diff --git a/services/backup/src/BackupServiceImpl.h b/services/backup/src/BackupServiceImpl.h
--- a/services/backup/src/BackupServiceImpl.h
+++ b/services/backup/src/BackupServiceImpl.h
@@ -31,6 +31,11 @@
   grpc::ServerWriteReactor<backup::PullBackupResponse> *PullBackup(
       grpc::CallbackServerContext *context,
       const backup::PullBackupRequest *request) override;
+
+  grpc::ServerUnaryReactor *AddAttachments(
+      grpc::CallbackServerContext *context,
+      const backup::AddAttachmentsRequest *request,
+      google::protobuf::Empty *response) override;
 };
 
 } // namespace network
diff --git a/services/backup/src/BackupServiceImpl.cpp b/services/backup/src/BackupServiceImpl.cpp
--- a/services/backup/src/BackupServiceImpl.cpp
+++ b/services/backup/src/BackupServiceImpl.cpp
@@ -1,6 +1,7 @@
 #include "BackupServiceImpl.h"
 
 #include "CreateNewBackupReactor.h"
+#include "DatabaseManager.h"
 #include "PullBackupReactor.h"
 #include "RecoverBackupKeyReactor.h"
 #include "SendLogReactor.h"
@@ -47,5 +48,48 @@
   return reactor;
 }
 
+grpc::ServerUnaryReactor *BackupServiceImpl::AddAttachments(
+    grpc::CallbackServerContext *context,
+    const backup::AddAttachmentsRequest *request,
+    google::protobuf::Empty *response) {
+  grpc::Status status = grpc::Status::OK;
+  std::string userID = request->userid();
+  std::string backupID = request->backupid();
+  std::string logID = request->logid();
+  const std::string holders = request->holders();
+  try {
+    if (userID.empty()) {
+      throw std::runtime_error("user id required but not provided");
+    }
+    if (backupID.empty()) {
+      throw std::runtime_error("backup id required but not provided");
+    }
+    if (holders.empty()) {
+      throw std::runtime_error("holders required but not provided");
+    }
+
+    if (logID.empty()) {
+      // add these attachments to backup
+      std::shared_ptr<database::BackupItem> backupItem =
+          database::DatabaseManager::getInstance().findBackupItem(
+              userID, backupID);
+      backupItem->addAttachmentHolders(holders);
+      database::DatabaseManager::getInstance().putBackupItem(*backupItem);
+    } else {
+      // add these attachments to log
+      std::shared_ptr<database::LogItem> logItem =
+          database::DatabaseManager::getInstance().findLogItem(backupID, logID);
+      logItem->addAttachmentHolders(holders);
+      database::DatabaseManager::getInstance().putLogItem(*logItem);
+    }
+  } catch (std::runtime_error &e) {
+    std::cout << "error: " << e.what() << std::endl;
+    status = grpc::Status(grpc::StatusCode::INTERNAL, e.what());
+  }
+  auto *reactor = context->DefaultReactor();
+  reactor->Finish(status);
+  return reactor;
+}
+
 } // namespace network
 } // namespace comm