When we implement security functionalities into information systems, many of them are realized by cryptographic protocol. Cryptographic protocol is formally a combination of cryptographic operations and communications among protocol participants. Though designing cryptographic protocol seems like building castle by LEGO block, it is much harder to build a secure cryptographic protocol than LEGO. In this talk, we revisit how difficult the designing of cryptographic protocol is from history of attacks on cryptographic protocols, recent attacks on SSL/TLS, and history of security evaluation. Then, we will discuss the way forward to securing new cryptographic protocols like TLS1.3 and blockchain.