International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Martijn Stam

Publications

Year
Venue
Title
2020
TCHES
Redundant Code-based Masking Revisited 📺
Nicolas Costes Martijn Stam
Masking schemes are a popular countermeasure against side-channel attacks. To mask bytes, the two classical options are Boolean masking and polynomial masking. The latter lends itself to redundant masking, where leakage emanates from more shares than are strictly necessary to reconstruct, raising the obvious question how well such “redundant” leakage can be exploited by a side-channel adversary. We revisit the recent work by Chabanne et al. (CHES’18) and show that, contrary to their conclusions, said leakage can—in theory—always be exploited. For the Hamming weight scenario in the low-noise regime, we heuristically determine how security degrades in terms of the number of redundant shares for first and second order secure polynomial masking schemes.Furthermore, we leverage a well-established link between linear secret sharing schemes and coding theory to determine when different masking schemes will end up with essentially equivalent leakage profiles. Surprisingly, we conclude that for typical field sizes and security orders, Boolean masking is a special case of polynomial masking. We also identify quasi-Boolean masking schemes as a special class of redundant polynomial masking and point out that the popular “Frobenius-stable” sets of interpolations points typically lead to such quasi-Boolean masking schemes, with subsequent degraded leakage performance.
2018
EUROCRYPT
2017
ASIACRYPT
2017
TCC
2017
JOFC
2017
TOSC
Modes of Operation Suitable for Computing on Encrypted Data
We examine how two parallel modes of operation for Authenticated Encryption (namely CTR+PMAC and OTR mode) work when evaluated in a multiparty computation engine. These two modes are selected because they suit the PRFs examined in previous works. In particular the modes are highly parallel, and do not require evaluation of the inverse of the underlying PRF. In order to use these modes one needs to convert them from their original instantiation of being defined on binary blocks of data, to working on elememts in a large prime finite field. The latter fitting the use case of many secret-sharing based MPC engines. In doing this conversion we examine the associated security proofs of PMAC and OTR, and show that they carry over to this new setting.
2017
TOSC
Turning Online Ciphers Off
CAESAR has caused a heated discussion regarding the merits of one-pass encryption and online ciphers. The latter is a keyed, length preserving function which outputs ciphertext blocks as soon as the respective plaintext block is available as input. The immediacy of an online cipher affords a clear performance advantage, but it comes at a price: ciphertext blocks cannot depend on later plaintext blocks, limiting diffusion and hence security. We show how one can attain the best of both worlds by providing provably secure constructions, achieving full cipher security, based on applications of an online cipher around blockwise reordering layers. Explicitly, we show that with just two calls to the online cipher, prp security up to the birthday bound is both attainable and maximal. Moreover, we demonstrate that three calls to the online cipher suffice to obtain beyond birthday bound security. We provide a full proof of this for a prp construction, and, in the ±prp setting, security against adversaries who make queries of any single length. As part of our investigation, we extend an observation by Rogaway and Zhang by further highlighting the close relationship between online ciphers and tweakable blockciphers with variable-length tweaks.
2016
EUROCRYPT
2016
CRYPTO
2016
ASIACRYPT
2015
ASIACRYPT
2014
ASIACRYPT
2013
EUROCRYPT
2013
FSE
2012
TCC
2012
EUROCRYPT
2012
ASIACRYPT
2011
CRYPTO
2011
CHES
2011
ASIACRYPT
2011
ASIACRYPT
2010
PKC
2010
JOFC
2010
JOFC
2010
ASIACRYPT
2010
ASIACRYPT
2010
FSE
2009
EUROCRYPT
2009
FSE
2008
CRYPTO
2007
TCC
2005
CRYPTO
2005
EUROCRYPT
2003
PKC
2002
CHES
2001
ASIACRYPT

Program Committees

Eurocrypt 2022
CHES 2021
CHES 2019
Eurocrypt 2019
Crypto 2018
FSE 2018
FSE 2017
Eurocrypt 2017
Eurocrypt 2015
FSE 2015
FSE 2014
Crypto 2013
Eurocrypt 2012
Eurocrypt 2011
FSE 2011
PKC 2010
PKC 2008