[takeda]

Oh this is not a big problem.

You simply encrypt the data, the protocol even has a support for marking encrypted data [1].

That said the NDN does not impose how you do it and it is left for the application.

Now if the data is only end-to-end you probably would do something similar to TLS. If the data supposed to be accessible by multiple users, then you encrypt it with generated key, and then encrypt the key using public keys of intended recipients.

[1] http://www.ccnx.org/pubs/ccnx-mosko-tlvmessages-01.html (Section 3.5.2.2.1. PayloadType)