Security on Demand for Mobile IPv6 and Dual-stack Mobile IPv6
draft-bajko-mext-sod-03

Abstract

Mobile IPv6 and Dual-stack Mobile IPv6 protocols require the signaling messages between the mobile node and home agent to be secured. However security for the user plane/traffic is optional and is a choice left to the mobile node. This document proposes extensions to Mobile IPv6 signaling which enables the user plane traffic to be secured on a need or on-demand basis. The mobile node or the home agent can request at any time security for the user plane traffic. Security for user plane traffic can be triggered as a result of policy or, mobility or, at the user's choice.

Status of this Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on May 04, 2012.

Copyright Notice

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Table of Contents

• 1. Introduction
• 2. When to apply Security to user plane traffic
• 3. Triggering user plane traffic security
• 4. Extensions to Mobile IPv6
• 4.1. Extensions to Binding Update and Binding Acknowledgement
• 4.2. New binding Update Mobility Options
• 5. HA initiated security for user plane traffic
• 6. IANA Considerations
• 7. Security Considerations
• 8. Summary
• 9. Acknowledgments
• 10. References
• 10.1. Informative References
• 10.2. Normative References
• Authors' Addresses

1. Introduction

Mobile IPv6 [RFC6275] and Dual-stack Mobile IPv6 [RFC5555] provide the option to secure the user plane data between the Mobile Node (MN) and and the Home Agent (HA) when needed. The user plane traffic between the MN and HA is secured via an IPsec security association (SA) which is established between them specifically for the purpose of user plane data. IPsec is used for securing the user plane traffic when the security between the MN and HA is based on IPsec. However security between the MN and HA could also be enabled via other protocols. The MEXT WG is evaluating on an experimental basis various alternatives to IPsec such as the one specified in [I-D.ietf-mext-mip6-tls].

As per the current specifications for MIP6 and DSMIP6, security of the user plane traffic is optional. When the MN is attached to 3G/4G network such as HSPA, LTE or EV-DO, the MN may not require security for the user plane traffic since these networks already provide ciphering over the air-interface and deploy hop-by-hop security, which makes these networks secure. However the MN may attach to less secure or unsecured accesses such as wireless lan (WLAN) or it may roam in countries where the user may prefer the data between the MN and the HA to be encrypted (even when using cellular accesses). There is no solution in the protocol specification today which provides the capability to trigger the security for the user plane traffic on a need basis.

The problem that is being addressed is the triggering of security for user plane traffic between the MN and HA on a need basis. Policy information at the MN or information provided to the MN via other means at the time of attachment may assist the MN to determine if security needs to be enabled for user plane traffic. The user may also consciously decide to enable security when attached to certain networks. Furthermore, the operator of HA may have policies that define when user plane security is to be used. This document describes a mechanism which can enable security for user plane traffic on-demand or need.

An obvious implementation alternative would be to encrypt user plane traffic always (as is commonly done with VPN use-cases), but that would unnecessarily consume resources on the HA. For the HA operator there is clear economic incentive to encrypt user-plane data only when necessary. The MIP6/DSMIP6 protocols only provide a means to secure the user plane traffic but do not provide any mechanisms by which the security is triggered as a result of mobility or the MN attaching via different access networks.

As per the current MIP6 [RFC6275] specification, only the MN has the ability to enable security for user-plane traffic. The HA has no ability to force the MN to secure user traffic.

2. When to apply Security to user plane traffic

An MN MUST have security for the control plane messages. Hence all signaling between the MN and HA are secured. The MN establishes an IPsec SA between itself and the assigned HA prior to sending a Binding Update. However, the MN is not required to establish an SA for securing the user plane traffic. It is up to the MN whether it establishes SAs for the control plane and user plane at the same time or if it only establishes the control plane SA. The MN may choose to establish the SA for user plane traffic at any time [RFC4877].

When the MN attaches to an access network, it is usually able to determine if the access network is viewed as trusted or untrusted. The MN can make this determination, for example, based on the PLMN ID of the cellular network; or wifi_SSID/MAC_address of a wifi network; or location information provided by the MN, or user input. The MN has either a stored policy about trusted and untrusted access networks or it may be provided with such information from policy stores such as the ANDSF [23.402] or AAA server at the time of network attachment. An interface exists generally between the policy store such as AAA or ANDSF and the Home Agent (HA). If the MN is attached to an access network which is viewed as trusted or where encryption is not allowed, the MN chooses not to secure the user plane traffic.

