From http://en.wikipedia.org/wiki/Mandatory_access_control "Apple's Mac OS X MAC framework is an implementation of the TrustedBSD MAC framework.[18] A limited high-level sandboxing interface is provided by the command-line function sandbox_init. See the sandbox_init manual page for documentation.[19]"

You cannot have encryption without authentication. Encryption is defined as the confidential transfer of information only to the intended parties. If you cannot be sure that you are exchanging session encryption keys with the intended party, you might just as well be talking to the man-in-ze-middle.