### Damaging, Simplifying, and Salvaging p-OMD

Tomer Ashur and Bart Mennink

##### Abstract

One of the submissions to the CAESAR competition for the design of a new authenticated encryption scheme is Offset Merkle-Damgård (OMD). At FSE 2015, Reyhanitabar et al. introduced p-OMD, an improvement of OMD that processes the associated data almost for free. As an extra benefit, p-OMD was claimed to offer integrity against nonce-misusing adversaries, a property that OMD does not have. In this work we show how a nonce-misusing adversary can forge a message for the original p-OMD using only 3 queries (including the forgery). As a second contribution, we generalize and simplify p-OMD. This is done via the introduction of the authenticated encryption scheme Spoed. The most important difference is the usage of a generalized padding function GPAD, which neatly eliminates the need for a case distinction in the design specification and therewith allows for a significantly shorter description of the scheme and a better security bound. Finally, we introduce the authenticated encryption scheme Spoednic, a variant of Spoed providing authenticity against a nonce-misusing adversary at a modest price.

Available format(s)
Category
Secret-key cryptography
Publication info
Published elsewhere. MINOR revision.ISC 2016
Keywords
Authenticated encryptionCAESARp-OMDnonce-misuseforgerysimplification
Contact author(s)
tashur @ esat kuleuven be
History
Short URL
https://ia.cr/2016/534

CC BY

BibTeX

@misc{cryptoeprint:2016/534,
author = {Tomer Ashur and Bart Mennink},
title = {Damaging, Simplifying, and Salvaging p-OMD},
howpublished = {Cryptology ePrint Archive, Paper 2016/534},
year = {2016},
note = {\url{https://eprint.iacr.org/2016/534}},
url = {https://eprint.iacr.org/2016/534}
}

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