fix(crypto): add RatchetCache::clear() for explicit key eviction (#178)#469
Merged
intendednull merged 1 commit intoApr 28, 2026
Conversation
RatchetCache stored derived ChannelKey values in BTreeMap + ratchet_states without any caller-driven way to wipe them. ChannelKey already implements ZeroizeOnDrop, but secrets only zeroize when the map drops the entry — so cached keys lingered until eviction pressure hit max_entries or the cache itself was dropped. Add `pub fn clear(&mut self)` that empties both maps. BTreeMap::clear and HashMap::clear drop each value in place, triggering the per-key ZeroizeOnDrop pass before the buckets are released, so secret material is wiped synchronously at the call point. Also add two unit tests: - ratchet_cache_clear_drops_all_state: populate three epochs, call clear(), assert both `cache` and `ratchet_states` are empty + the cache is still usable for fresh derivations. - ratchet_cache_clear_is_idempotent: clear-on-empty is a no-op. Brainstorm — wiring point. RatchetCache is currently API surface only: no client/web code calls `derive_or_cached`, so there is no live production cache to wire into leave_server / sign-out today. Speculatively integrating the cache into the client decrypt path was considered (runner-up) and rejected: that's a perf/correctness change distinct from this security cleanup, and the task explicitly cautions against scope creep. Filing a follow-up so the wire-up is not forgotten when the cache lands in the decrypt hot path. The HashMap<String, ChannelKey> that actually holds production keys (crates/client/src/state.rs, state_actors.rs) is already cleaned up correctly: leave_server removes the ServerEntry, dropping its keys map and zeroizing each ChannelKey via ZeroizeOnDrop. Verification: - cargo test -p willow-crypto: 64 passed - cargo clippy --workspace --all-targets -- -D warnings: clean - cargo check --target wasm32-unknown-unknown -p willow-crypto -p willow-client: clean - cargo fmt --check: clean Refs #178
This was referenced Apr 28, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
What
Add
pub fn clear(&mut self)toRatchetCache. Emptycachemap. Emptyratchet_statesmap. ChannelKey ZeroizeOnDrop, KeyRatchet ZeroizeOnDrop. BTreeMap::clear + HashMap::clear drop each value in place. Secret bytes zero before bucket release. Issue #178 want explicit eviction. Now exist.Two unit tests added:
ratchet_cache_clear_drops_all_state— populate three epochs, call clear(), check both maps empty, check cache still usable for fresh derive.ratchet_cache_clear_is_idempotent— clear empty cache no panic, repeat ok.Brainstorm — wiring point
Task say "wire clear() into channel-leave / server-disconnect — adding method nobody call is theatre".
Look. RatchetCache not used outside crypto crate own tests.
derive_or_cachedzero call sites in client/web/messaging. Production decrypt path (open_content) not consult cache. Cache is API surface waiting integration.Chosen wiring point: none today. Method exist + documented. Filed follow-up #468 so integrator wire clear() into
leave_server+ sign-out when cache lands in client decrypt path.Runner-up rejected: Speculatively integrate RatchetCache into client decrypt flow now, then wire teardown. Rejected because (a) scope creep beyond #178, (b) ratchet caching is perf/correctness change distinct from this cleanup work, (c) task warn don't balloon to refactor.
Note on existing key map:
HashMap<String, ChannelKey>incrates/client/src/state_actors.rsServerEntry hold actual production channel keys.leave_serveralready remove ServerEntry — that drop the map — that drop each ChannelKey — ZeroizeOnDrop fire. Path safe today. No change needed.Verification
cargo test -p willow-crypto: 64 passedcargo clippy --workspace --all-targets -- -D warnings: cleancargo check --target wasm32-unknown-unknown -p willow-crypto -p willow-client: cleancargo fmt --check: cleancargo test --workspace: passed exceptwillow-actor::send_dead_actor_returns_send_errorflaky pre-existing (unrelated, passes in isolation)Tradeoffs
Skipped client-tier test asserting cache.len()==0 after sign-out: cache not yet owned by client, no fixture exist. Unit test cover the contract. Follow-up #468 cover integration test when wire-up land.
Refs #178
Generated by Claude Code