Learning with Errors in the Exponent

Oded Regev

Zengpeng Li, Chunguang Ma, Ding Wang +3 more

Proxy re-encryption (PRE) is an important cryptographic primitive used for private information sharing. However, the recent advance in quantum computer has potentially crippled its security, as the traditional decisional Diffie-Hellman (DDH)-based PRE is venerable to the quantum attack. Thus, learning with errors (LWE)-based PRE schemes, as a kind of latticebased construction with the inherent quantum-resistant property, has attracted special research interest. Unfortunately, the main drawback of lattice-based public key encryption scheme is noise management after multiplication evaluation. Many cryptographers have been devoted to controlling the expansion of noise. In this line of work, Dagdelen-Gajek-G̈opfert (DGG) put forth the notion of learning with errors in the exponent (LWEE) which is based on lattice and group-theoretic assumption, meanwhile demonstrated a paradigm for constructing efficient quantum resistance public key schemes. In this paper, on top of DGG, we construct a single-bit, single-hop and unidirectional LWEE- based PRE scheme with indistinguishable chosen plaintext attack (IND-CPA) security. To the best of our knowledge, our scheme is the first LWEE-based PRE scheme.

K. Tamvakis

Özgür Dagdelen, Sebastian Gajek, Florian Göpfert

We initiate the study of a novel class of group-theoretic intractability problems. Inspired by the theory of learning in presence of errors [Regev, STOC’05] we ask if noise in the exponent amplifies intractability. We put forth the notion of Learning with Errors in the Exponent (LWEE) and rather surprisingly show that various attractive properties known to exclusively hold for lattices carry over. Most notably are worstcase hardness and post-quantum resistance. In fact, LWEE’s duality is due to the reducibility to two seemingly unrelated assumptions: learning with errors and the representation problem [Brands, Crypto’93] in finite groups. For suitable parameter choices LWEE superposes properties from each individual intractability problem. The argument holds in the classical and quantum model of computation. We give the very first construction of a semantically secure public-key encryption system in the standard model. The heart of our construction is an “error recovery” technique inspired by [Joye-Libert, Eurocrypt’13] to handle critical propagations of noise terms in the exponent.

Chunsheng Gu

Abstract: We introduce a new concept, called multiplicative learning with errors (MLWE), which is a corresponding multiplicative version of the additive learning with errors (LWE), and show the equivalence between the decisional version and the search version for MLWE such that p is a product of sufficiently large smoothing prime factors. Then we construct the MLWE-based private-key and public-key encryption schemes, whose securities are based on the worst-case hardness assumption of the MLWE problem. Finally, we discuss how to extend the LWE on additive group to the LWE on general abelian group.

Jean-Louis Basdevant