Multiparty key agreement protocols

A class of multiparty key agreement protocols based on secret sharing is presented. The trust infrastructure necessary to achieve the intended security goals is discussed

Construction of cubic homogeneous boolean bent functions

We prove that cubic homogeneous bent functions f : V2n → GF(2) exist for all n ≥ 3 except for n = 4

Hash-based Signatures Revisited: A Dynamic FORS with Adaptive Chosen Message Security

FORS is the underlying hash-based few-time signing scheme in SPHINCS+, one of the nine signature schemes which advanced to round 2 of the NIST Post-Quantum Cryptography standardization competition. In this paper, we analyze the security of FORS with respect to adaptive chosen message attacks. We show that in such a setting, the security of FORS decreases significantly with each signed message when compared to its security against non-adaptive chosen message attacks. We propose a chaining mechanism that with slightly more computation, dynamically binds the Obtain Random Subset (ORS) generation with signing, hence, eliminating the offline advantage of adaptive chosen message adversaries. We apply our chaining mechanism to FORS and present DFORS whose security against adaptive chosen message attacks is equal to the non-adaptive security of FORS. In a nutshell, using SPHINCS+-128s parameters, FORS provides 75-bit security and DFORS achieves 150-bit security with respect to adaptive chosen message attacks after signing one message. We note that our analysis does not affect the claimed security of SPHINCS+. Nevertheless, this work provides a better understanding of FORS and other HORS variants and furnishes a solution if new adaptive cryptanalytic techniques on SPHINCS+ emerge

Candida albicans-produced farnesol stimulates Pseudomonas quinolone signal production in LasR-defective Pseudomonas aeruginosa strains

Candida albicans has been previously shown to stimulate the production of Pseudomonas aeruginosa phenazine toxins in dual-species colony biofilms. Here, we report that P. aeruginosa lasR mutants, which lack the master quorum sensing system regulator, regain the ability to produce quorum-sensing-regulated phenazines when cultured with C. albicans. Farnesol, a signalling molecule produced by C. albicans, was sufficient to stimulate phenazine production in LasR− laboratory strains and clinical isolates. P. aeruginosa ΔlasR mutants are defective in production of the Pseudomonas quinolone signal (PQS) due to their inability to properly induce pqsH, which encodes the enzyme necessary for the last step in PQS biosynthesis. We show that expression of pqsH in a ΔlasR strain was sufficient to restore PQS production, and that farnesol restored pqsH expression in ΔlasR mutants. The farnesol-mediated increase in pqsH required RhlR, a transcriptional regulator downstream of LasR, and farnesol led to higher levels of N-butyryl-homoserine lactone, the small molecule activator of RhlR. Farnesol promotes the production of reactive oxygen species (ROS) in a variety of species. Because the antioxidant N-acetylcysteine suppressed farnesol-induced RhlR activity in LasR− strains, and hydrogen peroxide was sufficient to restore PQS production in las mutants, we propose that ROS are responsible for the activation of downstream portions of this quorum sensing pathway. LasR mutants frequently arise in the lungs of patients chronically infected with P. aeruginosa. The finding that C. albicans, farnesol or ROS stimulate virulence factor production in lasR strains provides new insight into the virulence potential of these strains

Explaining why simple liquids are quasi-universal

It has been known for a long time that many simple liquids have surprisingly similar structure as quantified, e.g., by the radial distribution function. A much more recent realization is that the dynamics are also very similar for a number of systems with quite different pair potentials. Systems with such non-trivial similarities are generally referred to as "quasi-universal". From the fact that the exponentially repulsive pair potential has strong virial potential-energy correlations in the low-temperature part of its thermodynamic phase diagram, we here show that a liquid is quasi-universal if its pair potential can be written approximately as a sum of exponential terms with numerically large prefactors. Based on evidence from the literature we moreover conjecture the converse, i.e., that quasi-universality only applies for systems with this property

Codes Identifying Bad Signatures in Batches

The work is concerned with identification of bad signatures in a sequence which is validated using batching. Identification codes (id-codes) are defined and their general properties are investigated. A taxonomy of id-codes is given. The generic construction for a wide range of id-codes is given and its instantiation using mutually orthogonal Latin squares is described. Hierarchical identification is studied for two cases when the identification procedure uses a family of id-codes and when there is a single underlying id-code. Remarks about future research conclude the work

Homogeneous Bent Functions

This paper discusses homogeneous bent functions. The space of homogeneous functions of degree three in six boolean variables was exhaustively searched and thirty bent functions were found. These are found to occur in a single orbit under the action of relabelling of the variables. The homogeneous bent functions identified exhibit interesting combinatorial structures and are, to the best of our knowledge, the first examples of bent functions without quadratic terms. A construction for other homogeneous bent functions of degree three in larger spaces is also given

Identification of Bad Signatures in Batches

The paper addresses the problem of bad signature identification in batch verification of digital signatures. The number of generic tests necessary to identify all bad signatures in a batch instance, is used to measure the efficiency of verifiers. The divide-and-conquer verifier DCVα(x,n) is defined. The verifier identifies all bad signatures in a batch instance x of the length n by repeatedly splitting the input into α sub-instances. Its properties are investigated. In particular, probability distributions for the number of generic tests necessary to identify one, two and three bad signatures, are derived. The average numbers of GT tests necessary to identify bad signatures ranging from 1 to 16 are obtained from computer simulation. Further, a Hamming verifier (HV) is defined which allows to identify a single bad signature in a batch of the length n = 2k –1 using k + 2 tests. HV is generalised into the two-layer Hamming verifier (2HV). Given a batch instance of the length 2k – 2, the 2HV verifier identifies a single bad signature using k + 2 tests and two bad signatures in expense of 3k + 3 tests. The work is concluded by comments about a general model for verification codes identifying t bad signatures and the design of verifiers using combinatorial structures