package gcp import ( "encoding/json" "errors" "io" "cloud.google.com/go/compute/metadata" "github.com/edgelesssys/constellation/coordinator/attestation/vtpm" "github.com/edgelesssys/constellation/coordinator/oid" tpmclient "github.com/google/go-tpm-tools/client" "github.com/google/go-tpm-tools/proto/attest" ) // Issuer for GCP confidential VM attestation. type Issuer struct { oid.GCP *vtpm.Issuer } // NewIssuer initializes a new GCP Issuer. func NewIssuer() *Issuer { return &Issuer{ Issuer: vtpm.NewIssuer( vtpm.OpenVTPM, tpmclient.GceAttestationKeyRSA, getGCEInstanceInfo(metadataClient{}), ), } } // getGCEInstanceInfo fetches VM metadata used for attestation. func getGCEInstanceInfo(client gcpMetadataClient) func(io.ReadWriteCloser) ([]byte, error) { // Ideally we would want to use the endorsement public key certificate // However, this is not available on GCE instances // Workaround: Provide ShieldedVM instance info // The attestating party can request the VMs signing key using Google's API return func(io.ReadWriteCloser) ([]byte, error) { projectID, err := client.projectID() if err != nil { return nil, errors.New("unable to fetch projectID") } zone, err := client.zone() if err != nil { return nil, errors.New("unable to fetch zone") } instanceName, err := client.instanceName() if err != nil { return nil, errors.New("unable to fetch instance name") } return json.Marshal(attest.GCEInstanceInfo{ Zone: zone, ProjectId: projectID, InstanceName: instanceName, }) } } type gcpMetadataClient interface { projectID() (string, error) instanceName() (string, error) zone() (string, error) } type metadataClient struct{} func (c metadataClient) projectID() (string, error) { return metadata.ProjectID() } func (c metadataClient) instanceName() (string, error) { return metadata.InstanceName() } func (c metadataClient) zone() (string, error) { return metadata.Zone() }