s3proxy: add keyservice integration

Encrypt each object with a random DEK and attach
the encrypted DEK as object metadata.
Encrpt the DEK with a key from the keyservice.
All objects use the same KEK until a keyrotation
takes place.

bazel/toolchains/go_module_deps.bzl

@@ -3050,6 +3050,7 @@ def go_dependencies():
         sum = "h1:YjkZLJ7K3inKgMZ0wzCU9OHqc+UqMQyXsPXnf3Cl2as=",
         version = "v1.9.2",
     )
+
     go_repository(
         name = "com_github_hexops_gotextdiff",
         build_file_generation = "on",
@@ -5017,6 +5018,15 @@ def go_dependencies():
         sum = "h1:RWIZEg2iJ8/g6fDDYzMpobmaoGh5OLl4AXtGUGPcqCs=",
         version = "v1.2.0",
     )
+    go_repository(
+        name = "com_github_tink_crypto_tink_go_v2",
+        build_file_generation = "on",
+        build_file_proto_mode = "disable_global",
+        importpath = "github.com/tink-crypto/tink-go/v2",
+        replace = "github.com/derpsteb/tink-go/v2",
+        sum = "h1:FVii9oXvddz9sFir5TRYjQKrzJLbVD/hibT+SnRSDzg=",
+        version = "v2.0.0-20231002051717-a808e454eed6",
+    )
 
     go_repository(
         name = "com_github_titanous_rocacheck",

go.mod

@@ -35,6 +35,7 @@ replace (
 	github.com/edgelesssys/constellation/v2/operators/constellation-node-operator/v2/api => ./operators/constellation-node-operator/api
 	github.com/google/go-tpm => github.com/thomasten/go-tpm v0.0.0-20230629092004-f43f8e2a59eb
 	github.com/martinjungblut/go-cryptsetup => github.com/daniel-weisse/go-cryptsetup v0.0.0-20230705150314-d8c07bd1723c
+	github.com/tink-crypto/tink-go/v2 v2.0.0 => github.com/derpsteb/tink-go/v2 v2.0.0-20231002051717-a808e454eed6
 )
 
 require (
@@ -108,6 +109,7 @@ require (
 	github.com/spf13/cobra v1.7.0
 	github.com/stretchr/testify v1.8.4
 	github.com/theupdateframework/go-tuf v0.5.2
+	github.com/tink-crypto/tink-go/v2 v2.0.0
 	go.uber.org/goleak v1.2.1
 	go.uber.org/zap v1.26.0
 	golang.org/x/crypto v0.13.0

go.sum

@@ -298,6 +298,8 @@ github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSs
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/denisenkom/go-mssqldb v0.9.0/go.mod h1:xbL0rPBG9cCiLr28tMa8zpbdarY27NDyej4t/EjAShU=
+github.com/derpsteb/tink-go/v2 v2.0.0-20231002051717-a808e454eed6 h1:FVii9oXvddz9sFir5TRYjQKrzJLbVD/hibT+SnRSDzg=
+github.com/derpsteb/tink-go/v2 v2.0.0-20231002051717-a808e454eed6/go.mod h1:QAbyq9LZncomYnScxlfaHImbV4ieNIe6bnu/Xcqqox4=
 github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=
 github.com/dgryski/go-sip13 v0.0.0-20181026042036-e10d5fee7954/go.mod h1:vAd38F8PWV+bWy6jNmig1y/TA+kYO4g3RSRF0IAv0no=
 github.com/dimchansky/utfbom v1.1.1 h1:vV6w1AhK4VMnhBno/TPVCoK9U/LP0PkLCS9tbxHdi/U=

s3proxy/cmd/main.go

@@ -57,7 +57,10 @@ func main() {
 func runServer(flags cmdFlags, log *logger.Logger) error {
 	log.With(zap.String("ip", flags.ip), zap.Int("port", defaultPort), zap.String("region", flags.region)).Infof("listening")
 
