Krzysztof Pietrzak

A New Randomness Extraction Paradigm for Hybrid Encryption

We present a new approach to the design of IND-CCA2 secure hybrid encryption schemes in the standard model. Our approach provides an efficient generic transformation from 1-universal to 2-universal hash proof systems. The transformation involves a randomness extractor based on a 4-wise independent hash function as the key derivation function. Our methodology can be instantiated with efficient schemes based on standard intractability assumptions such as Decisional Diffie-Hellman, Quadratic Residuosity, and Pailliers Decisional Composite Residuosity. Interestingly, our framework also allows to prove IND-CCA2 security of a hybrid version of 1991s Damgards ElGamal public-key encryption scheme under the DDH assumption.

On the generic insecurity of the full domain hash

The Full-Domain Hash (FDH) signature scheme forms [3] one the most basic usages of random oracles. It works with a family

Intrusion-Resilient Secret Sharing

\mathcal{F}

Improved security analyses for CBC MACs

of trapdoor permutations (TDP), where the signature of m is computed as f−−1(h(m)) (here

Leakage-resilient signatures

{f} \in_{\mathcal{R}} \mathcal{F}

The security of many-round Luby-Rackoff pseudo-random permutations

and h is modelled as a random oracle). It is known to be existentially unforgeable for any TDP family

Leakage Resilient ElGamal Encryption

\mathcal{F}

Efficient authentication from hard learning problems

[3], although a much tighter security reduction is known for a restrictive class of TDPs [10,14]— namely, those induced by a family of claw-free permutations (CFP) pairs. The latter result was shown [11] to match the best possible “black-box” security reduction in the random oracle model, irrespective of the TDP family

Proofs of Space

\mathcal{F}

Composition of random systems: When two weak make one strong

(e.g., RSA) one might use. In this work we investigate the question if it is possible to instantiate the random oracle h with a “real” family of hash functions