CWI Cryptology Group

Abstract: In this talk, we give an overview of information-theoretic key agreement from classical correlations and outline parallels to quantum entanglement. We show that when the latter is studied from a classical information-theoretic viewpoint, insights can be gained in cryptography as well as communication-complexity theory.

Abstract: We study unconditionally secure 1-out-of-2 Oblivious Transfer (1-2 OT). We first point out that a standard security requirement for 1-2 OT of bits, namely that the receiver only learns one of the bits sent, holds if and only if the receiver has no information on the XOR of the two bits. We then generalize this to 1-2 OT of strings and show that the security can be characterized in terms of binary linear functions. More precisely, we show that the receiver learns only one of the two strings sent if and only if he has no information on the result of applying any binary linear function (which non-trivially depends on both inputs) to the two strings.
We then argue that this result not only gives new insight into the nature of 1-2 OT, but it in particular provides a very powerful tool for analyzing 1-2 OT protocols. We demonstrate this by showing that with our characterization at hand, the reduceability of 1-2 OT (of strings) to a wide range of weaker primitives follows by a very simple argument. This is in sharp contrast to previous literature, where reductions of 1-2 OT to weaker flavors have rather complicated and sometimes even incorrect proofs.

Abstract: Oblivious Transfer (OT) is an important primitive in multi-party computation, which we often only can implement in a weak form. We will present two different (but connected) ways of strengthening OT.
An OT combiner securely implements OT based on a set of candidate implementations from which only an unknown subset is secure. We give two refinement of previous definitions and give strictly stronger combiners than previously known.
OT amplification takes as input a weak OT, i.e., an OT where with some probability the output may contain errors and the players may gain additional information, and constructs a correct and secure version of OT. We will correct previous results that were imprecise and present new bounds.
We will also show how OT amplification and OT combiners are connected.

Abstract: Physical Unclonable Functions (PUFs) have been developed to make devices unclonable and hence protected against counterfeiting. Recently, it was shown how PUFs integrated with an IC can be used as Read-Proof Hardware. In order to fulfill these roles, they need to be a source of a lot of randomness. In this talk we explain how the entropy of PUFs can be computed and why entropy is a relevant measure for these systems. Additionally, we explain how secure keys can be extracted from PUFs by using Helper Data Algorithms/Fuzzy Extractors.