Generate random salt for key derivation on init (#309)

Signed-off-by: Daniel Weiße <dw@edgeless.systems>

CHANGELOG.md

@@ -12,12 +12,14 @@ Styleguide for this document:
 -->
 
 # Changelog
+
 All notable changes to Constellation will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+
 ### Added
 
 - Kubernetes version is configured through an entry in `constellation-config.yaml`.
@@ -28,7 +30,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 
 - Nodes add themselves to the cluster after `constellation init` is done
-
 - Owner ID and Unique ID merged into a single value: Cluster ID
 
 ### Deprecated
@@ -38,27 +39,35 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - User facing WireGuard VPN
 
 ### Fixed
+
 - Correctly wait for `bootstrapper` to come online in `constellation init`
 
 ### Security
+
 - Create Kubernetes CA signed kubelet certificates on activation.
+- Add salt to key derivation
 
 ### Internal
 
 ## [1.3.1] - 2022-07-11
 
 ### Changed
+
 - Update default CoreOS image to latest version (1657199013).
 
 ### Fixed
+
 - Add load balancer path to Azure deployment so that PCR values can be read.
 - Show correct version number in `constellation version`.
 
 ### Removed
+
 - Support for Azure `Standard_*_v3` types.
 
 ## [1.3.0] - 2022-07-05
+
 ### Added
+
 - Early boot logging for GCP and Azure. [[Docs]](https://constellation-docs.edgeless.systems/6c320851-bdd2-41d5-bf10-e27427398692/#/workflows/troubleshooting?id=cloud-logging)
 - `constellation-access-manager` allows users to manage SSH users over a ConfigMap. Enables persistent and dynamic management of SSH users on multiple nodes, even after a reboot. [[Docs]](https://constellation-docs.edgeless.systems/6c320851-bdd2-41d5-bf10-e27427398692/#/workflows/ssh)
 - GCP-native Kubernetes load balancing. [[Docs]](https://constellation-docs.edgeless.systems/6c320851-bdd2-41d5-bf10-e27427398692/#/architecture/networking)
@@ -67,23 +76,30 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `constellation-id.json` in Constellation workspace now holds cluster IDs, to reduce required arguments in Constellation commands, e.g., `constellation verify`.
 
 ### Changed
+
 - New `constellation-activation-service` offloads Kubernetes node activation from monolithic Coordinator to Kubernetes native micro-service. [[ReadMe]](https://github.com/edgelesssys/constellation/blob/main/activation/README.md)
 - Improve user-friendliness of error messages in Constellation CLI.
 - Move verification from extracting attestation statements out of aTLS handshake to a dedicated `verify-service` in Kubernetes with gRPC and HTTP endpoints.
 
 ### Security
+
 - GCP WireGuard encryption via cilium.
 
 ### Internal
+
 - Refactore folder structure of repository to better reflect `internal` implementation and public API.
 - Extend `goleak` checks to all tests.
 
 ## [1.2.0] - 2022-06-02
+
 ### Changed
+
 - Replace flannel CNI with Cilium.
 
 ## [1.1.0] - 2022-06-02
+
 ### Added
+
 - CLI
   - Command `constellation recover` to re-initialize a completely stopped cluster.
   - Command `constellation config generate` to generate a default configuration file for a specific cloud provider.
@@ -96,6 +112,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Option to add SSH users on init.
 
 ### Changed
+
 - CLI UX
   - `constellation create` now requires a configuration file. The usual workflow is to run `constellation config generate` first.
   - Consistent command format with at most one argument and named flags otherwise.
@@ -110,17 +127,21 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - Rename *PCRs* to *Measurements*.
 
 ### Removed
+
 - Support for non-CVMs on GCP.
 
 ### Fixed
+
 - Pin Kubernetes version deployed by `kubeadm init`.
 
 ### Security
+
 - Replace single, never expiring Kubernetes join token with expiring unique tokens.
 - Apply CIS benchmark for kubeadm clusterconf and kubelet conf.
 - Enable Kubernetes audit log.
 
 ### Internal
+
 - Create GCP images in `constellation-images` project so that they can be shared with customers.
 - Add customer onboarding docs.
 - Add E2E test as Github Action.
@@ -128,6 +149,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Preparations for mutual ATLS.
 
 ## [1.0.0] - 2022-04-28
+
 Initial release of Constellation. With underlying WireGuard and Kubernetes compliant.
 
 [Unreleased]: https://github.com/edgelesssys/constellation/compare/v1.3.1...HEAD

bootstrapper/cmd/bootstrapper/test.go

@@ -3,7 +3,7 @@ package main
 import (
 	"context"
 
-	"github.com/edgelesssys/constellation/bootstrapper/internal/kubernetes"
+	"github.com/edgelesssys/constellation/bootstrapper/internal/kubernetes/k8sapi/resources"
 	"github.com/edgelesssys/constellation/bootstrapper/role"
 	"github.com/edgelesssys/constellation/internal/cloud/metadata"
 	"github.com/edgelesssys/constellation/internal/logger"
@@ -14,7 +14,7 @@ import (
 type clusterFake struct{}
 
 // InitCluster fakes bootstrapping a new cluster with the current node being the master, returning the arguments required to join the cluster.
-func (c *clusterFake) InitCluster(context.Context, []string, string, string, []byte, kubernetes.KMSConfig, map[string]string, *logger.Logger,
+func (c *clusterFake) InitCluster(context.Context, []string, string, string, []byte, resources.KMSConfig, map[string]string, *logger.Logger,
 ) ([]byte, error) {
 	return []byte{}, nil
 }

bootstrapper/initproto/init.pb.go

@@ -34,6 +34,7 @@ type InitRequest struct {
 	CloudServiceAccountUri string        `protobuf:"bytes,7,opt,name=cloud_service_account_uri,json=cloudServiceAccountUri,proto3" json:"cloud_service_account_uri,omitempty"`
 	KubernetesVersion      string        `protobuf:"bytes,8,opt,name=kubernetes_version,json=kubernetesVersion,proto3" json:"kubernetes_version,omitempty"`
 	SshUserKeys            []*SSHUserKey `protobuf:"bytes,9,rep,name=ssh_user_keys,json=sshUserKeys,proto3" json:"ssh_user_keys,omitempty"`
+	Salt                   []byte        `protobuf:"bytes,10,opt,name=salt,proto3" json:"salt,omitempty"`
 }
 
 func (x *InitRequest) Reset() {
@@ -131,6 +132,13 @@ func (x *InitRequest) GetSshUserKeys() []*SSHUserKey {
 	return nil
 }
 
+func (x *InitRequest) GetSalt() []byte {
+	if x != nil {
+		return x.Salt
+	}
+	return nil
+}
+
 type InitResponse struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
@@ -253,7 +261,7 @@ var File_init_proto protoreflect.FileDescriptor
 
 var file_init_proto_rawDesc = []byte{
 	0x0a, 0x0a, 0x69, 0x6e, 0x69, 0x74, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x12, 0x04, 0x69, 0x6e,
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@@ -279,26 +287,27 @@ var file_init_proto_rawDesc = []byte{
 	0x12, 0x34, 0x0a, 0x0d, 0x73, 0x73, 0x68, 0x5f, 0x75, 0x73, 0x65, 0x72, 0x5f, 0x6b, 0x65, 0x79,
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 }
 
 var (

bootstrapper/initproto/init.proto

@@ -18,6 +18,7 @@ message InitRequest {
   string cloud_service_account_uri = 7;
   string kubernetes_version = 8;
   repeated SSHUserKey ssh_user_keys = 9;
+  bytes salt = 10;
 }
 
 message InitResponse {

bootstrapper/internal/initserver/initserver.go

@@ -8,7 +8,7 @@ import (
 
 	"github.com/edgelesssys/constellation/bootstrapper/initproto"
 	"github.com/edgelesssys/constellation/bootstrapper/internal/diskencryption"
-	"github.com/edgelesssys/constellation/bootstrapper/internal/kubernetes"
+	"github.com/edgelesssys/constellation/bootstrapper/internal/kubernetes/k8sapi/resources"
 	"github.com/edgelesssys/constellation/bootstrapper/nodestate"
 	"github.com/edgelesssys/constellation/bootstrapper/role"
 	"github.com/edgelesssys/constellation/internal/atls"
@@ -79,7 +79,7 @@ func (s *Server) Init(ctx context.Context, req *initproto.InitRequest) (*initpro
 	log.Infof("Init called")
 
