A Closer Look at HMAC

Krzysztof Pietrzak

Paper 2013/212

A Closer Look at HMAC

Krzysztof Pietrzak

Abstract

Bellare, Canetti and Krawczyk~\cite{FOCS:BelCanKra96} show that cascading an $\eps$-secure (fixed input length) PRF gives an $O(\eps n q)$-secure (variable input length) PRF when making at most $q$ prefix-free queries of length $n$ blocks. We observe that this translates to the same bound for NMAC (which is the cascade without the prefix-free requirement but an additional application of the PRF at the end), and give a matching attack, showing this bound is tight. This contradicts the $O(\eps n)$ bound claimed by Koblitz and Menezes~\cite{KobMen12}.

Metadata

Available format(s): PDF
Category: Secret-key cryptography
Publication info: Published elsewhere. unpublished manuscript
Keywords: HMAC cascade
Contact author(s): krzpie @ gmail com
History: 2013-04-14: received
Short URL: https://ia.cr/2013/212
License: CC BY

BibTeX

@misc{cryptoeprint:2013/212,
      author = {Krzysztof Pietrzak},
      title = {A Closer Look at {HMAC}},
      howpublished = {Cryptology {ePrint} Archive, Paper 2013/212},
      year = {2013},
      url = {https://eprint.iacr.org/2013/212}
}