feat(rs): surface rotation drain signal via decrypt_indexed (LAB-1678) - #74
feat(rs): surface rotation drain signal via decrypt_indexed (LAB-1678)#7427Bslash6 wants to merge 3 commits into
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Bump cachekit-core 0.5 -> 0.6 and read through Keyring::decrypt_indexed so the winning key position reaches the SDK. EncryptionLayer counts reads served by each previous key (AtomicU64 per position, current-key reads not counted) and exposes them via previous_key_hits(), also on SecureCache. An operator running a rotation grace window watches the retiring key's count stop growing before dropping it, instead of guessing at a hard cut-over. Error-class mapping and attempt sequencing are unchanged (core owns the loop, LAB-683). No key material in the signal: positions and counts only.
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WalkthroughThe encryption layer now counts successful decryptions made with previous rotation keys. ChangesPrevious-key rotation telemetry
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🟡 Moderate · up to The change adds rotation-hit counters that may prevent the supported WebAssembly build from compiling without atomic support. Merge should wait for a compatible counter implementation or target-specific gating. Sequence Diagram(s)sequenceDiagram
participant SecureCache
participant EncryptionLayer
participant Keyring
SecureCache->>EncryptionLayer: decrypt payload
EncryptionLayer->>Keyring: request indexed decryption
Keyring-->>EncryptionLayer: return plaintext and key position
EncryptionLayer->>EncryptionLayer: increment previous-key hit counter
EncryptionLayer-->>SecureCache: return decrypted value
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Full details: Docstring CoverageExplanation Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 12 functions across 3 files. (2 skipped: 2 unsupported.) ✨ Finishing Touches📝 Generate docstrings
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Docs: state that counts are per process and reset on restart, so operators aggregate across every instance holding the retiring key and watch a full TTL window before dropping it (a single restarted replica reading [0] is not a drained key). Operator workflow now lives in one Rust location (previous_key_hits rustdoc); type/field/handle docs point there. README code fence that restated the inline call removed. Code: debug_assert on the keyring index so an out-of-range index from core is loud under test while the release path stays panic-free. Integration test trimmed to the handle-wiring proof; index-0 silence is owned at the layer.
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Expert panel (critical stakes) — run in-session, findings applied at
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| Agent | Result |
|---|---|
| bug-hunter-supreme | NO FINDINGS |
| security-specialist | NO FINDINGS — verified: signal is Vec<u64> only, Debug omits it, no export; core 0.6.0 decrypt is a byte-equivalent delegate of decrypt_indexed, error-class mapping unchanged; lockfile checksum matches the crates.io .crate, 0.5→0.6 source diff is additive only |
| code-craftsman | MAJ applied: counters are per process and reset on restart, so the docs now tell operators to aggregate across every instance holding the retiring key and watch a full TTL window. MIN applied: debug_assert! on the keyring index (loud under test, release path stays panic-free) |
| catchphrase-agent | Cuts applied: operator workflow lives in one Rust location (previous_key_hits rustdoc; type/field/handle docs point there), README code fence that restated the inline call removed, integration test trimmed to the handle-wiring proof. Rejected: folding the drain assertions into rotation_round_trip_without_reencryption — the ticket requires the existing rotation tests to pass unmodified |
Verdict after fixes: SHIP. Vec<AtomicU64> + Relaxed + one guard + one delegate was judged the shortest working shape; the SecureCache passthrough is kept because both encryption fields are private and the alternative (an EncryptionLayer accessor) exposes raw encrypt/decrypt.
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Inline comments:
In `@crates/cachekit/src/encryption.rs`:
- Line 194: Update the counter increment around hits.fetch_add in the encryption
code to compile for wasm32-unknown-unknown without atomics, using a
WASM-compatible implementation or gating the counter while preserving hit
counting on targets that support AtomicU64.
