diff --git a/src/crypto-support/crypto-helper.hpp b/src/crypto-support/crypto-helper.hpp
index 88f1519..95879b3 100644
--- a/src/crypto-support/crypto-helper.hpp
+++ b/src/crypto-support/crypto-helper.hpp
@@ -69,10 +69,19 @@
      int saltLen, uint8_t* okm, int okm_len,
      const uint8_t* info = INFO, int info_len = INFO_LEN);
 
+/**
+ * HMAC SHA 256 keyed hash function
+ * @param key the key for the function
+ * @param key_len the length of the key
+ * @param data the array to hmac
+ * @param data_length the length of the array
+ * @param result result. Enough memory (32 Bytes) must be allocated beforehand
+ * @return 0 if successful, -1 if failed
+ */
 int
 ndn_compute_hmac_sha256(const uint8_t* data, const unsigned data_length,
                         const uint8_t* key, const unsigned key_length,
-                        uint8_t* prk);
+                        uint8_t* result);
 
 /**
  * Authentication GCM 128 Encryption