Protocol syntax (cryptography)

Protocols A typical protocol description combines prose, data type specifications, various diagrams, ad hoc notations, and message sequences like:

$$\begin{array}{rl}1.A\to B:& \{N1,A{\}}_{K_B}\\ 2.B\to A:& \{N1,N2{\}}_{K_A}\\ 3.A\to B:& \{N2{\}}_{K_B}\end{array}$$

Often includes informal statements concerning properties and why they should hold.