-	router := router.New(flags.region, log)
+	router, err := router.New(flags.region, flags.kmsEndpoint, log)
+	if err != nil {
+		return fmt.Errorf("creating router: %w", err)
+	}
 
 	server := http.Server{
 		Addr:    fmt.Sprintf("%s:%d", flags.ip, defaultPort),
@@ -92,6 +95,7 @@ func parseFlags() (cmdFlags, error) {
 	ip := flag.String("ip", defaultIP, "ip to listen on")
 	region := flag.String("region", defaultRegion, "AWS region in which target bucket is located")
 	certLocation := flag.String("cert", defaultCertLocation, "location of TLS certificate")
+	kmsEndpoint := flag.String("kms", "key-service.kube-system:9000", "endpoint of the KMS service to get key encryption keys from")
 	level := flag.Int("level", defaultLogLevel, "log level")
 
 	flag.Parse()
@@ -107,7 +111,14 @@ func parseFlags() (cmdFlags, error) {
 	// 	return cmdFlags{}, fmt.Errorf("parsing log level: %w", err)
 	// }
 
-	return cmdFlags{noTLS: *noTLS, ip: netIP.String(), region: *region, certLocation: *certLocation, logLevel: *level}, nil
+	return cmdFlags{
+		noTLS:        *noTLS,
+		ip:           netIP.String(),
+		region:       *region,
+		certLocation: *certLocation,
+		kmsEndpoint:  *kmsEndpoint,
+		logLevel:     *level,
+	}, nil
 }
 
 type cmdFlags struct {
@@ -115,6 +126,7 @@ type cmdFlags struct {
 	ip           string
 	region       string
 	certLocation string
+	kmsEndpoint  string
 	// TODO(derpsteb): enable once we are on go 1.21.
 	// logLevel slog.Level
 	logLevel int

s3proxy/deploy/README.md

@@ -1,5 +1,8 @@
 # Deploying s3proxy
 
+**Caution:** Using s3proxy outside Constellation is insecure as the connection between the key management service (KMS) and s3proxy is protected by Constellation's WireGuard VPN.
+The VPN is a feature of Constellation and will not be present by default in other environments.
+
 Disclaimer: the following steps will be automated next.
 - Within `constellation/build`: `bazel run //:devbuild`
 - Copy the container name displayed for the s3proxy image. Look for the line starting with `[@//bazel/release:s3proxy_push]`.

s3proxy/internal/crypto/BUILD.bazel

@@ -1,8 +1,24 @@
 load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("//bazel/go:go_test.bzl", "go_test")
 
 go_library(
     name = "crypto",
     srcs = ["crypto.go"],
     importpath = "github.com/edgelesssys/constellation/v2/s3proxy/internal/crypto",
     visibility = ["//s3proxy:__subpackages__"],
+    deps = [
+        "@com_github_tink_crypto_tink_go_v2//aead/subtle",
+        "@com_github_tink_crypto_tink_go_v2//kwp/subtle",
+        "@com_github_tink_crypto_tink_go_v2//subtle/random",
+    ],
+)
+
+go_test(
+    name = "crypto_test",
+    srcs = ["crypto_test.go"],
+    embed = [":crypto"],
+    deps = [
+        "@com_github_stretchr_testify//assert",
+        "@com_github_stretchr_testify//require",
+    ],
 )

s3proxy/internal/crypto/crypto.go

@@ -7,73 +7,67 @@ SPDX-License-Identifier: AGPL-3.0-only
 /*
 Package crypto provides encryption and decryption functions for the s3proxy.
 It uses AES-256-GCM to encrypt and decrypt data.
-A new nonce is generated for each encryption operation.
 */
 package crypto
 
 import (
-	"crypto/aes"
-	"crypto/cipher"
-	"crypto/rand"
-	"io"
+	"fmt"
+
+	aeadsubtle "github.com/tink-crypto/tink-go/v2/aead/subtle"
+	kwpsubtle "github.com/tink-crypto/tink-go/v2/kwp/subtle"
+	"github.com/tink-crypto/tink-go/v2/subtle/random"
 )
 
