Single-Round-Trip TPM Key Certification via AIK Binding
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Solution Overview
Problem
The existing process of certifying non-migratable keys secured by a Trusted Platform Module (TPM) requires multiple round-trips between the client and the certificate authority, one for certifying the Attestation Identity Key (AIK) and another for the new key, which is inefficient.
Innovation Solution
A method where the client requests the TPM to create a new non-migratable key, generates a certificate request, and uses the TPM to create an AIK bound to the request digest and sign the key, allowing the certificate authority to verify the key's non-migratability in a single round-trip by including a conditional certificate that can only be decrypted by a trusted TPM, thus ensuring the key's trustworthiness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the certificate authority verifies the AIK separately before certifying the new key, then the trustworthiness and security of the key certification is improved, but the number of round-trips between client and certificate authority increases
Solution Approach 1:
The patent combines the AIK certification process and the new key certification process into a single integrated operation. The certificate authority verifies the AIK and issues the certificate for the new key within the same round-trip interaction, eliminating the need for separate verification and certification steps. This merging resolves the contradiction by maintaining comprehensive verification (preserving reliability) while reducing communication overhead (reducing round-trips).
Solution Approach 2:
The client performs preliminary actions by generating the AIK and binding it to the new key before submitting the certification request. The certificate authority then uses this pre-established AIK binding to verify and certify the new key in a single operation. This preliminary preparation enables the certificate authority to perform thorough verification without requiring additional round-trips, as the verification data is already prepared and included in the initial request.
2Reliability
If the certificate authority issues a certificate with an encrypted signature that requires TPM decryption, then the security assurance of the key is improved, but the complexity of the certification process increases
Solution Approach 1:
The patent introduces the TPM as an intermediary component that bridges the certificate authority and the client. The TPM holds the private key and performs the decryption of the encrypted signature, acting as a secure mediator that verifies the certificate's authenticity without exposing private keys. This intermediary approach enhances security assurance by ensuring that only the legitimate TPM can validate the certificate, while the added complexity is confined to the TPM module rather than the overall certification system.
Solution Approach 2:
The TPM performs self-service by autonomously decrypting the encrypted signature using its internal private key without requiring external intervention or additional verification steps. This self-service capability simplifies the overall process by eliminating the need for separate key exchange or verification protocols, as the TPM independently validates the certificate's authenticity. The security assurance is improved through this autonomous verification, while the process complexity is managed by leveraging the TPM's built-in cryptographic capabilities.
Data Source
AI summary
Certification of a key, which a Trusted Platform Module (TPM) has attested as being non-migratable, can be performed in a single round trip between the certificate authority (CA) and the client that requests the certificate. The client creates a certificate request, and then has the TPM create an attestation identity key (AIK) that is bound to the certificate request. The client then asks the TPM to sign the new key as an attestation of non-migratability. The client then sends the certificate request, along with the attestation of non-migratability to the CA. The CA examines the certificate request and attestation of non-migratability. However, since the CA does not know whether the attestation has been made by a trusted TPM, it certifies the key but includes, in the certificate, an encrypted signature that can only be decrypted using the endorsement key of the trusted TPM.