Abstract. We study an adaptive variant of oblivious transfer in which a sender has N messages, of which a receiver can adaptively choose to re-ceive k one-after-the-other, in such a way that (a) the sender learns noth-ing about the receiver’s selections, and (b) the receiver only learns about the k requested messages. We propose two practical protocols for this primitive that achieve a stronger security notion than previous schemes with comparable efficiency. In particular, by requiring full simulatabil-ity for both sender and receiver security, our notion prohibits a subtle selective-failure attack not addressed by the security notions achieved by previous practical schemes. Our first protocol is a very efficient generic construction from unique blind signatures in the random oracle model. The second construction does not assume random oracles, but achieves remarkable efficiency with only a constant number of group elements sent during each transfer. This second construction uses novel techniques for building efficient simulat-able protocols. 1
Oblivious transfer, first introduced by Rabin, is one of the basic building blocks of cryp-tographic protocols. In an oblivious transfer (or more exactly, in its 1-out-of-2 variant), one party known as the sender has a pair of messages and the other party known as the receiver obtains one of them. Somewhat paradoxically, the receiver obtains exactly one of the messages (and learns nothing of the other), and the sender does not know which of the messages the receiver obtained. Due to its importance as a building block for secure protocols, the efficiency of oblivious transfer protocols has been extensively studied. However, to date, there are almost no known oblivious transfer protocols that are secure in the presence of malicious adversaries under the real/ideal model simulation paradigm (without using general zero-knowledge proofs). Thus, efficient protocols that reach this level of security are of great interest. In this paper we present efficient oblivious transfer protocols that are secure according to the ideal/real model simulation paradigm. We achieve constructions under the DDH, Nth residuosity and quadratic residuosity assumptions, as well as under the assumption that homomorphic encryption exists. 1
In an adaptive oblivious transfer (OT) protocol, a sender commits to a database of messages and then repeatedly interacts with a receiver in such a way that the receiver obtains one message per interaction of his choice (and nothing more) while the sender learns nothing about any of the choices. Recently, there has been significant effort to design practical adaptive OT schemes and to use these protocols as a building block for larger database applications. To be well suited for these applications, the underlying OT protocol should: (1) support an efficient initialization phase where one commitment can support an arbitrary number of receivers who are guaranteed of having the same view of the database, (2) execute transfers in time independent of the size of the database, and (3) satisfy a strong notion of security under a simple assumption in the standard model. We present the first adaptive OT protocol simultaneously satisfying these requirements. The sole complexity assumption required is that given (g, g a, g b, g c, Q), where g generates a bilinear group of prime order p and a, b, c are selected randomly from Zp, it is hard to decide if Q = g abc. All prior protocols in the standard model either do not meet our efficiency requirements or
Oblivious transfer protocol,which is an important and useful cryptographic protocol,has been widely applied in cryptographic field,especially in construction of secure multi-party computation protocol.However,all of present oblivious transfer protocols have two drawbacks for requirement of their secrets: ① the receiver does not know whether message received is one of the messages held by the sender;② the sender does not know whether message received by the receiver is one of the messages designated by himself.In order to conquer these drawbacks,we firstly introduce the notion of verifiable oblivious transfer protocol,and firstly construct it by using proof protocol of knowledge,i.e.,∑-protocol,as main tool.
We aim at constructing adaptive oblivious transfer protocols, enjoying fully simulatable security, from various well-known assumptions such as DDH, d-Linear, QR, and DCR. To this end, we present two generic constructions of adaptive OT, one of which utilizes verifiable shuffles together with threshold decryption schemes, while the other uses permutation networks together with what we call loosely-homomorphic key encapsulation schemes. The constructions follow a novel designing approach called “blind permutation”, which completely differs from existing ones. We then show that specific choices of the building blocks lead to concrete adaptive OT protocols with fully simulatable security in the standard model under the targeted assumptions. Our generic methods can be extended to build universally composable (UC) secure OT protocols, with a loss in efficiency.
Based on the RSA signature and (string) oblivious transfer, an enhanced oblivious transfer protocol is proposed which solves the access control problem for an oblivious transfer protocol. The protocol proposed has the property that only the receiver who has the signture issued by the central authority can open the message which he choose and that the sender can not decide whether the receiver has the signature or not. That is to say, the identity of the receiver can not be confirmed after the protocol. Under the decisional Diffie-Hellman assumption the proposed scheme has provable security.