Hardware Anti-Replay Synchronization & Trip Counter Governance
Preventing replay attacks on vehicular networks through synchronized cryptographic freshness values.
The Necessity of Cryptographic Freshness
Even if a message has a valid MAC, an attacker can capture it and replay it later (such as replaying an 'accelerate' or 'deploy airbag' command). CanHSM combines payload data with an internal Freshness Value before computing the MAC, rendering replayed frames instantly invalid.
Hardware FVM State Architecture
CanHSM stores Trip Reset Counters, Trip Counters, and Message Counters in dedicated secure non-volatile memory, ensuring freshness state persists across battery disconnections and ECU brownouts.
- Monotonic Trip Counters: Hardware-enforced non-volatile counters that increment upon vehicle power cycles.
- Broadcast Freshness Synchronization: Distributing authoritative freshness synchronization messages across bus segments.
- Sub-Counter Validation: Tracking individual message sequence numbers to detect dropped or replayed packets.
- Desynchronization Recovery: Automated cryptographic re-synchronization protocols when ECUs recover from sleep states.
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