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IEEE International Symposium on Information Theory (ISIT)

On the Oblivious Transfer Capacity of the Erasure Channel

Hideki Imai, Kirill Morozov, Anderson C. A. Nascimento

Published Jul 1, 2006• 40 citations
Publisher

Abstract

One of the most important primitives in two-party distrustful cryptography is oblivious transfer, a complete primitive for two-party computation. Recently introduced, the oblivious transfer capacity of a noisy channel measures an efficiency of information theoretical reductions from 1-out-of-k, l-string oblivious transfer to noisy channels. It is defined as the maximal achievable ratio l/n, where l is the length of the strings which are to be transferred and n is the number of times the noisy channel is invoked. This quantity is unknown in a general case. For discrete memoryless channels, it is known to be nonnegligible for honest-but-curious players, but the non-zero rates have not ever been proved achievable in the case of malicious players. Here, we show that in the particular case of the erasure channel, more precise answers can be obtained. We compute the OT capacity of the erasure channel for the case of honest-but-curious players and, for the fully malicious players, we give its lower bound.

DOI
10.1109/isit.2006.262082

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One of the most important primitives in two-party distrustful cryptography is oblivious transfer, a complete primitive for two-party computation. Recently introduced, the oblivious transfer capacity of a noisy channel measures an efficiency of information theoretical reductions from 1-out-of-k, l-string oblivious transfer to noisy channels. It is defined as the maximal achievable ratio l/n, where l is the length of the strings which are to be transferred and n is the number of times the noisy channel is invoked. This quantity is unknown in a general case. For discrete memoryless channels, it is known to be nonnegligible for honest-but-curious players, but the non-zero rates have not ever been proved achievable in the case of malicious players. Here, we show that in the particular case of the erasure channel, more precise answers can be obtained. We compute the OT capacity of the erasure channel for the case of honest-but-curious players and, for the fully malicious players, we give its lower bound.
Noisy channels are a powerful resource for cryptography as they can be used to obtain information-theoretically secure key agreement, commitment and oblivious transfer protocols, among others. Oblivious transfer (OT) is a fundamental primitive since it is complete for secure multi-party computation, and the OT capacity characterizes how efficiently a channel can be used for obtaining string oblivious transfer. Ahlswede and Csiszár (\emph{ISIT'07}) presented upper and lower bounds on the OT capacity of generalized erasure channels (GEC) against passive adversaries. In the case of GEC with erasure probability at least 1/2, the upper and lower bounds match and therefore the OT capacity was determined. It was later proved by Pinto et al. (\emph{IEEE Trans. Inf. Theory 57(8)}) that in this case there is also a protocol against malicious adversaries achieving the same lower bound, and hence the OT capacity is identical for passive and malicious adversaries. In the case of GEC with erasure probability smaller than 1/2, the known lower bound against passive adversaries that was established by Ahlswede and Csiszár does not match their upper bound and it was unknown whether this OT rate could be achieved against malicious adversaries as well. In this work we show that there is a protocol against malicious adversaries achieving the same OT rate that was obtained against passive adversaries. In order to obtain our results we introduce a novel use of interactive hashing that is suitable for dealing with the case of low erasure probability (p∗<1/2p^* <1/2p∗<1/2).
Noisy channels are a powerful resource for cryptography as they can be used to obtain information-theoretic secure key agreement, commitment, and oblivious transfer protocols, among others. Oblivious transfer (OT) is a fundamental primitive, since it is complete for secure multi-party computation, and the OT capacity characterizes how efficiently a channel can be used for obtaining string oblivious transfer. Ahlswede and Csiszár (ISIT'07) presented upper and lower bounds on the OT capacity of generalized erasure channels (GECs) against passive adversaries. In the case of GEC with erasure probability at least 1/2, the upper and lower bounds match and, therefore, the OT capacity was determined. It was later proved by Pinto et al. [IEEE Trans. Inf. Theory 57(8)] that the OT capacity is identical for passive and malicious adversaries. In the case of GEC with erasure probability smaller than 1/2, the known lower bound against passive adversaries that was established by Ahlswede and Csiszár does not match their upper bound and it was unknown whether this OT rate could be achieved against malicious adversaries as well. In this paper, we show that there is a protocol against malicious adversaries achieving the same OT rate that was obtained against passive adversaries. We obtain our results by a new combination of interactive hashing and typicality tests that are suitable for dealing with the case of low erasure probability (p* <;1/2 ).
Oblivious Transfer (OT) is a broadly studied cryptographic primitive which involves two mutually distrustful users who wish to interact with each other in order to transfer messages in an oblivious manner. Noise is an important resource to realize information-theoretically secure cryptographic protocols including oblivious transfer. However, oftentimes these noisy channels may be poorly characterized and the complete channel characteristics might be unknown to both users. Such channels are studied in the literature through the lens of compound channels. We study 1-out-of-2 oblivious transfer over a compound binary erasure channel (compound-BEC) and characterize the oblivious transfer capacity of compound-BEC. Our OT capacity characterization involves a general alphabet compound-DMC converse, subsequently specialized to compound-BEC along with an optimal and computationally-efficient achievability scheme for honest-but-curious users.
In this paper, we study the information-theoretic limits of oblivious transfer via noisy channels. We also investigate oblivious transfer over a noisy multiple-access channel with two non-colluding senders and a single receiver. The channel is modeled through correlations among the parties, who may be honest-but-curious or, in the case of the receiver, potentially malicious. We first revisit the information-theoretic limits of two-party oblivious transfer and then extend these results to the multiple-access setting. For honest-but-curious participants, we introduce a multiparty protocol that reduces a general multiple access channel to a suitable correlation model. In scenarios with a malicious receiver, we characterize an achievable oblivious transfer rate region.
Information-theoretically secure string oblivious transfer (OT) can be constructed based on discrete memoryless channel (DMC). The oblivious transfer capacity of a channel characterizes - similarly to the (standard) information capacity - how efficiently it can be exploited for secure oblivious transfer of strings. The OT capacity of a generalized erasure channel (GEC) - which is a combination of a (general) DMC with the erasure channel - has been established by Ahlswede and Csizar at ISIT'07 in the case of passive adversaries. In this paper, we present the protocol that achieves this capacity against malicious adversaries for GEC with erasure probability at least 1/2. Our construction is based on the protocol of Crepeau and Savvides from Eurocrypt'06 which uses interactive hashing (IH). We solve an open question posed by the above paper, by basing it upon a constant round IH scheme (previously proposed by Ding et al. at TCC'04). As a side result, we show that the Ding et al. IH protocol can deal with transmission errors.
We study quantum-state oblivious transfer over the quantum erasure channel under information-theoretic security guarantees. Specifically, Alice holds two quantum systems, Bob wishes to recover one of them, and the parties have access to independent channel uses and authenticated public classical communication, with no initial shared entanglement. We consider both honest-but-curious and malicious behavior. We establish finite-blocklength converse and achievability bounds, which match in the honest-but-curious setting. The malicious setting construction combines interactive hashing with tests of whether Bob received selected channel outputs, and distributes each input across several qubits so that erasures conceal an entire input from a dishonest receiver, even when the inputs are entangled with an external reference. We also derive fixed-error asymptotic expansions and show that both malicious and honest-but-curious settings have the same capacity.