Multiple forgery attacks against Message Authentication Codes.
David A. McGrew, Scott R. Fluhrer · IACR Cryptology ePrint Archive · 2005
Some message authentication codes (MACs) are vulnerable to multiple forgery attacks, in which an attacker can gain information that allows her to succeed in forging multiple message/tag pairs. This property was first noted in MACs based on universal hashing, such as the Galois/Counter Mode (GCM) of operation for block ciphers. However, we show that CBC-MAC and HMAC also have this property, and for some parameters are more vulnerable than GCM. We present multiple-forgery attacks against these algorithms, then analyze the security against these attacks by using the expected number of forgeries. We compare the different MACs using this measure. This document is a pre-publication draft manuscript.