Secret_box.BytesBytes offers versions of each of the above formatters, which get their value from a bytes value.
val secret_key : storage Fmt.tsecret_key formats a secret_key in this fashion: (Secret_box.secret_key AAAAAA==). If the storage value is not Sodium.Secret_box.secret_key_size bytes long, it will be formatted as (Secret_box.secret_key <size mismatch>).