Some Constructions for Authentication-Secrecy Codes

We deal with authentication / secrecy codes having unconditional security. Besides some new results for a "spoofing attack of order L", we give several constructions using finite incidence structures (designs, generalized quadrangles). 1 AUTHENTICATION-SECRECY It is the aim to deal in this paper with codes having unconditional security, which means that the security is independent of the computing power. Analogously to the theory of unconditional secrecy due to Shannon [12], Simmons developed a theory of unconditional authentication ~ 4 1 Consider a transmitter who wants t o communicate a source to a remote receiver by sending messages through an imperfect communication channel. Then there are two fundamentally different ways in which the receiver can be deceived. The channel may be noisy so that the symbols in the transmitted message can be received in error, or the channel may be under control of an opponent who can either deliberately modify legitimate messages or else introduce fraudulent ones. Simmons [14] showed that both problems could be modeled in complete generality by replacing the classical noisy communications channel of coding theory with a C.G. Guenther (Ed.): Advances in Cryptology EUROCRYPT '88, LNCS 330, pp. 57-75, 1988. 0 Spnnger-Verlag Berlin Heidelberg 1988