BlueTrace
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BlueTrace is an
open-source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized sof ...
application protocol An application layer is an abstraction layer that specifies the shared communications protocols and interface methods used by hosts in a communications network. An ''application layer'' abstraction is specified in both the Internet Protocol Su ...
that facilitates digital
contact tracing In public health, contact tracing is the process of identifying persons who may have been exposed to an infected person ("contacts") and subsequent collection of further data to assess transmission. By tracing the contacts of infected individua ...
of users to stem the spread of 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 ...
. Initially developed by the
Singaporean Government The Government of Singapore is defined by the Constitution of Singapore to mean the executive branch of the state, which is made up of the president and the Cabinet. Although the president acts in their personal discretion in the exercise o ...
, BlueTrace powers the
contact tracing In public health, contact tracing is the process of identifying persons who may have been exposed to an infected person ("contacts") and subsequent collection of further data to assess transmission. By tracing the contacts of infected individua ...
for the
TraceTogether TraceTogether is a digital system implemented by the Government of Singapore to facilitate contact tracing efforts in response to the COVID-19 pandemic in Singapore. The main goal is quick identification of persons who may have come into close co ...
app.
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
and the
United Arab Emirates The United Arab Emirates (UAE; ar, اَلْإِمَارَات الْعَرَبِيَة الْمُتَحِدَة ), or simply the Emirates ( ar, الِْإمَارَات ), is a country in Western Asia (The Middle East). It is located at th ...
have already adopted the protocol in their gov apps, and other countries were considering BlueTrace for adoption. A principle of the protocol is the preservation of privacy and health authority co-operation.


Overview

Preservation of user privacy was one of the core considerations around which BlueTrace was designed. To achieve this, personal information is collected only once at the point of registration and is only used to contact potentially infected patients. Additionally, users can opt-out at any time, clearing all personal information and rendering any recorded data untraceable. Contact tracing is done entirely locally on a client device using
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 ...
, storing all encounters in a contact history log chronicling encounters for the past 21 days. Users in the contact log are identified using anonymous time-shifting "temporary IDs" issued by the health authority. This means a user's identity cannot be ascertained by anyone except the health authority with which they are registered. Additionally, since temporary IDs change on a regular basis, malicious third parties cannot track users by observing log entries over time. Once a user tests positive for infection, the health authority requests the contact log. If the user chooses to share their log, it is sent to the health authority where they match the temporary ID with contact information. Health authorities are not able to access log entries about foreign users, so those entries are sent to the appropriate foreign health authority to be processed there. Once a log has been processed, the health authority contacts the user identified by the record.


Technical specification

The protocol is focused on two areas: locally logging registered users in the vicinity of a device and the transmission of the log to the operating health authority, all while preserving privacy. To achieve this, the protocol can be divided into the areas of ''device to device communication'' (DDC), and ''device to reporting server communication'' (DRSC). The DDC component operates on top of the existing
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 ...
protocol, defining how two devices acknowledge each other's presence. The DRSC component 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 communicate a timeline of visits to a centralized server owned by a health authority once a user has tested positive for an infection. The health authority can then, using the log, notify the users who came in contact with the infected patient.


