CPU–TPM Identity Authentication Against Bus Interposers
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Solution Overview
Problem
TPM communications in computing systems are vulnerable to interposers that can intercept or modify traffic between the CPU and the TPM, compromising security and authenticity.
Innovation Solution
The CPU generates a policy alias key through a key derivation function using its device identity value and the TPM's public endorsement key, signing challenges to prove its identity, ensuring only the specific TPM can decrypt the communication, thus securing the communication session.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If TPM communications use plain-text communication paths, then ease of operation is improved, but security is worsened due to vulnerability to interposers
Solution Approach 1:
The patent introduces an intermediary authentication mechanism where the CPU proves its identity to the TPM through cryptographic challenge-response. The TPM acts as a mediator that verifies the CPU's identity before allowing secret access, preventing interposers from hijacking communications while maintaining operational simplicity.
Solution Approach 2:
The patent transforms the communication security model by changing the parameter of authentication from none to cryptographic verification. The CPU generates a policy alias key and signs challenges from the TPM, fundamentally altering how identity is verified without complicating the communication path.
2Adaptability or versatility
If TPM stores secrets accessible by any CPU, then adaptability is improved, but security is worsened due to inability to verify CPU identity
Solution Approach 1:
The patent applies local quality by making TPM access rights specific to individual CPU identities. Each CPU must prove its unique identity through cryptographic challenges, so the TPM's secret storage capability is adapted to work with specific authenticated CPUs rather than any CPU generically.
Solution Approach 2:
The patent implements preliminary action by requiring the CPU to prove its identity before the TPM releases secrets. The authentication process happens in advance of any secret access operations, ensuring that only verified CPUs can subsequently access TPM resources.
3Device complexity
If remote attestation verifiers cannot detect TPM actions, then device complexity is reduced, but measurement precision is worsened
Solution Approach 1:
The patent implements feedback by having the TPM issue challenges to the CPU and verifying the signed responses. This creates a closed-loop authentication system where the TPM actively verifies CPU identity through cryptographic challenges, providing precise detection of authenticated actions without requiring complex external attestation infrastructure.
Data Source
AI summary
The present disclosure provides systems and methods for demonstrating the identity of a central processing unit (CPU) to a Trusted Platform Module (TPM) with improved security against, for example, interposers on a communications bus. In particular, according to an aspect of the present disclosure, a CPU can generate a policy alias key that can be used to sign a challenge to prove the identity of the CPU to the TPM. Specifically, the policy alias key can be generated by the CPU by performing a key derivation function on a combined identity value generated by the CPU for the CPU and TPM. The combined identity value can be generated by the CPU from a CPU device identity value and a public endorsement key (EK) associated with the TPM.