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International Journal of Computer Theory and Engineering, Vol. 1, No. 3, August 2009
1793-8201
- 216 -
Abstract—Authentication of mobile subscriber is a challenge
of future researchers due to increasing security threats and
attacks with the enhanced population of wireless traffic. 3G
mobile communication system has been developed to speed up
the data communication. In general the authentication
technique in 2G mobile communication is solely dependent on
checking the authenticity of MS (Mobile Station or Subscriber)
by challenge/response mechanism. Here authenticity is one-way
for which MSC (Mobile or Main Switching Center) checks the
validity of MS. 3G mobile communication works on two
different switching techniques. One is circuit switching for voice
and low speed data communications. The other one is packet
switching mainly for data communication, but can afford voice
communication like VoIP (Voice Over Internet Protocol), video
telephony, multimedia service etc. Generally high speed data
communication is established by packet switching process
through PDSN (Packet Data Serving Node) servers. In circuit
switching (3G network) authentication is mutual where both
MS and MSC or network authenticate each other, but in packet
switching only network (servers in PDSN) examines the
authenticity of MS. In this paper, we enlighten different new
approaches that can be effectively used as an authentication tool
in 3G mobile communications.
Index Terms—Authenticity of Mobile Station or Subscriber,
Challenge/Response Mechanism, Circuit Switching, Identifier,
Packet Switching, PDSN, Password.
I. INTRODUCTION
The influence of the Internet and IP technology has
extended to enlighten the cellular area in high speed data
transmission [1]–[5]. Data rates reach upto 2 Mbps or more
for 3-G mobile communications, opening opportunities for
Chandan Koner is an Assistant Professor in the Department of Computer
Science and Engineering, Bengal Institute of Technology and Management,
Santiniketan, P.O. Doranda, West Bengal, Pin-731236, India. He is pursuing
PhD course. He is member of IACSIT and IAENG (phone:
+91-9434535556).
Pijush Kanti Bhattacharjee is an Assistant Professor in the Department
of Electronics and Communication Engineering, Bengal Institute of
Technology and Management, Santiniketan, P.O. Doranda, West Bengal,
Pin-731236, India. He was an Ex Asssitant Director in the Department of
Telecommunications (DoT), Government of India, India. He has possessed
vast working experience in the field of Telecommunications including
Mobile Communications, Image Processing, VLSI etc during last 29 years.
(phone: +91-33-25954148, +91-9432166768; fax: +91-3463-271354; ).
Chandan Tilak Bhunia is a Director, Bengal Institute of Technology
and Management, Santiniketan, P.O. Doranda, West Bengal, Pin-731236,
India. He is a Senior Member of IEEE, FIE (I) and FIETE.(phone:
+91-9434033157).
Ujjwal Maulik is currently a Professor in the Department of Computer
Science and Technology, Jadavpur University, Kolkata, India. He is a Senior
Member of IEEE and FIE(I). (phone: +91-33-24131766).
extensive wireless multimedia services. Enabling packet data
services off the RAN (Radio Access Network) in UMTS
(Universal Mobile Telecommunication System in USA) and
by passing the MSC is the beginning step for separating the
circuit based world of the PSTN and the packet based world
of PDNs (Public Data Networks) and the Internet [6]-[9]. The
European counterpart of UMTS is WCDMA (Wideband
Code Division Multiple Access), generally marketed as
3GSM. The WCDMA scheme has been developed as a joint
effort between ETSI and ARIB (Japanese) during the second
half of 1997, whereas, in March 1998, the TIA
(Telecommunications Industry Association) TR45.5
committee, adopted an innovation for wideband CDMA,
compatible with IS -95, which is called CDMA-2000. This
3-G network can provide circuit switched voice service,
circuit switched data service like 2-G (CDMA One or GSM),
in addition to this, packet switched data service [1]. The
packet switched can be enhanced in different speeds such as
38.4 kbps, 76.8 kbps, 153.6 kbps, 307.2 kbps, 614.4 kbps,
921.6 kbps, 1228.8 kbps, 1843.2 kbps, 2457.6 kbps etc. There
are different control channels e.g. MAC channel, Reverse
Traffic Channel, Access Channel etc which are associated to
and fro MS to MSC or PDSN to set up the communication
path implemented by proper authentication scheme.
