diff --git a/src/crypto-support/crypto-helper.cpp b/src/crypto-support/crypto-helper.cpp
index 7813187..915dce2 100644
--- a/src/crypto-support/crypto-helper.cpp
+++ b/src/crypto-support/crypto-helper.cpp
@@ -374,6 +374,48 @@
   }
 }
 
+int
+hmac_sha_256(const uint8_t* key, size_t key_len,
+             const uint8_t* cleartext, size_t cleartext_len,
+             uint8_t* output, size_t* output_len)
+{
+    if (!key || !cleartext || !output) {
+        return -1;
+    }
+
+    auto private_key = EVP_PKEY_new_mac_key(EVP_PKEY_HMAC, nullptr, key, key_len);
+    auto hmac_context = EVP_MD_CTX_new();
+    if (!private_key || !hmac_context) {
+        handleErrors("Cannot create and initialise the context when calling HMAC_CTX_new()");
+        return -1;
+    }
+
+    if (EVP_DigestSignInit(hmac_context, nullptr, EVP_sha256(), nullptr, private_key) != 1) {
+        handleErrors("Cannot initialize DigestSign when calling EVP_DigestSignInit()");
+        EVP_MD_CTX_free(hmac_context);
+        EVP_PKEY_free(private_key);
+        return -1;
+    }
+
+    if (EVP_DigestSignUpdate(hmac_context, cleartext, cleartext_len) != 1) {
+        handleErrors("Cannot update DigestSign when calling EVP_DigestSignUpdate()");
+        EVP_MD_CTX_free(hmac_context);
+        EVP_PKEY_free(private_key);
+        return -1;
+    }
+
+    if (EVP_DigestSignFinal(hmac_context, output, output_len) != 1) {
+        handleErrors("Cannot finish DigestSign when calling EVP_DigestSignFinal()");
+        EVP_MD_CTX_free(hmac_context);
+        EVP_PKEY_free(private_key);
+        return -1;
+    }
+
+    EVP_MD_CTX_free(hmac_context);
+    EVP_PKEY_free(private_key);
+    return 0;
+}
+
 void
 handleErrors(const std::string& errorInfo)
 {
diff --git a/src/crypto-support/crypto-helper.hpp b/src/crypto-support/crypto-helper.hpp
index aaa4237..88f1519 100644
--- a/src/crypto-support/crypto-helper.hpp
+++ b/src/crypto-support/crypto-helper.hpp
@@ -108,6 +108,21 @@
 aes_gcm_128_decrypt(const uint8_t* ciphertext, size_t ciphertext_len, const uint8_t* associated, size_t associated_len,
                     const uint8_t* tag, const uint8_t* key, const uint8_t* iv, uint8_t* plaintext);
 
+/**
+ * HMAC SHA 256 keyed hash function
+ * @param key the key for the function
+ * @param key_len the length of the key
+ * @param cleartext the cleartext array to be hashed
+ * @param cleartext_len the length of the array
+ * @param output the output array
+ * @param output_len the longest output len possible (changed to actual on return).
+ * @return 0 if successful, -1 if failed
+ */
+int
+hmac_sha_256(const uint8_t* key, size_t key_len,
+             const uint8_t* cleartext, size_t cleartext_len,
+             uint8_t* output, size_t* output_len);
+
 void
 handleErrors(const std::string& errorInfo);