use HKDF from openSSL
Change-Id: Iade1523bc46ac44b9b5540cdd91b9283ac537a31
diff --git a/src/detail/crypto-helper.hpp b/src/detail/crypto-helper.hpp
index 50aa7bb..38110c5 100644
--- a/src/detail/crypto-helper.hpp
+++ b/src/detail/crypto-helper.hpp
@@ -84,9 +84,9 @@
* @p key, intput, the key for the function
* @p key_len, intput, the length of the key
* @p result, output, result of the HMAC. Enough memory (32 Bytes) must be allocated beforehands
- * @return 0 if successful, -1 if failed
+ * @throw runtime_error when an error occurred in the underlying HMAC.
*/
-int
+void
hmac_sha256(const uint8_t* data, const unsigned data_length,
const uint8_t* key, const unsigned key_length,
uint8_t* result);