Logical Analysis and Verification of Cryptographic Protocols - Loria

Chapter 1
Introduction
In our society, the use of electronic applications such as ecommunication,
e-voting, e-banking, e-commerce, etc is increasing.
Among several important requirements, security figures as one crucial
aspect. To guarantee security, such applications use cryptographic
protocols. These are small concurrent programs executed by
several distant agents through a network. Messages, or part of the
messages, are produced using cryptographic functions (encryption,
signature, hashing, etc). Cryptography has been used for thousands
of years to safeguard military and diplomatic communications. For
example, the famous Roman emperor Julius Caesar used encryption
to securely communicate with his troops.
Unfortunately, the usage of cryptographic primitives in a protocol
is not sufficient to ensure its security and several attacks were
found on established protocols [78]. The most stating example is the
bug (a so-called man-in-the-middle attack) of the Needham-Schroeder
protocol found by G. Lowe [144] 17 years after the publication of the
protocol. This situation leads to, and shows the importance of, the
development of tools and decision procedures for the formal verification
of security protocols.
1.1 Cryptographic protocols
1.1.1 Communication via exchanges of messages
A communication protocol, or simply protocol can be described by exchanges of
messages between many participants. These exchanges are usually described
by a scenario, sequence of rules each one specifying the sender, the receiver, and
the exchanged message. The scenario describes a normal (also said correct) run of
the protocol, that is how the execution of the protocol should proceed in the
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