Obfuscation from Circular Security
Obfuscation from Circular Security
We describe a new approach to indistinguishability obfuscation, which yields candidate schemes that are secure under assumptions having a "circular security" flavor. Furthermore the approach is relatively simple to describe and can be instantiated using LWE-style techniques, which makes our candidates presumably post-quantum secure.
We start by reducing the task of constructing iO to that of constructing a "functional encoding scheme", which is a fully homomorphic encryption (FHE) scheme that allows us to give out succinct hints to reveal some specified function outputs. We then present an approach for constructing functional encodings. This relies on a new notion: "shielded randomness leakage" (SRL), which allows to leak "properly blurred" information about the randomness of FHE ciphertexts. While basic SRL security provably follows from LWE, the construction relies on circular variant where security is assumed to hold even if the FHE ciphertext encrypts its own secret key (or, more generally, is part of some key-cycle or key-randomness cycle).
Based on the following works:
[BDGM20a] Brakerski, Döttling, Garg, Malavolta: "Candidate Obfuscation from Homomorphic Encryption Schemes"
[BDGM20b] Brakerski, Döttling, Garg, Malavolta: "Factoring and Pairings are not Necessary for iO: Circular-Secure LWE Suffices"
About the speaker
Faculty at Max Planck Institute
Giulio is a faculty at the Max Planck Institute for Security and Privacy (MPI-SP) where he is the head of the Cryptographic Systems group. His research work revolves around theoretical and applied aspects of cryptography and he is broadly interested in the intersection with other disciplines, e.g. computer security, concurrent systems, cryptocurrencies, game theory, and quantum computation.