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at_client_sdk
The main repository for libraries used to build applications on the
Atsign Platform. Three categories: SDKs, libraries, and Flutter
widgets.
SDKs
- at_client: the platform-neutral Dart SDK,
for command-line apps, headless services, and Internet-of-Things
devices. Owns the whole atSign lifecycle —
Atsign('@alice').open,
.activate and .enroll hand back an AtClient — as well as
collections, sync, notifications and encryption.
- at_client_flutter: the Flutter
layer on top of
at_client, for mobile and desktop apps.
Adds onboarding / authentication dialogs and device-keychain
storage. Flutter web is not a supported target.
Libraries
Dart libraries for building Atsign Platform applications. All are
published on
pub.dev.
- at_auth: the protocol layer under
at_client's lifecycle verbs: CRAM activation, the APKAM
enrollment handshakes, the .atKeys key stores and the registrar
client. Applications reach it through at_client.
- at_chops: cryptographic and hashing
operations (encryption, decryption, signing, hashing) used by the
rest of the SDK, including the post-quantum primitives.
- at_cli_commons: helpers for Dart CLI
/ server programs that use
at_client. Wraps the boilerplate of
parsing flags, loading keys, and producing an authenticated
AtClient.
- at_commons: foundational types used
across every package: keys, metadata, atSign validation,
root-domain parsing, verb builders for the Atsign Protocol wire
format, and the exception hierarchy.
- at_contact: contacts library that
persists across different Atsign Platform applications.
- at_lookup: low-level direct
implementation of the Atsign Protocol verbs. Used by
at_client
and at_client_flutter.
- at_onboarding_cli: the
at_register and at_activate command-line tools for registering,
activating and enrolling atSigns, and a small library for programs
that drive the same flows headlessly.
- at_policy: scaffolding for building
policy-management services that talk to enforcement endpoints
via the Atsign Protocol.
- at_server_status: logs the status
of the root server and the atServer for an atSign of your
choice.
- at_utils: utility library: atSign,
metadata, configuration, logger.
- base2e15: fork of the upstream
base2e15 package, kept here
for null-safety support.
- dart_utf7: fork of the upstream
utf7 package, kept here for
null-safety support.
Flutter packages
Status: Most of the at_*_flutter packages listed below are
in the process of being deprecated. Over the next few months
they'll be replaced by example application code rather than
reusable widget packages. The recommended path for new Flutter
work is to read the example app at
packages/at_client_flutter/examples/todos
and adapt it directly. The packages will continue to publish
until that migration completes.
Post-quantum cryptography
The SDK can protect everything an adversary could record today — data
shared between atSigns, an atSign's own data, and the secrets an
enrollment approval hands a new device — with post-quantum key
establishment, and can authenticate with a post-quantum signature. It is
opt-in per client, through one setting:
final preference = AtClientPreference(posture: PqPosture.pqReady)
..namespace = 'todos';
| Posture |
Authentication |
Data written |
Reads post-quantum data |
PqPosture.legacy (default) |
RSA-2048 |
legacy encryption |
no |
PqPosture.pqReady |
ML-DSA-65; publishes a key package and this atSign's namespace keys |
legacy encryption, so pre-quantum peers read it |
yes |
PqPosture.pqActive |
ML-DSA-65, and an ML-DSA-65 data signing key |
post-quantum by default; legacy writes refused |
yes |
Under the hood, each namespace an atSign owns gets a key-establishment
keypair — the X-Wing hybrid (ML-KEM-768 + X25519) by default, pure
ML-KEM-1024 on request — published as a signed advertisement; a writer
establishes a content key to the recipient's namespace key and encrypts
the record with AES-256-GCM, and a sender follows whatever the recipient
advertised. An enrollment submitted under a post-quantum posture
advertises a key package, and the approving client seals the atSign's
secrets to it rather than wrapping them with RSA. A client whose posture
asks for a stronger authentication key than its enrollment holds
re-enrolls itself at its first start, filing the new enrollment in the
same keys store beside the legacy fields. ML-DSA authentication needs an
atServer that verifies it; a legacy client makes no such demand.
The default posture moves one stage per major of at_client — 3.x
legacy, 4.x pqReady, 5.x pqActive — because a record may only be
written in a scheme every reader of it supports, so the stage that reads
post-quantum data rolls out before the stage that writes it by default. An
app on 3.x names pqReady or pqActive to move first.
The developer's view, the goals and the ladder are in the
at_client README;
the design is under docs/projects/pq/.
Upgrading
Applications talk to at_client (3.x, a minor release), so most need no
code change: the new lifecycle verbs sit beside AtClientManager, whose
setCurrentAtSign is deprecated rather than removed. The packages that
take a major are the ones that used to hand at_auth's types to an app:
- at_client_flutter 1.x → 2.0:
AuthService and
FlutterEnrollmentService are gone; the dialogs take the atSign, the
keys store and the preference, and hand back the AtClient. Nothing
from at_auth is re-exported. The table is in the
at_client_flutter README.
- at_onboarding_cli 1.x → 2.0:
at_activate names its command
(at_activate onboard -a @alice), --posture replaces
--signingAlgoType, and AtOnboardingService keeps authenticate()
and atClient while onboard, enroll and close become
Atsign.activate, Atsign.enroll and atClient.stop(). The table is in
the at_onboarding_cli README.
- at_auth 3.x → 4.0:
AtAuth and its request and response objects
are gone; activation is activateAtSign(...), logging in and every
enrollment decision are at_client's. The table is in the
at_auth README.
If you happen to import at_onboarding_cli or at_auth directly — which
almost no application does — the short version is: replace the call that
built your client with Atsign('@alice').open(keys: ..., preference: ...),
.activate(...) or .enroll(...), drop the import, and read everything
else off the AtClient you get back.
Installation
Each package's own README and pub.dev page have the installation
details. Click any of the links above.
AI Agent Skill
The at_client_skills package gives AI agents accurate, up-to-date knowledge of
at_client and at_client_flutter — covering AtCollection<T>, auth flows,
querying, sub-collections, testing patterns, and common pitfalls.
dart pub add --dev at_client_skills skills
dart run skills get
Works with Claude Code, Cursor, GitHub Copilot, Cline, and any agent
supporting the agentskills.io specification.
Maintainers
Atsign Foundation core devs
