Decentralized Privacy-Preserving Proximity Tracing (DP-3T, stylized as dp
3t) is an
open protocol
Open or OPEN may refer to:
Music
* Open (band), Australian pop/rock band
* The Open (band), English indie rock band
* ''Open'' (Blues Image album), 1969
* ''Open'' (Gotthard album), 1999
* ''Open'' (Cowboy Junkies album), 2001
* ''Open'' (YF ...
developed in response to the
COVID-19 pandemic
The COVID-19 pandemic, also known as the coronavirus pandemic, is an ongoing global pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The novel virus was first identif ...
to facilitate
digital contact tracing
Digital contact tracing is a method of contact tracing relying on tracking systems, most often based on mobile devices, to determine contact between an infected patient and a user. It came to public prominence in the form of COVID-19 apps during ...
of infected participants. The protocol, like competing protocol
Pan-European Privacy-Preserving Proximity Tracing
Pan-European Privacy-Preserving Proximity Tracing (PEPP-PT/PEPP) is a full-stack open protocol designed to facilitate digital contact tracing of infected participants. The protocol was developed in the context of the ongoing COVID-19 pandemic. Th ...
(PEPP-PT), uses
Bluetooth Low Energy
Bluetooth Low Energy (Bluetooth LE, colloquially BLE, formerly marketed as Bluetooth Smart) is a wireless personal area network technology designed and marketed by the Bluetooth Special Interest Group (Bluetooth SIG) aimed at novel applications in ...
to track and log encounters with other users.
The protocols differ in their reporting mechanism, with PEPP-PT requiring clients to upload contact logs to a central reporting server, whereas with DP-3T, the central reporting server never has access to contact logs nor is it responsible for processing and informing clients of contact.
Because contact logs are never transmitted to third parties, it has major privacy benefits over the PEPP-PT approach; however, this comes at the cost of requiring more computing power on the client side to process infection reports.
The Apple/Google
Exposure Notification
The (Google/Apple) Exposure Notification (GAEN) system, originally known as the Privacy-Preserving Contact Tracing Project, is a framework and protocol specification developed by Apple Inc. and Google to facilitate digital contact tracing during ...
project is based on similar principles as the DP-3T protocol, and supports a variant of it since May 2020.
Huawei
Huawei Technologies Co., Ltd. ( ; ) is a Chinese multinational technology corporation headquartered in Shenzhen, Guangdong, China. It designs, develops, produces and sells telecommunications equipment, consumer electronics and various smar ...
added a similar implementation of DP-3T to its Huawei Mobile Services APIs known as "Contact Shield" in June 2020.
The DP-3T SDK and calibration apps intend to support the Apple/Google API as soon as it is released to iOS and Android devices.
On the 21 April 2020, the
Swiss
Swiss may refer to:
* the adjectival form of Switzerland
* Swiss people
Places
* Swiss, Missouri
* Swiss, North Carolina
*Swiss, West Virginia
* Swiss, Wisconsin
Other uses
*Swiss-system tournament, in various games and sports
*Swiss Internation ...
Federal Office of Public Health
The Federal Office of Public Health (FOPH) is the Swiss federal government’s centre for public health and a part of the Swiss Federal Department of Home Affairs.
In addition to developing national health policy, it also represents the inte ...
announced that the Swiss national coronavirus contact tracing app will be based on DP-3T. On the 22 April 2020, the
Austrian Red Cross
The Austrian Red Cross (German: ''Österreichisches Rotes Kreuz'', ÖRK) is the national Red Cross Organization in Austria and is part of the International Red Cross and Red Crescent Movement. It was established on March 14, 1880, by Doctor Adam L ...
, leading on the national digital contact tracing app, announced its migration to the approach of DP-3T.
Estonia
Estonia, formally the Republic of Estonia, is a country by the Baltic Sea in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the sea across from Sweden, to the south by Latvia, a ...
also confirmed that their app would be based on DP-3T. On April 28, 2020, it was announced that
Finland
Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...
was piloting a version of DP-3T called "Ketju". In
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, a national app is being built upon DP-3T by
SAP SE
Sap is a fluid transported in xylem cells (vessel elements or tracheids) or phloem sieve tube elements of a plant. These cells transport water and nutrients throughout the plant.
Sap is distinct from latex, resin, or cell sap; it is a sepa ...
and
Deutsche Telekom
Deutsche Telekom AG (; short form often just Telekom, DTAG or DT; stylised as ·T·) is a German telecommunications company that is headquartered in Bonn and is the largest telecommunications provider in Europe by revenue. Deutsche Telekom was ...
alongside
CISPA, one of the organisations that authored the protocol. As of September 30, 2020, contact tracing apps using DP-3T are available in
Austria
Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
,
Belgium
Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to th ...
,
Croatia
, image_flag = Flag of Croatia.svg
, image_coat = Coat of arms of Croatia.svg
, anthem = "Lijepa naša domovino"("Our Beautiful Homeland")
, image_map =
, map_caption =
, capit ...
