Function check_sig 

pub fn check_sig(
    msg: Message<'_>,
    sig: Signature<'_>,
    key: &PublicKey,
) -> Result<bool>

Verify sig over msg for public key key.

msg and sig are wrapped in the distinct Message and Signature newtypes so the compiler rejects a caller that swaps them; &PublicKey (33 bytes) enforces the key size at the call site.

• secp256k1 keys (0x02/0x03): the host pre-hashes msg with SHA-512Half before ECDSA verify.
• Ed25519 keys (0xED): the host verifies the raw msg directly (no pre-hash), stripping the 0xED prefix; a non-canonical signature returns Ok(false).

An empty msg or empty sig is not an error — the host returns Ok(false).

Errors: InvalidParams if the key is malformed (not 33 bytes / bad prefix); DataFieldTooLarge if any parameter exceeds 1024 bytes.