Generic Security of NMAC and HMAC with Input Whitening

HMAC and its variant NMAC are the most popular approaches to deriving a MAC (and more generally, a PRF) from a cryptographic hash function. Despite nearly two decades of research, their exact security still remains far from understood in many different contexts. Indeed, recent works have re-surfaced interest for generic attacks, i.e., attacks that treat the compression function of the underlying hash function as a black box. Generic security can be proved in a model where the underlying compression function is modeled as a random function – yet, to date, the question of proving tight, non-trivial bounds on the generic security of HMAC/NMAC even as a PRF remains a challenging open question. In this paper, we ask the question of whether a small modification to HMAC and NMAC can allow us to exactly characterize the security of the resulting constructions, while only incurring little penalty with respect to efficiency. To this end, we present simple variants of NMAC and HMAC, for which...

• Type: Journal
• Year: 2015
• Where: ASIACRYPT
• Authors: Peter Gazi, Krzysztof Pietrzak, Stefano Tessaro
• Keywords: ASIACRYPT 2015, Cryptology