Description
Aggregate message authentication codes, as introduced by Katz and Lindell (CT-RSA 2008), combine several MACs into a single value, which has roughly the same size as an ordinary MAC. These schemes reduce the communication overhead significantly and are therefore a promising approach to achieve authenticated communication in mobile ad-hoc networks, where communication is prohibitively expensive. Here we revisit the unforgeability notion for aggregate MACs and discuss that the definition does not prevent "mix-and-match" attacks in which the adversary turns several aggregates into a "fresh" combination, i.e., into a valid aggregate on a sequence of messages which the attacker has not requested before. In particular, we show concrete attacks on the previous scheme.<br/> To capture the broader class of combination attacks, we provide a stronger security notion of aggregation unforgeability. While we can provide stateful transformations lifting (non-ordered) schemes to meet our stronger security notion, for the statefree case we switch to the new notion of history-free se- quential aggregation. This notion is somewhat between non-ordered and se- quential schemes and basically says that the aggregation algorithm is carried out in a sequential order but must not depend on the preceding messages in the sequence, but only on the shorter input aggregate and the local message. We finally show that we can build an aggregation-unforgeable, history-free sequential MAC scheme based on general assumptions.
Next sessions
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On the average hardness of SIVP for module lattices of fixed rank
Speaker : Radu Toma - Sorbonne Université
In joint work with Koen de Boer, Aurel Page, and Benjamin Wesolowski, we study the hardness of the approximate Shortest Independent Vectors Problem (SIVP) for random module lattices. We use here a natural notion of randomness as defined originally by Siegel through Haar measures. By proving a reduction, we show it is essentially as hard as the problem for arbitrary instances. While this was[…] -
Lightweight (AND, XOR) Implementations of Large-Degree S-boxes
Speaker : Marie Bolzer - LORIA
The problem of finding a minimal circuit to implement a given function is one of the oldest in electronics. In cryptography, the focus is on small functions, especially on S-boxes which are classically the only non-linear functions in iterated block ciphers. In this work, we propose new ad-hoc automatic tools to look for lightweight implementations of non-linear functions on up to 5 variables for[…]-
Cryptography
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Symmetrical primitive
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Implementation of cryptographic algorithm
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Algorithms for post-quantum commutative group actions
Speaker : Marc Houben - Inria Bordeaux
At the historical foundation of isogeny-based cryptography lies a scheme known as CRS; a key exchange protocol based on class group actions on elliptic curves. Along with more efficient variants, such as CSIDH, this framework has emerged as a powerful building block for the construction of advanced post-quantum cryptographic primitives. Unfortunately, all protocols in this line of work are[…] -
Endomorphisms via Splittings
Speaker : Min-Yi Shen - No Affiliation
One of the fundamental hardness assumptions underlying isogeny-based cryptography is the problem of finding a non-trivial endomorphism of a given supersingular elliptic curve. In this talk, we show that the problem is related to the problem of finding a splitting of a principally polarised superspecial abelian surface. In particular, we provide formal security reductions and a proof-of-concept[…]-
Cryptography
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