Analysing Mutual Exclusion using Process Algebra with Signals

In contrast to common belief, the Calculus of Communicating Systems (CCS) and similar process algebras lack the expressive power to accurately capture mutual exclusion protocols without enriching the language with fairness assumptions. Adding a fairness assumption to implement a mutual exclusion protocol seems counter-intuitive. We employ a signalling operator, which can be combined with CCS, or other process calculi, and show that this minimal extension is expressive enough to model mutual exclusion: we confirm the correctness of Peterson's mutual exclusion algorithm for two processes, as well as Lamport's bakery algorithm, under reasonable assumptions on the underlying memory model. The correctness of Peterson's algorithm for more than two processes requires stronger, less realistic assumptions on the underlying memory model.Comment: In Proceedings EXPRESS/SOS 2017, arXiv:1709.0004

Somewhat Homomorphic Encryption based on Random Codes

We present a secret-key encryption scheme based on random rank metric ideal linear codes with a simple decryption circuit. It supports unlimited homomorphic additions and plaintext absorptions as well as a fixed arbitrary number of homomorphic multiplications. We study a candidate bootstrapping algorithm that requires no multiplication but additions and plaintext absorptions only. This latter operation is therefore very efficient in our scheme, whereas bootstrapping is usually the main reason which penalizes the performance of other fully homomorphic encryption schemes. However, the security reduction of our scheme restricts the number of independent ciphertexts that can be published. In particular, this prevents to securely evaluate the bootstrapping algorithm as the number of ciphertexts in the key switching material is too large. Our scheme is nonetheless the first somewhat homomorphic encryption scheme based on random ideal codes and a first step towards full homomorphism. Random ideal codes give stronger security guarantees as opposed to existing constructions based on highly structured codes. We give concrete parameters for our scheme that shows that it achieves competitive sizes and performance, with a key size of 3.7 kB and a ciphertext size of 0.9 kB when a single multiplication is allowed

LowMS: a new rank metric code-based KEM without ideal structure

We propose and analyze LowMS, a new rank-based key encapsulation mechanism (KEM). The acronym stands for Loidreau with Multiple Syndromes, since our work combines the cryptosystem of Loidreau (presented at PQCrypto 2017) together with the multiple syndrome approach, that allows to reduce parameters by sending several syndromes with the same error support in one ciphertext. Our scheme is designed without using ideal structures. Considering cryptosystems without such an ideal structure, like the FrodoKEM cryptosystem, is important since structure allows to compress objects, but gives reductions to specific problems whose security may potentially be weaker than for unstructured problems. For 128 bits of security, we propose parameters with a public key size of 4,6KB and a ciphertext size of 1,1KB. To the best of our knowledge, our scheme is the smallest among all existing unstructured post-quantum lattice or code-based algorithms, when taking into account the sum of the public key size and the ciphertext size. In that sense, our scheme is for instance about 4 times shorter than FrodoKEM. Our system relies on the hardness of the Rank Support Learning problem, a well-known variant of the Rank Syndrome Decoding problem, and on the problem of indistinguishability of distorted Gabidulin codes, i.e. Gabidulin codes multiplied by an homogeneous matrix of given rank. The latter problem was introduced by Loidreau in his paper

LowMS: a new rank metric code-based KEM without ideal structure

International audienc

PERK

Submission to the NIST Call for Additional Digital Signature Schemes for the Post-Quantum Cryptography Standardization Proces

MIRA Specifications

Submission to the NIST Call for Additional Digital Signature Schemes for the Post-Quantum Cryptography Standardization Proces

RYDE specifications

Submission to the NIST Call for Additional Digital Signature Schemes for the Post-Quantum Cryptography Standardization Proces