diff --git a/lib/include/srslte/interfaces/epc_interfaces.h b/lib/include/srslte/interfaces/epc_interfaces.h
new file mode 100644
index 000000000..09377878d
--- /dev/null
+++ b/lib/include/srslte/interfaces/epc_interfaces.h
@@ -0,0 +1,17 @@
+#ifndef EPC_INTERFACE_H
+#define EPC_INTERFACE_H
+
+#include "srslte/srslte.h"
+
+#include "srslte/common/common.h"
+
+namespace srsepc {
+
+class hss_interface_s1ap
+{
+public:
+  virtual bool gen_auth_info_answer(uint64_t imsi, uint8_t *k_asme, uint8_t *autn, uint8_t *rand, uint8_t *xres) = 0;
+};
+
+}
+#endif // ENB_METRICS_INTERFACE_H
diff --git a/srsepc/hdr/hss/hss.h b/srsepc/hdr/hss/hss.h
index 34cd71b7c..7cafe21ce 100644
--- a/srsepc/hdr/hss/hss.h
+++ b/srsepc/hdr/hss/hss.h
@@ -38,6 +38,7 @@
 #include "srslte/common/logger_file.h"
 #include "srslte/common/log_filter.h"
 #include "srslte/common/buffer_pool.h"
+#include "srslte/interfaces/epc_interfaces.h"
 #include <fstream>
 #include <map>
 
@@ -64,7 +65,7 @@ enum hss_auth_algo {
   HSS_ALGO_MILENAGE
 };
 
-class hss
+class hss : public srsepc::hss_interface_s1ap
 {
 public:
   static hss* get_instance(void);