We propose the first leakage-resilient Identity-Based Encryption (IBE) scheme with full domain hash structure. Our scheme is leakageresilient in the relative leakage model and the random oracle model under the decisional bilinear Diffie-Hellman (DBDH) assumption.

We formalize the notion of several weakened random oracle models in order to capture which property of a hash function is crucial to prove the security of a cryptographic scheme. In particular, we focus on augmenting the random oracle with additional oracles that respectively return collisions, secondpreimages, and first-preimages. We study the security of the full domain hash signature scheme,...

We construct an Identity-Based Encryption (IBE) system without random oracles from hard problems on lattices. The system provides full ciphertext anonymity, and also extends to HIBE by properly randomizing lattice trapdoors used as private keys during delegation.

Recently, methods from provable security, that had been developped for the last twenty years within the research community, have been extensively used to support emerging standards. This in turn has led researchers as well as practitioners to raise some concerns about this methodology. Should provable security be restricted to the standard computational model or can it rely on the so-called ran...

Starting with Shoup’s seminal paper [24], the generic group model has been an important tool in reductionist security arguments. After an informal explanation of this model and Shoup’s theorem, we discuss the danger of flaws in proofs. We next describe an ontological difference between the generic group assumption and the random oracle model for hash functions. We then examine some criticisms t...

We present the first blind identity-based signcryption (BIBSC). We formulate its security model and define the security notions of blindness and parallel one-more unforgeability (p1m-uf). We present an efficient construction from pairings, then prove a security theorem that reduces its p1m-uf to Schnorr’s ROS Problem in the random oracle model plus the generic group and pairing model. The latte...

We present a construction for non-interactive zero-knowledge proofs of knowledge in the random oracle model from general sigma-protocols. Our construction is secure against quantum adversaries. Prior constructions (by Fiat-Shamir and by Fischlin) are only known to be secure against classical adversaries, and Ambainis, Rosmanis, Unruh (FOCS 2014) gave evidence that those constructions might not ...

We study the quantum query complexity of finding a collision for a function f whose outputs are chosen according to a distribution with min-entropy k. We prove that Ω(2) quantum queries are necessary to find a collision for function f . This is needed in some security proofs in the quantum random oracle model (e.g. Fujisaki-Okamoto transform).

We present a theoretical analysis of active learning with more realistic interactions with human oracles. Previous empirical studies have shown oracles abstaining on difficult queries until accumulating enough information to make label decisions. We formalize this phenomenon with an “oracle epiphany model” and analyze active learning query complexity under such oracles for both the realizable a...