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AN IMPROVED AUTHENTICATION AND KEY AGREEMENT PROTOCOL OF 3G
ABSTRACT
With the development of mobile communication network, the requirements of mobile users for data services are higher and higher, which makes data service become more diversiform and various service providers appear on after the other. As a result, data services increasingly become the main service in mobile network.
The Universal Mobile Telecommunications System (UMTS) is one of the new ‘third generation’ (3G) mobile cellular communication systems being developed within the framework defined by the International Telecommunications Union (ITU) known as IMT-20001.UMTS aims to provide a broadband, packet-based service for transmitting video, text, digitized voice, and multimedia at data rates of up to 2 Mbps while remaining cost effective. The AKA procedure is the essence of authenticating a user to the network and vice versa. AKA procedures in UMTS have increased security compared with GSM.
However, during its development some security problems emerged. Although the authentication and key agreement (AKA) protocol solve some, it still has some flaws such as lacking complete authentication and interworking and so on. In order to those problem preferable, aiming at the security threaten for services based on mobile network and the problems with the existing AKA, we analyzed the existing Authentication and Key Agreement (AKA) protocol, and points out the security flaws among it and possible methods of attack. For the security flaws, an improved AKA protocol is proposed. In the end, we analyzes the improved AKA protocol.
1. INTRODUCTION
The third generation mobile communication system (3G) not only support the tradition pronunciation service, it will also provide other services, such as the multimedia services, the data service, electronic commerce, the electronics trade as well as the Internet serves and so on. If we apply 3G in the special domain of information based society construction, it will certainly to enhance the process of information based society construction effectively. As the openness of 3G wireless channel, the security problem always a key factor of affecting the system performance. Most information in the special domain is confidential information and should be controlled in a secure scope, therefore, it is the key problem that preventing this information from being tampered and being got by illegal users in the wireless channel. In the safe communication, the implementation of the authentication and the key agreement is the premise and guarantee of the encrypted communication.
The Authentication and Key Agreement (AKA) protocol is a security protocol used in 3G networks. AKA is also used for one-time password generation mechanism for Digest access authentication. It is a challenge-response based mechanism that uses symmetric cryptography.AKA provides procedures for mutual authentication of the MS and serving system. The successful execution of AKA results in the establishment of a security association (i.e., set of security data) between the MS and serving system that enables a set of security services to be provided. AKA is typically run in a UMTS IP Multimedia Services Identity Module (ISIM), which resides on a smart card like device that also provides tamper resistant storage of shared secrets.
At present the 3GPP-AKA protocol using in current 3G system has the shortage of security, it cannot satisfy the high secure demand of the special domain. In order to those problem preferable, aiming at the security threaten for services based on mobile network and the problems with the existing AKA, we analyzed the existing Authentication and Key Agreement (AKA) protocol, and points out the security flaws among it and possible methods of attack. For the security flaws, an improved AKA protocol is proposed and it is further analyzed.
2. WHEN TO USE AKA?
 Registration of a user in a SN
 After a service request
 Location Update Request
 Attach Request
 Detach request
 Connection re-establishment request
Registration of a subscriber in a SN (Serving Network) typically occurs when the user goes to another country. The first time the subscriber then connects to the SN, he gets registered in the SN. Service Request is the possibility for higher-level protocols/applications to ask for AKA to be performed. E.g. performing AKA to increase security before an online banking transaction. The terminal updates the Home Location Register (HLR) regularly with its position in Location Update Requests. Attach request and detach request are procedures to connect and disconnect the subscriber to the network. Connection re-establishment request is performed when the maximum number of local authentications has been conducted.
3. TRADITIONAL AUTHENTICATION AND KEY AGREEMENT (AKA) PROTOCOL
3.1. PROTOCOL DESCRIPTION
Participators in the implementation of authentication and key agreement (AKA) protocol include:
 User terminal: Mobile Equipment/Universal Subscriber Identity Module(ME/USIM),
 Visit network: Visit Location Register/Serving GPRS Support Node (VLR/SGSN) and
 Ownership network: Home Environment/Home Location Register (HE/HLR).
The implementation of AKA takes the following conditions as the premise:
(1)The user and ownership network shared the system key K.
(2)The user trust the ownership network HE.
(3)The user's HE believes VLR can manage the information safely.
(4)The communication between HE and VLR is secure enough.
The process of authentication includes five steps as followed:
(1)MS→VLR: IMSI, HLR
(2)VLR→HLR: IMSI
(3)HLR→VLR: AV=RAND||XRES||CK||IK||AUTN
(4)VLR→MS:RAND||AUTN
(5)MS→VLR: RES