add key-rotation for SSE-S3 objects (#6755)

This commit adds key-rotation for SSE-S3 objects.
To execute a key-rotation a SSE-S3 client must
 - specify the `X-Amz-Server-Side-Encryption: AES256` header
   for the destination
 - The source == destination for the COPY operation.

Fixes #6754

cmd/encryption-v1.go

@@ -156,6 +156,30 @@ func rotateKey(oldKey []byte, newKey []byte, bucket, object string, metadata map
 		sealedKey = objectKey.Seal(extKey, sealedKey.IV, crypto.SSEC.String(), bucket, object)
 		crypto.SSEC.CreateMetadata(metadata, sealedKey)
 		return nil
+	case crypto.S3.IsEncrypted(metadata):
+		if globalKMS == nil {
+			return errKMSNotConfigured
+		}
+		keyID, kmsKey, sealedKey, err := crypto.S3.ParseMetadata(metadata)
+		if err != nil {
+			return err
+		}
+		oldKey, err := globalKMS.UnsealKey(keyID, kmsKey, crypto.Context{bucket: path.Join(bucket, object)})
+		if err != nil {
+			return err
+		}
+		var objectKey crypto.ObjectKey
+		if err = objectKey.Unseal(oldKey, sealedKey, crypto.S3.String(), bucket, object); err != nil {
+			return err
+		}
+
+		newKey, encKey, err := globalKMS.GenerateKey(globalKMSKeyID, crypto.Context{bucket: path.Join(bucket, object)})
+		if err != nil {
+			return err
+		}
+		sealedKey = objectKey.Seal(newKey, crypto.GenerateIV(rand.Reader), crypto.S3.String(), bucket, object)
+		crypto.S3.CreateMetadata(metadata, globalKMSKeyID, encKey, sealedKey)
+		return nil
 	}
 }
 

cmd/object-handlers.go

@@ -829,19 +829,24 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 				return
 			}
 		}
-		// AWS S3 implementation requires us to only rotate keys
-		// when/ both keys are provided and destination is same
-		// otherwise we proceed to encrypt/decrypt.
-		if sseCopyC && sseC && cpSrcDstSame {
-			// Get the old key which needs to be rotated.
+
+		// If src == dst and either
+		// - the object is encrypted using SSE-C and two different SSE-C keys are present
+		// - the object is encrypted using SSE-S3 and the SSE-S3 header is present
+		// than execute a key rotation.
+		if cpSrcDstSame && ((sseCopyC && sseC) || (sseS3 && sseCopyS3)) {
+			if sseCopyC && sseC {
 				oldKey, err = ParseSSECopyCustomerRequest(r.Header, srcInfo.UserDefined)
 				if err != nil {
 					writeErrorResponse(w, toAPIErrorCode(err), r.URL)
 					return
 				}
+			}
 			for k, v := range srcInfo.UserDefined {
 				encMetadata[k] = v
 			}
+
+			// In case of SSE-S3 oldKey and newKey aren't used - the KMS manages the keys.
 			if err = rotateKey(oldKey, newKey, srcBucket, srcObject, encMetadata); err != nil {
 				writeErrorResponse(w, toAPIErrorCode(err), r.URL)
 				return
@@ -914,7 +919,7 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 	// metadataOnly is true indicating that we are not overwriting the object.
 	// if encryption is enabled we do not need explicit "REPLACE" metadata to
 	// be enabled as well - this is to allow for key-rotation.
-	if !isMetadataReplace(r.Header) && srcInfo.metadataOnly && !crypto.SSEC.IsEncrypted(srcInfo.UserDefined) {
+	if !isMetadataReplace(r.Header) && srcInfo.metadataOnly && !crypto.IsEncrypted(srcInfo.UserDefined) {
 		// If x-amz-metadata-directive is not set to REPLACE then we need
 		// to error out if source and destination are same.
 		writeErrorResponse(w, ErrInvalidCopyDest, r.URL)