 	// generate values for cluster attestation
-	measurementSalt, clusterID, err := deriveMeasurementValues(req.MasterSecret)
+	measurementSalt, clusterID, err := deriveMeasurementValues(req.MasterSecret, req.Salt)
 	if err != nil {
 		return nil, status.Errorf(codes.Internal, "deriving measurement values: %s", err)
 	}
@@ -98,7 +98,7 @@ func (s *Server) Init(ctx context.Context, req *initproto.InitRequest) (*initpro
 		return nil, status.Error(codes.FailedPrecondition, "node is already being activated")
 	}
 
-	if err := s.setupDisk(req.MasterSecret); err != nil {
+	if err := s.setupDisk(req.MasterSecret, req.Salt); err != nil {
 		return nil, status.Errorf(codes.Internal, "setting up disk: %s", err)
 	}
 
@@ -115,8 +115,9 @@ func (s *Server) Init(ctx context.Context, req *initproto.InitRequest) (*initpro
 		req.CloudServiceAccountUri,
 		req.KubernetesVersion,
 		measurementSalt,
-		kubernetes.KMSConfig{
+		resources.KMSConfig{
 			MasterSecret:       req.MasterSecret,
+			Salt:               req.Salt,
 			KMSURI:             req.KmsUri,
 			StorageURI:         req.StorageUri,
 			KeyEncryptionKeyID: req.KeyEncryptionKeyId,
@@ -141,7 +142,7 @@ func (s *Server) Stop() {
 	s.grpcServer.GracefulStop()
 }
 
-func (s *Server) setupDisk(masterSecret []byte) error {
+func (s *Server) setupDisk(masterSecret, salt []byte) error {
 	if err := s.disk.Open(); err != nil {
 		return fmt.Errorf("opening encrypted disk: %w", err)
 	}
@@ -153,8 +154,7 @@ func (s *Server) setupDisk(masterSecret []byte) error {
 	}
 	uuid = strings.ToLower(uuid)
 
-	// TODO: Choose a way to salt the key derivation
+	diskKey, err := crypto.DeriveKey(masterSecret, salt, []byte(crypto.HKDFInfoPrefix+uuid), 32)
-	diskKey, err := crypto.DeriveKey(masterSecret, []byte("Constellation"), []byte(crypto.HKDFInfoPrefix+uuid), 32)
 	if err != nil {
 		return err
 	}
@@ -170,16 +170,16 @@ func sshProtoKeysToMap(keys []*initproto.SSHUserKey) map[string]string {
 	return keyMap
 }
 
-func deriveMeasurementValues(masterSecret []byte) (salt, clusterID []byte, err error) {
+func deriveMeasurementValues(masterSecret, hkdfSalt []byte) (salt, clusterID []byte, err error) {
 	salt, err = crypto.GenerateRandomBytes(crypto.RNGLengthDefault)
 	if err != nil {
 		return nil, nil, err
 	}
-	secret, err := attestation.DeriveMeasurementSecret(masterSecret)
+	secret, err := attestation.DeriveMeasurementSecret(masterSecret, hkdfSalt)
 	if err != nil {
 		return nil, nil, err
 	}
-	clusterID, err = attestation.DeriveClusterID(salt, secret)
+	clusterID, err = attestation.DeriveClusterID(secret, salt)
 	if err != nil {
 		return nil, nil, err
 	}
@@ -196,7 +196,7 @@ type ClusterInitializer interface {
 		cloudServiceAccountURI string,
 		k8sVersion string,
 		measurementSalt []byte,
-		kmsConfig kubernetes.KMSConfig,
+		kmsConfig resources.KMSConfig,
 		sshUserKeys map[string]string,
 		log *logger.Logger,
 	) ([]byte, error)

bootstrapper/internal/initserver/initserver_test.go

@@ -9,7 +9,7 @@ import (
 	"time"
 
 	"github.com/edgelesssys/constellation/bootstrapper/initproto"
-	"github.com/edgelesssys/constellation/bootstrapper/internal/kubernetes"
+	"github.com/edgelesssys/constellation/bootstrapper/internal/kubernetes/k8sapi/resources"
 	"github.com/edgelesssys/constellation/internal/file"
 	"github.com/edgelesssys/constellation/internal/logger"
 	"github.com/spf13/afero"
@@ -218,7 +218,7 @@ type stubClusterInitializer struct {
 	initClusterErr        error
 }
 
-func (i *stubClusterInitializer) InitCluster(context.Context, []string, string, string, []byte, kubernetes.KMSConfig, map[string]string, *logger.Logger,
+func (i *stubClusterInitializer) InitCluster(context.Context, []string, string, string, []byte, resources.KMSConfig, map[string]string, *logger.Logger,
 ) ([]byte, error) {
 	return i.initClusterKubeconfig, i.initClusterErr
 }

bootstrapper/internal/joinclient/client.go

@@ -231,7 +231,7 @@ func (c *JoinClient) startNodeAndJoin(ticket *joinproto.IssueJoinTicketResponse,
 		}
 	}()
 
-	clusterID, err := attestation.DeriveClusterID(ticket.MeasurementSalt, ticket.MeasurementSecret)
+	clusterID, err := attestation.DeriveClusterID(ticket.MeasurementSecret, ticket.MeasurementSalt)
 	if err != nil {
 		return err
 	}

bootstrapper/internal/kubernetes/k8sapi/resources/kms.go

@@ -23,8 +23,18 @@ type kmsDeployment struct {
 	ImagePullSecret    k8s.Secret
 }
 
+// KMSConfig is the configuration needed to set up Constellation's key management service.
+type KMSConfig struct {
+	MasterSecret       []byte
+	Salt               []byte
+	KMSURI             string
+	StorageURI         string
+	KeyEncryptionKeyID string
+	UseExistingKEK     bool
+}
+
 // NewKMSDeployment creates a new *kmsDeployment to use as the key management system inside Constellation.
-func NewKMSDeployment(csp string, masterSecret []byte) *kmsDeployment {
+func NewKMSDeployment(csp string, config KMSConfig) *kmsDeployment {
 	return &kmsDeployment{
 		ServiceAccount: k8s.ServiceAccount{
 			TypeMeta: meta.TypeMeta{
@@ -187,7 +197,11 @@ func NewKMSDeployment(csp string, masterSecret []byte) *kmsDeployment {
 													Items: []k8s.KeyToPath{
 														{
 															Key:  constants.ConstellationMasterSecretKey,
-															Path: constants.MasterSecretFilename,
+															Path: constants.ConstellationMasterSecretKey,
+														},
+														{
+															Key:  constants.ConstellationMasterSecretSalt,
+															Path: constants.ConstellationMasterSecretSalt,
 														},
 													},
 												},
@@ -228,7 +242,8 @@ func NewKMSDeployment(csp string, masterSecret []byte) *kmsDeployment {
 				Namespace: "kube-system",
 			},
 			Data: map[string][]byte{
-				constants.ConstellationMasterSecretKey: masterSecret,
+				constants.ConstellationMasterSecretKey:  config.MasterSecret,
+				constants.ConstellationMasterSecretSalt: config.Salt,
 			},
 			Type: "Opaque",
 		},

bootstrapper/internal/kubernetes/k8sapi/resources/kms_test.go

@@ -11,8 +11,7 @@ func TestKMSMarshalUnmarshal(t *testing.T) {
 	require := require.New(t)
 	assert := assert.New(t)
 
-	testMS := []byte{0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8}
+	kmsDepl := NewKMSDeployment("test", KMSConfig{MasterSecret: []byte{0x0, 0x1, 0x2}, Salt: []byte{0x3, 0x4, 0x5}})
-	kmsDepl := NewKMSDeployment("test", testMS)
 	data, err := kmsDepl.Marshal()
 	require.NoError(err)
 

bootstrapper/internal/kubernetes/kubernetes.go

@@ -68,18 +68,10 @@ func New(cloudProvider string, clusterUtil clusterUtil, configProvider configura
 	}
 }
 
