diff --git a/hmac.h b/hmac.h
new file mode 100644
index 0000000..fb68029
--- /dev/null
+++ b/hmac.h
@@ -0,0 +1,11 @@
+#ifndef HMAC_H
+#define HMAC_H
+
+unsigned char *
+hmac(
+    EVP_MD *evp_md,
+    unsigned int seqno,
+    unsigned char *data, int datalen,
+    unsigned char *key, int len);
+
+#endif