### Beyond 2^{c/2} Security in Sponge-Based Authenticated Encryption Modes

Philipp Jovanovic, Atul Luykx, and Bart Mennink

##### Abstract

The Sponge function is known to achieve 2^{c/2} security, where c is its capacity. This bound was carried over to keyed variants of the function, such as SpongeWrap, to achieve a min{2^{c/2},2^kappa} security bound, with kappa the key length. Similarly, many CAESAR competition submissions are designed to comply with the classical 2^{c/2} security bound. We show that Sponge-based constructions for authenticated encryption can achieve the significantly higher bound of min{2^{b/2},2^c,2^kappa} asymptotically, with b>c the permutation size, by proving that the CAESAR submission NORX achieves this bound. Furthermore, we show how to apply the proof to five other Sponge-based CAESAR submissions: Ascon, CBEAM/STRIBOB, ICEPOLE, Keyak, and two out of the three PRIMATEs. A direct application of the result shows that the parameter choices of these submissions are overly conservative. Simple tweaks render the schemes considerably more efficient without sacrificing security. For instance, NORX64 can increase its rate and decrease its capacity by 128 bits and Ascon-128 can encrypt three times as fast, both without affecting the security level of their underlying modes in the ideal permutation model.

Available format(s)
Category
Secret-key cryptography
Publication info
A minor revision of an IACR publication in ASIACRYPT 2014
Keywords
Authenticated encryptionCAESARAsconCBEAMICEPOLEKeyakNORXPRIMATEsSTRIBOB
Contact author(s)
bart mennink @ esat kuleuven be
History
2014-09-10: revised
See all versions
Short URL
https://ia.cr/2014/373

CC BY

BibTeX

@misc{cryptoeprint:2014/373,
author = {Philipp Jovanovic and Atul Luykx and Bart Mennink},
title = {Beyond 2^{c/2} Security in Sponge-Based Authenticated Encryption Modes},
howpublished = {Cryptology ePrint Archive, Paper 2014/373},
year = {2014},
note = {\url{https://eprint.iacr.org/2014/373}},
url = {https://eprint.iacr.org/2014/373}
}

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