-type KMSConfig struct {
-	MasterSecret       []byte
-	KMSURI             string
-	StorageURI         string
-	KeyEncryptionKeyID string
-	UseExistingKEK     bool
-}
-
 // InitCluster initializes a new Kubernetes cluster and applies pod network provider.
 func (k *KubeWrapper) InitCluster(
 	ctx context.Context, autoscalingNodeGroups []string, cloudServiceAccountURI, versionString string,
-	measurementSalt []byte, kmsConfig KMSConfig, sshUsers map[string]string, log *logger.Logger,
+	measurementSalt []byte, kmsConfig resources.KMSConfig, sshUsers map[string]string, log *logger.Logger,
 ) ([]byte, error) {
 	k8sVersion, err := versions.NewValidK8sVersion(versionString)
 	if err != nil {
@@ -187,7 +179,7 @@ func (k *KubeWrapper) InitCluster(
 		return nil, fmt.Errorf("setting up pod network: %w", err)
 	}
 
-	kms := resources.NewKMSDeployment(k.cloudProvider, kmsConfig.MasterSecret)
+	kms := resources.NewKMSDeployment(k.cloudProvider, kmsConfig)
 	if err = k.clusterUtil.SetupKMS(k.client, kms); err != nil {
 		return nil, fmt.Errorf("setting up kms: %w", err)
 	}

bootstrapper/internal/kubernetes/kubernetes_test.go

@@ -296,7 +296,7 @@ func TestInitCluster(t *testing.T) {
 				kubeconfigReader:       tc.kubeconfigReader,
 				getIPAddr:              func() (string, error) { return privateIP, nil },
 			}
-			_, err := kube.InitCluster(context.Background(), autoscalingNodeGroups, serviceAccountURI, string(tc.k8sVersion), nil, KMSConfig{MasterSecret: masterSecret}, nil, logger.NewTest(t))
+			_, err := kube.InitCluster(context.Background(), autoscalingNodeGroups, serviceAccountURI, string(tc.k8sVersion), nil, resources.KMSConfig{MasterSecret: masterSecret}, nil, logger.NewTest(t))
 
 			if tc.wantErr {
 				assert.Error(err)

cli/internal/cmd/init.go

@@ -115,7 +115,8 @@ func initialize(cmd *cobra.Command, dialer grpcDialer, serviceAccCreator service
 
 	req := &initproto.InitRequest{
 		AutoscalingNodeGroups:  autoscalingNodeGroups,
-		MasterSecret:           flags.masterSecret,
+		MasterSecret:           flags.masterSecret.Key,
+		Salt:                   flags.masterSecret.Salt,
 		KmsUri:                 kms.ClusterKMSURI,
 		StorageUri:             kms.NoStoreURI,
 		KeyEncryptionKeyId:     "",
@@ -129,11 +130,7 @@ func initialize(cmd *cobra.Command, dialer grpcDialer, serviceAccCreator service
 		return err
 	}
 
-	if err := writeOutput(resp, controlPlanes.PublicIPs()[0], cmd.OutOrStdout(), fileHandler); err != nil {
+	return writeOutput(resp, controlPlanes.PublicIPs()[0], cmd.OutOrStdout(), fileHandler)
-		return err
-	}
-
-	return nil
 }
 
 func initCall(ctx context.Context, dialer grpcDialer, ip string, req *initproto.InitRequest) (*initproto.InitResponse, error) {
@@ -185,7 +182,7 @@ func writeOutput(resp *initproto.InitResponse, ip string, wr io.Writer, fileHand
 	fmt.Fprintln(wr)
 
 	if err := fileHandler.Write(constants.AdminConfFilename, resp.Kubeconfig, file.OptNone); err != nil {
-		return fmt.Errorf("write kubeconfig: %w", err)
+		return fmt.Errorf("writing kubeconfig: %w", err)
 	}
 
 	idFile := clusterIDsFile{
@@ -236,38 +233,52 @@ func evalFlagArgs(cmd *cobra.Command, fileHandler file.Handler) (initFlags, erro
 // initFlags are the resulting values of flag preprocessing.
 type initFlags struct {
 	configPath   string
-	masterSecret []byte
+	masterSecret masterSecret
 	autoscale    bool
 }
 
+// masterSecret holds the master key and salt for deriving keys.
+type masterSecret struct {
+	Key  []byte `json:"key"`
+	Salt []byte `json:"salt"`
+}
+
 // readOrGenerateMasterSecret reads a base64 encoded master secret from file or generates a new 32 byte secret.
-func readOrGenerateMasterSecret(writer io.Writer, fileHandler file.Handler, filename string) ([]byte, error) {
+func readOrGenerateMasterSecret(writer io.Writer, fileHandler file.Handler, filename string) (masterSecret, error) {
 	if filename != "" {
-		// Try to read the base64 secret from file
+		var secret masterSecret
-		encodedSecret, err := fileHandler.Read(filename)
+		if err := fileHandler.ReadJSON(filename, &secret); err != nil {
-		if err != nil {
+			return masterSecret{}, err
-			return nil, err
 		}
-		decoded, err := base64.StdEncoding.DecodeString(string(encodedSecret))
+
-		if err != nil {
+		if len(secret.Key) < crypto.MasterSecretLengthMin {
-			return nil, err
+			return masterSecret{}, fmt.Errorf("provided master secret is smaller than the required minimum of %d Bytes", crypto.MasterSecretLengthMin)
 		}
-		if len(decoded) < crypto.MasterSecretLengthMin {
+		if len(secret.Salt) < crypto.RNGLengthDefault {
-			return nil, errors.New("provided master secret is smaller than the required minimum of 16 Bytes")
+			return masterSecret{}, fmt.Errorf("provided salt is smaller than the required minimum of %d Bytes", crypto.RNGLengthDefault)
 		}
-		return decoded, nil
+		return secret, nil
 	}
 
 	// No file given, generate a new secret, and save it to disk
-	masterSecret, err := crypto.GenerateRandomBytes(crypto.MasterSecretLengthDefault)
+	key, err := crypto.GenerateRandomBytes(crypto.MasterSecretLengthDefault)
 	if err != nil {
-		return nil, err
+		return masterSecret{}, err
 	}
-	if err := fileHandler.Write(constants.MasterSecretFilename, []byte(base64.StdEncoding.EncodeToString(masterSecret)), file.OptNone); err != nil {
+	salt, err := crypto.GenerateRandomBytes(crypto.RNGLengthDefault)
-		return nil, err
+	if err != nil {
+		return masterSecret{}, err
+	}
+	secret := masterSecret{
+		Key:  key,
+		Salt: salt,
+	}
+
+	if err := fileHandler.WriteJSON(constants.MasterSecretFilename, secret, file.OptNone); err != nil {
+		return masterSecret{}, err
 	}
 	fmt.Fprintf(writer, "Your Constellation master secret was successfully written to ./%s\n", constants.MasterSecretFilename)
-	return masterSecret, nil
+	return secret, nil
 }
 
 func getScalingGroupsFromState(stat state.ConstellationState, config *config.Config) (controlPlanes, workers cloudtypes.ScalingGroup, err error) {

