On the Security of NMAC and Its Variants

Based on the three earlier MAC (Message Authentication Code) construction approaches, we propose and analyze some variants of NMAC. We propose  some key recovery attacks to  these  NMAC  variants, for  example, we can  recover  the  equivalent  inner  key  of NMAC  in  about O(2n/2) MAC  operations, in  a related key  setting. We  propose  NMAC-E, a  variant of NMAC  with  secret  envelop,  to  achieve  more  process  efficiency  and  no  loss  of security, which needs only one call to the  underlying hash  function, instead of two invocations in HMAC

The Exact PRF-Security of NMAC and HMAC

NMAC is a mode of operation which turns a fixed input-length keyed hash function f into a variable input-length function. A~practical single-key variant of NMAC called HMAC is a very popular and widely deployed message authentication code (MAC). Security proofs and attacks for NMAC can typically be lifted to HMAC. NMAC was introduced by Bellare, Canetti and Krawczyk [Crypto\u2796], who proved it to be a secure pseudorandom function (PRF), and thus also a MAC, assuming that (1) f is a PRF and (2) the function we get when cascading f is weakly collision-resistant. Unfortunately, HMAC is typically instantiated with cryptographic hash functions like MD5 or SHA-1 for which (2) has been found to be wrong. To restore the provable guarantees for NMAC, Bellare [Crypto\u2706] showed its security based solely on the assumption that f is a PRF, albeit via a non-uniform reduction. Our first contribution is a simpler and uniform proof: If f is an \eps-secure PRF (against q queries) and a \delta-non-adaptively secure PRF (against q queries), then NMAC^f is an (\eps+lq\delta)-secure PRF against q queries of length at most l blocks each. We then show that this \eps+lq\delta bound is basically tight. For the most interesting case where lq\delta>=\eps we prove this by constructing an f for which an attack with advantage lq\delta exists. This also violates the bound O(l\eps) on the PRF-security of NMAC recently claimed by Koblitz and Menezes. Finally, we analyze the PRF-security of a modification of NMAC called NI [An and Bellare, Crypto\u2799] that differs mainly by using a compression function with an additional keying input. This avoids the constant rekeying on multi-block messages in NMAC and allows for a security proof starting by the standard switch from a PRF to a random function, followed by an information-theoretic analysis. We carry out such an analysis, obtaining a tight lq^2/2^c bound for this step, improving over the trivial bound of l^2q^2/2^c. The proof borrows combinatorial techniques originally developed for proving the security of CBC-MAC [Bellare et al., Crypto\u2705]. We also analyze a variant of NI that does not include the message length in the last call to the compression function, proving a l^{1+o(1)}q^2/2^c bound in this case

Distinguishing Attack and Second-Preimage Attack on the CBC-like MACs

In this paper, we first present a new distinguisher on the CBC-MAC based on a block cipher in Cipher Block Chaining (CBC) mode. It can also be used to distinguish other CBC-like MACs from random functions. The main results of this paper are on the second-preimage attack on CBC-MAC and CBC-like MACs include TMAC, OMAC, CMAC, PC-MAC and MACs based on three-key encipher CBC mode. Instead of exhaustive search, this attack can be performed with the birthday attack complexity

Quantum linearization attacks

Recent works have shown that quantum period-finding can be used to break many popular constructions (some block ciphers such as Even-Mansour, multiple MACs and AEs...) in the superposition query model. So far, all the constructions broken exhibited a strong algebraic structure, which enables to craft a periodic function of a single input block. Recoverin

Comparison of authentication schemes for wireless sensor networks as applied to secure data aggregation

Il processo di aggregazione è fondamentale nell'economia energetica di una rete di sensori wireless (WSN). Tale processo, però, pone delle nuove sfide sul piano della sicurezza, dettate dagli stringenti vincoli di complessità tipici di una WSN. In questa tesi, in particolare, si indaga l'applicabilità degli algoritmi di autenticazione al contesto dell'aggregazion