The functions `relay_crypt`, `relay_crypt_one_payload`, and `relay_init_cpath_crypto`, as well as extractable parts of `onionskin_answer` and `circuit_free_cpath_node` -- belong in their own conceptual module. Considered as such, they become fairly easy to test. We have identified this work as valuable for modularization, for testing, and potentially valuable for testing future relay crypto designs.