Date de l'exposé : 20 septembre 2024
elliptic curves for SNARK and proof systems
This talk is based on joint works with Diego Aranha, Youssef El Housni, and Simon Masson.
Elliptic curves make possible in practice very interesting mechanisms of proofs. The security relies on the difficulty of the discrete log problem and variants. Succinct non-interactive arguments of knowledge (SNARK) are a very fruitful topic, so that given a sequence of instructions that can be quite large, it is possible to extract a single equation such that if satisfied, it will convince a verifier that the set of instructions were correctly executed. To ensure the zero-knowledge property, the equation is hidden "in the exponents", in other words, "homomorphic hiding" is required. Such a property is made possible with a pairing on elliptic curves: a bilinear map e : G1 x G2 -> GT, where e([a]g1, [b]g2) = e(g1, g2)^{ab}, that can multiply secret scalars/exponents together. The solution of Groth at Eurocrypt'16 (Groth16) made possible a SNARK verification in three pairings, the proof size being two G1 and one G2 elements.
The design of dedicated elliptic curves is required at different stages: finding ``inner'' pairing-friendly elliptic curves (first SNARK), finding ``outer'' pairing-friendly elliptic curves (second SNARK, a first construction was given in the Geppetto paper), finding ``embedded'' elliptic curves (such as JubJub for BLS12-381). This talk will recall the construction of particular pairing-friendly elliptic curves for SNARK, and the recent works on finding embedded curves. A generalisation of the work of Sanso and El Housni will be presented, that allows to obtain in about some hours a 2-cycle of elliptic curves with CM, given any input prime. The parameterized version will be given.
