Paper 2024/1416

Circuit ABE with poly(depth, λ)-sized Ciphertexts and Keys from Lattices

Abstract

We present new lattice-based attribute-based encryption (ABE) and laconic function evaluation (LFE) schemes for circuits with *sublinear* ciphertext overhead. For depth $d$ circuits over $\ell$-bit inputs, we obtain * an ABE with ciphertext and secret key size $O(1)$; * a LFE with ciphertext size $$ and digest size $$; * an ABE with public key and ciphertext size $$ and secret key size $$, where $$ hides $$ factors. The first two results achieve almost optimal ciphertext and secret key / digest sizes, up to the $$ dependencies. The security of our schemes relies on $$-succinct LWE, a falsifiable assumption which is implied by evasive LWE. At the core of our results is a new technique for compressing LWE samples $$ as well as the matrix $$.