Anti-Rollback Protection

Anti-rollback protection prevents an attacker or misconfiguration from replaying an older bundle to restore previously-revoked certificates to “good” status. This is a critical security property — without it, an adversary with access to historical bundles could silently undo revocations.

The Threat

Consider a certificate revoked in epoch 40. If an attacker can replace the current bundle (epoch 42) with a bundle from epoch 38 (before the revocation), the edge would start serving “good” responses for the revoked certificate. Anti-rollback makes this impossible.

flowchart LR
    subgraph Epoch Chain
        E38[Epoch 38<br/>cert: good] --> E39[Epoch 39] --> E40[Epoch 40<br/>cert: revoked] --> E41[Epoch 41] --> E42[Epoch 42<br/>cert: revoked]
    end
    E38 -.->|"Rollback attempt<br/>REJECTED"| Edge[Edge Node]
    E42 -->|"Current bundle<br/>ACCEPTED"| Edge

Epoch Chain

Each bundle carries a monotonically increasing epoch number, scoped per CA. The signer increments the epoch on every bundle production — whether scheduled or triggered by an urgent revocation.

The epoch chain forms a simple sequence:

epoch N → epoch N+1 → epoch N+2 → ...

Every bundle’s epoch is recorded in its CBOR manifest and covered by the CMS seal, so it cannot be altered without breaking the signature.

High-Water Marks

The state_db directory persists the highest epoch seen for each CA. On every bundle load, the edge enforces:

new_epoch ≥ stored_high_water_mark

If the new bundle’s epoch is less than the stored high-water mark, the bundle is rejected as a rollback.

Example

Fork Detection

If two bundles arrive with the same epoch but different content digests, this is a fork — it means two signers produced bundles independently for the same CA, or a single signer’s state was cloned.

Fork detection catches:

• Misconfigured duplicate signers: Two signer instances both believe they are authoritative for the same CA
• State cloning: A signer’s state directory was copied, producing a second lineage
• Compromise: An attacker with the signing key producing alternative bundles

Fork is always a critical security event requiring immediate investigation.

Rejection Reasons

Bundle load failures are categorized into four reasons:

The first two (rollback and fork) are security events. The latter two (digest and seal) typically indicate data corruption during transfer, though tampering should not be ruled out.

state_db Persistence

The state_db directory is where epoch high-water marks live. It must persist across process restarts, container recreations, and node replacements.

[storage]
state_db = "/var/lib/hoike/state"

If state_db is lost, the node loses all high-water marks and becomes vulnerable to rollback attacks until it loads a current-epoch bundle. This is why state_db is a separate path from bundle_dir:

• bundle_dir can be ephemeral — bundles are replaceable (re-pull from signer or re-import)
• state_db is persistent state — mount it on durable storage, back it up, and include it in disaster recovery plans

In containerized environments, state_db should be on a persistent volume, not an ephemeral container filesystem.

Critical Alerts

Two metrics form the foundation of hoike operational monitoring:

bundle_next_update_seconds

What: Gauge showing seconds until the current bundle’s nextUpdate timestamp.

Why it matters: When this reaches zero, the edge is serving responses past their validity window. Relying parties that check freshness will reject them.

Alert thresholds:

The warning threshold should be comfortably above batch_interval (default 1h). With a 24h validity and 1h batch interval, alerting at 4h gives you three missed batches before going critical.

bundle_load_failures (by reason)

What: Counter of failed bundle loads, labeled by rejection reason (rollback, fork, digest, seal).

Why it matters: Any non-zero increment for rollback or fork is a critical security alert requiring immediate investigation.

Alert rules:

Recovery Procedures

Rollback Detected

1. Investigate the source. Why was an old bundle offered? Common causes:
   • Stale bundle cached in a CDN or reverse proxy
   • Misconfigured bundle distribution pipeline pointing at an old directory
   • An attacker replaying a captured bundle
2. Fix the distribution path. Purge stale caches, correct directory pointers.
3. Produce a new bundle from the authoritative signer. The new epoch will be above the high-water mark and will load successfully.

Fork Detected

1. Identify the duplicate signer. Check which hosts are running in signer mode for the affected CA.
2. Shut down the unauthorized signer. Only one signer should be authoritative per CA at any time.
3. Produce a new bundle from the authoritative signer with the next epoch.
4. Audit the fork window. Determine whether any responses from the forked lineage were served, and whether they differed in revocation status.

Digest or Seal Failure

1. Check for media corruption. Re-download or re-transfer the bundle.
2. Verify with ahu verify on a trusted workstation to confirm the bundle is intact at the source.
3. If the source bundle also fails verification, investigate the signer — the signing key may have changed, or the signer may be compromised.