Journal: Designs, Codes and Cryptography

Abbreviation

Des. Codes Cryptogr.

Publisher

Springer

Journal Volumes

ISSN

0925-1022
1573-7586

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Filters

2015 - 201942020 - 20243
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Publications 1 - 7 of 7
  • Strengthening the security of authenticated key exchange against bad randomness
    Item type: Journal Article
    Feltz, Michèle; Cremers, Cas (2018)
    Designs, Codes and Cryptography
    Recent history has revealed that many random number generators (RNGs) used in cryptographic algorithms and protocols were not providing appropriate randomness, either by accident or on purpose. Subsequently, researchers have proposed new algorithms and protocols that are less dependent on the RNG. One exception is that all prominent authenticated key exchange (AKE) protocols are insecure given bad randomness, even when using good long-term keying material. We analyse the security of AKE protocols in the presence of adversaries that can perform attacks based on chosen randomness, i.e., attacks in which the adversary controls the randomness used in protocol sessions. We propose novel stateful protocols, which modify memory shared among a user’s sessions, and show in what sense they are secure against this worst case randomness failure. We develop a stronger security notion for AKE protocols that captures the security that we can achieve under such failures, and prove that our main protocol is correct in this model. Our protocols make substantially weaker assumptions on the RNG than existing protocols.
  • Beyond eCK: Perfect Forward Secrecy Under Actor Compromise and Ephemeral-key Reveal
    Item type: Journal Article
    Cremers, Cas; Feltz, Michèle (2015)
    Designs, Codes and Cryptography
    We show that it is possible to achieve perfect forward secrecy (PFS) in two-message or one-round key exchange (KE) protocols even in the presence of very strong active adversaries that can reveal random values of sessions and compromise long-term secret keys of parties. We provide two new game-based security models for KE protocols with increasing security guarantees, namely, eCK𝑤 and eCK-PFS. The eCK𝑤 model is a slightly stronger variant of the extended Canetti–Krawczyk (eCK) security model. The eCK-PFS model captures PFS in the presence of eCK𝑤 adversaries. We propose a security-strengthening transformation (i. e., a compiler) from eCK𝑤 to eCK-PFS that can be applied to protocols that only achieve security in a weaker model than eCK𝑤, which we call eCKpassive. We show that, given a two-message Diffie–Hellman type protocol secure in eCKpassive, our transformation yields a two-message protocol that is secure in eCK-PFS. We demonstrate how our transformation can be applied to concrete KE protocols. In particular, our methodology allows us to prove the security of the first known one-round protocol that achieves PFS under actor compromise and ephemeral-key reveal.
  • Coloring linear hypergraphs: the Erdős–Faber–Lovász conjecture and the Combinatorial Nullstellensatz
    Item type: Journal Article
    Janzer, Oliver; Nagy, Zoltán Lóránt (2022)
    Designs, Codes and Cryptography
    The long-standing Erdos-Faber-Lovasz conjecture states that every n-uniform linear hypergaph with n edges has a proper vertex-coloring using n colors. In this paper we propose an algebraic framework to the problem and formulate a corresponding stronger conjecture. Using the Combinatorial Nullstellensatz, we reduce the Erdos-Faber-Lovasz conjecture to the existence of non-zero coefficients in certain polynomials. These coefficients are in turn related to the number of orientations with prescribed in-degree sequences of some auxiliary graphs. We prove the existence of certain orientations, which verifies a necessary condition for our algebraic approach to work.
  • Average case error estimates of the strong Lucas test
    Item type: Journal Article
    Einsele, Semira; Paterson, Kenneth (2024)
    Designs, Codes and Cryptography
    Reliable probabilistic primality tests are fundamental in public-key cryptography. In adversarial scenarios, a composite with a high probability of passing a specific primality test could be chosen. In such cases, we need worst-case error estimates of the test. However, in many scenarios, the numbers are randomly chosen and thus have a significantly smaller error probability. We are hence interested in average-case error estimates. In this paper we establish such bounds for the strong Lucas primality test, as there exist only worst-case, but no average-case error bounds. This allows us to use this test with more confidence. Let us examine an algorithm that draws odd k-bit integers uniformly and independently, runs t independent iterations of the strong Lucas test with randomly chosen parameters, and outputs the first number that passes all t consecutive rounds. We attain numerical upper bounds on the probability that a composite is returned. Moreover, we examine a slight modification of this algorithm that only considers integers that are not divisible by small primes, yielding improved bounds. In addition, we classify the numbers that contribute most to our estimate.
  • Unconditionally secure non-malleable secret sharing and circular external difference families
    Item type: Journal Article
    Veitch, Shannon; Stinson, Douglas R. (2024)
    Designs, Codes and Cryptography
    Various notions of non-malleable secret sharing schemes have been considered. In this paper, we review the existing work on non-malleable secret sharing and suggest a novel game-based definition. We provide a new construction of an unconditionally secure non-malleable threshold scheme with respect to a specified relation. To do so, we introduce a new type of algebraic manipulation detection code and construct examples of new variations of external difference families, which are of independent combinatorial interest.
  • Zero-knowledge proofs of knowledge for group homomorphisms
    Item type: Journal Article
    Maurer, Ueli (2015)
    Designs, Codes and Cryptography
    A simple zero-knowledge proof of knowledge protocol is presented of which many known protocols are instantiations. These include Schnorr’s protocol for proving knowledge of a discrete logarithm, the Fiat–Shamir and Guillou–Quisquater protocols for proving knowledge of a modular root, protocols for proving knowledge of representations (like Okamoto’s protocol), protocols for proving equality of secret values, a protocol for proving the correctness of a Diffie–Hellman key, protocols for proving the multiplicative relation of three commitments (as required in secure multi-party computation), and protocols used in credential systems. This unifies a substantial body of work and can also lead to instantiations of the protocol for new applications.
Publications 1 - 7 of 7