cli/internal/cmd/init_test.go

@@ -256,59 +256,80 @@ func TestInitCompletion(t *testing.T) {
 
 func TestReadOrGeneratedMasterSecret(t *testing.T) {
 	testCases := map[string]struct {
-		filename    string
+		filename       string
-		filecontent string
+		createFileFunc func(handler file.Handler) error
-		createFile  bool
+		fs             func() afero.Fs
-		fs          func() afero.Fs
+		wantErr        bool
-		wantErr     bool
 	}{
 		"file with secret exists": {
-			filename:    "someSecret",
+			filename: "someSecret",
-			filecontent: base64.StdEncoding.EncodeToString([]byte("ConstellationSecret")),
+			fs:       afero.NewMemMapFs,
-			createFile:  true,
+			createFileFunc: func(handler file.Handler) error {
-			fs:          afero.NewMemMapFs,
+				return handler.WriteJSON(
-			wantErr:     false,
+					"someSecret",
+					masterSecret{Key: []byte("constellation-master-secret"), Salt: []byte("constellation-32Byte-length-salt")},
+					file.OptNone,
+				)
+			},
+			wantErr: false,
 		},
 		"no file given": {
-			filename:    "",
+			filename:       "",
-			filecontent: "",
+			createFileFunc: func(handler file.Handler) error { return nil },
-			fs:          afero.NewMemMapFs,
+			fs:             afero.NewMemMapFs,
-			wantErr:     false,
+			wantErr:        false,
 		},
 		"file does not exist": {
-			filename:    "nonExistingSecret",
+			filename:       "nonExistingSecret",
-			filecontent: "",
+			createFileFunc: func(handler file.Handler) error { return nil },
-			createFile:  false,
+			fs:             afero.NewMemMapFs,
-			fs:          afero.NewMemMapFs,
+			wantErr:        true,
-			wantErr:     true,
 		},
 		"file is empty": {
-			filename:    "emptySecret",
+			filename: "emptySecret",
-			filecontent: "",
+			createFileFunc: func(handler file.Handler) error {
-			createFile:  true,
+				return handler.Write("emptySecret", []byte{}, file.OptNone)
-			fs:          afero.NewMemMapFs,
+			},
-			wantErr:     true,
+			fs:      afero.NewMemMapFs,
+			wantErr: true,
 		},
-		"secret too short": {
+		"salt too short": {
-			filename:    "shortSecret",
+			filename: "shortSecret",
-			filecontent: base64.StdEncoding.EncodeToString([]byte("short")),
+			createFileFunc: func(handler file.Handler) error {
-			createFile:  true,
+				return handler.WriteJSON(
-			fs:          afero.NewMemMapFs,
+					"shortSecret",
-			wantErr:     true,
+					masterSecret{Key: []byte("constellation-master-secret"), Salt: []byte("short")},
+					file.OptNone,
+				)
+			},
+			fs:      afero.NewMemMapFs,
+			wantErr: true,
 		},
-		"secret not encoded": {
+		"key too short": {
-			filename:    "unencodedSecret",
+			filename: "shortSecret",
-			filecontent: "Constellation",
+			createFileFunc: func(handler file.Handler) error {
-			createFile:  true,
+				return handler.WriteJSON(
-			fs:          afero.NewMemMapFs,
+					"shortSecret",
-			wantErr:     true,
+					masterSecret{Key: []byte("short"), Salt: []byte("constellation-32Byte-length-salt")},
+					file.OptNone,
+				)
+			},
+			fs:      afero.NewMemMapFs,
+			wantErr: true,
+		},
+		"invalid file content": {
+			filename: "unencodedSecret",
+			createFileFunc: func(handler file.Handler) error {
+				return handler.Write("unencodedSecret", []byte("invalid-constellation-master-secret"), file.OptNone)
+			},
+			fs:      afero.NewMemMapFs,
+			wantErr: true,
 		},
 		"file not writeable": {
-			filename:    "",
+			filename:       "",
-			filecontent: "",
+			createFileFunc: func(handler file.Handler) error { return nil },
-			createFile:  false,
+			fs:             func() afero.Fs { return afero.NewReadOnlyFs(afero.NewMemMapFs()) },
-			fs:          func() afero.Fs { return afero.NewReadOnlyFs(afero.NewMemMapFs()) },
+			wantErr:        true,
-			wantErr:     true,
 		},
 	}
 
@@ -318,10 +339,7 @@ func TestReadOrGeneratedMasterSecret(t *testing.T) {
 			require := require.New(t)
 
 			fileHandler := file.NewHandler(tc.fs())
-
+			require.NoError(tc.createFileFunc(fileHandler))
-			if tc.createFile {
-				require.NoError(fileHandler.Write(tc.filename, []byte(tc.filecontent), file.OptNone))
-			}
 
 			var out bytes.Buffer
 			secret, err := readOrGenerateMasterSecret(&out, fileHandler, tc.filename)
@@ -337,9 +355,10 @@ func TestReadOrGeneratedMasterSecret(t *testing.T) {
 					tc.filename = strings.Trim(filename[1], "\n")
 				}
 
-				content, err := fileHandler.Read(tc.filename)
+				var masterSecret masterSecret
-				require.NoError(err)
+				require.NoError(fileHandler.ReadJSON(tc.filename, &masterSecret))
-				assert.Equal(content, []byte(base64.StdEncoding.EncodeToString(secret)))
+				assert.Equal(masterSecret.Key, secret.Key)
+				assert.Equal(masterSecret.Salt, secret.Salt)
 			}
 		})
 	}

cli/internal/cmd/recover.go

@@ -1,7 +1,6 @@
 package cmd
 
 import (
-	"encoding/base64"
 	"errors"
 	"fmt"
 	"regexp"
@@ -35,11 +34,11 @@ func NewRecoverCmd() *cobra.Command {
 	must(cmd.MarkFlagRequired("endpoint"))
 	cmd.Flags().String("disk-uuid", "", "disk UUID of the encrypted state disk (required)")
 	must(cmd.MarkFlagRequired("disk-uuid"))
-	cmd.Flags().String("master-secret", constants.MasterSecretFilename, "path to base64-encoded master secret")
+	cmd.Flags().String("master-secret", constants.MasterSecretFilename, "path to master secret file")
 	return cmd
 }
 
-func runRecover(cmd *cobra.Command, args []string) error {
+func runRecover(cmd *cobra.Command, _ []string) error {
 	fileHandler := file.NewHandler(afero.NewOsFs())
 	recoveryClient := &proto.KeyClient{}
 	defer recoveryClient.Close()
@@ -47,11 +46,16 @@ func runRecover(cmd *cobra.Command, args []string) error {
 }
 
 func recover(cmd *cobra.Command, fileHandler file.Handler, recoveryClient recoveryClient) error {
-	flags, err := parseRecoverFlags(cmd, fileHandler)
+	flags, err := parseRecoverFlags(cmd)
 	if err != nil {
 		return err
 	}
 
+	var masterSecret masterSecret
+	if err := fileHandler.ReadJSON(flags.secretPath, &masterSecret); err != nil {
+		return err
+	}
+
 	var stat state.ConstellationState
 	if err := fileHandler.ReadJSON(constants.StateFilename, &stat); err != nil {
 		return err
@@ -74,12 +78,12 @@ func recover(cmd *cobra.Command, fileHandler file.Handler, recoveryClient recove
 		return err
 	}
 
-	diskKey, err := deriveStateDiskKey(flags.masterSecret, flags.diskUUID)
+	diskKey, err := deriveStateDiskKey(masterSecret.Key, masterSecret.Salt, flags.diskUUID)
 	if err != nil {
 		return err
 	}
 
-	measurementSecret, err := attestation.DeriveMeasurementSecret(flags.masterSecret)
+	measurementSecret, err := attestation.DeriveMeasurementSecret(masterSecret.Key, masterSecret.Salt)
 	if err != nil {
 		return err
 	}
@@ -92,7 +96,7 @@ func recover(cmd *cobra.Command, fileHandler file.Handler, recoveryClient recove
 	return nil
 }
 
-func parseRecoverFlags(cmd *cobra.Command, fileHandler file.Handler) (recoverFlags, error) {
+func parseRecoverFlags(cmd *cobra.Command) (recoverFlags, error) {
 	endpoint, err := cmd.Flags().GetString("endpoint")
 	if err != nil {
 		return recoverFlags{}, fmt.Errorf("parsing endpoint argument: %w", err)
@@ -115,10 +119,6 @@ func parseRecoverFlags(cmd *cobra.Command, fileHandler file.Handler) (recoverFla
 	if err != nil {
 		return recoverFlags{}, fmt.Errorf("parsing master-secret path argument: %w", err)
 	}
-	masterSecret, err := readMasterSecret(fileHandler, masterSecretPath)
-	if err != nil {
-		return recoverFlags{}, fmt.Errorf("reading the master secret from file %s: %w", masterSecretPath, err)
-	}
 
 	configPath, err := cmd.Flags().GetString("config")
 	if err != nil {
@@ -126,35 +126,21 @@ func parseRecoverFlags(cmd *cobra.Command, fileHandler file.Handler) (recoverFla
 	}
 
 	return recoverFlags{
-		endpoint:     endpoint,
+		endpoint:   endpoint,
-		diskUUID:     diskUUID,
+		diskUUID:   diskUUID,
-		masterSecret: masterSecret,
+		secretPath: masterSecretPath,
-		configPath:   configPath,
+		configPath: configPath,
 	}, nil
 }
 
 type recoverFlags struct {
-	endpoint     string
+	endpoint   string
-	diskUUID     string
+	diskUUID   string
-	masterSecret []byte
+	secretPath string
-	configPath   string
+	configPath string
 }
 
