  This white paper presents an analysis done by the MAMI project of the privacy
and security concerns surrounding middlebox cooperation protocols (MCPs), based
on our experimental experience with the Path Layer UDP Substrate (PLUS)
proposal. Our key finding is that adding explicit signaling meant for on-path
devices presents no significant new attack surface as compared to the status
quo in the Internet architecture. While middlebox cooperation can make a
passive adversary's job easier, it does not enable entirely new attacks.
