typedef bool_t transform_setkey_fn(void *st, uint8_t *key, int32_t keylen);
typedef void transform_delkey_fn(void *st);
typedef void transform_destroyinstance_fn(void *st);
-/* Returns 0 for 'all is well', any other value for a problem */
+/* Returns:
+ * 0: all is well
+ * 1: for any other problem
+ * 2: message decrypted but sequence number was out of range
+ */
typedef uint32_t transform_apply_fn(void *st, struct buffer_if *buf,
const char **errmsg);