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…678) The 'safe to drop' guidance said a flat counter over one TTL window was enough. The normative runbook (protocol decisions/key-rotation.md) is stricter, and the counter cannot see the gap: during a rolling promotion a lagging instance still writes under the retiring key and reads it as its own current key, which is deliberately silent (index 0). Per-entry TTLs via set_with_ttl can also outlive the default window. Both surfaces (README Key Rotation, previous_key_hits rustdoc) now state: complete the two-phase promotion first, start the clock when that deploy finishes fleet-wide, wait the longest TTL in use, aggregate across instances, and only then read a flat counter as drained. Adversarial finding by Helly R on PR #74.
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Closes LAB-1678. Consumes the cachekit-core 0.6.0
decrypt_indexedsurface (cachekit-io/cachekit-core#73) that #63 deferred: a previous-key hit is now observable, so an operator can watch a rotation drain reach zero before dropping the retired master key.What changed
crates/cachekit/Cargo.toml:cachekit-corepin0.5→0.6(features unchanged; 0.6.0 is additive).EncryptionLayer::decryptreads viaKeyring::decrypt_indexed. Plaintext, attempt sequencing (core-owned, LAB-683) and the error-class mapping (KeyDerivation/KeyringIndexOutOfRange→Config, elseEncryption) are unchanged; existing rotation tests pass unmodified.AtomicU64per previous key on the layer. Index 0 (current key) is not counted; indexi ≥ 1increments sloti - 1.EncryptionLayer::previous_key_hits() -> Vec<u64>(hits[i]↔previous_keys[i]) plus aSecureCache::previous_key_hits()passthrough so builder-configured clients can reach it. Pull-style, matching the crate'sMetricsProviderpattern; no new dependency, no user code on the decrypt hot path. The payload is positions and counts only, no key material, by type.current=k3, previous=[k2, k1]), and a failed decrypt counting nothing; an integration test reading the signal offSecureCache; a doc-test onprevious_key_hitsasserting the drain signal.### Key Rotationgains the operator workflow paragraph;EncryptionLayerrustdoc gains a "Rotation drain signal" section mirroring core'sdecrypt_indexedlanguage.Verification
cargo clippy --all-targets --features "cachekitio,redis,encryption,l1,macros,memcached,file" -- -D warnings: clean.cargo testwith the same feature set: all suites green (92 lib tests, doc-tests included).cargo +1.85 check --all-targets --features "cachekitio,redis,encryption,l1,macros": passes (MSRV).cargo check --target wasm32-unknown-unknown --no-default-features --features workers,cachekitio,encryption: builds; the 33 unused-import warnings are pre-existing in backend modules.prek run --all-files: every hook passes except detect-secrets, which flagstests/vectors/interop-mode.jsonon a cleanmaintoo (pre-existing, not touched here).Dependency bump evidence (cachekit-core 0.5 → 0.6)
Securityworkflow (cargo deny checkadvisories/bans/licenses/sources with--all-features+cargo auditonCargo.lock) passed on this branch: run 33617757729.cachekit-core@0.6.0(crates.io) returns no advisories (2026-09-03).Cargo.lock: sole change iscachekit-core 0.5.0 → 0.6.0, checksum93adc5646956ba8da140f4179a02e60a2cc7a401b83ebb1270cc4d03748e1fac(matches the published.crate); no new transitive packages. Pin form"0.6"matches the existing"0.5"convention; the lockfile carries the exact version.Adversarial review (Helly R) — applied at
067ad65The "safe to drop" guidance omitted the runbook's write-fence and longest-TTL preconditions. README
### Key Rotationand theprevious_key_hitsrustdoc now state: complete the two-phase promotion first, start the clock only when that deploy completes fleet-wide (a lagging instance still writes under the retiring key and reads it silently as index 0), wait at least the longest TTL in use including explicitset_with_ttlvalues, aggregate across instances, and only then read a flat counter as drained. Positions are comparable across instances only once they share one keyring configuration.Out of scope, deliberately: switching the layer to core's new
TenantKeyring(LAB-1638 follow-up), py/ts exposure (neither has multi-key decrypt), the docs.cachekit.io runbook page (LAB-687).Summary by CodeRabbit
New Features
Documentation