An m out of n oblivious transfer (OT) protocol is a cryptographic protocol for a sender to transfer m out of n messages to a receiver such that the sender has no idea which m messages are obtained by the receiver (receiver security ) and at the same time the receiver cannot obtain more than m messages ( sender security ). Three such protocols are proposed in [1], which have the advantage that the communication overhead of the protocols is much smaller than that of m implementations of a 1 out of n OT protocol. In this paper we give a security analysis of the three protocols. First we show that the first protocol cannot guarantee both the sender security and the receiver security simultaneously. Next, we point out an obvious security flaw in the second protocol which allows the receiver to obtain all the n messages. The third protocol is nicely designed to be non-interactive. However, we show that the security of the protocol is based on a sort of parallel discrete logarithm problem, instead of the discrete logarithm problem as claimed in the paper. Using the technique of “generalized birthday attack”, the former problem can be solved with a computation complexity much smaller than that required to solve the discrete logarithm problem. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
An m out of n oblivious transfer (OT) protocol is a cryptographic protocol for a sender to transfer m out of n messages to a receiver such that the sender has no idea which m messages are obtained by the receiver (receiver security ) and at the same time the receiver cannot obtain more than m messages ( sender security ). Three such protocols are proposed in [1], which have the advantage that the communication overhead of the protocols is much smaller than that of m implementations of a 1 out of n OT protocol. In this paper we give a security analysis of the three protocols. First we show that the first protocol cannot guarantee both the sender security and the receiver security simultaneously. Next, we point out an obvious security flaw in the second protocol which allows the receiver to obtain all the n messages. The third protocol is nicely designed to be non-interactive. However, we show that the security of the protocol is based on a sort of parallel discrete logarithm problem, instead of the discrete logarithm problem as claimed in the paper. Using the technique of “generalized birthday attack”, the former problem can be solved with a computation complexity much smaller than that required to solve the discrete logarithm problem. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
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.
The Oblivious Transfer (OT), introduced by Rabin in 1981, has become an important and fundamental cryptography technique. An OT protocol should have two important characteristics: sender's privacy and chooser's privacy. The sender is a party who will deliver a secret to chooser. The chooser is another party who acts as receiver to learn some information about input from sender. The chooser learns of certain information concerning sender's input while sender is not allowed to know what chooser has learned. Moreover, chooser cannot acquire any messages that he/she did not choose. Naor and Pinkas have recently proposed an efficient oblivious transfer protocol (EOT) that implementes 1-out-of-n protocol, but this EOT has a flaw: it cannot withstand the same message attack. In this paper, we will improve Naor and Pinkas EOT and make it resistant to the same message attack.
Oblivious transfer (OT) protocol is a fundamental building block of cryptography and can be applied widely in many fields. A secure oblivious transfer protocol is supposed to ensure the privacy of both senders and receivers. The privacy of receivers means that the information being selected by receivers would never be revealed to senders. On the other hand, the privacy of senders means that receivers have no further information except for the one that has been selected. In this case, senders are able to deceive receivers by sending same messages. Likewise, in existing 1-out-of-n OT protocols, malicious senders can make all the n messages the same, so that receivers will always get the specific one assigned by senders. This indicates that privacy of receivers wouldnt work under the 1-out-of-n OT protocol. To prevent this kind of attack, this paper provides a general framework on how to design a secure OT protocol based on commutative and ciphertext equality test and take RSA as an example to explain how the protocol is processed.
Oblivious Transfer (OT) is an important cryptographic tool, which has found its usage in many crypto protocols, such as Secure Multiparty Computations [9], Certified E-mail [2] and Simultaneous Contract Signing [20].In this paper, we propose three k-out-of-n OT (OT n k ) protocols based on additive homomorphic encryption.Two of these protocols prohibit malicious behaviors from both sender and receiver.We also achieve efficient communication complexity bounded by O(l • n) in bits, where l is the size of the encryption key.The computational complexity is same or better than the most efficient existing protocols.Due to the semantic security property, the sender cannot get receiver's selection.When the receiver tries to retrieve more than k values, the receiver is caught cheating with 1 -1/m probability (Protocol II) or the receiver is unable to get any value at all (Protocol III).We introduce a novel technique based on the solvability of linear equations, which could find its way into other applications.We also provide an experimental analysis to compare the efficiency of the 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].
T wo non-interactive three parties k out of n oblivious transfer protocols from bilinear pairings are proposed i n this paper. In these protocols , a sender can obliviously transfer n messages to a receiver without communication with him/her. The public keys that a sender used to encrypt his/her messages are made by a third party. The receiver can extract k out of n messages at his/her choices by using the corresponding secret keys. The choices of the receiver are unconditionally secure. The sender's secrecy is guaranteed if the receiver is semi-honest in the standard model since the decision bilinear Diffie-Hellman problem (DBDH) is hard and the sender's secrecy is achieved when the receiver is a malicious party in the random oracle model since the bilinear Diffie-Hellman problem assumption (BDHA) holds. When a sender is a cheating party, the receiver will detect him/her and halt the protocol. A precise proof of the security of the protocols is presented.