Paper 2016/534

Damaging, Simplifying, and Salvaging p-OMD

Tomer Ashur and Bart Mennink


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)
Secret-key cryptography
Publication info
Published elsewhere. MINOR revision.ISC 2016
Authenticated encryptionCAESARp-OMDnonce-misuseforgerysimplification
Contact author(s)
tashur @ esat kuleuven be
2016-05-31: received
Short URL
Creative Commons Attribution


      author = {Tomer Ashur and Bart Mennink},
      title = {Damaging, Simplifying, and Salvaging p-OMD},
      howpublished = {Cryptology ePrint Archive, Paper 2016/534},
      year = {2016},
      note = {\url{}},
      url = {}
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