-// readMasterSecret reads a base64 encoded master secret from file.
+// deriveStateDiskKey derives a state disk key from a master key, a salt, and a disk UUID.
-func readMasterSecret(fileHandler file.Handler, filename string) ([]byte, error) {
+func deriveStateDiskKey(masterKey, salt []byte, diskUUID string) ([]byte, error) {
-	// Try to read the base64 secret from file
+	return crypto.DeriveKey(masterKey, salt, []byte(crypto.HKDFInfoPrefix+diskUUID), crypto.StateDiskKeyLength)
-	encodedSecret, err := fileHandler.Read(filename)
-	if err != nil {
-		return nil, err
-	}
-	decoded, err := base64.StdEncoding.DecodeString(string(encodedSecret))
-	if err != nil {
-		return nil, err
-	}
-	return decoded, nil
-}
-
-// deriveStateDiskKey derives a state disk key from a master secret and a disk UUID.
-func deriveStateDiskKey(masterKey []byte, diskUUID string) ([]byte, error) {
-	return crypto.DeriveKey(masterKey, []byte("Constellation"), []byte(crypto.HKDFInfoPrefix+diskUUID), crypto.StateDiskKeyLength)
 }

cli/internal/cmd/recover_test.go

@@ -42,6 +42,13 @@ func TestRecover(t *testing.T) {
 	validState := state.ConstellationState{CloudProvider: "GCP"}
 	invalidCSPState := state.ConstellationState{CloudProvider: "invalid"}
 
+	writeMasterSecret := func(require *require.Assertions) afero.Fs {
+		fs := afero.NewMemMapFs()
+		handler := file.NewHandler(fs)
+		require.NoError(handler.WriteJSON("constellation-mastersecret.json", masterSecret{Key: []byte("master-secret"), Salt: []byte("salt")}, file.OptNone))
+		return fs
+	}
+
 	testCases := map[string]struct {
 		setupFs          func(*require.Assertions) afero.Fs
 		existingState    state.ConstellationState
@@ -55,62 +62,51 @@ func TestRecover(t *testing.T) {
 		wantKey          []byte
 	}{
 		"works": {
-			setupFs: func(require *require.Assertions) afero.Fs {
+			setupFs:       writeMasterSecret,
-				fs := afero.NewMemMapFs()
-				require.NoError(afero.WriteFile(fs, "constellation-mastersecret.base64", []byte("Y29uc3RlbGxhdGlvbi1tYXN0ZXItc2VjcmV0LWxlbmc="), 0o777))
-				return fs
-			},
 			existingState: validState,
 			client:        &stubRecoveryClient{},
 			endpointFlag:  "192.0.2.1",
 			diskUUIDFlag:  "00000000-0000-0000-0000-000000000000",
-			wantKey:       []byte{0x4d, 0x34, 0x19, 0x1a, 0xf9, 0x23, 0xb9, 0x61, 0x55, 0x9b, 0xb2, 0x6, 0x15, 0x1b, 0x5f, 0xe, 0x21, 0xc2, 0xe5, 0x18, 0x1c, 0xfa, 0x32, 0x79, 0xa4, 0x6b, 0x84, 0x86, 0x7e, 0xd7, 0xf6, 0x76},
+			wantKey: []byte{
+				0xcb, 0x31, 0x9d, 0x3d, 0xe0, 0xb7, 0x8a, 0xe9, 0x20, 0xc0, 0x62, 0x00, 0x8f, 0xe4, 0x58, 0xa1,
+				0x87, 0x85, 0x5d, 0xa0, 0xca, 0xe2, 0x04, 0x5c, 0x80, 0xe8, 0xe6, 0xd5, 0x8a, 0x6c, 0xcb, 0x49,
+			},
 		},
 		"uppercase disk uuid works": {
-			setupFs: func(require *require.Assertions) afero.Fs {
+			setupFs:       writeMasterSecret,
-				fs := afero.NewMemMapFs()
-				require.NoError(afero.WriteFile(fs, "constellation-mastersecret.base64", []byte("Y29uc3RlbGxhdGlvbi1tYXN0ZXItc2VjcmV0LWxlbmc="), 0o777))
-				return fs
-			},
 			existingState: validState,
 			client:        &stubRecoveryClient{},
 			endpointFlag:  "192.0.2.1",
 			diskUUIDFlag:  "ABCDEFAB-CDEF-ABCD-ABCD-ABCDEFABCDEF",
-			wantKey:       []byte{0x7e, 0xc0, 0xa8, 0x84, 0xc4, 0x7, 0xda, 0x1, 0xed, 0xa9, 0xc8, 0x87, 0x77, 0xad, 0x86, 0x7c, 0x7d, 0x40, 0xa7, 0x28, 0x3d, 0xbd, 0x92, 0xea, 0xa1, 0x84, 0x67, 0x78, 0x58, 0x76, 0x13, 0x70},
+			wantKey: []byte{
+				0x9b, 0xb8, 0x4a, 0x62, 0x01, 0xb3, 0x32, 0xf6, 0xf2, 0x79, 0x43, 0x09, 0x86, 0xe7, 0x25, 0x0e,
+				0xd2, 0x77, 0xcb, 0x14, 0xe8, 0x8f, 0x38, 0xab, 0xe7, 0xd6, 0x25, 0x14, 0xa5, 0xa1, 0xff, 0xda,
+			},
 		},
 		"lowercase disk uuid results in same key": {
-			setupFs: func(require *require.Assertions) afero.Fs {
+			setupFs:       writeMasterSecret,
-				fs := afero.NewMemMapFs()
-				require.NoError(afero.WriteFile(fs, "constellation-mastersecret.base64", []byte("Y29uc3RlbGxhdGlvbi1tYXN0ZXItc2VjcmV0LWxlbmc="), 0o777))
-				return fs
-			},
 			existingState: validState,
 			client:        &stubRecoveryClient{},
 			endpointFlag:  "192.0.2.1",
 			diskUUIDFlag:  "abcdefab-cdef-abcd-abcd-abcdefabcdef",
-			wantKey:       []byte{0x7e, 0xc0, 0xa8, 0x84, 0xc4, 0x7, 0xda, 0x1, 0xed, 0xa9, 0xc8, 0x87, 0x77, 0xad, 0x86, 0x7c, 0x7d, 0x40, 0xa7, 0x28, 0x3d, 0xbd, 0x92, 0xea, 0xa1, 0x84, 0x67, 0x78, 0x58, 0x76, 0x13, 0x70},
+			wantKey: []byte{
+				0x9b, 0xb8, 0x4a, 0x62, 0x01, 0xb3, 0x32, 0xf6, 0xf2, 0x79, 0x43, 0x09, 0x86, 0xe7, 0x25, 0x0e,
+				0xd2, 0x77, 0xcb, 0x14, 0xe8, 0x8f, 0x38, 0xab, 0xe7, 0xd6, 0x25, 0x14, 0xa5, 0xa1, 0xff, 0xda,
+			},
 		},
 		"missing flags": {
 			setupFs: func(require *require.Assertions) afero.Fs { return afero.NewMemMapFs() },
 			wantErr: true,
 		},
 		"missing config": {
-			setupFs: func(require *require.Assertions) afero.Fs {
+			setupFs:      writeMasterSecret,
-				fs := afero.NewMemMapFs()
-				require.NoError(afero.WriteFile(fs, "constellation-mastersecret.base64", []byte("Y29uc3RlbGxhdGlvbi1tYXN0ZXItc2VjcmV0LWxlbmc="), 0o777))
-				return fs
-			},
 			endpointFlag: "192.0.2.1",
 			diskUUIDFlag: "00000000-0000-0000-0000-000000000000",
 			configFlag:   "nonexistent-config",
 			wantErr:      true,
 		},
 		"missing state": {
-			setupFs: func(require *require.Assertions) afero.Fs {
+			setupFs:       writeMasterSecret,
-				fs := afero.NewMemMapFs()
-				require.NoError(afero.WriteFile(fs, "constellation-mastersecret.base64", []byte("Y29uc3RlbGxhdGlvbi1tYXN0ZXItc2VjcmV0LWxlbmc="), 0o777))
-				return fs
-			},
 			existingState: validState,
 			endpointFlag:  "192.0.2.1",
 			diskUUIDFlag:  "00000000-0000-0000-0000-000000000000",
@@ -118,22 +114,14 @@ func TestRecover(t *testing.T) {
 			wantErr:       true,
 		},
 		"invalid cloud provider": {
-			setupFs: func(require *require.Assertions) afero.Fs {
+			setupFs:       writeMasterSecret,
-				fs := afero.NewMemMapFs()
-				require.NoError(afero.WriteFile(fs, "constellation-mastersecret.base64", []byte("Y29uc3RlbGxhdGlvbi1tYXN0ZXItc2VjcmV0LWxlbmc="), 0o777))
-				return fs
-			},
 			existingState: invalidCSPState,
 			endpointFlag:  "192.0.2.1",
 			diskUUIDFlag:  "00000000-0000-0000-0000-000000000000",
 			wantErr:       true,
 		},
 		"connect fails": {
-			setupFs: func(require *require.Assertions) afero.Fs {
+			setupFs:       writeMasterSecret,
-				fs := afero.NewMemMapFs()
-				require.NoError(afero.WriteFile(fs, "constellation-mastersecret.base64", []byte("Y29uc3RlbGxhdGlvbi1tYXN0ZXItc2VjcmV0LWxlbmc="), 0o777))
-				return fs
-			},
 			existingState: validState,
 			client:        &stubRecoveryClient{connectErr: errors.New("connect failed")},
 			endpointFlag:  "192.0.2.1",
@@ -141,11 +129,7 @@ func TestRecover(t *testing.T) {
 			wantErr:       true,
 		},
 		"pushing state key fails": {
-			setupFs: func(require *require.Assertions) afero.Fs {
+			setupFs:       writeMasterSecret,
-				fs := afero.NewMemMapFs()
-				require.NoError(afero.WriteFile(fs, "constellation-mastersecret.base64", []byte("Y29uc3RlbGxhdGlvbi1tYXN0ZXItc2VjcmV0LWxlbmc="), 0o777))
-				return fs
-			},
 			existingState: validState,
 			client:        &stubRecoveryClient{pushStateDiskKeyErr: errors.New("pushing key failed")},
 			endpointFlag:  "192.0.2.1",
@@ -160,7 +144,7 @@ func TestRecover(t *testing.T) {
 			require := require.New(t)
 
