Multiple group membership
draft-park-mls-multiple-groups-requirement-00

Abstract

This document proposes a functional requirement of Message Level Security (MLS) which provide an efficient management for multiple groups. Although MLS defines an architecture and an abstract protocol for a secure group communication, it overlooks the need of multiple groups. This document describes a usecase of the multiple groups, and the need for an efficient multiple group membership management.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Re-keying for membership change
• 4. Multiple groups scenario
• 5. Multiple group membership
• 6. Informative References
• Appendix A. Acknowledgements
• Author's Address

1. Introduction

With the emergence of diverse group-based applications, e.g. a channel-based charged TV or telematics services, multiple group applications are likely to coexist, and users may have multiple memberships. Of course, although the functional requirements defined in the mls architecture draft can satisfy the multiple membership management, we need to consider the efficient management of multiple membership. This document mentions the inefficiency which may occur in the multiple membership management and the motivation of the functional requirement, multiple group membership.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

3. Re-keying for membership change

Let us consider a situation where a member is about to leave a group. Before this member leaves, all the members have shared a group key to encrypt/decrypt messages among themselves. After the member leaves, the old group key must be revoked and updated with a new group key. This rekeying process may cause a lot of key management overhead. Since the existing members do not have any shared secret keys except for the old group key, a new group key should be distributed to these members in a secure manner. As a result, it is obvious that the more the number of users in a group service, the larger the rekeying overhead would be.

4. Multiple groups scenario

There can be various group messaging services. Generally, the group messaging services can be considered as the commercial services such as a charged TV streaming service, a telematics service, and an information service (Sports or stock). Let us assume these three services are Delivery Services (DS) as shown in Figure 1. In this case, there will be at least three groups for the three services, each of which should be managed according to the membership records of the DSs. Moreover, if the subscription to a DS is charged for either each channel (Ch1, Ch2, and Ch3) or content (sports and stock), the service provider should manage the additional user groups (e.g., channel-based or content-based groups) for accurate accounting like Figure 2. As a result, the management overhead stemming from membership management including rekeying can significantly increase due to the number of such groups.

			
   ----------------      --------------     -----------------
  | A Charged TV   |    | Telematics   |   | Information     |
  |                |    | Service      |   | Service         |
  |<Ch1><Ch2><Ch3> |    |              |   | <Sports> <Stock>|
   ----------------      --------------     -----------------
     \         / \________________           /          |    
      \       /              _____\_________/           | 
       \     /              /      \                    |
        -------       ------        -------        -------
       | User0 |     | User1 |     | User2 |      | User3 |
        -------       ------        -------        -------                                            
            

Figure 1: Multiple groups scenario

			
   Ch1 group          Ch2 group         Ch3 group       
   ****************   ****************  ****************
   * -------      *   * -------      *  * -------      *
   *| User0 |  ...*   *| User1 | ... *  *| User2 | ... *
   * -------      *   * -------      *  * -------      *
   ****************   ****************  ****************

   Telematics group   Sports group      Stock group       
   ****************   ****************  ****************
   * -------      *   * -------      *  * -------      *
   *| User2 |  ...*   *| User1 | ... *  *| User3 | ... *
   * -------      *   * -------      *  * -------      *
   ****************   ****************  ****************
            

Figure 2: Six delivery service groups

5. Multiple group membership

The multiple group scenario in the previous section can be implemented with multiple independent groups, where each service group has an independent AS. However, a single service provider may manage multiple groups, e.g., multiple channel groups in a channel-based charged service. In this case, the service provider should have multiple independent groups corresponding to each channel, which may increase the management cost such as many Ass as the number of groups and re-keying. Therefore, the protocol should be able to allow a single Authentication Service to manage multiple group memberships in order to support more than two Delivery Services as shown in Figure 3.

	
    ----------------      --------------     -------------- 
   | Authentication |    | Delivery     |   | Delivery     |
   | Service (AS)   |    | Service(DS1) |   | Service(DS2) |
    ----------------      --------------     --------------
   Multiple memberships /                 \       / |   
   *********************************************************
   *                  /             ________\___/   |       *
   *                 /             /         \      |       *
   *      ----------       ----------       ----------     *
   *     | Client 0 |     | Client 1 |     | Client N |    *
   *      ----------       ----------       ----------     *
   *      ............................      ...........    *
   *      Member 0                          Member 1       *
   *                                                       *
   *********************************************************
            

Figure 3: Multiple membership

6. Informative References

Appendix A. Acknowledgements

This work was supported by Institute for Information & communications Technology Promotion(IITP) grant funded by the Korea government(MSIT) (No.2018-0-00254, SDN security technology development).

Author's Address