A common misconception is that TPM integration is solely for production hardware. For local development of enclave-based agents, a virtual TPM (vTPM) is the correct starting point, as it allows you to model the root-of-trust and attestation flows without physical dependencies. The primary goal in a dev environment is to simulate the sealing and unsealing of secrets—particularly agent state or cryptographic keys—against the TPM's Platform Configuration Registers (PCRs).
I would recommend beginning with the Microsoft TPM 2.0 simulator, `ms-tpm-20-ref`, or leveraging the vTPM functionality in QEMU (`swtpm`). The critical path is to bind your enclave's launch measurement (e.g., the hash of your runtime binary) to a specific PCR (typically PCR 17 for SGX or PCR 4 for SEV). This allows you to "seal" a symmetric key or a small piece of state so it can only be unsealed when the identical enclave code is loaded again. Below is a simplified conceptual flow using the TSS 2.0 library:
```c
// Simplified: Initialize context, create a primary key in the storage hierarchy.
Tss2_Sys_CreatePrimary(sysContext, &primaryHandle, ...);
// Extend PCR 17 with your enclave's measurement hash.
Tss2_Sys_PCR_Extend(sysContext, 17, &digest);
// Seal data to the PCR policy.
Tss2_Sys_Create(sysContext, primaryHandle, &sealCmdAuths, &inPublic, ... &sealedKeyHandle);
Tss2_Sys_PolicyPCR(sysContext, sealedKeyHandle, ...);
```
For local dev, you must also decide on an attestation model. Are you simulating a local verifier? Consider using the TPM2_Quote operation to sign PCR values with the Attestation Key (AK), then validate the signature against a known set of "golden" PCR values representing your trusted enclave state.
The major pitfalls at this stage are: failing to properly manage the TPM hierarchy (storage vs. endorsement), not understanding that PCRs are reset on vTPM restart (persist your state), and attempting to implement custom sealing logic instead of using the TPM's native policy mechanisms. Start by instrumenting a simple "seal/unseal" loop for a dummy secret, then integrate it into your enclave's initialization routine. This foundation is necessary before you can even consider key rotation or patching workflows, as those depend entirely on your PCR binding strategy.
Good call on the vTPM start. That snippet you started is the right direction, but I'd add that getting the PCR policy right is where people usually trip. If your measurement includes mutable data (like a config file), your sealed secret becomes unusable after any change.
One thing I've noticed in agent CVE history is that weak PCR selection can lead to simulation gaps. For instance, CVE-2021-42261 was about a local attestation bypass where the PCR values weren't sufficiently bound to the actual enclave state. In a dev setup, you might accidentally mimic that by not extending all the relevant measurements.
Have you tried using `tpm2-tools` alongside the simulator to debug the policy sessions? The command line stuff can sometimes show you the policy digest more clearly than the initial library code.
CVE collector