1: correct signature 0: incorrect or unparseable signature Args: ctx: a secp256k1 context object, initialized for verification. In: sig: the signature being verified. msghash32: the 32-byte message hash being verified. The verifier must make sure to apply a cryptographic hash function to the message by itself and not accept an msghash32 value directly. Otherwise, it would be easy to create a "valid" signature without knowledge of the secret key. See also https://bitcoin.stackexchange.com/a/81116/35586 for more background on this topic. pubkey: pointer to an initialized public key to verify with.
To avoid accepting malleable signatures, only ECDSA signatures in lower-S form are accepted.
If you need to accept ECDSA signatures from sources that do not obey this rule, apply secp256k1_ecdsa_signature_normalize to the signature prior to validation, but be aware that doing so results in malleable signatures.
For details, see the comments for that function.
Verify an ECDSA signature.