Efficient oblivious transfer with adaptive queries in UC framework

We propose an efficient adaptive oblivious transfer protocol with hidden access policies. This scheme allows a receiver to anonymously recover a message from a database which is protected by hidden attribute based access policy if the receiver's attribute set satisfies the associated access policy implicitly. The proposed scheme is secure in the presence of malicious adversary under the q-Strong Diffie-Hellman (SDH), q-Power Decisional Diffie-Hellman (PDDH) and Decision Bilinear Diffie-Hellman (DBDH) assumption in full-simulation security model. The scheme covers disjunction of attributes. The proposed protocol outperforms the existing similar schemes in terms of both communication and computation.

Distributed networks remarkably enhance the convenience of network connectivity. How to achieve efficient cooperative computation while preserving data privacy is a challenge in the scenario of distributed networks. Secure computation, as the key technology of information security and privacy protection in the distributed networks, attracts more and more attention. In the paper, we develop the protocols of secure two-party computation in the presence of malicious adversaries which are constructed with homomorphic probabilistic cryptosystem, and propose four honest-verifier zero-knowledge proof protocols to detect two cheating behaviours of the malicious adversary. The proposed protocols are more targeted than the existing work. The analysis shows that the proposed protocols are complete, sound and zero-knowledge. As an application, we show how to use our protocols in a secure two-party protocol to detect cheating, which can make it secure in the presence of malicious adversaries.

In this paper, a new notion which we call private data deduplication protocol, a deduplication technique for private data storage is introduced and formalized. Intuitively, a private data deduplication protocol allows a client who holds a private data proves to a server who holds a summary string of the data that he/she is the owner of that data without revealing further information to the server. Our notion can be viewed as a complement of the state-of-the-art public data deduplication protocols of Halevi et al [7]. The security of private data deduplication protocols is formalized in the simulation-based framework in the context of two-party computations. A construction of private deduplication protocols based on the standard cryptographic assumptions is then presented and analyzed. We show that the proposed private data deduplication protocol is provably secure assuming that the underlying hash function is collision-resilient, the discrete logarithm is hard and the erasure coding algorithm can erasure up to α-fraction of the bits in the presence of malicious adversaries in the presence of malicious adversaries. To the best our knowledge this is the first deduplication protocol for private data storage.

Oblivious transfer (OT) is a significant primitive with wide use in secure two-party computation, private set intersection private and other cryptographic schemes. In the past ten years, different variants of OT primitive like cut-and-choose OT (CCOT) and outsourced OT (OOT), have been proposed so as to satisfy various emerging models. In this paper, we firstly propose and formalize a new primitive called permutable cut-and-choose OT (PCCOT) which generalizes the original CCOT functionality. Furthermore, we construct an efficient PCCOT protocol in the presence of malicious adversaries using the Decisional Diffie-Hellman (DDH) hard assumption. It is worth mentioning that we apply the PCCOT primitive to the efficient construction of secure wildcard pattern matching (WPM) protocol. The WPM functionality allows a party to determine the locations of its pattern with wildcard characters occurs in a long text of another party while revealing nothing to either party in addition to the length of their own inputs. Our proposed secure WPM protocol via PCCOT is secure against semi-honest adversary with 2 rounds and has identical communication cost as the the state-of-the-art scheme.

Recently, there has been huge progress in the field of concretely efficient secure computation, even while providing security in the presence of malicious adversaries. This is especially the case in the two-party setting, where constant-round protocols exist that remain fast even over slow networks. However, in the multi-party setting, all concretely efficient fully-secure protocols, such as SPDZ, require many rounds of communication.

Recently, there has been huge progress in the field of concretely efficient secure computation, even while providing security in the presence of malicious adversaries. This is especially the case in the two-party setting, where constant-round protocols exist that remain fast even over slow networks. However, in the multi-party setting, all concretely efficient fully-secure protocols, such as SPDZ, require many rounds of communication.

Web search has become an integral part of our lives and we use it daily for business and pleasure. Unfortunately, however, we unwittingly reveal a huge amount of private information about ourselves when we search the web. A look at a user's search terms over a period of a few months paints a frighteningly clear and detailed picture about the user's life. In this paper, we build on previous work by Castella-Roca et al. (Computer Communications 2009) and show how to achieve privacy in web searches efficiently and practically without resorting to full-blown anonymous routing. In contrast to previous work, our protocol is secure in the presence of malicious adversaries.

