Decision forests are classical models to efficiently make decision on complex inputs with multiple features. While the global structure of the trees or forests is public, sensitive information have to be protected during the evaluation of some client inputs with respect to some server model. Indeed, the comparison thresholds on the server side may have economical value while the client inputs might be critical personal data. In addition, soundness is also important for the receiver. In our case, we will consider the server to be interested in the outcome of the model evaluation so that the client should not be able to bias it. In this paper, we propose a new offline/online protocol between a client and a server with a constant number of rounds in the online phase, with both privacy and soundness against malicious clients.

Designing code-based signatures is both an important and challenging problem. A standard way to tackle it consists to use the Fiat-Shamir heuristic along with an identification scheme that is required to be zero-knowledge. The authors of [1] have highlighted an issue within the zero-knowledge proof of the Veron identification scheme [2]. It turns out that the zero-knowledge proof of the AGS protocol [3] is impacted in a similar way. In this paper, we present a masking technique that solves the aforementioned issue without inducing any performance penalty. We introduce the Masked Veron and Masked AGS protocols that both leverage this masking technique and provide their zero-knowledge proofs. In addition, we present a new technique improving the performances of signatures built from code-based identification schemes subject to the attack described in [4]. The Masked Veron and Masked AGS protocols feature all the existing performance improvements from the literature.

In this paper, we introduce a new hard problem opening up the construction for new quantum resistant cryptographic schemes. The latter is called Learning Rank with Errors (LRE) and can be seen as an adaptation of the LPN problem to the rank metric setting. In addition, we describe HBLRE, an HB-like authentication protocol that constitutes an application of the aforementioned problem. We also prove that HTLRE is secure against passive attacks and compare its parameters to those of the initial HB scheme.