Clarified definition of "Dispatcher".

Author: marco-tiloca-sics

draft-ietf-ace-key-groupcomm.md

@@ -204,11 +204,11 @@ The following participants (see {{fig-roles}}) take part in the authorization an
 
 * Key Distribution Center (KDC): maintains the keying material to protect group communications, and provides it to Clients authorized to join a given group. During the first part of the exchange ({{sec-auth}}), it takes the role of the RS in the ACE Framework. During the second part ({{key-distr}}), which is not based on the ACE Framework, it distributes the keying material. In addition, it provides the latest keying material to group members when requested or, if required by the application, when membership changes.
 
-* Dispatcher: entity through which the Clients communicate with the group, when sending a message intended to multiple group members. That is, the Dispatcher distributes such a one-to-many message to the group members as intended recipients. A single-recipient message intended to only one group member may be delivered by alternative means, with no assistance from the Dispatcher.
+* Dispatcher: entity through which the Clients communicate with the group, when sending a message intended to multiple group members. That is, the Dispatcher distributes such a one-to-many message to the group members as intended recipients. The Dispatcher does not have access to the group keying material. A single-recipient message intended to only one group member may be delivered by alternative means, with no assistance from the Dispatcher.
 
    Examples of a Dispatcher are: the Broker in a pub-sub setting; a relayer for group communication that delivers group messages as multiple unicast messages to all group members; an implicit entity as in a multicast communication setting, where messages are transmitted to a multicast IP address and delivered on the transport channel.
 
-   If it consists of an explicit entity such as a pub-sub Broker or a message relayer, the Dispatcher is comparable to an untrusted on-path intermediary, and as such it is able to read the messages sent by Clients in the group.
+   If it consists of an explicit entity such as a pub-sub Broker or a message relayer, the Dispatcher is comparable to an untrusted on-path intermediary, and as such it is able to see the messages sent by Clients in the group, but not to decrypt them and read their plain content.
 
 This document specifies a mechanism for: