The no-go theorem regarding unconditionally secure Quantum Bit Commitment protocols is a relevant result in quantum cryptography. Such result has been used to prove the impossibility of unconditional security for other protocols such as Quantum Oblivious Transfer or One-Sided Two Party Computation. In this paper, we formally define two non-deterministic versions of Quantum Private Queries, a protocol addressing the Symmetric-Private Information Retrieval problem. We show that the strongest variant of such scheme is formally equivalent to Quantum Bit Commitment, Quantum Oblivious Transfer and One-Sided Two-Party Computation protocols. This equivalence serves as conclusive evidence of the impracticality of achieving unconditionally secure Strong Probabilistic Quantum Private Queries.
The no-go theorem regarding unconditionally secure Quantum Bit Commitment protocols is a relevant result in quantum cryptography. Such result has been used to prove the impossibility of unconditional security for other protocols such as Quantum Oblivious Transfer or One-Sided Two Party Computation. In this paper, we formally define two non-deterministic versions of Quantum Private Queries, a protocol addressing the Symmetric-Private Information Retrieval problem. We show that the strongest variant of such scheme is formally equivalent to Quantum Bit Commitment, Quantum Oblivious Transfer and One-Sided Two-Party Computation protocols. This equivalence serves as conclusive evidence of the impracticality of achieving unconditionally secure Strong Probabilistic Quantum Private Queries.
We present an unconditionally secure Oblivious Transfer protocol relying on two rounds of entanglement-free quantum communication. When played honestly, the protocol only requires the ability to measure a single qubit in a fixed basis, and to perform a coherent bit-flip (Pauli X) operation. We present a generalization to a "Private Data Sampling" protocol, where a player (Bob) can obtain a random sample of fixed size from a classical database of size N, while the database owner (Alice) remains oblivious as to which bits were accessed. The protocol is efficient in the sense that the communication complexity per query scales at most linearly with the size of the database. It does not violate Lo's "no-go" theorem for one-sided two-party secure computation, since a given joint input by Alice and Bob can result in randomly different protocol outcomes. Finally it could be used to implement a practical bit string commitment protocol, among other applications.
Based on quantum uncertainty and quantum entanglement, an quantum allor-nothing oblivious transfer protocol is proposed. It is illustrated in detail that the protocol is unconditionally secure. The distinct merit of the present protocol lies in that it is not based on quantum bit commitment. The full utilization of the entanglement makes the protocol different from previous insecure ones, thus its security is not restricted by the no-go theorem of twoparty secure computations. Typeset using REVTEX 1 The research on the oblivious transfer (OT) problem may be traced back to more than twenty years ago [1,2]. Kilian [3] pointed out later that OT is very important in two-party and multi-party protocols. This is because in most symmetrical protocols, the participants always know each others ’ data. If some participants are dishonest or try to get extra information, the protocols become insecure. OT can create some secret between the participants and break this symmetry. Thus it can be used to implement multi-party protocols such as
Symmetric private information retrieval is a cryptographic task allowing a user to query a database and obtain exactly one entry without revealing to the owner of the database which element was accessed. The task is a variant of general two-party protocols called and is closely related to oblivious transfer. Under the name , quantum protocols have been proposed to solve this problem in a cheat-sensitive way: In such protocols, it is not impossible for dishonest participants to cheat, but they risk detection [Giovannetti , ]. We give an explicit attack against any cheat-sensitive symmetric private information retrieval protocol, showing that any protocol that is secure for the user cannot have nontrivial security guarantees for the owner of the database: The user is even able to retrieve the database.
Bit commitment involves the submission of evidence from one party to another so that the evidence can be used to confirm a later revealed bit value by the first party, while the second party cannot determine the bit value from the evidence alone. It is widely believed that unconditionally secure quantum bit commitment is impossible due to quantum entanglement cheating, which is codified in a general impossibility theorem. In this paper, the scope of this general impossibility proof is analyzed, and gaps are found. Two variants of a bit commitment scheme utilizing anonymous quantum states and decoy states are presented. In the first variant, the exact verifying measurement is independent of the committed bit value, thus the second party can make it before the first party opens, making possible an unconditional security proof based on no-cloning. In the second variant, the impossibility proof fails because quantum entanglement purification of a mixed state does not render the protocol determinate. Whether impossibility holds in this or similar protocols is an open question, although preliminary results already show that the impossibility proof cannot work as it stands.
Oblivious transfer (OT) and bit commitment (BC) are two-party cryptographic protocols which play crucial roles in the construction of various cryptographic protocols. We propose three practical quantum cryptographic protocols in this paper. We first construct a practical quantum random oblivious transfer (R-OT) protocol based on the fact that non-orthogonal states cannot be reliably distinguished. Then, we construct a fault-tolerant one-out-of-two oblivious transfer ( O T 1 2 ) protocol based on the quantum R-OT protocol. Afterwards, we propose a quantum bit commitment (QBC) protocol which executes the fault-tolerant O T 1 2 several times. Mayers, Lo and Chau (MLC) no-go theorem proves that QBC protocol cannot be unconditionally secure. However, we find that computing the unitary transformation of no-go theorem attack needs so many resources that it is not realistically implementable. We give a definition of physical security for QBC protocols and prove that the practical QBC we proposed is physically secure and can be implemented in the real world.
In this thesis, we are interested in the theory of unconditional secure two-party computations of which Oblivious Transfer (OT) and Bit Commitment (BC) are the central primitives. On one hand, my works are inspired from Crépeau's et al.'s framework of building of OT protocol from noisy communication channels. The principle of this framework is to conceive, from noisy channels, an intermediate erasure model which is a variant of OT. We contributed to this framework by proposing a more general intermediate model, the Binary Symmetric Multi-Error-Rate Channel, which also can be built from noisy channels. With this intermediate model, we can build OT protocol from the noisy channels more effectively. In addition, we expose some case studies on emulating noisy models by a quantum nonorthogonal coding (QNOC) scheme which uses two non-orthogonal pure states for encoding two values of the classical bit. On the other hand, we revise the quantum model for general two-party protocols concerning classical and quantum computations and communications. We state that in the general model, a classical channel is inevitably macroscopic and its decoherence is so strong that quantum information is not accepted to be transfered on it. Thus, the quantum model for two-party protocols becomes three-party, including an environment of the channel. Indeed, with the faithful interpretation of general quantum two-party protocols in this three-party model, we reaffirm the no-go theorems of Mayers and Lo & Chau on the impossibilities of quantum OT, BC. In addion, we can go further to apply these negative results to protocols using some quantum trusted oracles, such as Coin-Flipping.