Avishek Dutta & Vikram Raju R.

 

Abstract— Mobile Nodes (MN) in Mobile IPv6 (MIPv6) are given the opportunity to eliminate triangle routing that is inefficient with their own corresponding node (CN) using Route Optimization (RO). This greatly improves the performance of the network. Unfortunately, using this method allows several security vulnerabilities to manifest itself with the MIPv6. Among those, common issues are those concerns the verification of authenticity and authorization of Binding Updates during the process of RO. These types of unauthenticated and unauthorized BUs are the key to various types of malicious attacks. Since it is expected that MIPv6 will be supported by IPv6, several mechanism to ensure BU security will be crucial in the next generation Internet. This article focuses on Mobile IPv6 and security considerations.

Keywords/Index Term—IKE, Mobile IPv6, Network Security, Potential threats in MIPv6

I. Introduction

The way MIPv6 operates can be seen in Figure 1 [1], with 3 node types, namely the Home Agent (HA), Mobile Node (MN) and the Corresponding Node (CN) [2], while MN’s mobility is detected by a router advertisement message including an MN able to make a router send its advertisement message by request, if needed. Following mobility detection, the MN gets a CoA unlike in MIPv4, after which it sends the BU message to the HA and the communicated corresponding node (a node wishing to connect to, or is communicating with MN). The HA and corresponding node update the binding list and send acknowledgement messages [1], meaning that the Mobile IPv6 allows an MN to alter its attachment point to the internet while maintaining established communications [3]. This paper presents an analysis of both Route Optimisation (RO) and Identity Based Encryption (IBE) protocol with proposal to strengthen the level of security of a BU method. This method uses the public key to create an authentication that is stronger.

II. MN-HA Authentication

Mutual authentication between an MN and its HA is mandatory in MIPv6, and usually performed with IPSec and IKE, while session key generation and authentication are done with IKE. Using X.509 certificates in IKE is the existing method of performing these tasks.

1. The MN moves to a foreign network and obtains a new CoA.

2. MN carries out a BU on its HA (where the new CoA is registered). HA sends a binding acknowledgement to MN.
3. A Correspondent Node (CN) tries to contact MN, with HA intercepting packets destined to MN.

4. Next, HA tunnels all packets from CN to MN using MN’s CoA.

5. When MN replies to the CN, it may use its current CoA (and bind to the CN) and communicate with the CN directly (“route optimization”), or it could tunnel all its packets through the HA.

Sometimes MN and HA share a common secret, possibly occurring in WLAN instances when MN shifts to another WLAN which requires authentication [4]. If there are no shared secrets, extending the IKEv2 authentication process to identity-based authentication as opposed to X.509-based authentication certificates is usual. It can also be assumed that both MN and HA use the same PKG, and according to the relationship between these three entities, any trust level from I to III may be applied during private key delivery. Regarding IKE, two main methods of implementing IBE exist, the first of which involves modifying IKE’s four-way handshake while the second utilizes EAP to generate a new IBE-based EAP authentication method [4].

A. Modifying IKE

IKE could implement IBE through the addition of a third authentication method, other than the previous shared secret and X.509 authentication. Instead of X.509 certificates, IKE also uses “IBE certificates”. IBE-based authentication functions fundamentally the same as X.509 authentication, in that to authenticate peers the same information block should be signed as in the X.509-based authentication, in addition to a signature based on IBE (i.e. the Hess signature). Currently, identities are replacing certificates and revocation lists do not need to be checked. Ehmke (2007) implemented a prototype which can realize this idea. Performance wise, clearly transmit certificates or certificate requests are no longer necessary since the IKE identity can be used straight as the public key for authentication. Also, expensive certificate-chain checking is redundant while elliptic curve cryptography-based hardware- accelerated IBE algorithms are sometimes quite efficient, particularly in embedded devices [4].

B. Extensible Authentication Protocol

Several wireless networks utilize the Extensible Authentication Protocol (EAP) [5] for access authentication. EAP techniques commonly deal with AAA servers which affect the required authentications, after which notifications are relayed back to a functional module (Network Access Server) in the access network. For Mobile IPv6 [6], the Binding Authentication Data option [7] helps enable different authentication techniques, while a subtype exists for AAA- based authentication like EAP. On the other hand, there still are EAP methods requiring extra handling and specifications which present Binding Authentication Data option documentation does not provide. Currently, specification from this document is for at least some very widely deployed EAP methods, so, often, when EAP is needed, Mobile IPv6 tunnel redirection to a wireless device’s new CoA can be done much faster [8-10].