Secure two-party computation provides a way for two parties to compute a function, that depends on the two parties’ inputs, while keeping them private. Known since the 1980s, Yao’s garbled circuits appear to be a general solution to this problem, in the semi-honest model. Decades of optimizations have made this tool a very practical solution. However, it is well known that a malicious adversary could modify a garbled circuit before submitting it. Many protocols, mostly based on cut-&-choose, have been proposed to secure Yao’s garbled circuits in the presence of malicious adversaries. Nevertheless, how much an adversary can modify a circuit and make it still executable has not been studied yet. The main contribution of this paper is to prove that any modification made by an adversary is equivalent to adding/removing NOT gates arbitrarily in the original circuit, otherwise the adversary can get caught. Thereafter, we study some evaluation functions for which, even without using cut-&-choose, no adversary can gain more information about the inputs by modifying the circuit. We also give an improvement over most recent cut-&-choose solutions by requiring that different circuits of the same function are used instead of just one.

Adaptive Oblivious Transfer Protocol with Hidden Access Policy (AOT-HAP) is a well known cryptographic primitive that combines each message of a database with an access policy which is kept hidden. The database is held by a sender who encrypts each message of the database under its access policy and publishes encrypted database in which access policies are embedded implicitly. A receiver possesses an attribute set and recovers the message correctly if the attribute set satisfies the access policy implicitly. Otherwise, a garbage message is recovered by the receiver. In this paper, an efficient \(\mathsf{AOT{\text {-}}HAP}\) is presented. The proposed protocol realizes more expressive access policies, i.e., conjunction as well as disjunction of attributes. The proposed \(\mathsf{AOT{\text {-}}HAP}\) is secure assuming the hardness of standard assumptions in the presence of malicious adversary in full-simulation security model. It exhibits significant improvement over the existing similar schemes in terms of both communication and computation.KeywordsOblivious transferAccess policyAttribute based encryptionFull simulation security model

Location-dependent services are services that adapt their behavior based on the locations of mobile devices. For many applications, it is critical that location-dependent services use trustworthy device locations, namely locations that are both accurate and recent. These properties are captured by a security goal called locale authentication whereby an entity can authenticate the physical location of a device, even in the presence of malicious adversaries. In this paper, we present a systematic technique for verifying that location discovery protocols satisfy this security goal. We base our work on the strand space theory which provides a framework for determining which security goals a cryptographic protocol achieves. We extend this theory with a metric that captures the geometric properties of time and space. We use the extended theory to prove that several prominent location discovery protocols including GPS do not satisfy the locale authentication goal. We also analyze a location discovery protocol that does satisfy the goal under some reasonable assumptions.

In this paper we show that using standard smartcards it is possible to construct truly practical secure protocols for a variety of tasks. Our protocols achieve full simulation-based security in the presence of malicious adversaries, and can be run on very large inputs. We present protocols for secure set intersection, oblivious database search and more. We have also implemented our set intersection protocol in order to show that it is truly practical: on sets of size 30,000 elements takes 20 seconds for one party and 30 minutes for the other (where the latter can be parallelized to further reduce the time). This demonstrates that in settings where physical smartcards can be sent between parties (as in the case of private data mining tasks between security and governmental agencies), it is possible to use secure protocols with proven simulation-based security.

