fun KeyPair.signWithECDSA(bitsToSign: ByteArray): WithKey
fun KeyPair.signWithECDSA(bitsToSign: OpaqueBytes): WithKey
fun KeyPair.signWithECDSA(bitsToSign: OpaqueBytes, party: Party): LegallyIdentifiable
fun KeyPair.signWithECDSA(bitsToSign: ByteArray, party: Party): LegallyIdentifiable