ABSTRACT
Any unordered pair {x, y} occurs in three columns of A. Within these three columns, x occurs once in each of the three rows, as does y.
B Authentication with Arbitration
52.44 Remark Authentication with arbitration deals with the situation where Alice and Bob do not trust each other. Motivated by this scenario, Simmons described a variation of authentication codes that protect against certain “insider attacks.” A trusted arbiter is an essential feature of these schemes, which are sometimes termed A2 codes. The arbiter chooses an encoding rule eK that is given only to Alice and a verification rule fK that is given only to Bob. Later, the arbiter resolves any disputes that occur. As well as impersonation or substitution by an outsider, authentication with arbitration protects against three kinds of insider attacks:
1. Impersonation by the transmitter occurs when Alice may claim not to have sent a message to Bob when, in fact, she did. The attack succeeds if Bob accepts the message as authentic, and the arbiter confirms that the message was not generated using Alice’s encoding rule.