 			cmd := NewRecoverCmd()
-			cmd.Flags().String("config", "", "") // register persisten flag manually
+			cmd.Flags().String("config", "", "") // register persistent flag manually
 			out := &bytes.Buffer{}
 			cmd.SetOut(out)
 			cmd.SetErr(&bytes.Buffer{})
@@ -212,36 +196,29 @@ func TestParseRecoverFlags(t *testing.T) {
 			args:    []string{"-e", "192.0.2.1:2", "--disk-uuid", "invalid"},
 			wantErr: true,
 		},
-		"invalid master secret path": {
-			args:    []string{"-e", "192.0.2.1:2", "--disk-uuid", "12345678-1234-1234-1234-123456789012", "--master-secret", "invalid"},
-			wantErr: true,
-		},
 		"minimal args set": {
 			args: []string{"-e", "192.0.2.1:2", "--disk-uuid", "12345678-1234-1234-1234-123456789012"},
 			wantFlags: recoverFlags{
-				endpoint:     "192.0.2.1:2",
+				endpoint:   "192.0.2.1:2",
-				diskUUID:     "12345678-1234-1234-1234-123456789012",
+				diskUUID:   "12345678-1234-1234-1234-123456789012",
-				masterSecret: []byte("constellation-master-secret-leng"),
+				secretPath: "constellation-mastersecret.json",
 			},
 		},
 		"all args set": {
-			args: []string{
+			args: []string{"-e", "192.0.2.1:2", "--disk-uuid", "12345678-1234-1234-1234-123456789012", "--config", "config-path", "--master-secret", "/path/super-secret.json"},
-				"-e", "192.0.2.1:2", "--disk-uuid", "12345678-1234-1234-1234-123456789012",
-				"--master-secret", "constellation-mastersecret.base64", "--config", "config-path",
-			},
 			wantFlags: recoverFlags{
-				endpoint:     "192.0.2.1:2",
+				endpoint:   "192.0.2.1:2",
-				diskUUID:     "12345678-1234-1234-1234-123456789012",
+				diskUUID:   "12345678-1234-1234-1234-123456789012",
-				masterSecret: []byte("constellation-master-secret-leng"),
+				secretPath: "/path/super-secret.json",
-				configPath:   "config-path",
+				configPath: "config-path",
 			},
 		},
 		"uppercase disk-uuid is converted to lowercase": {
 			args: []string{"-e", "192.0.2.1:2", "--disk-uuid", "ABCDEFAB-CDEF-ABCD-ABCD-ABCDEFABCDEF"},
 			wantFlags: recoverFlags{
-				endpoint:     "192.0.2.1:2",
+				endpoint:   "192.0.2.1:2",
-				diskUUID:     "abcdefab-cdef-abcd-abcd-abcdefabcdef",
+				diskUUID:   "abcdefab-cdef-abcd-abcd-abcdefabcdef",
-				masterSecret: []byte("constellation-master-secret-leng"),
+				secretPath: "constellation-mastersecret.json",
 			},
 		},
 	}
@@ -251,12 +228,10 @@ func TestParseRecoverFlags(t *testing.T) {
 			assert := assert.New(t)
 			require := require.New(t)
 
-			fs := afero.NewMemMapFs()
-			require.NoError(afero.WriteFile(fs, "constellation-mastersecret.base64", []byte("Y29uc3RlbGxhdGlvbi1tYXN0ZXItc2VjcmV0LWxlbmc="), 0o777))
 			cmd := NewRecoverCmd()
 			cmd.Flags().String("config", "", "") // register persistent flag manually
 			require.NoError(cmd.ParseFlags(tc.args))
-			flags, err := parseRecoverFlags(cmd, file.NewHandler(fs))
+			flags, err := parseRecoverFlags(cmd)
 
 			if tc.wantErr {
 				assert.Error(err)
@@ -268,52 +243,10 @@ func TestParseRecoverFlags(t *testing.T) {
 	}
 }
 
