Garbled circuits, a classical idea rooted in the work of Yao, have long been understood as a cryptographic technique, not a cryptographic goal. Here we cull out a primitive corresponding to this technique. We call it a garbling scheme. We provide a provable-security treatment for garbling schemes, endowing them with a versatile syntax and multiple security definitions. The most basic of these, privacy, suffices for two-party secure function evaluation (SFE) and private function evaluation (PFE). Starting from a PRF, we provide an efficient garbling scheme achieving privacy and we analyze its concrete security. We next consider obliviousness and authenticity , properties needed for private and verifiable outsourcing of computation. We extend our scheme to achieve these ends. We provide highly efficient blockcipher-based instantiations of both schemes. Our treatment of garbling schemes presages more efficient garbling, more rigorous analyses, and more modularly designed higher-level protocols.

We advocate schemes based on fixed-key AES as the best route to highly efficient circuit-garbling. We provide such schemes making only one AES call per garbled-gate evaluation. On the theoretical side, we justify the security of these methods in the random-permutation model, where parties have access to a public random permutation. On the practical side, we provide the JustGarble system, which implements our schemes. JustGarble evaluates moderate-sized garbled-circuits at an amortized cost of 23.2 cycles per gate (7.25 nsec), far faster than any prior reported results.

This paper provides a (standard-model) notion of security for (keyed) hash functions, called UCE, that we show enables instantiation of random oracles (ROs) in a fairly broad and systematic way. Goals and schemes we consider include deterministic PKE, message-locked encryption, hardcore functions, pointfunction obfuscation, OAEP, encryption secure for key-dependent messages, encryption secure under related-key attack, proofs of storage and adaptively-secure garbled circuits with short tokens. We can take existing, natural and efficient ROM schemes and show that the instantiated scheme resulting from replacing the RO with a UCE function is secure in the standard model. In several cases this results in the first standard-model schemes for these goals. The definition of UCE-security itself asks that outputs of the function look random given some "leakage," even if the adversary knows the key, as long as the leakage is appropriately restricted.

Abstract. With a scheme for robust authenticated-encryption a user can select an arbitrary value λ ≥ 0 and then encrypt a plaintext of any length into a ciphertext that's λ characters longer. The scheme must provide all the privacy and authenticity possible for the requested λ. We formalize and investigate this idea, and construct a well-optimized solution, AEZ, from the AES round function. Our scheme encrypts strings at almost the same rate as OCB-AES or CTR-AES (on Haswell, AEZ has a peak speed of about 0.7 cpb). To accomplish this we employ an approach we call prove-then-prune: prove security and then instantiate with a scaled-down primitive (e.g., reducing rounds for blockcipher calls).