NDR Pseudonymisation Service

The pseudonymisation_service project is a Rails API-only application from PHE's National Disease Registration team that allows identifiers to be submitted, and pseudonymised versions to be returned.

Usage

The easiest way to use the pseudonymisation service is through a NdrPseudonymise::Client object, provided by the ndr_pseudonymise gem. This provides Ruby access to the three endpoints (described below, in "Endpoints").

Basic Table Structure

Users can use pseudonymisation keys when a key grant has been given, and any usage is then logged.

+------+      +----------+      +---------------------+
| User | ---> | KeyGrant | <--- | PseudonymisationKey |
+------+      +----------+      +---------------------+
     |                            |
     |        +----------+        |
     +------> | UsageLog | <------+
              +----------+

Secrets Management

This project uses Rails' per-environment credentials API. Stored using are:

• pseudonymisation key secret salts
• per-environment identifier-logging encryption keys
• database credentials

For testing, the test environment credentials file and key file have been committed, and can be viewed/updated using:

$ rails credentials:edit --environment test

To edit the credentials on the server (where the application user has read-only acces), you need to do the following (as a deployer, who can write to the filesystem):

$ export PATH="~pseudo_live/.rbenv/bin:~pseudo_live/.rbenv/shims:${PATH}"
$ read -rsp '> ' RAILS_MASTER_KEY
$ export RAILS_MASTER_KEY
$ cd ~pseudo_live/pseudonymisation_service/current
$ RAILS_ENV=production bundle exec rails credentials:edit

To supply the unlock key to an ad-hoc production rake task, you can use the following:

$ RAILS_ENV=production rails credentials:unlock do:some:admin:task

Authentication

Users are authenticated with tokens supplied in the request headers. To set up a user, run:

$ rails users:create

A token can be (re)generated for a user using:

$ rails users:generate_token[the_username]

Users' key grants can be managed using the following tasks:

$ rails users:grants:list[the_username]
$ rails users:grants:add[the_username]
$ rails users:grants:revoke[the_username]

Key Generation

To add new keys, first put salts into the credentials.yml.enc. Note that the application must be restarted to reload the encrypted credentials.

Then, create PseudonymistionKey records from a Rails console:

primary_key   = PseudonymisationKey.create!(name: 'primary_test_key')
secondary_key = PseudonymisationKey.create!(name: 'repseudo_test_key', parent_key: primary_key)

compound_key = PseudonymisationKey.create!(
  key_type: 'compound',
  name: 'compound_test_key',
  start_key: primary_key,
  end_key: secondary_key
)

Grants can then be done using the users:grants:add task.

Endpoints

The service currently offers three endpoints, listed below.

GET /keys

GET requests to /keys will return a JSON-encoded list of pseudonymisation keys availble to the current user.

curl -sH 'Authorization: Bearer user:token' site.dev/api/v1/keys

[
  {
    "name": "test key1",
    "supported_variants": [
      1,
      2
    ]
  },
  {
    "name": "test key3",
    "supported_variants": [
      1,
      2
    ]
  }
]

GET /variants

GET requests to /variants will return a JSON-encoded list of variants available to the current user, along with required identifier fields.

curl -sH 'Authorization: Bearer user:token' site.dev/api/v1/variants

[
  {
    "variant": 1,
    "required_identifiers": [
      "nhs_number"
    ]
  },
  {
    "variant": 2,
    "required_identifiers": [
      "birth_date",
      "postcode"
    ]
  }
]

POST /pseudonymise

POST requests to /pseudonymise will return JSON-encoded pseudonymised identifiers for supplied "identifiers". In addition, "variants" and "key_names" can be supplied, but if they are omitted sensible default choices are made.

curl -sH 'Authorization: Bearer user:token' \
     --header "Content-Type:application/json" \
     --data '{"identifiers":{"nhs_number":"1234567890"},"context":"README demo"}' \
     site.dev/api/v1/pseudonymise

[
  {
    "key_name": "test key1",
    "variant": 1,
    "identifiers": {
      "nhs_number": "1234567890"
    },
    "context": "README demo",
    "pseudoid": "1e03fdf3..."
  },
  {
    "key_name": "test key3",
    "variant": 1,
    "identifiers": {
      "nhs_number": "1234567890"
    },
    "context": "README demo",
    "pseudoid": "8cc142ecb..."
  }
]

Development

After checking out the repo, run bin/setup to install dependencies, set up a database, and start a web server. You'll need to have PostgreSQL installed already.

Tests can be run with bin/rake.

Contributing

1. Fork it ( https://github.com/publichealthengland/pseudonymisation_service/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.