lib: identity_key: Add identity key free function

Add identity_key_free function which calls the
nrf_cc3xx_platform_identity_key_free function.
This makes the identity_key library a complete abstraction over the
nrf_cc3xx_platform library.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>

Author: joerchan

include/identity_key.h

@@ -71,6 +71,16 @@ bool identity_key_is_written(void);
  */
 int identity_key_read(uint8_t key[IDENTITY_KEY_SIZE_BYTES]);
 
+/** @brief Function to clear out an identity key after usage
+ *
+ * @details This function will clear out the memory of an identity key.
+ *          This must be called after the identity key is used to ensure that
+ *          it is not leaked in the system.
+ *
+ * @param[in,out]   key         Key to clear out
+ */
+void identity_key_free(uint8_t key[IDENTITY_KEY_SIZE_BYTES]);
+
 /**
  * @brief Function to write a random identity key to KMU
  *

lib/identity_key/identity_key.c

@@ -171,3 +171,8 @@ int identity_key_read(uint8_t key[IDENTITY_KEY_SIZE_BYTES])
 
 	return IDENTITY_KEY_SUCCESS;
 }
+
+void identity_key_free(uint8_t key[IDENTITY_KEY_SIZE_BYTES])
+{
+	nrf_cc3xx_platform_identity_key_free(key);
+}