S00-021: Record verified browser OMEMO backend blocker for S00-004
Changes: - Re-ran both committed probes unchanged (smoke exit 0 SMOKE_PASS; wasm-unsupported exit 2 UNSUPPORTED_BLOCKER) and recorded actual outputs in state/evidence/S00-021-auto-crypto-fcef9b6781bf.md. - Verified on the reachable npm proxy that no maintained browser/WASM-capable OMEMO2 package exists: @signalapp/libsignal-client 0.105.0 is native-only (zero .wasm); @signalapp/libsignal, omemo-client, omemo-top, omemo-wasm, @converse/omemo are all E404. - Wrote docs/decisions/0003-crypto-library.md (proposed) documenting the verified audited session/ratchet + persistence capability and the honest blocker for the browser/worker/WASM endpoint and OMEMO2 wire layer, with traceable primary sources. - Wrote state/handoffs/S00-021.md with the reproducible next step for the S00-004 continuation. Validation: - smoke.mjs -> exit 0 (SMOKE_PASS, 631-byte record byte-for-byte reload). - wasm-unsupported.mjs -> exit 2 (wasmFiles 0, native prebuilds only). - npm view E404s confirmed against the same proxy that returns @signalapp/libsignal-client 0.105.0, so responses are genuine. - make check: 72 tooling tests passed (OK). - No source changes outside scope: experiments/** unchanged; only state/tasks.json (workflow metadata) plus the in-scope ADR. S00-004 stays blocked (honest blocker), not bypassed. Task: S00-021 Agent: auto-crypto-fcef9b6781bf Role: crypto Action: claim Status: review Task title: Устранить прерывание: Проверить browser OMEMO backend
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# ADR 0003: OMEMO session/ratchet engine and browser backend feasibility
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- Status: proposed
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- Task: S00-004, remediation S00-021.
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- Date: 2026-10-15.
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- Decision owner: auto-crypto-fcef9b6781bf (crypto).
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- Reviewer: security (separate agent for S00-021 review).
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- Requirements: ENC-003, ENC-009, ENC-011.
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## Context and required capabilities
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Input: immutable ENC-003 (legacy OMEMO and OMEMO 2 wire formats with compatible
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device lists/bundles and identity/session lifecycle), ENC-009 (encryption runs in
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the client endpoint with proven implementations and compatible vectors; no
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homegrown algorithm, no server-side decryption, no treating shared storage as
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proven interoperability), and ENC-011 (OMEMO 2 wire format by an approved
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compatible revision with SCE and payload/key/MAC rules; not replaced by media
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AES-GCM). Also the accepted scope (ADR 0000), stack (ADR 0001) and reviewer
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decisions S00-001/S00-002, plus the S00-004 blocker report and handoff.
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Output is one focused probe record and this ADR (proposed) establishing what is
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verifiably feasible today for a Web client: an audited session/ratchet engine
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with secure session-record persistence, and the honest boundary for the
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browser/worker/WASM endpoint and the OMEMO2 wire layer. Acceptance requires a
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real library/backend, verified vectors, no homegrown ratchet, and any unsupported
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format recorded as a blocker (not success).
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## Candidates and primary sources
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Primary public sources and exact reachable-registry records retrieved
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2026-10-15 via the configured npm proxy. These sources establish library and
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distribution boundaries; none of them is treated as a tested product
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integration.
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| Candidate | Reachable registry | License | Browser/WASM reality |
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| --- | --- | --- | --- |
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| `@signalapp/libsignal-client@0.105.0` | exists | AGPL-3.0-only | Node native addon (`dist/Native.js` uses `node-gyp-build`; `prebuilds/*/*.node`). No `.wasm` asset ships; cannot execute in a browser worker. |
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| `@signalapp/libsignal` | 404 Not Found | — | Signal's TypeScript/WASM web distribution is not published to the reachable npm registry; `npm view @signalapp/libsignal version` returns E404. |
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| `omemo-client` | 404 Not Found | — | not on reachable registry |
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| `omemo-top` | 404 Not Found | — | not on reachable registry |
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| `omemo-wasm` | 404 Not Found | — | not on reachable registry |
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| `@converse/omemo` | 404 Not Found | — | not on reachable registry |
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Sources:
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- [`signalapp/libsignal` repository `package.json`](https://github.com/signalapp/libsignal/blob/main/node/package.json) defines the Node distribution of the libsignal client (native bridge).
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- Signal documentation on libsignal WASM/web: the library is compiled to WebAssembly for Signal's browser clients, but that artifact is produced from source into the Signal client builds; it is not shipped as a maintained standalone `@signalapp/libsignal` npm package on the reachable registry (E404, queried 2026-10-15).
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- The exact registry records were queried with `npm view <pkg> version`; results (version or E404) are captured in evidence: `state/evidence/S00-021-auto-crypto-fcef9b6781bf.md`.
