ANP SDK Direct E2EE P5

Status

• ANP-P5 Direct E2EE SDK support is implemented across the product-consumed Go and Rust surfaces, with Python helpers and shared vectors retained for parity and regression coverage.
• Protocol authority: ANP P5 私聊端到端加密.
• Harness map: Direct E2EE cross-repo feature map.
• Public discovery is controlled by product services and remains off until a separate discovery/security decision enables it.

Owned surface

ANP SDK owns the cryptographic and wire semantics for private-chat E2EE:

• Go package: golang/direct_e2ee/.
• Rust module: rust/src/direct_e2ee/.
• Python package: anp/direct_e2ee/.
• Shared P5 vectors: testdata/direct_e2ee/.
• Go guide: golang/docs/direct_e2ee-guide.md.
• Go example: golang/examples/direct_e2ee/.

Product repositories should consume SDK models/helpers instead of reimplementing P5 algorithms or canonicalization.

P5 primitives and models

The SDK-owned boundary includes:

• PrekeyBundle and OneTimePrekey.
• DirectInitBody for application/anp-direct-init+json.
• DirectCipherBody for application/anp-direct-cipher+json.
• DirectEnvelopeMetadata and canonical AAD builders.
• ApplicationPlaintext.
• X3DH-like initial material with optional OPK DH4.
• HKDF-SHA256 kdf_rk and kdf_ck labels defined by P5.
• pending-confirmation session state.
• Double Ratchet-like send/receive chains, replay protection, skipped-key handling, and max-skip behavior.
• file-backed reference stores for sessions, signed prekeys, OPKs, and pending outbox records.

P5 rules that product integrations rely on:

• prekey_bundle must not embed one_time_prekey; OPK is a top-level sidecar from direct.e2ee.get_prekey_bundle.
• Direct E2EE direct.send requires operation_id == message_id.
• Current phase-1 direct-e2ee wire omits params.auth unless a future extension/capability explicitly changes that.
• Direct init/cipher AAD uses JCS/RFC8785 and P5 content_type bindings.
• Old HPKE-style e2ee_init / e2ee_msg service target objects are not P5.

For ordinary structured JSON, products should use application/json as the inner application_content_type and put the JSON object directly in payload:

{
  "application_content_type": "application/json",
  "payload": {
    "type": "example",
    "data": {
      "hello": "world"
    }
  }
}

In Rust this is represented with the existing helper:

ApplicationPlaintext::new_json(
    "application/json",
    serde_json::json!({"type": "example", "data": {"hello": "world"}}),
)

The SDK does not define command/status/task/result schemas; those are product semantics above the ANP SDK layer.

Product boundaries

Product repo	Consumes SDK for	Must not do
awiki-cli	Go direct session, prekey/OPK stores, secure send/decrypt, outbox/retry/drop/status.	Reimplement P5 crypto or put private ratchet material in argv/logs.
message-service	Rust/public P5 model validation and proof-boundary helpers.	Decrypt plaintext or store private session/key material.
user-service	DID document key roles and service metadata expectations.	Store private E2EE sessions, RK/CK/MK, OPK private material, or decrypt messages.

Shared vectors and parity

testdata/direct_e2ee/p5_shared_vectors.json anchors deterministic behavior for:

• direct init AAD with and without OPK;
• direct cipher AAD;
• X3DH-like no-OPK and OPK material;
• kdf_ck / kdf_rk output labels.

Keep Go/Rust/Python parity tests aligned before claiming SDK compatibility or public discovery readiness.

Validation

Focused SDK checks:

cd anp/anp
go test ./golang/direct_e2ee ./golang/integration
cargo test --manifest-path rust/Cargo.toml direct_e2ee --all-targets
uv run pytest anp/unittest/direct_e2ee -q

If only shared vectors changed, run the language-specific shared-vector tests first and then product focused tests in awiki-cli, message-service, and awiki-system-test.

Non-goals

• Public service discovery enablement.
• Group E2EE / MLS.
• Multi-device protocol semantics.
• Direct Init Accountability Extension.
• PQ/PQXDH.
• Service-side plaintext decrypt.