-// Encrypt takes a 32 byte key and encrypts a plaintext using AES-256-GCM.
-// Output format is 12 byte nonce + ciphertext.
-func Encrypt(plaintext, key []byte) ([]byte, error) {
-	// Enforce AES-256
-	if len(key) != 32 {
-		return nil, aes.KeySizeError(len(key))
-	}
-
-	// None should not be reused more often that 2^32 times:
-	// https://pkg.go.dev/crypto/cipher#NewGCM
-	// Assuming n encryption operations per second, the key has to be rotated every:
-	// n=1: 2^32 / (60*60*24*365*10) = 135 years.
-	// n=10: 2^32 / (60*60*24*365*10) = 13.5 years.
-	// n=100: 2^32 / (60*60*24*365*10) = 1.3 years.
-	// n=1000: 2^32 / (60*60*24*365*10) = 50 days.
-	nonce := make([]byte, 12)
-	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
-		return nil, err
-	}
-
-	block, err := aes.NewCipher(key)
+// Encrypt generates a random key to encrypt a plaintext using AES-256-GCM.
+// The generated key is encrypted using the supplied key encryption key (KEK).
+// The ciphertext and encrypted data encryption key (DEK) are returned.
+func Encrypt(plaintext []byte, kek [32]byte) (ciphertext []byte, encryptedDEK []byte, err error) {
+	dek := random.GetRandomBytes(32)
+	aesgcm, err := aeadsubtle.NewAESGCMSIV(dek)
 	if err != nil {
-		return nil, err
+		return nil, nil, fmt.Errorf("getting aesgcm: %w", err)
 	}
-	aesgcm, err := cipher.NewGCM(block)
+
+	ciphertext, err = aesgcm.Encrypt(plaintext, []byte(""))
 	if err != nil {
-		return nil, err
+		return nil, nil, fmt.Errorf("encrypting plaintext: %w", err)
 	}
-	ciphertext := aesgcm.Seal(nil, nonce, plaintext, nil)
 
-	// Prepend the nonce to the ciphertext.
-	ciphertext = append(nonce, ciphertext...)
+	keywrapper, err := kwpsubtle.NewKWP(kek[:])
+	if err != nil {
+		return nil, nil, fmt.Errorf("getting kwp: %w", err)
+	}
 
-	return ciphertext, nil
+	encryptedDEK, err = keywrapper.Wrap(dek)
+	if err != nil {
+		return nil, nil, fmt.Errorf("wrapping dek: %w", err)
+	}
+
+	return ciphertext, encryptedDEK, nil
 }
 
-// Decrypt takes a 32 byte key and decrypts a ciphertext using AES-256-GCM.
-// ciphertext is formatted as 12 byte nonce + ciphertext.
-func Decrypt(ciphertext []byte, key []byte) ([]byte, error) {
-	// Enforce AES-256
-	if len(key) != 32 {
-		return nil, aes.KeySizeError(len(key))
-	}
-
-	// Extract the nonce from the ciphertext.
-	nonce := ciphertext[:12]
-	ciphertext = ciphertext[12:]
-
-	block, err := aes.NewCipher(key)
+// Decrypt decrypts a ciphertext using AES-256-GCM.
+// The encrypted DEK is decrypted using the supplied KEK.
+func Decrypt(ciphertext, encryptedDEK []byte, kek [32]byte) ([]byte, error) {
+	keywrapper, err := kwpsubtle.NewKWP(kek[:])
 	if err != nil {
-		return nil, err
-	}
-	aesgcm, err := cipher.NewGCM(block)
-	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("getting kwp: %w", err)
 	}
 