, Germany,
Ireland
Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
,
Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...
, the
Netherlands
)
, anthem = ( en, "William of Nassau")
, image_map =
, map_caption =
, subdivision_type = Sovereign state
, subdivision_name = Kingdom of the Netherlands
, established_title = Before independence
, established_date = Spanish Netherl ...
,
Portugal
Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of ...
and
Switzerland
). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...
.
Overview
The DP-3T protocol works off the basis of Ephemeral IDs (EphID), semi-random rotating strings that uniquely identify clients. When two clients encounter each other, they exchange EphIDs and store them locally in a contact log. Then, once a user tests positive for infection, a report is sent to a central server. Each client on the network then collects the reports from the server and independently checks their local contact logs for an EphID contained in the report. If a matching EphID is found, then the user has come in close contact with an infected patient, and is warned by the client. Since each device locally verifies contact logs, and thus contact logs are never transmitted to third parties, the central reporting server cannot by itself ascertain the identity or contact log of any client in the network. This is in contrast to competing protocols like PEPP-PT, where the central reporting server receives and processes client contact logs.
Ephemeral ID
![DP-3T Ephemeral ID](https://upload.wikimedia.org/wikipedia/commons/e/e6/DP-3T_Ephemeral_ID.svg)
Similar to the
TCN Protocol
The Temporary Contact Numbers Protocol, or TCN Protocol, is an open source, decentralized, anonymous exposure alert protocol developed by Covid Watch in response to the COVID-19 pandemic. The Covid Watch team, started as an independent research ...
and its Temporary Contact Numbers, the DP-3T protocol makes use of 16 byte ''Ephemeral IDs'' (EphID) to uniquely identify devices in the proximity of a client. These EphIDs are logged locally on a receiving client's device and are never transmitted to third parties.
To generate an EphID, first a client generates a secret key that rotates daily (
) by computing
, where
is a cryptographic hash function such as
SHA-256
SHA-2 (Secure Hash Algorithm 2) is a set of cryptographic hash functions designed by the United States National Security Agency (NSA) and first published in 2001. They are built using the Merkle–Damgård construction, from a one-way compression ...
.
is calculated by a standard secret key algorithm such as
Ed25519
In public-key cryptography, Edwards-curve Digital Signature Algorithm (EdDSA) is a digital signature scheme using a variant of Schnorr signature based on twisted Edwards curves.
It is designed to be faster than existing digital signature schemes ...
. The client will use
during day
to generate a list of EphIDs. At the beginning of the day, a client generates a local list of size
new EphIDs to broadcast throughout the day, where
is the lifetime of an EphID in minutes. To prevent malicious third parties from establishing patterns of movement by tracing static identifiers over a large area, EphIDs are rotated frequently. Given the secret day key
, each device computes
, where
is a global fixed string,
is a pseudo-random function like
HMAC-SHA256
In cryptography, an HMAC (sometimes expanded as either keyed-hash message authentication code or hash-based message authentication code) is a specific type of message authentication code (MAC) involving a cryptographic hash function and a secret ...
, and
is a stream cipher producing
bytes. This stream is then split into 16-byte chunks and randomly sorted to obtain the EphIDs of the day.
Technical specification
The DP-3T protocol is made up of two separate responsibilities, tracking and logging close range encounters with other users (device handshake), and the reporting of those encounters such that other clients can determine if they have been in contact with an infected patient (infection reporting). Like most digital contact tracing protocols, the device handshake uses
Bluetooth Low Energy
Bluetooth Low Energy (Bluetooth LE, colloquially BLE, formerly marketed as Bluetooth Smart) is a wireless personal area network technology designed and marketed by the Bluetooth Special Interest Group (Bluetooth SIG) aimed at novel applications in ...
to find and exchange details with local clients, and the infection reporting stage uses
HTTPS
Hypertext Transfer Protocol Secure (HTTPS) is an extension of the Hypertext Transfer Protocol (HTTP). It is used for secure communication over a computer network, and is widely used on the Internet. In HTTPS, the communication protocol is enc ...
to upload a report to a central reporting server. Additionally, like other
decentralized reporting protocols, the central reporting server never has access to any client's contact logs; rather the report is structured such that clients can individually derive contact from the report.
Device handshake
In order to find and communicate with clients in proximity of a device, the protocol makes use of both the server and client modes of Bluetooth LE, switching between the two frequently. In server mode the device advertises its EphID to be read by clients, with clients scanning for servers. When a client and server meet, the client reads the EphID and subsequently writes its own EphID to the server. The two devices then store the encounter in their respective contact logs in addition to a coarse
timestamp
A timestamp is a sequence of characters or encoded information identifying when a certain event occurred, usually giving date and time of day, sometimes accurate to a small fraction of a second. Timestamps do not have to be based on some absolut ...
and signal strength. The signal strength is later used as part of the infection reporting process to estimate the distance between an infected patient and the user.
