Security Protocols with Conventional Cryptography - A Classical Introduction to Cryptography: Applications for Communications Security - page 152

Master A Slave B

user inputs PIN code
pick IN RAND

IN RAND
−−−−−−−−−−−−−−−−−−−→

user inputs PIN code (or not)

K init = E22 ( PIN , IN RAND ) K init = E22 ( PIN , IN RAND )

C B
←−−−−−−−−−−−−−−−−−−−

C B = K unit ⊕ K init

K = C B ⊕ K init K = K unit

Figure 5.12. A pairing protocol with a device with low capacities.

against attempts to erase frames. Like in GSM, the integrity protection is very poor so
frame authentication is not guaranteed.

5.7 Exercises

Exercise 5.1. We consider an arbitrary secret function f of C

challenges to a finite set R of R responses. We consider an access control scheme in
which a server picks a challenge uniformly at random in

from a finite set C

and the client sends the
corresponding response after one f application. Explain how the chance of cheating
increases when looking at access control communications. Describe an attack and
compute its probability of success.

C

Exercise 5.2. The Kerberos authentication protocol is presented using secret-key en-
cryption function C K . Identify the accurate security property which is required here.
(Confidentiality? Integrity? Authentication?)