On security of universal hash function based multiple authentication

Abstract

Universal hash function based multiple authentication was originally proposed by Wegman and Carter in 1981. In this authentication, a series of messages are authenticated by first hashing each message by a fixed (almost) strongly universal 2 hash function and then encrypting the hash value with a preshared one-time pad. This authentication is unconditionally secure. In this paper, we show that the unconditional security cannot be guaranteed if the hash function output for the first message is not encrypted, as remarked in [1]. This means that it is not only sufficient, but also necessary, to encrypt the hash of every message to be authenticated in order to have unconditional security. The security loss is demonstrated by a simple existential forgery attack. The impact of the attack is also discussed at the end. © 2012 Springer-Verlag.