* verified. If crypto->decrypt is NOTMUCH_DECRYPT_TRUE, encrypted
* child parts will be decrypted using either stored session keys or
* asymmetric crypto. If crypto->decrypt is NOTMUCH_DECRYPT_AUTO,
* verified. If crypto->decrypt is NOTMUCH_DECRYPT_TRUE, encrypted
* child parts will be decrypted using either stored session keys or
* asymmetric crypto. If crypto->decrypt is NOTMUCH_DECRYPT_AUTO,