Data Protection and Security

VII

Identification and Entity Authentication

VII.III

Authentication Protocols

Authenticated Key Exchange:

With symmetric-key protocols, for encryption take the session key as (KAB+1){R}. It is not secure to use (KAB){R} as the session key because it is transmitted by Alice as the third message and is seen by other parties.

With public-key protocols, send additional random nonces {R}A (R encrypted with Alice’s public key), {R}B (R encrypted with Bob’s public key) and use them to derive a session key.
Alternatively, Alice and Bob can do a Diffie Hellman key exchange (see Chapter 4) where each signs the quantity they are sending (Authenticated Diffie-Hellman).

VII.III.V Q