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Device-Bound Session Credentials

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Device-Bound Session Credentials (DBSC) is a browser-level security feature that binds a session to the device that created it. Even if a session cookie is stolen, it cannot be used from another device.

Subnoto automatically activates DBSC for browsers that support it (Chromium-based browsers with TPM/secure-element support). No action is required from developers or end users — DBSC is negotiated transparently during login.

How it works

Section titled “How it works”

DBSC ties a session to an unforgeable proof of device identity using the browser’s Trusted Platform Module (TPM) or equivalent secure element:

  1. Login — When a user logs in, the server returns a Secure-Session-Registration header with a challenge and algorithm requirements.
  2. Registration — The browser generates an ECDSA P-256 key pair inside the TPM (the private key never leaves the hardware) and sends a self-signed JWT (dbsc+jwt) containing the public key and the signed challenge.
  3. Server stores public key — The server verifies the JWT, extracts the public key, and stores it alongside the session.
  4. Short-lived cookie — Instead of a long-lived session cookie, the server sets a short-lived DBSC cookie (4 minutes). When it expires, the browser must refresh it.
  5. Refresh — The browser calls the refresh endpoint. The server issues a challenge; the browser signs it with the TPM-held private key and returns the proof. The server verifies the signature against the stored public key and issues a fresh cookie.

Because the private key is hardware-bound and cannot be extracted, a stolen cookie expires within minutes and cannot be refreshed from a different machine.

Session lifecycle with DBSC

Section titled “Session lifecycle with DBSC”
Diagram

What users see

Section titled “What users see”

In the Sessions settings page, sessions with DBSC active display a Device bound badge. This indicates that the session is protected by a hardware key and cannot be replayed from another device.

Browser support

Section titled “Browser support”

DBSC is currently supported on Chrome/Chromium-based browsers. Support varies by platform:

  • Windows — Enabled by default (Chrome 145+). No action required.
  • macOS — Requires enabling three flags in chrome://flags:
    1. #enable-bound-session-credentials
    2. #enable-standard-device-bound-session-credentials (set to “Enabled - For developers”)
    3. #enable-standard-device-bound-session-credentials-persistence

On unsupported browsers or when flags are not enabled, sessions fall back to standard cookie-based authentication. DBSC is an additional security layer — it does not replace existing protections.

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