Lawful Device Access without Mass Surveillance Risk: A Technical Design Discussion

This paper proposes a systems-oriented design for supporting courtordered data access to "locked" devices with system-encrypted storage, while explicitly resisting large-scale surveillance use. We describe a design that focuses entirely on passcode self-escrow (i.e., storing a copy of the user passcode into a write-only component on the device) and thus does not require any changes to underlying cryptographic algorithms. Further, by predicating any lawful access on extended-duration physical seizure, we foreclose mass-surveillance use cases while still supporting reasonable investigatory interests. Moreover, by couching per-device authorization protocols with the device manufacturer, this design avoids creating new trusted authorities or organizations while providing particularity (i.e., no "master keys" exist). Finally, by providing a concrete description of one such approach, we hope to encourage further technical consideration of the possibilities and limitations of tradeoffs in this design space.