 3), mode.endsWith("NoPadding"));
        return outputType === "Hex" ? toHex(output) : Utils.byteArrayToUtf8(output);
    }

}

export default SM4Encrypt;

View on GitHub (pinned to 4290ea7539)

Solutions

1. Ensure the decoded key is exactly 16 bytes; for a hex key use the 'Hex' toggle.
2. Confirm the toggle matches the key encoding.
3. Strip trailing newlines/whitespace from the key field.

Example fix

// before
sm4Encrypt.run(pt, [{string:"0123456789abcdef0123456789abcdef", option:"UTF8"}, ...])
// after
sm4Encrypt.run(pt, [{string:"0123456789abcdef0123456789abcdef", option:"Hex"}, ...])

const key = Utils.convertToByteArray(keyArg.string, keyArg.option);
if (key.length !== 16) {
  throw new Error(`SM4 key must decode to 16 bytes, got ${key.length}. Check toggle.`);
}

function isSm4KeyArg(arg) {
  return Utils.convertToByteArray(arg.string, arg.option).length === 16;
}

When it happens

Trigger: Same shape as the decrypt variant: the decoded key byte length is not 16. Most often a toggle/encoding mismatch where a 32-char hex key is interpreted as UTF8 (32 bytes) or the key is the wrong length entirely.

Common situations: Toggle set to UTF8 for a hex key; blank key (0 bytes); pasting a 256-bit key (32 bytes) intended for AES-256; trailing whitespace.

Related errors

• Invalid key length: ${key.length} bytes SM4 uses a key leng
• Invalid IV length: ${iv.length} bytes SM4 uses an IV length
• Invalid IV length: ${iv.length} bytes SM4 uses an IV length
• Invalid key length: ${key.length} bytes. Salsa20 uses a key
• Input private key must be in hex; and should be 32 bytes

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/a61b2f849fb446f1. Report an issue: GitHub.