conceptually different ciphers
1Rotor machine — In cryptography, a rotor machine is an electro mechanical device used for encrypting and decrypting secret messages. Rotor machines were the cryptographic state of the art for a brief but prominent period of history; they were in widespread use… …
2IPsec — Internet Protocol Security (IPsec) is a suite of protocols for securing Internet Protocol (IP) communications by authenticating and/or encrypting each in a data stream. IPsec also includes protocols for cryptographic key establishment.… …
3P versus NP problem — Unsolved problems in computer science Is P = NP ? …
