diff --git a/c/auth.c b/c/auth.c
index 40b910b..380a5a7 100644
--- a/c/auth.c
+++ b/c/auth.c
@@ -27,6 +27,7 @@
 #include "secp256k1_helper_20210801.h"
 #include "include/secp256k1_schnorrsig.h"
 
+#include "ckb_auth_internal.h"
 #include "ckb_auth.h"
 #undef CKB_SUCCESS
 #include "ckb_hex.h"
diff --git a/c/auth_libecc.c b/c/auth_libecc.c
index aaf0c51..10d1e1e 100644
--- a/c/auth_libecc.c
+++ b/c/auth_libecc.c
@@ -1,3 +1,4 @@
+#include "ckb_auth_internal.h"
 #include "ckb_auth.h"
 
 // clang-format off
diff --git a/c/ckb_auth_internal.h b/c/ckb_auth_internal.h
new file mode 100644
index 0000000..6cd4ebd
--- /dev/null
+++ b/c/ckb_auth_internal.h
@@ -0,0 +1,12 @@
+#ifndef CKB_PRODUCTION_SCRIPTS_CKB_AUTH_INTERNAL_H_
+#define CKB_PRODUCTION_SCRIPTS_CKB_AUTH_INTERNAL_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+typedef int (*validate_signature_t)(void *prefilled_data, const uint8_t *sig,
+                                    size_t sig_len, const uint8_t *msg,
+                                    size_t msg_len, uint8_t *output,
+                                    size_t *output_len);
+
+#endif  // CKB_PRODUCTION_SCRIPTS_CKB_AUTH_INTERNAL_H_