Demystifying COVID-19 Digital Contact Tracing: A Survey on Frameworks and Mobile Apps

Table 1

Data storage in PEPP-PT subsystems.

Subsystem	Data
Smartphone	Set of current and future ephemeral BLE IDs (EBIDs) to broadcast
	Proximity history of the last 21 days (containing the observed EBIDs and timestamps)
	OAuth2 [122] client secret for access to backend services (long term)
	OAuth2 access token for access to backend services (short lived)
Backend	Persistent user ID (PUID)
	OAuth2 client credentials of an app
	OAuth2 temporary client access token (short term, 1 h)
	Medium term (days to weeks): backend keys (), EBIDs, observed EBID lists
	Push notification service ID (PID)
Not stored	Transaction Authentication Number (TAN): one-time password for uploading the observed EBID list to the backend