Infection reporting
When reporting infection, there exists a central reporting server controlled by the local health authority. Before a user can submit a report, the health authority must first confirm infection and generate a code authorizing the client to upload the report. The health authority additionally instructs the patient on which day their report should begin (denoted as
). The client then uploads the pair
and
to the central reporting server, which other clients in the network download at a later date. By using the same algorithm used to generate the original EphIDs, clients can reproduce every EphID used for the period past and including
, which they then check against their local contact log to determine whether the user has been in close proximity to an infected patient.
In the entire protocol, the health authority never has access to contact logs, and only serve to test patients and authorize report submissions.
Epidemiological analysis
When a user installs a DP-3T app, they are asked if they want to opt in to sharing data with
epidemiologists
Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population.
It is a cornerstone of public health, and shapes policy decisions and evidenc ...
. If the user consents, when they are confirmed to have been within close contact of an infected patient the respective contact log entry containing the encounter is scheduled to be sent to a central statistics server. In order to prevent malicious third parties from discovering potential infections by detecting these uploads, reports are sent at regular intervals, with indistinguishable dummy reports sent when there is no data to transmit.
Health authority cooperation
To facilitate compatibility between DP-3T apps administered by separate health authorities, apps maintain a local list of the regions a user has visited. Regions are large areas directly corresponding to health authority jurisdiction; the exact location is not recorded. The app will later connect these regions to their respective foreign central reporting server, and fetch reports from these servers in addition to its normal home reporting server. Apps will also submit reports to these foreign reporting servers if the user tests positive for infection.
Attacks on DP-3T and criticism
Cryptography and security scholar
Serge Vaudenay
Serge Vaudenay (born 5 April 1968) is a French cryptographer and professor, director of the Communications Systems Section at the École Polytechnique Fédérale de Lausanne
Serge Vaudenay entered the École Normale Supérieure in Paris as a '' ...
, analyzing the security of DP-3T
argued that:
Vaudenay's work presents several attacks against DP-3T and similar systems. In response, the DP-3T group claim that out of twelve risks Vaudenay presents, eight are also present in centralized systems, three do not work, and one, which involves physical access to the phone, works but can be mitigated.
In a subsequent work
Vaudenay reviews attacks against both centralized and decentralized tracing systems and referring to identification attacks of diagnosed people concludes that:
In the same work
Vaudenay advocates that, since neither the centralized nor the decentralized approaches offer sufficient level of privacy protection, different solutions should be explored, in particular suggesting the ConTra Corona, Epione and Pronto-C2 systems as a "third way".
Tang surveys the major
digital contact tracing
Digital contact tracing is a method of contact tracing relying on tracking systems, most often based on mobile devices, to determine contact between an infected patient and a user. It came to public prominence in the form of COVID-19 apps during ...
systems and shows that DP-3T is subject to what he calls "targeted identification attacks".
Theoretical attacks on DP-3T have been simulated showing that persistent tracking of users of the first version of the DP-3T system who have voluntarily uploaded their identifiers can be made easy to any 3rd party who can install a large fleet of
Bluetooth Low Energy
Bluetooth Low Energy (Bluetooth LE, colloquially BLE, formerly marketed as Bluetooth Smart) is a wireless personal area network technology designed and marketed by the Bluetooth Special Interest Group (Bluetooth SIG) aimed at novel applications in ...
devices. This attack leverages the linkability of a user during a day, and therefore is possible on within a day on all users of some centralized systems such as the system proposed in the United Kingdom, but does not function on 'unlinkable' versions of DP-3T where infected users' identifiers are not transmitted using a compact representation such as a key or seed.
See also
*
BlueTrace
BlueTrace is an open-source application protocol that facilitates digital contact tracing of users to stem the spread of the COVID-19 pandemic. Initially developed by the Singaporean Government, BlueTrace powers the contact tracing for the Tra ...
*
TCN Protocol
The Temporary Contact Numbers Protocol, or TCN Protocol, is an open source, decentralized, anonymous exposure alert protocol developed by Covid Watch in response to the COVID-19 pandemic. The Covid Watch team, started as an independent research ...
*
Pan-European Privacy-Preserving Proximity Tracing
Pan-European Privacy-Preserving Proximity Tracing (PEPP-PT/PEPP) is a full-stack open protocol designed to facilitate digital contact tracing of infected participants. The protocol was developed in the context of the ongoing COVID-19 pandemic. Th ...
*
Google / Apple contact tracing project
The (Google/Apple) Exposure Notification (GAEN) system, originally known as the Privacy-Preserving Contact Tracing Project, is a framework and protocol specification developed by Apple Inc. and Google to facilitate digital contact tracing during ...
References
External links
DP-3T Github
{{COVID-19 pandemic
Application layer protocols
Computer-related introductions in 2020
Software associated with the COVID-19 pandemic
Software using the MPL license
Software using the Mozilla license
Digital contact tracing protocols
Software using the Apache license
Digital contact tracing protocols with decentralized reporting
*