sign method
sign a message (digest) using the private key
Implementation
@override
AptosSecp256k1AnySignature sign(List<int> digest) {
digest = QuickCrypto.sha3256Hash(digest);
final signer = Secp256k1Signer.fromKeyBytes(toBytes());
return AptosSecp256k1AnySignature(signer.sign(digest, hashMessage: false));
}