gchq/CyberChef · error · OperationError

${err}

Error message

${err}

What it means

A catch-all around the crypto-gost-js engine calls in GOST Decrypt that re-throws any library exception as an OperationError. The underlying `err` is most often a key-length, IV-length, sBox, or hex-decode failure raised inside `GostEngine.getGostCipher` or `cipher.decrypt`. GOST keys must be 256 bits (32 bytes / 64 hex chars); block modes other than ECB require an IV equal to the block size (8 bytes for Magma, 16 for Kuznyechik).

Source

Thrown at src/core/operations/GOSTDecrypt.mjs:145

            version: versionNum,
            length: blockLength,
            mode: "ES",
            sBox: sBoxVal,
            block: blockMode,
            keyMeshing: keyMeshing,
            padding: padding
        };

        try {
            const Hex = CryptoGost.coding.Hex;
            if (iv) algorithm.iv = Hex.decode(iv);

            const cipher = GostEngine.getGostCipher(algorithm);
            const out = Hex.encode(cipher.decrypt(Hex.decode(key), Hex.decode(input)));

            return outputType === "Hex" ? out : Utils.byteArrayToChars(fromHex(out));
        } catch (err) {
            throw new OperationError(err);
        }
    }

}

export default GOSTDecrypt;

View on GitHub (pinned to 4290ea7539)

Solutions

1. Ensure the key is exactly 32 bytes; if Input type is Hex, that is 64 hex digits.
2. Provide an IV of the correct block size for any non-ECB mode (8 bytes for Magma, 16 for Kuznyechik).
3. Verify the Input type matches the actual input encoding; switch to Raw if the input is text.
4. Set padding to match how the data was encrypted (e.g. PKCS5).
5. Inspect the wrapped `err.message` (it is preserved) to identify the exact library failure.

Example fix

// before: key too short, no IV for CBC
args = ["aabb", "", "Hex", "Raw", "GOST R 34.12 (Magma, 2015)", "E-A", "CBC", "NO", "NO"];
// after: 32-byte key, 8-byte IV for 64-bit Magma CBC
args = ["aabb...dd".padEnd(64,"0"), "0011223344556677", "Hex", "Raw", "GOST R 34.12 (Magma, 2015)", "E-A", "CBC", "NO", "PKCS5"];

// Validate key/iv lengths before baking
const KEY_BYTES = 32;
if (hexKey.length !== KEY_BYTES * 2) throw new Error(`Key must be ${KEY_BYTES} bytes (${KEY_BYTES*2} hex chars)`);
if (mode !== "ECB" && hexIv.length !== (blockBits/8) * 2) throw new Error(`IV must be ${blockBits/8} bytes for ${mode}`);

/** Hex string of even length with only 0-9a-fA-F */
function isHex(s) { return typeof s === "string" && /^[0-9a-fA-F]*$/.test(s) && s.length % 2 === 0; }

try { chef.bake(input, recipe); }
catch (e) {
  if (e.message && /key|iv|length|sbox/i.test(e.message)) handleUserError(e);
  else throw e;
}

When it happens

Trigger: Supplying a key that is not exactly 32 bytes; choosing CBC/CFB/OFB/CTR but leaving the IV empty or the wrong length; passing non-hex characters when Input type is "Hex"; selecting an invalid sBox for the 1989 variant; decrypting data whose ciphertext length is not a whole number of blocks with NO padding.

Common situations: Pasting a key copied from a PEM/base64 source without converting to the configured key format; forgetting that the IV must match the block size of the chosen algorithm (Magma 64-bit vs Kuznyechik 128-bit); interop with another tool that used a different padding or mode.

Related errors

• ${err}
• ${err}
• ${err}
• ${err}
• ${err}

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/e64a2a3e057b0bf9. Report an issue: GitHub.