demo · v142

Software Key Fallback

DBSC degrades gracefully on devices without a hardware TPM — the session still works, but the binding guarantee weakens. On a headless Linux server, CI environment, or older PC, Chrome uses a software-generated key stored in the OS keychain instead of a hardware-protected key. This page shows how the four attack scenarios play out differently under each key type.

Key type:
Scenario: Honest user — Hardware TPM
🖥️
Client
Browser
TPM key 🔐
🌐
Server
DBSC endpoint
step 0/0

🔐 Hardware TPM / Secure Enclave

✓ BLOCKED Remote replay — cookie + signed probe can't be forged without TPM
✓ BLOCKED Session export — private key is non-exportable from hardware
⚠ PARTIAL Local malware — can request signatures but only while on device
✓ ALLOWED Honest user — session refresh works seamlessly

⚠️ Software fallback (no TPM)

⚠ REDUCED Remote replay — key lives in OS keychain, not hardware; could be exported by root-level malware
⚠ REDUCED Session export — key file accessible to admin processes
✗ SUCCEEDS Root-level malware — can read software key from OS store and sign from anywhere
✓ ALLOWED Honest user — session refresh works identically

see also