Resource-efficient OT combiners with active security.

*(English)*Zbl 1412.94160
Kalai, Yael (ed.) et al., Theory of cryptography. 15th international conference, TCC 2017, Baltimore, MD, USA, November 12–15, 2017. Proceedings. Part II. Cham: Springer. Lect. Notes Comput. Sci. 10678, 461-486 (2017).

Summary: An OT-combiner takes \(n\) candidate implementations of the oblivious transfer (OT) functionality, some of which may be faulty, and produces a secure instance of oblivious transfer as long as a large enough number of the candidates are secure. We see an OT-combiner as a 2-party protocol that can make several black-box calls to each of the \(n\) OT candidates, and we want to protect against an adversary that can corrupt one of the parties and a certain number of the OT candidates, obtaining their inputs and (in the active case) full control of their outputs.

In this work we consider perfectly (unconditionally, zero-error) secure OT-combiners and we focus on minimizing the number of calls to the candidate OTs.

First, we construct a single-use (one call per OT candidate) OT-combiner which is perfectly secure against active adversaries corrupting one party and a constant fraction of the OT candidates. This extends a previous result by Ishai et al. [Y. Ishai, H. K. Maji, A. Sahai, J. Wullschleger, Single-use OT combiners with near-optimal resilience. In: 2014 IEEE International Symposium on Information Theory, Honolulu, HI, USA, 29 June – 4 July 2014, 1544–1548 (2014)] that proves the same fact for passive adversaries.

Second, we consider a more general asymmetric corruption model where an adversary can corrupt different sets of OT candidates depending on whether it is Alice or Bob who is corrupted. We give sufficient and necessary conditions for the existence of an OT combiner with a given number of calls to the candidate OTs in terms of the existence of secret sharing schemes with certain access structures and share-lengths. This allows in some cases to determine the optimal number of calls to the OT candidates which are needed to construct an OT combiner secure against a given adversary.

For the entire collection see [Zbl 1374.94005].

In this work we consider perfectly (unconditionally, zero-error) secure OT-combiners and we focus on minimizing the number of calls to the candidate OTs.

First, we construct a single-use (one call per OT candidate) OT-combiner which is perfectly secure against active adversaries corrupting one party and a constant fraction of the OT candidates. This extends a previous result by Ishai et al. [Y. Ishai, H. K. Maji, A. Sahai, J. Wullschleger, Single-use OT combiners with near-optimal resilience. In: 2014 IEEE International Symposium on Information Theory, Honolulu, HI, USA, 29 June – 4 July 2014, 1544–1548 (2014)] that proves the same fact for passive adversaries.

Second, we consider a more general asymmetric corruption model where an adversary can corrupt different sets of OT candidates depending on whether it is Alice or Bob who is corrupted. We give sufficient and necessary conditions for the existence of an OT combiner with a given number of calls to the candidate OTs in terms of the existence of secret sharing schemes with certain access structures and share-lengths. This allows in some cases to determine the optimal number of calls to the OT candidates which are needed to construct an OT combiner secure against a given adversary.

For the entire collection see [Zbl 1374.94005].

##### MSC:

94A60 | Cryptography |