Құпиялы ақпаратты іздеу: Криптографиялық протоколдар

Information retrieval husing cryptography
In cryptography, a private information retrieval (PIR) protocol is a protocol that allows a user to retrieve an item from a server in possession of a database without revealing which item is retrieved. PIR is a weaker version of 1 out of n oblivious transfer, where it is also required that the user should not get information about other database items. One trivial, but very inefficient way to achieve PIR is for the server to send an entire copy of the database to the user. In fact, this is the only possible protocol (in the classical or the quantum setting) that gives the user information theoretic privacy for their query in a single server setting. There are two ways to address this problem: make the server computationally bounded or assume that there are multiple non cooperating servers, each having a copy of the database. The problem was introduced in 1995 by Chor, Goldreich, Kushilevitz and Sudan Since then, very efficient solutions have been discovered. Single database (computationally private) PIR can be achieved with constant (amortized) communication and k database (information theoretic) PIR can be done with communication.

One way functions are necessary, but not known to be sufficient, for nontrivial (i. e., with sublinear communication) single database computationally private information retrieval. In fact, such a protocol was proved by Giovanni Di Crescenzo, Tal Malkin and Rafail Ostrovsky to imply oblivious transfer (see below). Oblivious transfer, also called symmetric PIR, is PIR with the additional restriction that the user may not learn any item other than the one she requested. It is termed symmetric because both the user and the database have a privacy requirement. Collision resistant cryptographic hash functions are implied by any one round computational PIR scheme, as shown by Ishai, Kushilevitz and Ostrovsky.

The basic motivation for Private Information Retrieval is a family of two party protocols in which one of the parties (the sender) owns a database, and the other part (the receiver) wants to query it with certain privacy restrictions and warranties. So, as a result of the protocol, if the receiver wants the i th value in the database he must learn the i th entry, but the sender must learn nothing about i. In a general PIR protocol, a computationally unbounded sender can learn nothing about i so privacy is theoretically preserved. Since the PIR problem was posed, different approaches to its solution have been pursued and some variations were proposed. A CPIR (Computationally Private Information Retrieval) protocol is similar to a PIR protocol: the receiver retrieves an element chosen by him from the sender's database, so that the sender obtains no knowledge about which element was transferred. A CSPIR (Computationally Symmetric Private Information Retrieval) protocol is used in a similar scenario in which a CPIR protocol is used. If the sender owns a database, and the receiver wants to get the i th value in this database, at the end of the execution of a SPIR protocol, the receiver should have learned nothing about values in the database other than the i th one. is a CPIR implementation as a Postgres C/C++ Extension [GitHub, 2021]. SealPIR is a fast CPIR implementation [ACLS 2018]. Popcorn is a PIR implementation tailored for media [GCMSAW 2016]. Percy++ is an implementation of the ITPIR scheme of [DHS 2014]. XPIR is a fast CPIR implementation [ABFK 2014]. upPIR is an ITPIR implementation [Cappos 2013].