TCN Protocol

Temporary Contact Numbers Protocol

Developed by	TCN Coalition, incl. Covid Watch[1] and CoEpi[2]
Introduced	March 17, 2020 (2020-03-17)[3]
Industry	Exposure Notification
Physical range	~10 m (33 ft)[4]

The Temporary Contact Numbers Protocol, or TCN Protocol, is an open source, decentralized, anonymous exposure alert protocol developed by Covid Watch^[1] in response to the COVID-19 pandemic.^[5][6][7][8] The Covid Watch team, started as an independent research collaboration between Stanford University and the University of Waterloo was the first in the world to publish a white paper,^[9] develop,^[3] and open source^[10] fully anonymous Bluetooth exposure alert technology in collaboration with CoEpi^[2] after writing a blog post^[11] on the topic in early March.

Covid Watch's TCN Protocol received significant news coverage^[12] and was followed by similar decentralized protocols in early April 2020 like DP-3T, PACT,^[13] and Google/Apple Exposure Notification framework. Covid Watch then helped other groups like the TCN Coalition and MIT SafePaths^[14] implement the TCN Protocol within their open source projects to further the development of decentralized technology and foster global interoperability of contact tracing and exposure alerting apps, a key aspect of achieving widespread adoption.^[15] Covid Watch volunteers and nonprofit staff also built a fully open source mobile app for sending anonymous exposure alerts first using the TCN Protocol^[16] and later using the very similar Google/Apple Exposure Notification Framework (ENF).^[17][18]

The protocol, like BlueTrace and the Google / Apple contact tracing project, use Bluetooth Low Energy to track and log encounters with other users.^[19][20][21] The major distinction between TCN and protocols like BlueTrace is the fact the central reporting server never has access to contact logs nor is it responsible for processing and informing clients of contact.^[22][23] Because contact logs are never transmitted to third parties, it has major privacy benefits over approaches like the one used in BlueTrace.^[24][25][26] This approach however, by its very nature, does not allow for human-in-the-loop reporting, potentially leading to false positives if the reports are not verified by public health agencies.^{[19]: p. 6}

The TCN protocol received notoriety as one of the first widely released digital contact tracing protocols^[15][27][28] alongside BlueTrace,^[29] the Exposure Notification framework, and the Pan-European Privacy-Preserving Proximity Tracing (PEPP-PT) project.^[30][31] It also stood out for its incorporation of blockchain technology,^[32] and its influence over the Google/Apple project.^{[33][20][34][35][36]}