Group signatures for group agents
One way group agents could make agreements with other agents: https://github.com/dedis/cosi
...the CoSi protocol for scalable collective signing. CoSi enables authorities to have their statements collectively signed, or co-signed, by a scalable group of independent parties or witnesses. The signatures that CoSi produces convey the same information as a list of conventional signatures from all participants, but CoSi signatures are far more compact and efficient for clients to verify.