Section 4.3: If we’re specifying a ‘secure endpoint reference’ then we should say something about how these EPR 
documents are distributed. There are several possible attacks from modifying these documents in transit (man-in-the-
middle attacks, failing to sign and/or encrypt the message correctly). One option is to provide for signing of these 
documents by the service, in which case we should spec how they are signed. This is the most scalable approach. One 
could also assume distribution via trusted server over TLS/SSL, but that’s likely unacceptable  in a lot of 
environments.

by Blair Dillaway