Cryptanalysis of Boyen’s Attribute-Based Encryption Scheme in TCC 2013 Shweta Agrawal1, Rajarshi Biswas1, Ryo Nishimaki2, Keita Xagawa2, Xiang Xie3, and Shota Yamada4 1 IIT Madras, Chennai, India
[email protected],
[email protected] 2 NTT Secure Platform Laboratories, Tokyo, Japan [ryo.nishimaki.zk,keita.xagawa.zv]@hco.ntt.co.jp 3 Shanghai Key Laboratory of Privacy-Preserving Computation, China
[email protected] 4 National Institute of Advanced Industrial Science and Technology (AIST), Tokyo
[email protected] Abstract. In TCC 2013, Boyen suggested the first lattice based con- struction of attribute based encryption (ABE) for the circuit class NC1. Unfortunately, soon after, a flaw was found in the security proof of the scheme. However, it remained unclear whether the scheme is actually insecure, and if so, whether it can be repaired. Meanwhile, the construc- tion has been heavily cited and continues to be extensively studied due to its technical novelty. In particular, this is the first lattice based ABE which uses linear secret sharing schemes (LSSS) as a crucial tool to en- force access control. In this work, we show that the scheme is in fact insecure. To do so, we provide a polynomial-time attack that completely breaks the security of the scheme. We suggest a route to fix the security of the scheme, via the notion of admissible linear secret sharing schemes (LSSS) and instantiate these for the class of DNFs. Subsequent to our work, Datta, Komargodski and Waters (Eurocrypt 2021) provided a construction of admissible LSSS for NC1 and resurrected Boyen’s claimed result.