A message crossing public Wi‑Fi or internet servers may be copied, altered, or inspected. A cryptographic algorithm applies a designed method—usually involving keys—to protect against such attacks. section 1.3 section 1.0
An algorithm is a specific cryptographic method, while a cryptographic primitive is the broader kind of method it instantiates. AES, for example, is a symmetric-encryption algorithm. Algorithms may target confidentiality, authentication, or both, and may belong to symmetric or asymmetric cryptography. section 1.3 section 1.9
Judge a cryptographic algorithm by the assumptions it preserves and the way it reaches users:
- Keep the key secret, but do not rely on keeping the algorithm secret; public scrutiny is part of building trust. section 1.3
- Treat an algorithm as broken if attackers can recover the key, decrypt without it, or learn message information from ciphertext. section 1.3
- Separate an algorithm from a protocol: algorithms supply cryptographic operations, while protocols combine participant steps to achieve goals. section 1.9
- Prefer established, reviewed constructions and expert support over inventing or composing cryptography casually. section 1.8 section 1.7
From concept to deployed algorithm
Symmetric encryption is the primitive; AES is one concrete instantiation. An algorithm can move from a cryptographic concept to a standardized construction and then to implementations in different languages, improving interoperability. Standards still require scrutiny: hidden backdoors in Dual EC and GOST damaged confidence in government-led choices. section 1.7 section 1.9
Figure 1.4 The cryptographic algorithms you have learned so far. AES is an instantiation of a symmetric encryption algorithm, which is a cryptographic primitive that is part of the broader class of symmetric cryptographic algorithms.
Use the hierarchy diagram to distinguish AES from symmetric encryption and the broader family of symmetric cryptographic algorithms. section 1.3