We propose a protocol for the problem of secure two-party pattern matching, where Alice holds a text t?{0,1}? of length n, while Bob has a pattern p?{0,1}? of length m. The goal is for Bob to (only) learn where his pattern occurs in Alice's text, while Alice learns nothing. Private pattern matching is an important problem that has many applications in the area of DNA search, computational biology and more. Our construction guarantees full simulation in the presence of malicious, polynomial-time adversaries (assuming the hardness of DDH assumption) and exhibits computation and communication costs of O(n+m) group elements in a constant round complexity. This improves over previous work by Gennaro et al. (Public Key Cryptography, pp. 145---160, 2010) whose solution requires overhead of O(nm) group elements and exponentiations in O(m) rounds. In addition to the above, we propose a collection of protocols for important variations of the secure pattern matching problem that are significantly more efficient than the current state of art solutions: First, we deal with secure pattern matching with wildcards. In this variant the pattern may contain wildcards that match both 0 and 1. Our protocol requires O(n+m) communication and O(1) rounds using O(nm) computation. Then we treat secure approximate pattern matching. In this variant the matches may be approximated, i.e., have Hamming distance less than some threshold, ?. Our protocol requires O(n?) communication in O(1) rounds using O(nm) computation. Third, we have secure pattern matching with hidden pattern length. Here, the length, m, of Bob's pattern remains a secret. Our protocol requires O(n+M) communication in O(1) rounds using O(n+M) computation, where M is an upper bound on m. Finally, we have secure pattern matching with hidden text length. Finally, in this variant the length, n, of Alice's text remains a secret. Our protocol requires O(N+m) communication in O(1) rounds using O(N+m) computation, where N is an upper bound on n.

We propose a dedicated protocol for the highly motivated problem of secure two-party pattern matching: Alice holds a text t ∈ {0,1}*. of length n, while Bob has a pattern p ∈ {0,1}*. of length m. The goal is for Bob to learn where his pattern occurs in Alice’s text. Our construction guarantees full simulation in the presence of malicious, polynomial-time adversaries (assuming that ElGamal encryption is semantically secure) and exhibits computation and communication costs of O(n + m) in a constant round complexity. In addition to the above, we propose a collection of protocols for variations of the secure pattern matching problem: The pattern may contain wildcards (O(nm) communication in O(1) rounds). The matches may be approximated, i.e., Hamming distance less than some threshold ((O(nm) communication in O(1) rounds). The length, m, of Bob’s pattern is secret (O(nm) communication in O(1) rounds). The length, n, of Alice’s text is secret (O(n + m) communication in O(1) rounds).

The Yao’s protocol based on garbled circuits is the foundation of secure two-party computation protocols, and Oblivious Transfer (OT), as a important tool in modern cryptography, plays a crucial role in transmitting garbled keys in the Yao’s protocol. In the past decades, considerable attentions have been paid to the Cut-and-Choose technique which is applied to OT protocols to prevent malicious P 1 (called circuit generator) from constructing wrong garbled circuits. Additionally, Bilateral OT becomes a focus point, which can simultaneously transmit P 1 ’s and P 2 ’s (called circuit evaluator) garbled keys to guarantee input consistency of two parties and improve transmission efficiency. As can be seen, some Cut-and-Choose Bilateral OT (CCBOT) protocols have been proposed. Since CCBOT has emerged, the probability of malicious P 1 constructing wrong garbled circuits without being found becomes lower and the input consistency problem is properly resolved too. However, the security of most CCBOT protocols are facing challenges since they are based on the Decisional Diffie-Hellman (DDH) assumption, Quadratic Residues (QR) assumption and Decisional Composite Residuosity (DCR) assumption. In this paper, we present a novel CCBOT protocol with the security against malicious adversaries based on the Computational Diffie-Hellman (CDH) assumption, and analysize the correctness, efficiency and security of the constructed protocol. Besides, we analysize the cheating probability of P 1 in the CCBOT and extend the CCBOT to Single-Choice CCBOT to make the protocol more applicable.

In this paper, a new implementation of universally composable, 1-out-of-2 oblivious transfer in the presence of static adversaries is presented and analyzed. Our scheme is constructed from the state-of-the-art Bresson-Catalano-Pointcheval’s double trap-door public-key encryption scheme, where a trapdoor string comprises a master key and local keys. The idea behind our implementation is that the master key is used to extract input messages of a corrupted sender (as a result, a simulator designated for the corrupted sender is constructed) while the local keys are used to extract input messages of a corrupted receiver (as a result, a simulator designated for the corrupted receiver is defined). We show that the proposed oblivious transfer protocol realizes universally composable security in the presence of static adversaries in the common reference model assuming that the decisional Diffie-Hellman problem over a squared composite modulus of the form N =pq is hard.KeywordsOblivious transfersimulatoruniversally composable