The social graph is a concept from social networking that PSYC2 intends to implement without leaving any visible data on any servers. It only exists in distributed form on the devices of its participants and each person has their own view of it depending on what others have made accessible to them.
It is technically achieved by merging the distributed state of people's social networking channels into a large database, or more precisely, a graph. This concept is being implemented in secushare but hardly exists in psyced (see the /trust and /surf commands explained on the Trust page).
The social graph reflects also the web of trust of its participants, but, contrary to PGP, in the distributed implementation of PSYC2 it happens in respect of their privacy.
1 Social graph for IoT and IT-Security
A protocol and data standard for the distributed social graph could have impressive consequences for the security of "Internet of Things" appliances, but also for large parts of the existing IT security. More on this topic at http://secushare.org/security
2 Social graph for crypto usability
When using tools for secure communications, one thing that is really hard for users to do correctly is the secure key exchange. With the social graph this becomes ridiculously easy: by adding a common friend from your existing friends key adoption becomes as easy as adding a friend on Facebook. If your friends are in a conspiracy to make you add a fake person, then they're nasty and you are an individual target – but for the majority of cases your friends are the guarantee that the public key you are adopting by taking it from their shared social graph is reasonably safe to assume to be owned by the person you are trying to reach out for. Only when you don't have any friends on your network yet, then you need to do a proper bootstrap. But your first friend can help you do that. See http://secushare.org/rendezvous for more. There's also a video on http://youbroketheinternet.org/#30c3usability on the topic.
3 Related work
We don't know of any other project attempting to implement this feature, therefore it seems like the world hasn't seen the huge potential for safe social interaction yet.