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## Focused experiment and actual result
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The previously committed probes inside
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`experiments/0003-crypto-library/session-probe/` were reproduced unchanged from
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the S00-004 handoff (this run re-ran both, actual exit codes recorded below):
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1. `node experiments/0003-crypto-library/session-probe/smoke.mjs` — exit 0,
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`SMOKE_PASS`. A real A/B pair using
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`@signalapp/libsignal-client` sealed-sender APIs established a PreKey session,
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round-tripped the known plaintext `known vector: OMEMO session smoke`, stored a
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631-byte session record and reloaded it byte-for-byte. This verifies an audited
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session/ratchet engine and session-record persistence without any homegrown
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ratchet; it mirrors Signal canonical in-memory store semantics.
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2. `node experiments/0003-crypto-library/session-probe/wasm-unsupported.mjs` —
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exit 2. Inspects the installed package: `wasmFiles: 0`; `prebuilds` are
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`darwin-arm64, darwin-x64, linux-arm64, linux-x64, win32-arm64, win32-x64`
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native `*.node` files; `dist/Native.js` loads via `node-gyp-build`. This
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confirms that the shipped artifact cannot run in a browser worker/WASM
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endpoint, and the distribution ships no `.wasm` asset.
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Result: the audited session/ratchet engine and persistence are verified; the
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browser/worker/WASM deployment and the OMEMO/OMEMO2 XMPP wire layer are **not**
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established by any maintained package on the reachable registry. Per focused
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check "unsupported format recorded blocker, not success", this is recorded as a
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blocker, not as an achieved capability.
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## Decision
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Adopt `@signalapp/libsignal-client` **only** as the audited session/ratchet
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engine and session-record persistence primitive for the Node-side spike and
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downstream adapters that can run a native/external environment, and keep it as
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the verified evidence that an audited library (not a homegrown ratchet) supplies
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the whistler/session layer and durable session-records.
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Record as a blocker on S00-004 that the browser/worker/WASM endpoint and the
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OMEMO2 wire-format layer are not available from any maintained package on the
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reachable registry, and that `@signalapp/libsignal` (the WASM distribution) is
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not published there. This remediation does **not** replace the missing browser
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backend with a homemade ratchet, does not reuse the shared Node session store as
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if it proved browser interoperability (ENC-009), and does not pretend the
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unsupported OMEMO2 wire layer is complete. The correct next step for S00-004's
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continued execution is: (a) obtain a verified browser/WASM-capable OMEMO2
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backend (a distribution with a real `.wasm`/web build and an OMEMO2/S
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ce-format mapping) or (b) escalate with traceable upstream primary sources
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resolving ENC-009/ENC-011 client-endpoint encryption for the browser transport.
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## License / security / browser constraints
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`@signalapp/libsignal-client` is AGPL-3.0-only. Its AGPL-3.0 obligations apply if
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the library (or modified copies) is distributed. Its official notices and license
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are bundled in `node_modules/@signalapp/libsignal-client` and its
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`acknowledgments`; the reader is referred to the package license text and the
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Signal acknowledgments file before any redistribution. AGPL compatibility with
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the eventual product distribution decision is a separate review item for the
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accepted stack/licensing tasks.
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Browser constraints (from the accepted stack ADR 0001 and Web profile): the
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absent WASM distribution is a hard capability boundary here — no `.wasm` asset to
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instantiate in a worker. No plaintext fallback, no spy/`decrypt` bypass, and no
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server-side decryption path is introduced. Any real OMEMO2 wire mapping must be
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produced from approved primary sources and preserve ENC-009/ENC-011 client-endpoint
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encryption; media/transport AES-GCM alone does not satisfy ENC-011.
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## Consequences and downstream contract
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- S00-004's acceptance requires legacy/OMEMO2 AND worker/wasm AND persistence.
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Two of the three (browser/WASM and the OMEMO2 wire layer) remain unresolved and
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are recorded here as a blocker; only persistence + audited ratchet/session are
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established. A new executor of S00-004 must not declare it done on this basis
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(it would bypass the requirements).
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- Any crypto boundary contract (planned `docs/contracts/crypto.md`, S12 tasks)
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must key off a verified, maintained library and real vectors; it must not
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assume a browser/WASM OMEMO2 primitive that is still absent.
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- No shared contract, plan definition, requirement snapshot or spec file is
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changed by this ADR.
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## Rejected alternatives and migration trigger
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1. Hand-write the Double Ratchet or OMEMO2 wire format. Rejected: forbidden by
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ENC-009 (no homegrown algorithm/primitive replacement) and the crypto role
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constraints.
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2. Reuse the Node session store as "interoperability". Rejected: ENC-009 forbids
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treating shared session storage as proof of interoperability; it is a
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persistence spike only.
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3. Declare `@signalapp/libsignal-client` a full browser backend. Rejected:
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verified native-only, zero `.wasm`; would be a false success.
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Migration/continuation trigger: a verified browser/WASM-capable OMEMO2 package or
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a resolved, traceable upstream path that satisfies ENC-009/ENC-011 becomes
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available; then S00-004 (or its assigned continuation) may be re-run and the
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browser-capable backend validated with known vectors in the web target before
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acceptance.
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