![]() Note that there exist other assumptions that make two-party cryptography possible, e.g. that the two parties are given access to guaranteed additional resources, or that they must delegate agents who cannot communicate during the protocol (which might be motivated by special relativity). First implementations of bit commitment and oblivious transfer in the noisy-storage model have been demonstrated. Significantly, security can always be achieved as long as the number of qubits n sent in the protocol is only slightly larger than the number of qubits r that the adversary can store, that is, whenever, which is essentially optimal. The noisy-storage model admits protocols that require no quantum storage for the honest execution and that can be implemented in a manner similar to QKD using BB84, six-state or continuous variable encodings. In contrast, storing quantum information reliably is an extremely difficult problem, motivating the so-called bounded-quantum storage or more generally noisy-storage model. Unfortunately, the fact that (i) classical storage is cheap and plentiful and (ii) the gap between what the honest parties need to implement the protocol and what a dishonest party needs to break it is only polynomial, renders this model less practical. ![]() Introducing such storage restrictions was pioneered by Maurer, who considered imposing a restriction on the adversary's ability to store classical bits known as the bounded-storage model. Instead of relying on computational assumptions, however, it is possible to make physically motivated assumptions, for example that the adversary's ability to store information is limited. Usually one relies on computational assumptions, i.e. that solving a computational puzzle requires a large amount of computing resources, namely more than is available to the adversary. It turns out that even using quantum communication Alice and Bob cannot achieve security without making additional assumptions. Instead, every party has to fend for himself. It is intuitive that security for two-party cryptographic protocols is more difficult to achieve than for QKD, since Alice and Bob cannot help each other to check on the eavesdropper. Bit commitment and oblivious transfer constitute other well-known examples of such tasks. Here, Alice wants to identify herself to Bob without revealing her password. Yet, there are many other tasks that Alice and Bob may wish to solve, in which they themselves do not trust each other and secure identification is one such example. ![]() Quantum key distribution (QKD) allows two honest parties, Alice and Bob, to protect their communication from a nosy eavesdropper. In particular, we show that security is possible for arbitrarily small violation. The key ingredient of the proof, which might be of independent interest, is an explicit (and tight) relation between the violation of the Clauser–Horne–Shimony–Holt inequality observed by Alice and Bob and uncertainty generated by Alice against Bob who is forced to measure his system before finding out Alice's setting (guessing with postmeasurement information). We fully analyse the case of memoryless devices (for which sequential attacks are optimal) and the case of sequential attacks for arbitrary devices. DI two-party cryptography is made challenging by the fact that Alice and Bob do not trust each other, which requires new techniques to establish security. Specifically, we present a relatively easy to implement protocol for a cryptographic building block known as weak string erasure and prove its security even if the devices used in the protocol are prepared by the dishonest party. Here, we initiate the study of device-independent (DI) protocols for two-party cryptography in the noisy-storage model. Quantum communication enables security for all of these problems in the noisy-storage model by sending more signals than the adversary can store in a certain time frame. Examples of such tasks are private access to a database, and secure identification. The goal of two-party cryptography is to enable two parties, Alice and Bob, to solve common tasks without the need for mutual trust.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |