+ size_t (*get_block_size) (hmac_t *this);
+
+ /**
+ * @brief set the key for this hmac
+ *
+ * Any key length is accepted.
+ *
+ * @param this calling hmac
+ * @param key key to set
+ * @return block size in bytes
+ */
+ size_t (*set_key) (hmac_t *this, chunk_t key);