C. Using Extensible Authentication Protocol

Figure 2 illustrates possible steps in EAP implementation. It is advisable to use EAP as part when establishing a concurrent shared key to be used in the final two message exchanges leading to authentication [4]. Chen and Kudla’s key agreement with IBE technique is one alternative protocol (protocol 2’ in [11]) that can function in the absence of a key escrow, so CERTREQ and CERT messages in steps 2, 3, 4 are not necessary (Figure. 2). Figure 3 illustrates the resulting IKE Initial Message exchange.

1. I _ R: HDR, SAi1, KEi, Ni

2. R _ I: HDR, SAr1, KEr, Nr, [CERTREQ]

3. I _ R: HDR, ESK{IDi,[CERTREQ,][IDr,]SAi2,TSi,TSr}

4. R _ I: HDR, ESK{IDr,[CERT,]AUTH,EAP}

5. I _ R: HDR, ESK{EAP}

6. R _ I: HDR, ESK{EAP}

.. … …

n. R _ I: HDR, ESK{EAP(success)}

n+1. I _ R: HDR, ESK{AUTH}

n+2. R _ I: HDR, ESK{AUTH,SAr2,TSi,TSr}

Fig 2. IKE Initial Message Exchange: Authentication using EAP [12].

Here, the same PKG is shared by MN and HA, where P is a public PKG parameter, and HA and MN choose the random numbers a and b, respectively. The Chen-Kudla protocol produces a session key solely for message 7 and 8

authentication. The AUTH payloads have to authenticate

messages 3 and 4 based on MAC and a secret key generated

by an EAP protocol [11].

1. MN _ HA: HDR, SAMN1, KEMN, NMN

2. HA _ MN: HDR, SAHA1, KEHA, NHA

3. MN _ HA: HDR, ESK{IDMN,[IDHA,]SAMN2,TSMN,TSHA}

4. HA _ MN: HDR,

ESK{IDHA,AUTH,EAP_CK_Req(a·P,a·QHA)}

5. MN _ HA: HDR, ESK{EAP_CK_Res(b·P,b·QMN)}

6. HA _ MN: HDR, ESK{EAP(success)}

7. MN _ HA: HDR, ESK{AUTH}

8. HA _ MN: HDR, ESK{AUTH,SAHA2,TSMN,TSHA}

Fig 3. IKE Initial Message Exchange: EAP with IBE Authentication [12].

But since IBE uses PKG, it is almost impossible to guess

which MN will be communicated by the CN. We cannot

simply assume the same PKG is used by both MN and

CN. Multi-PKG is used instead but it is not recommended for

larger networks.

III. MN-CN Authentication

Via the MIPv6 protocol, MN can keep its network

connection even when the network attachment modifies

[13]. An MN can be reached at its home address (HA)

anytime, even when not physically in its home network.

When an MN is connected to a foreign network it obtains a

CoA from the local router through stateless or stateful

autoconfiguration. Next, for home r egistra tion, the MN

sends HA its current location information (CoA) in a BU

message, then HA can redirect and tunnel packets intended.

for the MN’s home address, to the MN’s CoA. When a

foreign network MN is in contact with a CN (a stationary

or mobile peer communicating with a MN) through the

HA, bidirectional tunnelling takes place for instances when

CN is not bound to the MN (registration is in progress) or

MIPv6 is not supported by CN [4].

If the CN supports MIPv6, a more effective mobile

routing technique, Route Optimization (RO), can be used.

RO is effective as it provides the most direct, shortest path

of transmitting messages between an MN and a CN,

eliminating the need for packets to pass through the HA, and

avoiding triangular routing (bidirectional tunnelling). Prior

to setting up RO, the MN must send CN a BU packet

containing its CoA with present location data. On the

other hand, security risks with RO [14] can be for example

that an MN may send CN a false BU packet and redirect

the communication stream to a desired location, resulting in

a Denial-of-Service (DoS) attack. Thus, for increased

security, it is important to authenticate BUs in RO [4] [15].

What happens between a CN and MN is not the same as

between an MN and its HA. Since CN could be any node,

MN and CN have no shared secrets or trusted certificates.

