Oblivious Transfer protocol (OTP) is a paramount important primitive tool in modern cryptography. Essentially, OTP can be used to construct a secure multi-party computation protocol and distributed oblivious transfer protocol (DOTP). DOTP is the general OTP in the distributed setting. Private information retrieval (PIR) and symmetric private information retrieval (SPIR) problems are also analogous to those of the OTP. Due to its importance, the task of constructing efficient and secure OTP has attracted a lot interests. In this paper, a paradigm of OPT protocol and a practical fully-simulatable OTP protocol based on blind GDH (Gap Diffie-Hellman) signature are presented. The proposed schemes can achieve higher efficiency and better security than the popular Malkhi & Sella scheme. The salient property of short signature length of GDH signature scheme enables our proposals applicable to low-bandwidth communication environments.
Oblivious Transfer protocol (OTP) is a paramount important primitive tool in modern cryptography. Essentially, OTP can be used to construct a secure multi-party computation protocol and distributed oblivious transfer protocol (DOTP). DOTP is the general OTP in the distributed setting. Private information retrieval (PIR) and symmetric private information retrieval (SPIR) problems are also analogous to those of the OTP. Due to its importance, the task of constructing efficient and secure OTP has attracted a lot interests. In this paper, a paradigm of OPT protocol and a practical fully-simulatable OTP protocol based on blind GDH (Gap Diffie-Hellman) signature are presented. The proposed schemes can achieve higher efficiency and better security than the popular Malkhi & Sella scheme. The salient property of short signature length of GDH signature scheme enables our proposals applicable to low-bandwidth communication environments.
Oblivious transfer (OT) protocol is an essential tool in cryptography that provides a wide range of applications such as secure multi-party computation, private information retrieval, private set intersection, contract signing, and privacy-preserving location-based services. The OT protocol has different variants such as one-out-of-2, one-out-of- n , k -out-of- n , and OT extension. In the OT (one-out-of-2, one-out-of- n , and OT extension) protocol, the sender has a set of messages, whereas the receiver has a key. The receiver sends that key to the sender in a secure way; the sender cannot get any information about the received key. The sender encrypts every message by operating on every message using the received key and sends all the encrypted messages to the receiver. The receiver is able to extract only the required message using his key. However, in the k -out-of- n OT protocol, the receiver sends a set of k keys to the sender, and in replay, the sender sends all the encrypted messages. The receiver uses his keys and extracts the required messages, but it cannot gain any information about the messages that it has not requested. Generally, the OT protocol requires high communication and computation cost if we transfer millions of oblivious messages. The OT extension protocol provides a solution for this, where the receiver transfers a set of keys to the sender by executing a few numbers of OT protocols. Then, the sender encrypts all the messages using cheap symmetric key cryptography with the help of a received set of keys and transfers millions of oblivious messages to the receiver. In this work, we present different variants of OT protocols such as one-out-of-2, one-out-of- n , k -out-of- n , and OT extension. Furthermore, we cover various aspects of theoretical security guarantees such as semi-honest and malicious adversaries, universally composable, used techniques, computation, and communication efficiency aspects. From the analysis, we found that the semi-honest adversary-based OT protocols required low communication and computation costs as compared to malicious adversary-based OT protocols.
We propose efficient and secure (string) oblivious transfer (OT/sup 1//sub n/) schemes for any n/spl ges/2. We build our OT/sup 1//sub n/ scheme from fundamental cryptographic techniques directly. The receiver's choice is unconditionally secure and the secrecy of the unchosen secrets is based on the hardness of the decisional Diffie-Hellman problem. Some schemes achieve optimal efficiency in terms of the number of rounds and the total number of exchanged messages for the case that the receiver's choice is unconditionally secure. The distinct feature of our scheme is that the system-wide parameters are independent of n and universally usable, that is, all possible receivers and senders use the same parameters and need no trapdoors specific to each of them. We extend our OT/sup 1//sub n/ schemes to distributed oblivious transfer schemes. Our distributed OT/sup 1//sub n/ schemes take full advantage of the research results of secret sharing. For applications, we present a method of transforming any (single-database) PIR protocol into a symmetric PIR protocol by slightly increasing the communication cost only.
Oblivious transfer (OT) is one of the most fundamental primitives in cryptography and is widely used in protocols for secure two-party and multi-party computation. As secure com-putation becomes more practical, the need for practical large scale oblivious transfer protocols is becoming more evident. Oblivious transfer extensions are protocols that enable a relatively small number of “base-OTs ” to be utilized to compute a very large number of OTs at low cost. In the semi-honest setting, Ishai et al. (CRYPTO 2003) presented an OT extension protocol for which the cost of each OT (beyond the base-OTs) is just a few hash function operations. In the malicious setting, Nielsen et al. (CRYPTO 2012) presented an efficient OT extension protocol for the setting of active adversaries, that is secure in the random oracle model. In this work, we present an OT extension protocol for the setting of malicious adversaries that is more efficient and uses less communication than previous works. In addition, our protocol can be proven secure in both the random oracle model, and in the standard model with a type of correlation robustness. Given the importance of OT in many secure computation protocols, increasing the efficiency of OT extensions is another important step forward to making secure
The Oblivious Transfer (OT) protocol is a privacy-preserving two-way communication protocol important for building secure multiparty computations. To exchange symmetric keys, this protocol is typically based on the Rivest—Shamir—Adleman (RSA) or Diffie—Hellman (DH) cryptographic systems, which are used for encryption during the message-encryption phase. However, in existing OT protocols, the generation of multiple pairs of public and private keys and data computations are time-consuming. Using bijective functions to transform the ciphertext within the same ciphertext domain can ensure indistinguishability after decryption and reduce the computational complexity. In the semi-honest model, a ciphertext obfuscation-based OT protocol framework is proposed and OT protocols are instantiated based on RSA and DH within this framework. Compared with RSA-based encryption schemes, the proposed protocol requires only one pair of public and private keys. When the number of public and private keys is reduced to one, the receiver can use the public key in the digital certificate of the sender to implement the OT protocol using an identity authentication function. Compared with the OT protocol based on the DH key exchange, this protocol has a small data transmission volume and low computational complexity. Experimental results show that, compared with existing OT protocols, the efficiency of instantiated protocols in the key exchange stage can be improved by at least 30%. Moreover, this protocol can be used as a basic protocol for privacy set intersections, obfuscation circuits, and OT extension protocols.
Oblivious transfer is an important cryptographic protocol in various security applications. For example, in on-line transactions, a k-out-of-n oblivious transfer scheme allows a buyer to privately choose k out of n digital goods from a merchant without learning information about other n-k goods. In this paper, we propose several efficient two-round k-out-of-n oblivious transfer schemes, in which the receiver R sends O(k) messages to the sender S, and S sends O(n) messages back to R. The schemes provide unconditional security for either sender or receiver. The computational security for the other side is based on the Decisional Diffie-Hellman (DDH) or Chosen-Target Computational Diffie-Hellman (CT-CDH) problems. Our schemes have the nice property of universal parameters, that is, each pair of R and S need not hold any secret before performing the protocol. The system parameters can be used by all senders and receivers without any trapdoor specification. In some cases, our OTkn schemes are the most efficient ones in terms of the communication cost, either in rounds or the number of messages. Moreover, one of our schemes is extended to an adaptive oblivious transfer scheme. In that scheme, S sends O(n) messages to R in one round in the commitment phase. For each query of R, only O(1) messages are exchanged and O(1) operations are performed. The preliminary version of this paper was published at PKC '05 [Chu and Tzeng 2005].
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