-	return aesgcm.Open(nil, nonce, ciphertext, nil)
+	dek, err := keywrapper.Unwrap(encryptedDEK)
+	if err != nil {
+		return nil, fmt.Errorf("unwrapping dek: %w", err)
+	}
+
+	aesgcm, err := aeadsubtle.NewAESGCMSIV(dek)
+	if err != nil {
+		return nil, fmt.Errorf("getting aesgcm: %w", err)
+	}
+
+	plaintext, err := aesgcm.Decrypt(ciphertext, []byte(""))
+	if err != nil {
+		return nil, fmt.Errorf("decrypting ciphertext: %w", err)
+	}
+
+	return plaintext, nil
 }

s3proxy/internal/crypto/crypto_test.go

@@ -0,0 +1,48 @@
+/*
+Copyright (c) Edgeless Systems GmbH
+
+SPDX-License-Identifier: AGPL-3.0-only
+*/
+package crypto
+
+import (
+	"crypto/rand"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestEncryptDecrypt(t *testing.T) {
+	tests := map[string]struct {
+		plaintext []byte
+	}{
+		"simple": {
+			plaintext: []byte("hello, world"),
+		},
+		"long": {
+			plaintext: []byte("Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed non risus. Suspendisse lectus tortor, dignissim sit amet, adipiscing nec, ultricies sed, dolor."),
+		},
+	}
+
+	for name, tt := range tests {
+		t.Run(name, func(t *testing.T) {
+			kek := [32]byte{}
+			_, err := rand.Read(kek[:])
+			require.NoError(t, err)
+
+			ciphertext, encryptedDEK, err := Encrypt(tt.plaintext, kek)
+			require.NoError(t, err)
+
+			assert.NotContains(t, ciphertext, tt.plaintext)
+
+			// Decrypt the ciphertext using the KEK and encrypted DEK
+			decrypted, err := Decrypt(ciphertext, encryptedDEK, kek)
+			require.NoError(t, err)
+
+			// Verify that the decrypted plaintext matches the original plaintext
+			assert.Equal(t, tt.plaintext, decrypted, fmt.Sprintf("expected plaintext %s, got %s", tt.plaintext, decrypted))
+		})
+	}
+}

s3proxy/internal/kms/BUILD.bazel

@@ -0,0 +1,29 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("//bazel/go:go_test.bzl", "go_test")
+
+go_library(
+    name = "kms",
+    srcs = ["kms.go"],
+    importpath = "github.com/edgelesssys/constellation/v2/s3proxy/internal/kms",
+    visibility = ["//s3proxy:__subpackages__"],
+    deps = [
+        "//internal/logger",
+        "//keyservice/keyserviceproto",
+        "@org_golang_google_grpc//:go_default_library",
+        "@org_golang_google_grpc//credentials/insecure",
+    ],
+)
+
+go_test(
+    name = "kms_test",
+    srcs = ["kms_test.go"],
+    embed = [":kms"],
+    deps = [
+        "//internal/logger",
+        "//keyservice/keyserviceproto",
+        "@com_github_stretchr_testify//assert",
+        "@org_golang_google_grpc//:go_default_library",
+        "@org_golang_google_grpc//test/bufconn",
+        "@org_uber_go_goleak//:goleak",
+    ],
+)