Thus, Return Routability (RR) can be used, as:

• An MN sends CN a home test init (HoTi) and

care-of test init (CoTi). HoTi is sent directly

through the HA and CoTi. HoTi has the home

address and CoTi has the CoA as source addresses,

both including a cookie.

• Upon receiving either HoTi or CoTi message,

CN immediately answers with a home test (HoT)

and care- of test (CoT) message which gets sent to

the respective source address. Each reply contains

the cookie recovered from the nonce indenx,

corresponding init message, and a keygen token,

later for BU authentication use.

When MN receives HoT and CoT, RR is done. Only

MN can receive packets sent to both its HA and CoA, and

can now hash the two tokens to calculate the binding key.

This key is utilized for generating a Message Authentication

Code (MAC) for BUs, and MAC can be verified by CN.

RR provides an analysis of a node’s reach-ability during

authentication but do not validate address ownership in IPv6.

IV. MIPv6 Security Analysis

Providing security against different types of malicious

attacks e.g. denial of service (DoS), connection hijacking,

man- in-the-middle and impersonation, are the basic

objectives for the development of IPv6. The objective of

improved security is to create routing changes that are safe

against all threats. Threats are based on the routing changes

that provides mobility in the network. Threats faced by

Mobile IPv6 security can be divided into different categories:

__ Binding update (BU) to HA type threats

__ Route Optimisation to CN type threats

__ Threats that attack the tunnelling process between

HA and MN

__ Threats that uses Mobile IPv6 routing header to

return traffic of other nodes

Binding update and route optimisation threats are related

to authentication of binding messages. Communication

between MN and HA needs trust and communication

authentication. This is because MN agrees to implement the

HA services therefore relationship between the two must

first be secure. However, the CN and MN does not have

prior relationship but authenticating messages between the

two is still possible. For example, this is possible by

authenticating the public key. If a malicious packet is sent to

the HA using the same source address as the MN, the HA

will then forward the packet containing the MN’s source

address contained in the malicious node. However, this DoS

attack can be prevented by using an algorithm to verify the

BU message receives by the HA. Such threat can also be

avoided when a new routing header is used to replaces the

incorrect header that manoeuvres around firewall rules and

obtaining a constrained address [16, 17].

V. Proposed Protection of BU Message

Corresponding Author: XYZ, [email protected]

Once the BU message is complete, the MN will receive

normal traffic from the CN with the new CoA. The CN

with the new nonce sends to the MN a Binding Update

Verification (BUV) within a specific time frame e.g. 10

seconds. The MN then needs to reply within 10 seconds

otherwise the connection between MN and CN will be

terminated. This method minimises any damages caused by

bombing attacks where packets are sent to the MN by

malicious nodes. Cryptography Generated Address (CGA)

can also be use to make spoofing type attacks more harder.

Private keys can be use to signed the message as well. Since

redirection attacks requires both public and private keys to

perform[18-20]. Possible threats and solution is listed in

table 1 [4, 17].

VI. Conclusion

The requirement for Mobile IPv6 is still not complete

considering there are some essential issues that are not

addressed. One of the most important issues are protocol

security because without secure protection against

attacks, the protocol would not be accepted thus will not

work at all. Presently, the standard method use for BU

protection in transport mode as well as securing the

connection for control message sent during home registration

method is the Encapsulation Security Payload (ESP). IPSec

has several advantages over SSL/TLS which is IPSec

can perform without IP restriction, any protocol can be

encrypted and also encrypt any packets with just their IP

headers. Unfortunately, IPSec needs to be configured with

various settings thus making it complicated. The IKE

protocol can control the mutual authentication and

cryptographic algorithm negotiations as well as dynamic

key management. Additionally, authentication method such

as shared secret, Extensible Authentication Protocol (EAP)

or X.509 certificates can be use to create safe communication

between peers.

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AUTHORS PROFILE

Taro Denshi received the B.S. and M.S. degrees in Electrical Engineering from Shibaura Institute of Technology in 1997 and 1999, respectively. During 1997-1999, he stayed in Communications Research Laboratory (CRL), Ministry of Posts and Telecommunications of Japan to study digital beam forming antennas, mobile satellite communication systems, and wireless access network using stratospheric platforms. He now with DDI Tokyo Pocket Telephone, Inc.