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Security Protocol Notation




The standard notation consists of a set of individuals (traditionally named Alice, Bob , Charlie and so on) who wish to communicate. They may have access to a server S, shared keys K, timestamps T, and can generate Nonce s N for authentication purposes.

A simple example might be the following:

:A ightarrow B:\{X_1\}_{K_{AB}}

This states that Alice intends a message for '''B'''ob consisting of a plain text '''X_1''' encrypted under shared key '''KAB'''.

Another example might be the following:

:B ightarrow A:\{N_B\}_{PK(A)}

This states that Bob intends a message for '''A'''lice consisting of a '''N'''once encrypted using public key of Alice.

A key with two subscripts is a Symmetric Key shared by the two corresponding individuals. A key with one subscript is the public key of the corresponding individual. A private key is represented as the inverse of the public key.

The notation specifies only the operation and not its semantics - for instance, public key encryption and signature are represented identically.

We can express more complicated protocols in such a fashion, see Kerberos as an example.