Paper 2024/1486

Adaptively Secure Attribute-Based Encryption from Witness Encryption

Abstract

Attribute-based encryption (ABE) enables fine-grained control over which ciphertexts various users can decrypt. A master authority can create secret keys $sk_f$ with different functions (circuits) $f$ for different users. Anybody can encrypt a message under some attribute $x$ so that only recipients with a key $sk_f$ for a function such that $f(x)=1$ will be able to decrypt. There are a number of different approaches toward achieving selectively secure ABE, where the adversary has to decide on the challenge attribute $x$ ahead of time before seeing any keys, including constructions via bilinear maps (for NC1 circuits), learning with errors, or witness encryption. However, when it comes adaptively secure ABE, the problem seems to be much more challenging and we only know of two potential approaches: via the ``dual systems'' methodology from bilinear maps, or via indistinguishability obfuscation. In this work, we give a new approach that constructs adaptively secure ABE from witness encryption (along with statistically sound NIZKs and one-way functions). While witness encryption is a strong assumption, it appears to be fundamentally weaker than indistinguishability obfuscation. Moreover, we have candidate constructions of witness encryption from some assumptions (e.g., evasive LWE) from which we do not know how to construct indistinguishability obfuscation, giving us adaptive ABE from these assumptions as a corollary of our work.