Device to reporting server communication protocol

Each app implementing the BlueTrace protocol has a corresponding central reporting server operated by a health authority. The reporting server is responsible for handling initial registration, provisioning unique user identifiers, and collecting contact logs created by the DDC part of the protocol. When the user first launches a BlueTrace app, they will be asked for their internationally formatted
phone number A telephone number is a sequence of digits assigned to a landline telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices f ...
and are assigned a static UserID. This phone number is later used if the user has registered an encounter in an infected patient's contact log. Once registered, users are provisioned Temporary IDs (TempID) uniquely identifying them to other devices. Each TempID has a lifetime of 15 minutes to prevent malicious parties from performing
replay attack A replay attack (also known as a repeat attack or playback attack) is a form of network attack in which valid data transmission is maliciously or fraudulently repeated or delayed. This is carried out either by the originator or by an adversary wh ...
s or tracking users over time with static unique identifiers. TempIDs are generated from a user's UserID, the TempID start time, and the TempID expiry time, which is encrypted and turned into a
Base64 In computer programming, Base64 is a group of binary-to-text encoding schemes that represent binary data (more specifically, a sequence of 8-bit bytes) in sequences of 24 bits that can be represented by four 6-bit Base64 digits. Common to all bina ...
encoded string by the server using a secret
symmetric encryption Symmetric-key algorithms are algorithms for cryptography that use the same cryptographic keys for both the encryption of plaintext and the decryption of ciphertext. The keys may be identical, or there may be a simple transformation to go between th ...
key. To ensure devices have a constant supply of TempIDs, even in an unstable network environment, TempIDs are transmitted to devices in forward dated batches. The composition of a TempID is shown below: Once a user has been tested positive for infection, the health authority generates a
PIN A pin is a device used for fastening objects or material together. Pin or PIN may also refer to: Computers and technology * Personal identification number (PIN), to access a secured system ** PIN pad, a PIN entry device * PIN, a former Dutch de ...
authenticating the user to upload their contact log to the reporting server. As part of the log, metadata about each encounter is included; the most important of which being the timestamp and health authority identifier (HAI). The HAI identifies to which health authority the logged contact reports. If the HAI represents a foreign health authority the log entry is transmitted to the identified authority to be processed there. Once a health authority has filtered log entries to only include home clients, they decrypt the TempID to reveal the UserID, start time, and expiry time. The start and expiry date are compared with the encounter timestamp to ensure validity, and the UserID is matched to a phone number. The health authority can then contact the phone number to inform a user of potential contact with an infected patient.


Device to device communication protocol

The DDC part of the protocol defines how two devices communicate and log their contact. Each device is in one of two states, Central or Peripheral, on a duty cycle of around 1:4, respectively. In Peripheral mode, a device advertises its presence, and in Central mode, it scans for advertising devices. Additionally, certain devices are incapable of operating in Central mode and thus operate purely in Peripheral mode. Once two devices have discovered each other, they communicate a characteristic packet containing information about themselves. The packet is formed as a
JSON JSON (JavaScript Object Notation, pronounced ; also ) is an open standard file format and data interchange format that uses human-readable text to store and transmit data objects consisting of attribute–value pairs and arrays (or other ser ...
file, containing the device's TempID, device model, HAI, and BlueTrace protocol version. When operating in Central mode, the device additionally sends the strength of the signal, allowing the approximate distance between the two devices to be calculated later. Below is an example Central characteristic packet: These characteristics are then added to a local database on the device where they are stored for 21 days and can be sent to the reporting server later. The contacted device is also added to a local blacklist for two duty cycles in order to stop two devices repeatedly contacting each other, saving power and storage.


Health authority cooperation

The cooperation between separate health authorities is a core component of the BlueTrace protocol, and it is designed such that multiple authorities can work together without revealing personal information to foreign authorities with which a user is not registered. Since each authority maintains its separate encryption key and user records, a health authority can't decrypt and see a foreign user's data. To ensure log entries are sent to the correct authority, part of the DDC handshake contains a health authority identifier (HAI), a unique
string String or strings may refer to: *String (structure), a long flexible structure made from threads twisted together, which is used to tie, bind, or hang other objects Arts, entertainment, and media Films * ''Strings'' (1991 film), a Canadian anim ...
assigned to registered health authorities. Once a foreign health authority's log entry is identified, the receiving health authority transmits the log entry to the foreign authority's reporting server where it is verified, and a static PseudoID is returned. The PseudoID is a salted
cryptographic hash A cryptographic hash function (CHF) is a hash algorithm (a map of an arbitrary binary string to a binary string with fixed size of n bits) that has special properties desirable for cryptography: * the probability of a particular n-bit output re ...
of the UserID, designed to allow foreign health authorities to perform statistical analysis on contact logs and communicate about a specific user without revealing unnecessary personal information. Once the PseudoID is assessed to have been in close contact with the infected patient, the foreign health authority that issued the PseudoID is informed and can follow up as necessary.


Withdrawal of consent

The ability of users to withdraw consent to the use and collection of their data at any time was an important consideration in the design of the protocol. To allow this, personally identifiable information is excluded from the DDC component of the protocol. This means the only place personal information is stored is on the reporting server, where it is associated with an anonymous static UserID. This UserID (encrypted in a TempID) is what is used for identification in the DDC part of the protocol. If a user withdraws consent, the user record is deleted from the reporting server, meaning UserIDs obtained through contact logs can no longer be matched to a phone number.


