Original text:
A model system is shown in [TODO: Figure]. <del> The messaging service presents as two abstract services: </del>  <del> An Authentication Server (AS) which is responsible for maintaining user identities, issuing credentials which allow them to authenticate to each other, and potentially distributing user </del>  keying material. <del> A Message Switch (MS) which is responsible for delivering messages between users.  In the case of group messaging, the message switch may also be responsible for acting as an "exploder" where the sender sends a single message to a group and the switch then forwards it to each recipient. </del>  <del> In many systems, the AS and the MS are actually operated by the same </del>  entity and may even be the same server.  However, they are logically distinct and, in other systems, may be operated by different entities so we show them as separate here.  Other partitions are also Alice, Bob, and Charlie create accounts with the messaging service and obtain credentials from the AS. <del> Alice, Bob, and Charlie authenticate to the MS and store some </del>  keying material which can be used to encrypt to them for the first time. When Alice wants to send a message to Bob and Charlie, she <del> contacts the MS and looks up their keying material.  She uses </del>  those keys to establish a set of keys which she can use to send to Bob and Charlie.  She then sends the encrypted message(s) to the <del> MS, which forwards them to the ultimate recipients. </del>  Bob and/or Charlie respond to Alice's message.  Their messages might include new keys which allow the joint keys to be updated,

Reviewer comments:
The current naming is confusing: MS stands for "Message Switch" and "Messaging Server" but not for "Messaging Service" AS stands for "Authentication Server" and "Authentication Service". The proposed change gives: MS as "Messaging Service" (AS* + DS) AS as "Authentication Service" DS as "Delivery Service" the "Server"s being the endpoints and not the functionality

Revised text:
A model system is shown in [TODO: Figure].  <ins> The Messaging Service (MS) presents as two abstract services: </ins>  <ins> An Authentication Service (AS) which is responsible for maintaining user identities, issuing credentials which allow them to authenticate to each other, and potentially distributing user </ins> keying material.  <ins> A Delivery Service (DS) which is responsible for delivering messages between users.  In the case of group messaging, the delivery service may also be responsible for acting as an "exploder" where the sender sends a single message to a group and the switch then forwards it to each recipient. </ins>  <ins> In many systems, the AS and the DS are actually operated by the same </ins> entity and may even be the same server.  However, they are logically distinct and, in other systems, may be operated by different entities so we show them as separate here.  Other partitions are also Alice, Bob, and Charlie create accounts with the messaging service and obtain credentials from the AS.  <ins> Alice, Bob, and Charlie authenticate to the DS and store some </ins> keying material which can be used to encrypt to them for the first time. When Alice wants to send a message to Bob and Charlie, she  <ins> contacts the DS and looks up their keying material.  She uses </ins> those keys to establish a set of keys which she can use to send to Bob and Charlie.  She then sends the encrypted message(s) to the  <ins> DS, which forwards them to the ultimate recipients. </ins> Bob and/or Charlie respond to Alice's message.  Their messages might include new keys which allow the joint keys to be updated,