s3proxy/internal/kms/kms.go

@@ -0,0 +1,76 @@
+/*
+Copyright (c) Edgeless Systems GmbH
+
+SPDX-License-Identifier: AGPL-3.0-only
+*/
+
+/*
+Package kms is used to interact with the Constellation keyservice.
+So far it is a copy of the joinservice's kms package.
+*/
+package kms
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/edgelesssys/constellation/v2/internal/logger"
+	"github.com/edgelesssys/constellation/v2/keyservice/keyserviceproto"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+)
+
+// Client interacts with Constellation's keyservice.
+type Client struct {
+	log      *logger.Logger
+	endpoint string
+	grpc     grpcClient
+}
+
+// New creates a new KMS.
+func New(log *logger.Logger, endpoint string) Client {
+	return Client{
+		log:      log,
+		endpoint: endpoint,
+		grpc:     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("keyID", keyID, "endpoint", c.endpoint)
+	// the KMS does not use aTLS since traffic is only routed through the Constellation cluster
+	// cluster internal connections are considered trustworthy
+	log.Infof("Connecting to KMS")
+	conn, err := grpc.DialContext(ctx, c.endpoint, grpc.WithTransportCredentials(insecure.NewCredentials()))
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+
+	log.Infof("Requesting data key")
+	res, err := c.grpc.GetDataKey(
+		ctx,
+		&keyserviceproto.GetDataKeyRequest{
+			DataKeyId: keyID,
+			Length:    uint32(length),
+		},
+		conn,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("fetching data encryption key from Constellation KMS: %w", err)
+	}
+
+	log.Infof("Data key request successful")
+	return res.DataKey, nil
+}
+
+type grpcClient interface {
+	GetDataKey(context.Context, *keyserviceproto.GetDataKeyRequest, *grpc.ClientConn) (*keyserviceproto.GetDataKeyResponse, error)
+}
+
+type client struct{}
+
+func (c client) GetDataKey(ctx context.Context, req *keyserviceproto.GetDataKeyRequest, conn *grpc.ClientConn) (*keyserviceproto.GetDataKeyResponse, error) {
+	return keyserviceproto.NewAPIClient(conn).GetDataKey(ctx, req)
+}

s3proxy/internal/kms/kms_test.go

@@ -0,0 +1,72 @@
+/*
+Copyright (c) Edgeless Systems GmbH
+
+SPDX-License-Identifier: AGPL-3.0-only
+*/
+
+package kms
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/edgelesssys/constellation/v2/internal/logger"
+	"github.com/edgelesssys/constellation/v2/keyservice/keyserviceproto"
+	"github.com/stretchr/testify/assert"
+	"go.uber.org/goleak"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/test/bufconn"
+)
+
+type stubClient struct {
+	getDataKeyErr error
+	dataKey       []byte
+}
+
+func (c *stubClient) GetDataKey(context.Context, *keyserviceproto.GetDataKeyRequest, *grpc.ClientConn) (*keyserviceproto.GetDataKeyResponse, error) {
+	return &keyserviceproto.GetDataKeyResponse{DataKey: c.dataKey}, c.getDataKeyErr
+}
+
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m)
+}
+
+func TestGetDataKey(t *testing.T) {
+	testCases := map[string]struct {
+		client  *stubClient
+		wantErr bool
+	}{
+		"GetDataKey success": {
+			client: &stubClient{dataKey: []byte{0x1, 0x2, 0x3}},
+		},
+		"GetDataKey error": {
+			client:  &stubClient{getDataKeyErr: errors.New("error")},
+			wantErr: true,
+		},
+	}
+
+	for name, tc := range testCases {
+		t.Run(name, func(t *testing.T) {
+			assert := assert.New(t)
+
+			listener := bufconn.Listen(1)
+			defer listener.Close()
+
+			client := New(
+				logger.NewTest(t),
+				listener.Addr().String(),
+			)
+
+			client.grpc = tc.client
+
+			res, err := client.GetDataKey(context.Background(), "disk-uuid", 32)
+			if tc.wantErr {
+				assert.Error(err)
+			} else {
+				assert.NoError(err)
+				assert.Equal(tc.client.dataKey, res)
+			}
+		})
+	}
+}

s3proxy/internal/router/BUILD.bazel

@@ -12,6 +12,7 @@ go_library(
     deps = [
         "//internal/logger",
         "//s3proxy/internal/crypto",
+        "//s3proxy/internal/kms",
         "//s3proxy/internal/s3",
         "@com_github_aws_aws_sdk_go_v2_service_s3//:s3",
         "@org_uber_go_zap//:zap",

