From Cryptography to Communication Security - A Classical Introduction to Cryptography: Applications for Communications Security - page 289

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From Cryptography to
Communication Security
Content
Security setup: certificates
Remote access: SSH
Secure Internet transactions: SSL
Security for individuals: PGP
To conclude this topic, this chapter shows how to put together materials from the
previous ones in order to build cryptographic applications that provide communication
security. We illustrate this with a few popular examples.
The main objective is to set up a notion of secure communication session.
One example is the (public-key-less) Bluetooth technology which was outlined in
Section 5.6.2. We will see some other examples here.
The session usually starts by peer authentication , exchange of public-key materi-
als, and goes on with an authenticated key agreement protocol. This ensures that both
peers share a common secret key. The secret key is derived into several symmetric secret
keys. Then message security, i.e. message integrity , message authentication , and mes-
sage confidentiality , is ensured by means of MAC and symmetric encryption. Session
security additionally requires to ensure the sequentiality of messages , i.e. no adversary
can replay a message, swap messages, or erase a message. This is usually achieved by
means of a synchronized message counter. Some additional security properties may be
required, such as
Timeliness of message delivery : a message sender is ensured that his message
will be delivered to the right receiver on time;
Termination fairness : peers are ensured to terminate the session in the same state
(either termination success or premature abortion);
Anonymity : a peer is ensured that her identity does not leak;
Untraceability : a peer is ensured that the other peer will no later be able to
identify her in other sessions;
Unlinkability : peers are ensured that we cannot even realize that two different
communication sessions share the same entity;