Strong Conditional Oblivious Transfer and Computing on Intervals (original) (raw)

Efficient and Universally Composable Committed Oblivious Transfer and Applications

Lecture Notes in Computer Science, 2004

Committed Oblivious Transfer (COT) is a useful cryptographic primitive that combines the functionalities of bit commitment and oblivious transfer. In this paper, we introduce an extended version of COT (ECOT) which additionally allows proofs of relations among committed bits, and we construct an efficient protocol that securely realizes an ECOT functionality in the universalcomposability (UC) framework in the common reference string (CRS) model. Our construction is more efficient than previous (non-UC) constructions of COT, involving only a constant number of exponentiations and communication rounds. Using the ECOT functionality as a building block, we construct efficient UC protocols for general two-party and multi-party functionalities (in the CRS model), each gate requiring a constant number of ECOT's.

Constant-round secure two-party computation from a linear number of oblivious transfer

We construct a protocol for constant round Two-Party Secure Function Evaluation in the standard model which improves previous protocols in several ways. We are able to reduce the number of calls to Oblivious Transfer by a factor proportional to the security parameter. In addition to being more efficient than previous instantiations, our protocol only requires black box calls to OT and Commitment. This is achieved by the use of a faulty variant of the Cutand-Choose OT. The concepts of Garbling Schemes, faulty Cut-and-Choose Oblivious Transfer and Privacy Amplification are combined using the Cut-and-Choose paradigm to obtain the final protocol.

Secure Two-Party Computation via Leaky Generalized Oblivious Transfer

We construct a protocol for constant round Two-Party Secure Function Evaluation in the standard model which improves previous protocols in several ways. We are able to reduce the number of calls to Oblivious Transfer by a factor proportional to the security parameter. In addition to being more efficient than previous instantiations, our protocol only requires black box calls to OT and Commitment. This is achieved by the use of a faulty variant of the Cutand-Choose OT. The concepts of Garbling Schemes, faulty Cut-and-Choose Oblivious Transfer and Privacy Amplification are combined using the Cut-and-Choose paradigm to obtain the final protocol.

Obtaining Efficient Fully Simulatable Oblivious Transfer from General Assumptions

Anais do XXI Simpósio Brasileiro de Segurança da Informação e de Sistemas Computacionais (SBSeg 2011)

We introduce a general construction of fully simulatable oblivious transfer based on lossy encryption. Furthermore, we extend the common definition of lossy encryption by introducing the notion of computationally lossy encryption. If the cryptosystem used is computationally lossy, our general construction yields oblivious transfer protocols with computational security for both parties. Otherwise, when regular statistically lossy cryptosystems are employed in this construction, it yields oblivious transfer protocols with statistical security for the sender. The construction introduced in this paper is realizable from rerandomizable, homomorphic and lossy cryptosystems in general. Thus, it yields specific constructions based on different assumptions, such as DDH, LWE and McEliece. Moreover, it proves the equivalence of fully simulatable oblivious transfer and lossy encryption.

Committed Oblivious Transfer and Private Multi-Party Computation

Lecture Notes in Computer Science, 1995

In this paper we present an eficient protocol for "Committed Oblivious Transfer" to perform oblivious transfer on committed bits: suppose Alice is committed to bits 00 and a1 and Bob is committed to b, they both want Bob to learn and commit to Ob without Alice learning b nor Bob learning ah. Our protocol, based on the properties of error correcting codes, uses Bit Commitment (BC) and one-out-of-two Oblivious Transfer (OT) as black boxes. Consequently the protocol may be implemented with or without a computational assumption, depending on the kind of BC and OT used by the participants. Assuming a Broadcast Channel is also available, we exploit this result to obtain a protocol for Private Multi-Party Computation, without making assumptions about a specific number or fraction of participants being honest. We analyze the protocol's efficiency in terms of BCs and OTS performed. Our approach connects Zero Knowledge proofs on BCS, Oblivious Circuit Evaluation and Private Multi-Party Computations in a conceptually simple and ejficient way.

Efficient oblivious transfers with access control

Computers & Mathematics with Applications, 2012

Oblivious transfer (OT) is a protocol where a receiver can obtain t-out-of-n services from the sender without releasing anything about his choices. OT can be used to protect user's privacy. In principle, any user can interact with a server to request some services. This might allow some undesirable users to obtain services from the server. How to ensure that only the authorized receivers can obtain services obliviously is a daunting task. In this paper, we introduce oblivious signature based-on envelope (OSBE) to OT and propose two novel OT schemes, which only allow the legitimate receivers to obtain services obliviously. The receiver is required to authenticate himself to the issuer to possess the required credential prior to access the protected services; while no authentication from the sender needs to be done. The sender knows the number of the services selected by the receiver, but does not know anything about his choices and personally identifiable information. The feature of our scheme also lies in avoiding zero knowledge proofs and achieving all-ornothing non-transferable credentials. Our schemes are efficient in the cost of communication and computation.

An Efficient Secure Oblivious Transfer

As traditional oblivious transfer protocols are treated as a cryptographic primitive, they are usually executed without the consideration of possible attacks, e.g., impersonation, replaying, and man-in-the-middle attacks. Therefore, when these protocols are applied in certain applications such as mental poker playing, some necessary mechanism must be executed first to ensure the security of subsequent communications. But doing this way, we found that almost all of the resulting mechanisms are not efficient enough in communicational cost which is a significant concern for commercial transactions. Inspired by these observations, we propose a novel secure oblivious transfer protocol based on bilinear pairing which not only can provide mutual authentication to resist malicious attacks but also is efficient in communicational cost, other than its original functions.