-func TestReadMasterSecret(t *testing.T) {
-	testCases := map[string]struct {
-		fileContents     []byte
-		filename         string
-		wantMasterSecret []byte
-		wantErr          bool
-	}{
-		"invalid base64": {
-			fileContents: []byte("invalid"),
-			filename:     "constellation-mastersecret.base64",
-			wantErr:      true,
-		},
-		"invalid filename": {
-			fileContents: []byte("Y29uc3RlbGxhdGlvbi1tYXN0ZXItc2VjcmV0LWxlbmc="),
-			filename:     "invalid",
-			wantErr:      true,
-		},
-		"correct master secret": {
-			fileContents:     []byte("Y29uc3RlbGxhdGlvbi1tYXN0ZXItc2VjcmV0LWxlbmc="),
-			filename:         "constellation-mastersecret.base64",
-			wantMasterSecret: []byte("constellation-master-secret-leng"),
-		},
-	}
-
-	for name, tc := range testCases {
-		t.Run(name, func(t *testing.T) {
-			assert := assert.New(t)
-			require := require.New(t)
-
-			fs := afero.NewMemMapFs()
-			require.NoError(afero.WriteFile(fs, "constellation-mastersecret.base64", tc.fileContents, 0o777))
-			masterSecret, err := readMasterSecret(file.NewHandler(fs), tc.filename)
-
-			if tc.wantErr {
-				assert.Error(err)
-				return
-			}
-			assert.NoError(err)
-			assert.Equal(tc.wantMasterSecret, masterSecret)
-		})
-	}
-}
-
 func TestDeriveStateDiskKey(t *testing.T) {
 	testCases := map[string]struct {
 		masterKey        []byte
+		salt             []byte
 		diskUUID         string
 		wantStateDiskKey []byte
 	}{
@@ -322,10 +255,14 @@ func TestDeriveStateDiskKey(t *testing.T) {
 				0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
 				0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
 			},
+			salt: []byte{
+				0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
+				0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
+			},
 			diskUUID: "00000000-0000-0000-0000-000000000000",
 			wantStateDiskKey: []byte{
-				0xc6, 0xe0, 0xae, 0xfc, 0xbe, 0x7b, 0x7e, 0x87, 0x7a, 0xdd, 0xb2, 0x87, 0xe0, 0xcd, 0x4c, 0xe4,
+				0x2b, 0x5c, 0x82, 0x9f, 0x69, 0x1b, 0xfd, 0x42, 0x32, 0xf8, 0xaa, 0xc4, 0x64, 0xbc, 0xcc, 0x07,
-				0xde, 0xee, 0xb3, 0x57, 0xaa, 0x6c, 0xc9, 0x44, 0x90, 0xc4, 0x07, 0x72, 0x01, 0x7d, 0xd6, 0xb1,
+				0xe6, 0x05, 0xc7, 0xc8, 0xe8, 0x2c, 0xbc, 0xa0, 0x98, 0x37, 0xe8, 0x6d, 0x0b, 0x6d, 0x06, 0x65,
 			},
 		},
 		"all 0xff": {
@@ -333,10 +270,14 @@ func TestDeriveStateDiskKey(t *testing.T) {
 				0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
 				0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
 			},
+			salt: []byte{
+				0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+				0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+			},
 			diskUUID: "ffffffff-ffff-ffff-ffff-ffffffffffff",
 			wantStateDiskKey: []byte{
-				0x00, 0x74, 0x4c, 0xb0, 0x92, 0x9d, 0x20, 0x08, 0xfa, 0x72, 0xac, 0xd2, 0xb6, 0xe4, 0xc6, 0x6f,
+				0x14, 0x84, 0xaa, 0x39, 0xd3, 0x41, 0x5e, 0x90, 0x6e, 0x07, 0x94, 0x0f, 0xf2, 0x15, 0xd8, 0xb1,
-				0xa3, 0x53, 0x16, 0xb1, 0x9e, 0x77, 0x42, 0xe8, 0xd3, 0x66, 0xe8, 0x22, 0x33, 0xfc, 0x63, 0x4d,
+				0xee, 0xe7, 0x05, 0xd3, 0x02, 0x7d, 0xba, 0x93, 0x30, 0x6a, 0xf4, 0xab, 0xff, 0x4f, 0x70, 0xbe,
 			},
 		},
 	}
@@ -345,7 +286,7 @@ func TestDeriveStateDiskKey(t *testing.T) {
 		t.Run(name, func(t *testing.T) {
 			assert := assert.New(t)
 
-			stateDiskKey, err := deriveStateDiskKey(tc.masterKey, tc.diskUUID)
+			stateDiskKey, err := deriveStateDiskKey(tc.masterKey, tc.salt, tc.diskUUID)
 
 			assert.NoError(err)
 			assert.Equal(tc.wantStateDiskKey, stateDiskKey)

internal/attestation/attestation.go

@@ -13,12 +13,11 @@ const (
 )
 
 // DeriveClusterID derives the cluster ID from a salt and secret value.
-func DeriveClusterID(salt, secret []byte) ([]byte, error) {
+func DeriveClusterID(secret, salt []byte) ([]byte, error) {
 	return crypto.DeriveKey(secret, salt, []byte(crypto.HKDFInfoPrefix+clusterIDContext), crypto.DerivedKeyLengthDefault)
 }
 
 // DeriveMeasurementSecret derives the secret value needed to derive ClusterID.
-func DeriveMeasurementSecret(masterSecret []byte) ([]byte, error) {
+func DeriveMeasurementSecret(masterSecret, salt []byte) ([]byte, error) {
-	// TODO: replace hard coded salt
+	return crypto.DeriveKey(masterSecret, salt, []byte(crypto.HKDFInfoPrefix+MeasurementSecretContext), crypto.DerivedKeyLengthDefault)
-	return crypto.DeriveKey(masterSecret, []byte("Constellation"), []byte(crypto.HKDFInfoPrefix+MeasurementSecretContext), crypto.DerivedKeyLengthDefault)
 }

internal/constants/constants.go

@@ -17,6 +17,8 @@ const (
 	ConstellationMasterSecretStoreName = "constellation-mastersecret"
 	// ConstellationMasterSecretKey is the name of the key for master secret in the master secret store secret.
 	ConstellationMasterSecretKey = "mastersecret"
+	// ConstellationMasterSecretSalt is the name of the key for salt in the master secret store secret.
+	ConstellationMasterSecretSalt = "salt"
 
 	//
 	// Ports.
@@ -50,7 +52,7 @@ const (
 	ConfigFilename          = "constellation-conf.yaml"
 	DebugdConfigFilename    = "cdbg-conf.yaml"
 	AdminConfFilename       = "constellation-admin.conf"
-	MasterSecretFilename    = "constellation-mastersecret.base64"
+	MasterSecretFilename    = "constellation-mastersecret.json"
 	WGQuickConfigFilename   = "wg0.conf"
 	CoreOSAdminConfFilename = "/etc/kubernetes/admin.conf"
 	KubeadmCertificateDir   = "/etc/kubernetes/pki"

internal/crypto/crypto.go

@@ -25,8 +25,6 @@ const (
 )
 
 // DeriveKey derives a key from a secret.
-//
-// TODO: decide on a secure key derivation function.
 func DeriveKey(secret, salt, info []byte, length uint) ([]byte, error) {
 	hkdf := hkdf.New(sha256.New, secret, salt, info)
 	key := make([]byte, length)

internal/versions/versions.go

@@ -30,9 +30,9 @@ func IsSupportedK8sVersion(version string) bool {
 const (
 	// Constellation images.
 	// These images are built in a way that they support all versions currently listed in VersionConfigs.
-	JoinImage          = "ghcr.io/edgelesssys/constellation/join-service:v1.3.2-0.20220725190044-ba09c9c6"
+	JoinImage          = "ghcr.io/edgelesssys/constellation/join-service:v1.3.2-0.20220720081316-baf7427f"
 	AccessManagerImage = "ghcr.io/edgelesssys/constellation/access-manager:v1.3.2-0.20220714151638-d295be31"
-	KmsImage           = "ghcr.io/edgelesssys/constellation/kmsserver:v1.3.2-0.20220722135959-3e250b12"
+	KmsImage           = "ghcr.io/edgelesssys/constellation/kmsserver:v1.3.2-0.20220720081316-baf7427f"
 	VerificationImage  = "ghcr.io/edgelesssys/constellation/verification-service:v1.3.2-0.20220714151638-d295be31"
 	GcpGuestImage      = "ghcr.io/edgelesssys/gcp-guest-agent:latest"
 

joinservice/internal/kms/kms.go

@@ -30,8 +30,8 @@ func New(log *logger.Logger, endpoint string) Client {
 // GetDataKey returns a data encryption key for the given UUID.
 func (c Client) GetDataKey(ctx context.Context, keyID string, length int) ([]byte, error) {
 	log := c.log.With(zap.String("keyID", keyID), zap.String("endpoint", c.endpoint))
-	// TODO: update credentials if we enable aTLS on the KMS
+	// the KMS does not use aTLS since traffic is only routed through the Constellation cluster
-	// For now this is fine since traffic is only routed through the Constellation cluster
+	// cluster internal connections are considered trustworthy
 	log.Infof("Connecting to KMS at %s", c.endpoint)
 	conn, err := grpc.DialContext(ctx, c.endpoint, grpc.WithTransportCredentials(insecure.NewCredentials()))
 	if err != nil {

kms/cmd/main.go

@@ -2,9 +2,9 @@ package main
 
 import (
 	"context"
+	"encoding/base64"
 	"errors"
 	"flag"
-	"fmt"
 	"path/filepath"
 	"strconv"
 	"time"
@@ -21,7 +21,8 @@ import (
 
 func main() {
 	port := flag.String("port", strconv.Itoa(constants.KMSPort), "Port gRPC server listens on")
-	masterSecretPath := flag.String("master-secret", filepath.Join(constants.ServiceBasePath, constants.MasterSecretFilename), "Path to the Constellation master secret")
+	masterSecretPath := flag.String("master-secret", filepath.Join(constants.ServiceBasePath, constants.ConstellationMasterSecretKey), "Path to the Constellation master secret")
+	saltPath := flag.String("salt", filepath.Join(constants.ServiceBasePath, constants.ConstellationMasterSecretSalt), "Path to the Constellation salt")
 	verbosity := flag.Int("v", 0, logger.CmdLineVerbosityDescription)
 
 	flag.Parse()
@@ -30,15 +31,28 @@ func main() {
 	log.With(zap.String("version", constants.VersionInfo)).
 		Infof("Constellation Key Management Service")
 
