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. The only difference is that privacy is safeguarded against a polynomially bounded sender. 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. PIR implementations Numerous Computational PIR and Information theoretic PIR schemes in the literature have been implemented. Here is an incomplete list: MuchPIR 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++ includes implementations of [AG 2007, DGH 2012, CGKS 1998, Goldberg 2007, HOG 2011, LG 2015]. RAID-PIR 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]. Notes See also k-anonymity Locally decodable code References A. Beimel, Y. Ishai, E. Kushilevitz, and J.-F. Raymond. Breaking the barrier for information-theoretic private information retrieval. Proceedings of the 43rd Annual IEEE Symposium on Foundations of Computer Science, Vancouver, Canada, pages 261–270, 2002. A. Beimel and Y. Stahl, Robust information-theoretic private information retrieval, in Proceedings of the 3rd International Conference on Security in Communication Networks (SCN'02), pp. 326–341, 2003. Cite is from DGH 2012, op. cit. [DGH 2012] Casey Devet, Ian Goldberg, and Nadia Heninger, Optimally Robust Private Information Retrieval, 21st USENIX Security Symposium, August 2012. [AG 2007] C. Aguilar-Melchor and P. Gaborit. A lattice-based computationally-efficient private information retrieval protocol, Western European Workshop on Research in Cryptology (WEWoRC), 2007. [CGKS 1998] B. Chor, O. Goldreich, E. Kushilevitz, and M. Sudan, Private information retrieval, Journal of the ACM, 45(6):965–981, 1998. [Goldberg 2007] I.