s3proxy/internal/router/object.go

@@ -8,6 +8,7 @@ package router
 
 import (
 	"context"
+	"encoding/hex"
 	"io"
 	"net/http"
 	"net/url"
@@ -23,15 +24,14 @@ import (
 )
 
 const (
-	// testingKey is a temporary encryption key used for testing.
-	// TODO (derpsteb): This key needs to be fetched from Constellation's keyservice.
-	testingKey = "01234567890123456789012345678901"
-	// encryptionTag is the key used to tag objects that are encrypted with this proxy. Presence of the key implies the object needs to be decrypted.
-	encryptionTag = "constellation-encryption"
+	// dekTag is the name of the header that holds the encrypted data encryption key for the attached object. Presence of the key implies the object needs to be decrypted.
+	// Use lowercase only, as AWS automatically lowercases all metadata keys.
+	dekTag = "constellation-dek"
 )
 
 // object bundles data to implement http.Handler methods that use data from incoming requests.
 type object struct {
+	kek                       [32]byte
 	client                    s3Client
 	key                       string
 	bucket                    string
@@ -113,10 +113,16 @@ func (o object) get(w http.ResponseWriter, r *http.Request) {
 	}
 
 	plaintext := body
-	decrypt, ok := output.Metadata[encryptionTag]
+	rawEncryptedDEK, ok := output.Metadata[dekTag]
+	if ok {
+		encryptedDEK, err := hex.DecodeString(rawEncryptedDEK)
+		if err != nil {
+			o.log.Errorf("GetObject decoding DEK", "error", err)
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
 
-	if ok && decrypt == "true" {
-		plaintext, err = crypto.Decrypt(body, []byte(testingKey))
+		plaintext, err = crypto.Decrypt(body, encryptedDEK, o.kek)
 		if err != nil {
 			o.log.With(zap.Error(err)).Errorf("GetObject decrypting response")
 			http.Error(w, err.Error(), http.StatusInternalServerError)
@@ -132,18 +138,13 @@ func (o object) get(w http.ResponseWriter, r *http.Request) {
 
 // put is a http.HandlerFunc that implements the PUT method for objects.
 func (o object) put(w http.ResponseWriter, r *http.Request) {
-	o.log.Debugf("putObject", "key", o.key, "host", o.bucket)
-
-	ciphertext, err := crypto.Encrypt(o.data, []byte(testingKey))
+	ciphertext, encryptedDEK, err := crypto.Encrypt(o.data, o.kek)
 	if err != nil {
 		o.log.With(zap.Error(err)).Errorf("PutObject")
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
 	}
-	// We need to tag objects that are encrypted with this proxy,
-	// because there might be objects in a bucket that are not encrypted.
-	// GetObject needs to be able to recognize these objects and skip decryption.
-	o.metadata[encryptionTag] = "true"
+	o.metadata[dekTag] = hex.EncodeToString(encryptedDEK)
 
 	output, err := o.client.PutObject(r.Context(), o.bucket, o.key, o.tags, o.contentType, o.objectLockLegalHoldStatus, o.objectLockMode, o.sseCustomerAlgorithm, o.sseCustomerKey, o.sseCustomerKeyMD5, o.objectLockRetainUntilDate, o.metadata, ciphertext)
 	if err != nil {

s3proxy/internal/router/router.go

@@ -10,11 +10,18 @@ It decides which packages to forward and which to intercept.
 
