A protocol is a prescribed sequence of steps that participants follow to achieve a shared outcome. In practice, the steps must account for adversaries who may exploit them. section 1.1
The unattended sword
Deposit a magic sword on the ground, take a nap, and recover it afterward. The sequence is a protocol, but it fails because anyone can steal the sword while its owner sleeps. section 1.1
A secure protocol is easier to reason about when you separate its purpose, ingredients, and risks:
- State the outcome participants need, such as exchanging confidential messages. section 1.9
- Treat cryptographic primitives as building blocks with specific security claims, rather than combining them casually. section 1.5
- Account for authentication and confidentiality, the two recurring properties protocols aim to provide. section 1.9
- Prefer respected, tried-and-tested protocols and implementations; assembling primitives yourself is dangerous. section 16.8
Cryptography augments ordinary protocols so they work in adversarial settings. Real-world failures usually arise from misuse, unsafe composition, complicated interfaces, or neglected noncryptographic parts of the system. section 1.5 section 16.8
