eth_keys.exceptions.BadSignature: Invalid signature

web3.py / eth-account / eth-keys (Python) — BadSignature from public-key recovery

What it means

The signature has the right length, but its values do not describe any valid secp256k1 signature, so no public key can be recovered: r or s is zero or not below the curve order, or r is not the x-coordinate of a point on the curve. This is different from a signature by the wrong key — such a signature recovers a different address without any exception. BadSignature means the bytes are not a signature at all.

Why it happens

• A zero-filled or default value

  common

  Zero-filled fixtures, a database column default, or an empty signature padded to 65 bytes by a client.

• Corrupted bytes

  occasional

  Signatures damaged by an encoding round trip (hex ↔ base64, string ↔ bytes) can still be 65 bytes long but no longer represent a curve point.

• A signature from another scheme

  occasional

  A P-256 (WebAuthn/passkey) or Ed25519 signature that happens to be 64 bytes, padded with a v byte. It is not an Ethereum signature.

How to fix it

1. 1.

   Treat it as a rejected signature

   Catch BadSignature together with length and value errors and reject the request; do not retry with other v values.

   from eth_keys.exceptions import BadSignature
   from eth_utils.exceptions import ValidationError
   
   def recover_or_none(message, signature) -> str | None:
       try:
           return Account.recover_message(message, signature=signature)
       except (BadSignature, ValidationError, ValueError):
           return None  # reject the request: the signature is malformed

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