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GCP & GoTPM Tools

Table of Contents

Variables

export GCI_NAME=PETES-SEV-SNP-TEST-0
export GCI_PROJECT=arweave-437622
export GCI_IMAGE=packer-1730219529 
export GCI_ZONE=us-central1-a

Create an AMD SEV-SNP Instance

gcloud compute instances create $GCI_NAME \
    --zone=$GCI_ZONE \
    --machine-type=n2d-standard-2 \
    --min-cpu-platform="AMD Milan" \
    --confidential-compute-type=SEV_SNP \
    --maintenance-policy=TERMINATE \
    --image-family=ubuntu-2404-lts-amd64 \
    --image-project=ubuntu-os-cloud \
    --project=$GCI_PROJECT \
    --network-interface=network-tier=PREMIUM,nic-type=GVNIC,stack-type=IPV4_ONLY,subnet=default \
    --tags=http-server,https-server \
    --shielded-secure-boot \
    --shielded-vtpm \
    --shielded-integrity-monitoring \
    --create-disk=auto-delete=yes,boot=yes,device-name=instance-20241030-131350,image=projects/$GCI_PROJECT/global/images/$GCI_IMAGE,mode=rw,size=20,type=pd-balanced

Create an Intel TDX Instance

gcloud compute instances create $GCI_NAME \
    --zone=$GCI_ZONE \
    --machine-type=c3-standard-4 \
    --confidential-compute-type=TDX \
    --maintenance-policy=TERMINATE \
    --image-family=ubuntu-2204-lts \
    --image-project=ubuntu-os-cloud \
    --project=$GCI_PROJECT \
    --network-interface=network-tier=PREMIUM,nic-type=GVNIC,stack-type=IPV4_ONLY,subnet=default \
    --tags=http-server,https-server \
    --shielded-secure-boot \
    --shielded-vtpm \
    --shielded-integrity-monitoring \
    --create-disk=auto-delete=yes,boot=yes,device-name=instance-20241030-131350,image=projects/$GCI_PROJECT/global/images/$GCI_IMAGE,mode=rw,size=20,type=pd-balanced

Connecting to the Instance

gcloud compute ssh --zone "$GCI_ZONE" "$GCI_NAME" --project "$GCI_PROJECT"

Useful Commands

List Available Machine Types

gcloud compute machine-types list --zones=$GCI_ZONE

Generate Random Nonces

  • 32-byte Nonce (for --nonce):

    head -c 32 /dev/urandom | xxd -p -c 64

  • 64-byte TEE Nonce (for --tee-nonce):

    head -c 64 /dev/urandom | xxd -p -c 128

Run gotpm Attestation

sudo gotpm attest --key AK --nonce <32 bytes (64 hex characters)> --tee-nonce <64 bytes (128 hex characters)> --tee-technology <sev-snp/tdx>

Notes

Note

The requirement to include both --nonce and --tee-nonce for the gotpm attest command, even when --tee-technology (e.g., sev-snp or tdx) is specified, indicates that both TPM and TEE layers of attestation are being validated in this command. Here’s why this is the case:

Dual-Layer Attestation in Confidential VMs

TPM Attestation Layer:

  • The --nonce parameter is required for the TPM (Trusted Platform Module) attestation. It acts as a freshness mechanism for the TPM-based portion of the attestation, preventing replay attacks by ensuring the response is unique to each request.
  • Even when the TEE technology is specified, gotpm still performs TPM-based attestation, which includes the TPM nonce (--nonce) in the attestation report.

TEE-Specific Attestation Layer:

  • The --tee-nonce parameter is required for the TEE (Trusted Execution Environment) attestation. This layer provides hardware-backed isolation (e.g., Intel TDX or AMD SEV-SNP), and the larger 64-byte nonce uniquely identifies the TEE attestation report.
  • The --tee-technology option (e.g., sev-snp or tdx) specifies which TEE environment to use, and --tee-nonce is essential for proving the freshness of the TEE report in that specific environment.

Why Both Nonces Are Required Together

Since the command produces an attestation report containing both TPM and TEE layers, each layer requires its own nonce:

  • --nonce (TPM layer): Required for the general TPM quote in the attestation.
  • --tee-nonce (TEE layer): Required specifically for the TEE report tied to sev-snp or tdx.

This design ensures that the attestation report is comprehensive and includes freshness proofs for both the TPM and TEE components, preventing replay attacks across both security layers. This dual nonce requirement is specific to environments where both TPM and TEE attestation are requested together, as in a Confidential VM using TEE.