Controversy

One of the largest privacy concerns raised about protocols such as BlueTrace or PEPP-PT is the usage of centralised report processing. In a centralised report processing protocol, a user must upload their entire contact log to a health authority administered server, where the health authority is then responsible for matching the log entries to contact details, ascertaining potential contact, and ultimately warning users of potential contact. Alternatively, decentralised report processing protocols, while still having a central reporting server, delegate the responsibility to process logs to clients on the network. Protocols using this approach, such as
TCN TCN is the flagship (television), flagship television station of the Nine Network in Australia. The station is currently located at 1 Denison Street, North Sydney, New South Wales, North Sydney. The licence, issued to a company named Television C ...
and DP-3T, have the client upload a number from which encounter tokens can be derived by individual devices. Clients then check these tokens against their local contact logs to determine if they have come in contact with an infected patient. Inherent in the fact the protocol never allows the government access to contact logs, this approach has major privacy benefits. However, this method also presents some issues, primarily the lack of human in the loop reporting, leading to a higher occurrence of false positives; and potential scale issues, as some devices might become overwhelmed with a large number of reports. Decentralised reporting protocols are also less mature than their centralised counterparts.


OpenTrace

OpenTrace is the open-source reference implementation of BlueTrace released under the GPL-3.0 license. The DRSC side of the protocol is implemented using the
Firebase Firebase is a set of hosting services for any type of application (Android, iOS, Javascript, Node.js, Java, Unity, PHP, C++ ...). It offers NoSQL and real-time hosting of databases, content, social authentication (Google, Facebook, Twitter an ...
platform, using Firebase functions, a
serverless computing Serverless computing is a cloud computing execution model in which the cloud provider allocates machine resources on demand, taking care of the servers on behalf of their customers. "Serverless" is a misnomer in the sense that servers are still ...
framework, for all client calls; and Firebase Secret Manager and Storage for storing the encryption key and contact logs respectively. For the app/DDC side of the protocol, a modified version of the TraceTogether app for Android and iOS devices is included.


COVIDSafe

COVIDSafe is a
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 ...
app announced by the Federal Australian Government based on OpenTrace/BlueTrace, announced on 14 April 2020 to help combat the ongoing
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 ...
. On 26 April 2020, the
Australian federal government The Australian Government, also known as the Commonwealth Government, is the national government of Australia, a federal parliamentary constitutional monarchy. Like other Westminster-style systems of government, the Australian Government i ...
publicly released the first version of the app. Within the first 24 hours after release, over 1 million people downloaded the app, and within 48 hours, over 2 million. By the second week, over 4 million users had registered. Accompanying the release,
Peter Dutton Peter Craig Dutton (born 18 November 1970) is an Australian politician who has been leader of the opposition and leader of the Liberal Party since May 2022. He has represented the Queensland seat of Dickson in the House of Representatives sinc ...
, the
Minister for Home Affairs An interior minister (sometimes called a minister of internal affairs or minister of home affairs) is a cabinet official position that is responsible for internal affairs, such as public security, civil registration and identification, emergency ...
, announced new legislation that would make it illegal to force anyone to hand over data from the app, even if they had registered and tested positive. The app source code was also released on 8 May 2020, after delays until a review by the
Australian Signals Directorate Australian Signals Directorate (ASD), formerly the Defence Signals Directorate (DSD) is the federal statutory agency in the Australian Government responsible for foreign signals intelligence, support to military operations, cyber warfare, and ...
had been completed.


See also

*
TraceTogether TraceTogether is a digital system implemented by the Government of Singapore to facilitate contact tracing efforts in response to the COVID-19 pandemic in Singapore. The main goal is quick identification of persons who may have come into close co ...
*
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) Exposure Notification (GAEN)


References


External links


White paper

OpenTrace GitHub

BlueTrace homepage
{{FOSS Government software Application layer protocols Computer-related introductions in 2020 Software associated with the COVID-19 pandemic 2020 software Software using the GPL license Android (operating system) software IOS software Bluetooth software Medical software Digital contact tracing protocols Digital contact tracing protocols with centralized reporting