7 Cryptographic Architecture

Explains the secure boot chain, cryptographic algorithms, and TrustZone architecture.

Secure Boot Chain

Algorithms Used

PurposeAlgorithm
Image hashingSHA-256
FWMD signingECDSA with P-256 (secp256r1)
Key wrappingPUF hardware key wrap (device-unique)
Key storageVSS in configuration Flash

TrustZone Architecture

The device application uses a TrustZone split:

  • Secure world: Contains vss_keystore module (reads VSS Flash), PUF driver, key dump and verification logic. All crypto operations and key material access happen here.

  • Non-secure world: LED/switch application. Calls secure-world veneers (secure_vss_dump_keys, secure_vss_verify_puf_keys). No key material ever crosses the TrustZone boundary.