The Distributed Numbering Architecture (DNA) is a necessary component of a distributed mesh telephone network that must function without any kind of infrastructure (such as known and reachable directory servers), for example in post-disaster or remote areas.
The problem in such situations is that even though people may have a Mesh network connection with nearby devices, most people only know the regular telephone number of other people they wish to call. Without a central directory that maps phone numbers to mesh network addresses, how can the mesh be used to call a well known phone number?
The solution arrived at by The Serval Project is:
The DNA mechanism for resolving phone numbers is open to abuse by people claiming a phone number in order to impersonate the true “owner” of that number. DID verification provides a way to record every authentic DNA REPLY so that imposters can be automatically excluded once the real owner of a number has been successfully contacted.
The DNA mechanism can be subverted by a man in the middle (MitM) attack. SID verification provides a mechanism to detect a MitM which is almost impossibly hard to defeat.