If the MN is attached to an access network which is not trusted, the MN may want to secure its user plane traffic. The HA may also be able to determine from the source address of the binding update (BU) message the access network to which the MN is currently attached. Based on this information, the HA may require that the user plane traffic be encrypted on the MN-HA link.

The MN or HA can determine when to use security for the user plane traffic using static policies or dynamic policies which can be obtained at the time of network attachment; or e.g. which are provisioned and maintained on a smartcard (eg, a UICC or SIM). 3GPP policy stores such as the ANDSF can also provide information about the access networks to which an MN is attached. Location of the MN can also be used as input.

3. Triggering user plane traffic security

This document proposes extensions to MIPv6/DSMIPv6 protocol, allowing the MN to signal to the HA its preference for user plane traffic security, and for the HA to override that preference based on the policy settings.

A new mobility option called as the "Security-on-demand" (SoD) is specified which is used to switch on or off the security for the user plane traffic.

The MN sends a binding update which includes the "Security-on-demand" mobility option set which is used to indicate whether security for the user plane traffic is to be switched On or Off. The HA processes the binding update message from the MN and sends a response acknowledging the request and including the "SoD" option for user plane traffic security.

The HA MAY always overwrite the MN's security preference on the user plane traffic indicated in the Binding Update message, by setting the SoD option in the the Binding Acknowledgement to a different value. The MN SHALL always follow the indication in the Binding Acknowledgement to set the security of the MN to HA user plane traffic.

4. Extensions to Mobile IPv6

4.1. Extensions to Binding Update and Binding Acknowledgement

This section defines the new Security-on-demand mobility option for the Binding Update and the corresponding Binding Acknowledgement message.

The security-on-demand mobility option has an alignment requirement of 2n. Its format is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |   Type =      |  Length =     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | SoD option    |     Reserved              	       	           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
				 
    
      

• Type = TBD (To be assigned by IANA)
• Length = 4
• SoD Option = This option field defines whether security is enabled or disabled as well as whether security is integrity protected or encrypted

4.2. New binding Update Mobility Options

    
       0                   1                   2                   3 
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      |   Type        |   Length      |N|   Reserved  |   Data ... 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
                            Data ...                                  | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         
      

A new mobility Options for carrying location of the MN is defined to be used in a Binding Update message with the following format:

Type: tbd

N set to 1 indicates that the data contains a location in XML format as defined in RFC5139, N set to zero indicates that the data part contains an http URI pointing to a resource where the MN uploaded its location

5. HA initiated security for user plane traffic

Mobile IPv6 signaling is primarily mobile initiated. The security for user plane traffic can be requested by the MN via the Binding Update request message and the HA has the ability to either approve or deny via the Binding Acknowledgment message. However the HA does not have a way to send an insolicited message to the MN and trigger the establishment of security for the user plane traffic.

Mobile IPv6 defines Binding Revocation [RFC5846] which enables an HA to send an unsolicited message to the MN to revoke a binding. This is the only unsolicited signaling message that can be sent by HA to an MN. This I-D proposes extending the binding revocation message to indicate to the MN that security for the user plane traffic is required. The effect of sending the binding revocation message to the MN with the appropriate option included in it will cause the MN to send a Binding update with the SoD mobility option requesting security for user plane traffic.

6. IANA Considerations

This document will require actions on the part of IANA to assign values for the new binding update mobility option.

7. Security Considerations

This I-D introduces extensions to Mobile IPv6 signaling messages. There is no impact to the security model and architecture that is currently specified for MIP6 [RFC6275]. The extensions specified in this document do not introduce any new vulnerabilities of threats to the security architecture of Mobile IPv6.

8. Summary

Security for the user plane traffic between the MN and Home agent can be switched on or off as a result of policy, location or, request by the user. The ability to control and trigger the security for the user plane traffic rests with the MN as well as the HA with the HA having the final say.

9. Acknowledgments

The authors acknowledge the reviews by Julien Laganier, Jouni Korhonen, Stefano Faccin and Kent Leung. Their comments and suggestions will be incorporated in the next revision.

10. References

10.1. Informative References

10.2. Normative References

Authors' Addresses