1. US Department of Defense. 2020. Global Positioning System (GPS) Standard Positioning Service (SPS) Performance Standard- 5th Edition. https://www.gps.gov/technical/ps/.
2. US CDC: Contact Tracing for COVID-19. 2021. https://www.cdc.gov/coronavirus/2019-ncov/php/contact-tracing/contact-tracing-plan/contact-tracing.html.
3. B. Johnson. 2020. Nearly 40% of icelanders are using a covid app and it hasn’t helped much. https://www.technologyreview.com/2020/05/11/1001541/iceland-rakning-c19-covid-contact-tracing/.
4. Pan-European privacy-preserving proximity tracing data protection and information security architecture illustrated on German implementation. Retrieved from https://github.com/pepp-pt/pepp-pt-documentation/blob/master/PEPP-PT-high-level-overview.pdf.
5. XPIR : Private Information Retrieval for Everyone