feat: prepare KMS data encryption for migration to AES-GCM

Signed-off-by: Anish Ramasekar <anish.ramasekar@gmail.com>
Co-authored-by: Monis Khan <mok@vmware.com>
Signed-off-by: Anish Ramasekar <anish.ramasekar@gmail.com>

Kubernetes-commit: 90b42f91fd904b71fd52ca9ae55a5de73e6b779a

pkg/server/options/encryptionconfig/config.go

@@ -17,6 +17,7 @@ limitations under the License.
 package encryptionconfig
 
 import (
+	"context"
 	"crypto/aes"
 	"crypto/cipher"
 	"encoding/base64"
@@ -32,6 +33,7 @@ import (
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/apimachinery/pkg/runtime/serializer"
+	utilerrors "k8s.io/apimachinery/pkg/util/errors"
 	apiserverconfig "k8s.io/apiserver/pkg/apis/config"
 	apiserverconfigv1 "k8s.io/apiserver/pkg/apis/config/v1"
 	"k8s.io/apiserver/pkg/apis/config/validation"
@@ -365,7 +367,13 @@ func secretboxPrefixTransformer(config *apiserverconfig.SecretboxConfiguration)
 }
 
 func envelopePrefixTransformer(config *apiserverconfig.KMSConfiguration, envelopeService envelope.Service, prefix string) (value.PrefixTransformer, error) {
-	envelopeTransformer, err := envelope.NewEnvelopeTransformer(envelopeService, int(*config.CacheSize), aestransformer.NewCBCTransformer)
+	baseTransformerFunc := func(block cipher.Block) value.Transformer {
+		// v1.24: write using AES-CBC only but support reads via AES-CBC and AES-GCM (so we can move to AES-GCM)
+		// TODO(aramase): swap this ordering in v1.25
+		return unionTransformers{aestransformer.NewCBCTransformer(block), aestransformer.NewGCMTransformer(block)}
+	}
+
+	envelopeTransformer, err := envelope.NewEnvelopeTransformer(envelopeService, int(*config.CacheSize), baseTransformerFunc)
 	if err != nil {
 		return value.PrefixTransformer{}, err
 	}
@@ -374,3 +382,27 @@ func envelopePrefixTransformer(config *apiserverconfig.KMSConfiguration, envelop
 		Prefix:      []byte(prefix + config.Name + ":"),
 	}, nil
 }
+
+type unionTransformers []value.Transformer
+
+func (u unionTransformers) TransformFromStorage(ctx context.Context, data []byte, dataCtx value.Context) (out []byte, stale bool, err error) {
+	var errs []error
+	for i, transformer := range u {
+		result, stale, err := transformer.TransformFromStorage(ctx, data, dataCtx)
+		if err != nil {
+			errs = append(errs, err)
+			continue
+		}
+		// when i != 0, we have transformed the data from storage using the new transformer,
+		// we want to issue a write to etcd even if the contents of the data haven't changed
+		return result, stale || i != 0, nil
+	}
+	if err := utilerrors.Reduce(utilerrors.NewAggregate(errs)); err != nil {
+		return nil, false, err
+	}
+	return nil, false, fmt.Errorf("unionTransformers: unable to transform from storage")
+}
+
+func (u unionTransformers) TransformToStorage(ctx context.Context, data []byte, dataCtx value.Context) (out []byte, err error) {
+	return u[0].TransformToStorage(ctx, data, dataCtx)
+}

pkg/storage/value/encrypt/aes/aes.go

@@ -96,7 +96,7 @@ func NewCBCTransformer(block cipher.Block) value.Transformer {
 }
 
 var (
-	errInvalidBlockSize    = fmt.Errorf("the stored data is not a multiple of the block size")
+	ErrInvalidBlockSize    = fmt.Errorf("the stored data is not a multiple of the block size")
 	errInvalidPKCS7Data    = errors.New("invalid PKCS7 data (empty or not padded)")
 	errInvalidPKCS7Padding = errors.New("invalid padding on input")
 )
@@ -110,7 +110,7 @@ func (t *cbc) TransformFromStorage(ctx context.Context, data []byte, dataCtx val
 	data = data[blockSize:]
 
 	if len(data)%blockSize != 0 {
-		return nil, false, errInvalidBlockSize
+		return nil, false, ErrInvalidBlockSize
 	}
 
 	result := make([]byte, len(data))