Paper 2024/119

R3PO: Reach-Restricted Reactive Program Obfuscation and its Application to MA-ABE

Abstract

In recent breakthrough results, novel use of garbled circuits yielded constructions for several primitives like Identity-Based Encryption (IBE) and 2-round secure multi-party computation, based on standard assumptions in public-key cryptography. While the techniques in these different results have many common elements, these works did not offer a modular abstraction that could be used across them. Our main contribution is to introduce a novel notion of obfuscation, called Reach-Restricted Reactive Program Obfuscation (R3PO) that captures the essence of these constructions, and exposes additional capabilities. We provide a powerful composition theorem whose proof fully encapsulates the use of garbled circuits in these works. As an illustration of the potential of R3PO, and as an important contribution of independent interest, we present a variant of Multi-Authority Attribute-Based Encryption (MA-ABE) that can be based on (single-authority) CP-ABE in a blackbox manner, using only standard cryptographic assumptions (e.g., DDH). This is in stark contrast to the existing constructions for MA-ABE, which rely on the random oracle model and/or support only limited policy classes.