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architecture.md

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Architecture

graph LR;
  subgraph k8s[Kubernetes managed by DigitalOcean]
    subgraph cloudflare[Cloudflare]
      pwa[Progressive Web App] -- /api/ --> grpc_gateway;
    end
    grpc_gateway --> server;
    server --> ip_geolocation[MaxMind IP Geolocation];
    server --> postgres[Postgres];
    server --> redis[Redis];
    mailer -- stream --> redis;
    janitor[TTL CronJob] --> postgres;
    archiver --> postgres;
    restorer[/restorer/] -.-> postgres;
  end
  style k8s fill:#deffff,stroke:#33aaaa;
  archiver --> gcs[Google Cloud Storage];
  restorer -.-> gcs;
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Authentication

The graph below demonstrates the remote authentication procedure.

graph TD;
  start["{ username, password }"] -- /get-salt/username --> parametrization;
  start --> hashing["hash = argon2(parametrization, password, 32 + 32)"];
  parametrization --> hashing;
  hashing --> authn_digest["authn_digest = hash[:32]"];
  hashing --> encryption_key["encryption_key = hash[32:]"];
  authn_digest -- "/log-in { username, authn_digest }" --> authn_check[("sha256(authn_digest) == User.hash")];
  authn_check -- ok --> user_data["{ encrypted_vault, session_token }"];
  user_data --> decrypted_vault;
  encryption_key -- XSalsa20-Poly1305 --> decrypted_vault;
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  • Argon2 parameters are generated on the client in argon2.ts during registration.
  • The recommended parameters can be changed if necessary — that will cause automated rehashes next time users log in.
  • All types of session tokens are 128-bit long.

If 2FA is enabled, /log-in does not immediately return the encrypted vault; it should be followed by /provide-otp, which accepts both time-based and 128-bit recovery codes and only then returns the encrypted vault.

Offline mode

Offline mode is based on localStorage. Once it's activated, separate Argon2 parameters are generated; username, local authn_digest and the vault encrypted by the local encryption_key are stored in localStorage ('the depot'). Note that authn_digest is not put through sha256 here.

graph LR;
  is_offline["Is the depot empty?"] -- yes --> remote_authn["Remote authentication"];
  is_offline -- no --> local_authn["Local authentication"];
  local_authn -. background .-> remote_authn;
  remote_authn --> display_vault["Display the vault"];
  local_authn --> display_vault;
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Once local (depot-based) authentication succeeds, the remote authentication procedure is attempted automatically in the background to pick up latest updates and enable editing. If 2FA is enabled, a 128-bit temporary token is provided to /provide-otp. This token is initially obtained by specifying yield_trusted_token in ProvideOtpRequest; it's then encrypted with the local encryption_key and stored in the depot. All subsequent background requests to /provide-otp renew the token by specifying yield_trusted_token again.

Changing the master key

  • Generates new Argon2 parameters (both remotely and locally).
  • Re-encrypts the vault (both remotely and locally).
  • Additionally disables all other sessions.

Encryption-at-rest

From 'Storage on DigitalOcean':

'...are encrypted at rest with AES-256 bit LUKS encryption within the storage cluster.'

Managing versions

Client and server binaries contain the information about the earliest version still permitted to run built in.

  • Newer service workers forcefully reload the pages with obsolete versions.
    • In general service workers attempt to load index.html from network if they can within the allowed time window.
    • It's important to remember about the Cloudflare cache, which may need to be invalidated in certain deployment scenarios.
  • Servers reject requests where the app version is obsolete (with UNIMPLEMENTED, 501).