 The routing logic in this file is taken from this blog post: https://benhoyt.com/writings/go-routing/#regex-switch.
 We should be able to replace this once this is part of the stdlib: https://github.com/golang/go/issues/61410.
+
+If the router intercepts a PutObject request it will encrypt the body before forwarding it to the S3 API.
+The stored object will have a tag that holds an encrypted data encryption key (DEK).
+That DEK is used to encrypt the object's body.
+The DEK is generated randomly for each PutObject request.
+The DEK is encrypted with a key encryption key (KEK) fetched from Constellation's keyservice.
 */
 package router
 
 import (
 	"bytes"
+	"context"
 	"crypto/md5"
 	"crypto/sha256"
 	"encoding/base64"
@@ -28,10 +35,17 @@ import (
 	"time"
 
 	"github.com/edgelesssys/constellation/v2/internal/logger"
+	"github.com/edgelesssys/constellation/v2/s3proxy/internal/kms"
 	"github.com/edgelesssys/constellation/v2/s3proxy/internal/s3"
 	"go.uber.org/zap"
 )
 
+const (
+	// Use a 32*8 = 256 bit key for AES-256.
+	kekSizeBytes = 32
+	kekID        = "s3proxy-kek"
+)
+
 var (
 	keyPattern          = regexp.MustCompile("/(.+)")
 	bucketAndKeyPattern = regexp.MustCompile("/([^/?]+)/(.+)")
@@ -40,12 +54,26 @@ var (
 // Router implements the interception logic for the s3proxy.
 type Router struct {
 	region string
+	kek    [32]byte
 	log    *logger.Logger
 }
 
 // New creates a new Router.
-func New(region string, log *logger.Logger) Router {
-	return Router{region: region, log: log}
+func New(region, endpoint string, log *logger.Logger) (Router, error) {
+	kms := kms.New(log, endpoint)
+
+	// Get the key encryption key that encrypts all DEKs.
+	kek, err := kms.GetDataKey(context.Background(), kekID, kekSizeBytes)
+	if err != nil {
+		return Router{}, fmt.Errorf("getting KEK: %w", err)
+	}
+
+	kekArray, err := byteSliceToByteArray(kek)
+	if err != nil {
+		return Router{}, fmt.Errorf("converting KEK to byte array: %w", err)
+	}
+
+	return Router{region: region, kek: kekArray, log: log}, nil
 }
 
 // Serve implements the routing logic for the s3 proxy.
@@ -243,6 +271,16 @@ func handleForwards(log *logger.Logger) http.HandlerFunc {
 	}
 }
 
+// byteSliceToByteArray casts a byte slice to a byte array of length 32.
+// It does a length check to prevent the cast from panic'ing.
+func byteSliceToByteArray(input []byte) ([32]byte, error) {
+	if len(input) != 32 {
+		return [32]byte{}, fmt.Errorf("input length mismatch, got: %d", len(input))
+	}
+
+	return ([32]byte)(input), nil
+}
+
 // containsBucket is a helper to recognizes cases where the bucket name is sent as part of the host.
 // In other cases the bucket name is sent as part of the path.
 func containsBucket(host string) bool {

s3proxy/internal/router/router_test.go

@@ -46,3 +46,42 @@ func TestValidateContentMD5(t *testing.T) {
 		})
 	}
 }
+
+func TestByteSliceToByteArray(t *testing.T) {
+	tests := map[string]struct {
+		input   []byte
+		output  [32]byte
+		wantErr bool
+	}{
+		"empty input": {
+			input:  []byte{},
+			output: [32]byte{},
+		},
+		"successful input": {
+			input:  []byte("AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"),
+			output: [32]byte{0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41},
+		},
+		"input too short": {
+			input:   []byte("AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"),
+			output:  [32]byte{0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41},
+			wantErr: true,
+		},
+		"input too long": {
+			input:   []byte("AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"),
+			output:  [32]byte{0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41, 0x41},
+			wantErr: true,
+		},
+	}
+
+	for name, tc := range tests {
+		t.Run(name, func(t *testing.T) {
+			result, err := byteSliceToByteArray(tc.input)
+			if tc.wantErr {
+				assert.Error(t, err)
+				return
+			}
+
+			assert.Equal(t, tc.output, result)
+		})
+	}
+}