-	// set up Key Management Service
+	// read master secret and salt
-	masterKey, err := readMainSecret(*masterSecretPath)
+	file := file.NewHandler(afero.NewOsFs())
+	masterKey, err := file.Read(*masterSecretPath)
 	if err != nil {
 		log.With(zap.Error(err)).Fatalf("Failed to read master secret")
 	}
+	if len(masterKey) < crypto.MasterSecretLengthMin {
+		log.With(zap.Error(errors.New("invalid key length"))).Fatalf("Provided master secret is smaller than the required minimum of %d bytes", crypto.MasterSecretLengthMin)
+	}
+	salt, err := file.Read(*saltPath)
+	if err != nil {
+		log.With(zap.Error(err)).Fatalf("Failed to read salt")
+	}
+	if len(salt) < crypto.RNGLengthDefault {
+		log.With(zap.Error(errors.New("invalid salt length"))).Fatalf("Expected salt to be %d bytes, but got %d", crypto.RNGLengthDefault, len(salt))
+	}
+	keyURI := setup.ClusterKMSURI + "?salt=" + base64.URLEncoding.EncodeToString(salt)
 
+	// set up Key Management Service
 	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Minute)
 	defer cancel()
-	conKMS, err := setup.SetUpKMS(ctx, setup.NoStoreURI, setup.ClusterKMSURI)
+	conKMS, err := setup.SetUpKMS(ctx, setup.NoStoreURI, keyURI)
 	if err != nil {
 		log.With(zap.Error(err)).Fatalf("Failed to setup KMS")
 	}
@@ -50,22 +64,3 @@ func main() {
 		log.With(zap.Error(err)).Fatalf("Failed to run KMS server")
 	}
 }
-
-// readMainSecret reads the base64 encoded main secret file from specified path and returns the secret as bytes.
-func readMainSecret(fileName string) ([]byte, error) {
-	if fileName == "" {
-		return nil, errors.New("no filename to master secret provided")
-	}
-
-	fileHandler := file.NewHandler(afero.NewOsFs())
-
-	secretBytes, err := fileHandler.Read(fileName)
-	if err != nil {
-		return nil, err
-	}
-	if len(secretBytes) < crypto.MasterSecretLengthMin {
-		return nil, fmt.Errorf("provided master secret is smaller than the required minimum of %d bytes", crypto.MasterSecretLengthMin)
-	}
-
-	return secretBytes, nil
-}

kms/kms/cluster/cluster.go

@@ -10,6 +10,12 @@ import (
 // ClusterKMS implements the kms.CloudKMS interface for in cluster key management.
 type ClusterKMS struct {
 	masterKey []byte
+	salt      []byte
+}
+
+// New creates a new ClusterKMS.
+func New(salt []byte) *ClusterKMS {
+	return &ClusterKMS{salt: salt}
 }
 
 // CreateKEK sets the ClusterKMS masterKey.
@@ -23,6 +29,5 @@ func (c *ClusterKMS) GetDEK(ctx context.Context, kekID string, dekID string, dek
 	if len(c.masterKey) == 0 {
 		return nil, errors.New("master key not set for Constellation KMS")
 	}
-	// TODO: Choose a way to salt key derivation
+	return crypto.DeriveKey(c.masterKey, c.salt, []byte(dekID), uint(dekSize))
-	return crypto.DeriveKey(c.masterKey, []byte("Constellation"), []byte(dekID), uint(dekSize))
 }

kms/setup/setup.go

@@ -2,6 +2,7 @@ package setup
 
 import (
 	"context"
+	"encoding/base64"
 	"fmt"
 	"net/url"
 	"strconv"
@@ -123,7 +124,11 @@ func getKMS(ctx context.Context, kmsURI string, store kms.Storage) (kms.CloudKMS
 		return gcp.New(ctx, project, location, keyRing, store, kmspb.ProtectionLevel(protectionLvl))
 
 	case "cluster-kms":
-		return &cluster.ClusterKMS{}, nil
+		salt, err := getClusterKMSConfig(uri)
+		if err != nil {
+			return nil, err
+		}
+		return cluster.New(salt), nil
 
 	default:
 		return nil, fmt.Errorf("unknown KMS type: %s", uri.Host)
@@ -186,6 +191,14 @@ func getGCPStorageConfig(uri *url.URL) (string, string, error) {
 	return r[0], r[1], err
 }
 
+func getClusterKMSConfig(uri *url.URL) ([]byte, error) {
+	r, err := getConfig(uri.Query(), []string{"salt"})
+	if err != nil {
+		return nil, err
+	}
+	return base64.URLEncoding.DecodeString(r[0])
+}
+
 // getConfig parses url query values, returning a map of the requested values.
 // Returns an error if a key has no value.
 // This function MUST always return a slice of the same length as len(keys).

kms/setup/setup_test.go

@@ -2,6 +2,7 @@ package setup
 
 import (
 	"context"
+	"encoding/base64"
 	"fmt"
 	"net/url"
 	"testing"
@@ -73,7 +74,7 @@ func TestGetKMS(t *testing.T) {
 		wantErr bool
 	}{
 		"cluster kms": {
-			uri:     ClusterKMSURI,
+			uri:     fmt.Sprintf("%s?salt=%s", ClusterKMSURI, base64.URLEncoding.EncodeToString([]byte("salt"))),
 			wantErr: false,
 		},
 		"aws kms": {
@@ -124,11 +125,11 @@ func TestGetKMS(t *testing.T) {
 func TestSetUpKMS(t *testing.T) {
 	assert := assert.New(t)
 
-	kms, err := SetUpKMS(context.TODO(), "storage://unknown", "kms://unknown")
+	kms, err := SetUpKMS(context.Background(), "storage://unknown", "kms://unknown")
 	assert.Error(err)
 	assert.Nil(kms)
 
-	kms, err = SetUpKMS(context.Background(), "storage://no-store", "kms://cluster-kms")
+	kms, err = SetUpKMS(context.Background(), "storage://no-store", "kms://cluster-kms?salt="+base64.URLEncoding.EncodeToString([]byte("salt")))
 	assert.NoError(err)
 	assert.NotNil(kms)
 }
@@ -186,6 +187,23 @@ func TestGetGCPKMSConfig(t *testing.T) {
 	assert.Error(err)
 }
 
+func TestGetClusterKMSConfig(t *testing.T) {
+	assert := assert.New(t)
+	require := require.New(t)
+
+	expectedSalt := []byte{
+		0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9, 0xa, 0xb, 0xc, 0xd, 0xe, 0xf,
+		0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9, 0xa, 0xb, 0xc, 0xd, 0xe, 0xf,
+	}
+
+	uri, err := url.Parse(ClusterKMSURI + "?salt=" + base64.URLEncoding.EncodeToString(expectedSalt))
+	require.NoError(err)
+
+	salt, err := getClusterKMSConfig(uri)
+	assert.NoError(err)
+	assert.Equal(expectedSalt, salt)
+}
+
 func TestGetConfig(t *testing.T) {
 	const testURI = "test://config?name=test-name&data=test-data&value=test-value"
 

state/setup/setup.go

@@ -82,7 +82,7 @@ getKey:
 	if err != nil {
 		return err
 	}
-	clusterID, err := attestation.DeriveClusterID(measurementSalt, measurementSecret)
+	clusterID, err := attestation.DeriveClusterID(measurementSecret, measurementSalt)
 	if err != nil {
 		return err
 	}