diff --git a/qomemo/CMakeLists.txt b/qomemo/CMakeLists.txt
index 5f92df4..0837eac 100644
--- a/qomemo/CMakeLists.txt
+++ b/qomemo/CMakeLists.txt
@@ -8,7 +8,7 @@ find_package(Qt5Core CONFIG REQUIRED)
 find_package(Qt5Xml CONFIG REQUIRED)
 find_package(LMDB REQUIRED)
 
-set(qomemo_SRC)
+set(qomemo_SRC signal.h)
 
 add_library(qomemo STATIC ${qomemo_SRC})
 
@@ -17,6 +17,8 @@ if(SYSTEM_QXMPP)
     target_include_directories(qomemo PUBLIC ${QXMPP_INTERFACE_INCLUDE_DIRECTORIES})
 endif()
 
+target_include_directories(qomemo PUBLIC ${CMAKE_SOURCE_DIR}/external/signal-protocol-c/src)
+
 target_link_libraries(qomemo Qt5::Core)
 target_link_libraries(qomemo Qt5::Xml)
 target_link_libraries(qomemo qxmpp)
diff --git a/qomemo/signal.h b/qomemo/signal.h
new file mode 100644
index 0000000..e7e4c8b
--- /dev/null
+++ b/qomemo/signal.h
@@ -0,0 +1,20 @@
+/*
+ * Created by victoria on 2021-05-11.
+ */
+
+#pragma once
+
+#include <signal_protocol.h>
+
+namespace Signal
+{
+
+class Context {};
+class RatchetIdentityPair {};
+class SessionSignedPreKey {};
+class ProtocolKeyHelper {};
+class ProtocolStoreContext {};
+class SessionBuilder {};
+class SessionCipher {};
+
+}