Protocol Building Blocks
Bruce Schneier · 2015
A cryptographic protocol involves some cryptographic algorithm, but generally the goal of the protocol is something beyond simple secrecy. The notion of a one-way function is central to public-key cryptography. A trapdoor one-way function is a special type of one-way function, one with a secret trapdoor. One-way hash functions are building block for many protocols. A message authentication code (MAC), also known as a data authentication code (DAC), is a one-way hash function with the addition of a secret key. The hash value is a function of both the pre-image and the key. By combining digital signatures with public-key cryptography, one develops a protocol that combines the security of encryption with the authenticity of digital signatures. Cryptography is extremely sensitive to the properties of random-number generators. Cryptographic applications demand much more of a pseudo-random-sequence generator than do most other applications.