Hardware Key Tunnel Unit for Secure Session-Key Delivery
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Solution Overview
Problem
The delivery of encryption keys from a central Root-of-Trust (RoT) to crypto engines over a public bus is risky due to untrusted micro-controller units and the significant distance, which makes dedicated wires or buses costly and insecure.
Innovation Solution
A hardware-based key tunnel unit (KTU) wraps and unwraps session keys within the RoT, using a sequence of wrapping keys to secure transmission over a public bus, ensuring only the crypto engine has access to plaintext keys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dedicated wires or a dedicated bus are used for key delivery, then security is improved, but cost increases
Solution Approach 1:
The patent introduces a key tunnel unit as an intermediary component that bridges the Root-of-Trust and crypto engines. This mediator securely encapsulates and transports encryption keys through the existing public bus infrastructure, eliminating the need for dedicated physical wires or buses while maintaining security through hardware-based key wrapping and unwrapping operations.
2Device complexity
If keys are sent over a public bus, then cost is reduced, but security risk increases
Solution Approach 1:
The patent implements a nested security structure where encryption keys are wrapped within multiple layers of protection. The key tunnel unit wraps session keys using wrapping keys in a nested manner, creating a secure tunnel where the inner key is protected by outer keys. This nested wrapping mechanism allows keys to traverse the public bus while remaining protected at multiple security levels.
Solution Approach 2:
The key tunnel unit serves as a trusted intermediary that handles all key wrapping and unwrapping operations. It receives wrapped keys from the Root-of-Trust, unwraps them using secure hardware operations, and delivers the plaintext keys to the crypto engines. This mediator isolates the vulnerable public bus from direct key exposure, as only wrapped keys traverse the bus infrastructure.
3Adaptability or versatility
If an MCU manages crypto engines, then functionality is improved, but trust is reduced
Solution Approach 1:
The patent extracts the key handling functionality from the untrusted MCU environment and places it directly in the trusted Root-of-Trust hardware. The key tunnel unit, implemented as dedicated hardware, performs all critical key wrapping and unwrapping operations outside the MCU's control. This extraction ensures that even if the MCU is compromised, the plaintext keys never enter untrusted software, maintaining security while the MCU continues to manage crypto engine functionality.
Data Source
AI summary
Approaches in accordance with various illustrative embodiments provide for the encryption of communications going into and out of a device, such as a chip or proprietary bus. The encryption can occur in a central Root-of-Trust (RoT), which can include agents for individual communication protocols to generate session keys used to encrypt communications for individual sessions, and the data can be sent to a crypto engine for the respective communication protocol. A key tunnel unit can be used to receive a wrapped session key over the public bus and then unwrap the key in hardware, then able to then transmit the unwrapped session key to the corresponding crypto engine without exposing the session key to software executing on the device outside the RoT. The receiving inline crypto engine can then use that session key to encrypt session data to be transmitted to a separate device or destination.