曝光通知：诊断服务器实施通知说明：Miseenœuvred.zip

[La version française suit.](#serveur-de-diagnostic-covid-shield) # COVID Alert Diagnosis Server > **COVID Alert is now retired**: For more information, visit the [Government of Canada COVID Alert home page](https://www.canada.ca/en/public-health/services/diseases/coronavirus-disease-covid-19/covid-alert.html). Adapted from <https://github.com/CovidShield/server> This repository implements a diagnosis server to use as a server for Apple/Google's [Exposure Notification](https://covid19.apple.com/contacttracing) framework, informed by the [guidance provided by Canada's Privacy Commissioners](https://priv.gc.ca/en/opc-news/speeches/2020/s-d_20200507/). The choices made in implementation are meant to maximize privacy, security, and performance. No personally-identifiable information is ever stored, and nothing other than IP address is available to the server. No data at all is retained past 21 days. This server is designed to handle use by up to 38 million Canadians, though it can be scaled to any population size. In this document: - [Overview](#overview) - [Retrieving diagnosis keys](#retrieving-diagnosis-keys) - [Retrieving Exposure Configuration](#retrieving-exposure-configuration) - [Submitting diagnosis keys](#submitting-diagnosis-keys) - [Data usage](#data-usage) - [Generating one-time codes](#generating-one-time-codes) - [Protocol documentation](#protocol-documentation) - [Deployment notes](#deployment-notes) - [Metrics and Tracing](#metrics-and-tracing) - [Contributing](#contributing) - [Who Built COVID Alert?](#who-built-covid-alert) ## Overview _[Apple/Google's Exposure Notification](https://covid19.apple.com/contacttracing) specifications provide important information to contextualize the rest of this document._ There are two fundamental operations conceptually: * **Retrieving diagnosis keys**: retrieving a list of all keys uploaded by other users; and * **Submitting diagnosis keys**: sharing keys returned from the EN framework with the server. These two operations are implemented as two separate servers (`key-submission` and `key-retrieval`) generated from this codebase, and can be deployed independently as long as they share a database. It is also possible to deploy any number of configurations for each of these components, connected to the same database, though there would be little value in deploying multiple configurations of `key-retrieval`. For a more technical overview of the codebase, especially of the protocol and database schema, see [this video](https://www.youtube.com/watch?v=5GNJo1hEj5I). ### Retrieving diagnosis keys When diagnosis keys are uploaded, the `key-submission` server stores the data defined and required by the Exposure Notification API in addition to the time at which the data was received by the server. This submission timestamp is rounded to the nearest hour for privacy preservation (to prevent correlation of multiple keys to the same user). The hour of submission is used to group keys into buckets, in order to prevent clients ([COVID Alert mobile app](https://github.com/cds-snc/covid-alert-app)) from having to download a given set of key data multiple times in order to repeatedly check for exposure. The published diagnosis keys are fetched—with some best-effort authentication—from a Content Distribution Network (CDN), backed by `key-retrieval`. This allows a functionally-arbitrary number of concurrent users. ### Retrieving _Exposure Configuration_ [_Exposure Configuration_](https://developer.apple.com/documentation/exposurenotification/enexposureconfiguration), used to determine the risk of a given exposure, is also retrieved from the `key-retrieval` server. A JSON document describing the current exposure configuration for a given region is available at the path `/exposure-configuration/<region>.json`, e.g. for Ontario (region `ON`): ```sh $ curl https://retrieval.covidshield.app/exposure-configuration/ON.json {"minimumRiskScore":0,"attenuationLevelValues":[1,2,3,4,5,6,7,8],"attenuationWeight":50,"daysSinceLastExposureLevelValues":[1,2,3,4,5,6,7,8],"daysSinceLastExposureWeight":50,"durationLevelValues":[1,2,3,4,5,6,7,8],"durationWeight":50,"transmissionRiskLevelValues":[1,2,3,4,5,6,7,8],"transmissionRiskWeight":50} ``` ### Submitting diagnosis keys In brief, upon receiving a positive diagnosis, a health care professional will generate a _One Time Code_ through a web application frontend ([COVID Alert Portal](https://github.com/cds-snc/covid-alert-portal)), which communicates with `key-submission`. This code is sent to the patient, who enters the code into their [COVID Alert mobile app](https://github.com/cds-snc/covid-alert-app). This code is used to authenticate the Application (once) to the diagnosis server. Encryption keypairs are exchanged by the Application and the `key-submission` server to be stored for fourteen days, and the One Time Code is immediately purged from the database. These keypairs are used to encrypt and authorize _Diagnosis Key_ uploads for the next fourteen days, after which they are purged from the database. The encryption scheme employed for key upload is _NaCl Box_ (a public-key encryption scheme using Curve25519, XSalsa20, and Poly1305). This is widely regarded as an exceedingly secure implementation of Elliptic-Curve cryptography. ## Data usage The _Diagnosis Key_ retrieval protocol used in _COVID Alert_ was designed to restrict the data transfer to a minimum. With large numbers of keys and assuming the client fetches using compression, there is minimal protocol overhead on top of the key data size of 16 bytes. In all examples below: * Each case may generate up to 28 keys. * Keys are valid and distributed for 14 days. * Each key entails just under 18 bytes of data transfer when using compression. * Key metadata and protocol overhead should in reality be minimal, but: * Assume 50% higher numbers than you see below to be on the safe side. This README will be updated soon with more accurate real-world data sizes. **Data below is current at May 12, 2020**. For each case, we assume the example daily new cases is a steady daily recurrence. ### Deployed only to province of Ontario There were 350 new cases in Ontario on May 10, 2020. 350 * 28 * 18 = 170kB per day, thus, deploying to the province of Ontario at current infection rates would cause **7.1kB of download each hour**. ### Deployed to Canada There were 1100 new cases in Canada on May 10, 2020. 1100 * 28 * 18 = 540kB per day, thus, deploying to Canada at current infection rates would cause **23kB of download each hour**. ### Deployed to entire United States of America There were 18,000 new cases in America on May 10, 2020. 18,000 * 28 * 18 = 8.9MB per day, thus, deploying to the all of America at current infection rates would cause: **370kB of download each hour**. ### Deployed to entire world If _COVID Alert_ were deployed for the entire world, we would be inclined to use the "regions" built into the protocol to implement key namespacing, in order to not serve up the entire set of global diagnosis keys to each and every person in the world, but let's work through the number in the case that we wouldn't: There were 74,000 new cases globally on May 10, 2020. 74,000 * 28 * 16 = 36MB per day, thus, deploying to the entire world at current infection rates would cause: **1.5MB of download each hour**. ## Generating one-time codes We use a one-time code generation scheme that allows authenticated case workers to issue codes, which are to be passed to patients with positive diagnoses via whatever communication channel is convenient. This depends on a separate service, holding credentials to talk to this (`key-submission`) server. We have a sample implementation we will open source soon, but we anticipate that health authorities will prefer to integrate this feature into their existing systems. The integration is extremely straightforward, and we have [minimal examples in several languages