II. ARCHITECTURE OF 3-G MOBILE SYSTEM
Architecture of a 3rd Generation wireless network
CDMA-2000 or WCDMA is described below in Fig. 1. This
3-G network can provide circuit switched voice service,
circuit switched data service like 2-G (CDMA One or GSM)
[3], [5], in addition to this packet switched data and
multimedia service [6]-[9]. In 2000 A.D, TIA
(Telecommunication Industry Association) publishes IS-856
(Interim Standard-856) network. It is known CDMA 2000 1X
EV-DO (Evolution Data Optimized). CDMA-2000 1X is
having chip rate 1.2288 Mcps, While WCDMA chip rate is
3.84 Mcps, but CDMA-2000 3X chip rate is 3.6864 Mcps.
MS - Mobile Station or Mobile Subscriber for transmitting
and receiving signals in air interface. It consists of USIM
(Universal Subscriber Identity Module) or SIM which
contains user identity i.e. subscriber’s number, data bases,
call charging etc.
MS to BTS path - Reverse or Up link,
BTS to MS path - Forward or Down link.
BTS – Base Transceiver Station serves mobile connection
to one or more cells and sectors in the cellular network,
A Novel Approach for Authentication Technique
in Mobile Communications
C. Koner, Member, IACSIT, P. K. Bhattacharjee, Member, IACSIT, C. T. Bhunia, Sr. Member, IEEE and
U Maulik Sr. Member, IEEE
International Journal of Computer Theory and Engineering, Vol. 1, No. 3, August 2009
1793-8201
217
Fig.1. A typical 3G wireless network architecture with high speed data network
contains TRXs i.e. transceivers or radio units.
BSS – Base Station Sub Sys-BSCs & BTSs.
Submit your manuscript electronically for review.
BSC – Base Switching Center controls one or more BTSs
and perform inter BTS and intra BTS switching and
handovers.
MSC – Mobile Switching Center or Main Switching
Center which is a basic digital electronics exchange e.g.
5ESS means 5th version of Electronics Switching System.
MSC controls all the functions of a mobile network via
different registers or servers, specially for voice and low
speed data communications.
HLR – Home Location Register occupies identities of
mobile subscriber as IMSI [International Mobile Subs
Identity], service parameters, location information etc.
VLR – Visitor Location Register contains permanent and
temporary (roaming) mobile subscriber’s identity as TMSI,
ISDN directory number, routing etc.
EIR – Equipment Identity Register contains identity of
mobile equipment called IMEI [International Mobile
Equipment Identity], connected with MSC or PDSN. It may
be valid, suspect or prohibited.
AUC – Authentication Center contains authentication
data called Ki in 2-G and in 3-G several keys or encryption
codes
with algorithm for encrypting user speech and data due to
security purpose.
Billing Center – It provides all sorts of charging or
commercial information. One billing center can handle the
calls from several MSCs. In case of data transfer, this billing
function is done by AAA server associated with PDSN in
data communication network.
In data network, MS is called AT (Access Terminal)
where data or messages in written form is originated or
terminated, where as BTS with BSC are called AN (Access
Network) which handles data and further transports to
PDSN through IS-2001 (Interim Standard-2001) network
specified by ITU [2], [6], [7]. Thus AN acts as an interface
between AT and PDSN. AT and AN are connected by
IS-856 network.
For increasing data rate in 2-G, the first step begins
with deploying GPRS or the PSDN (Public Switched Data
Network) for enabling packet data services in GSM and
CDMA-One networks. The VoIP (Voice-over-IP) gateway
function could be provided as an extended feature to the
circuit gateway or the PDSN for 3-G mobile
communications. The VoIP gateway will hold the vocoding
algorithms converting between a voice call encapsulated in
an air
Internet
ISP
BTS
PSTN
MSC
VLR
IS-41
IS-41
VLR
MSC
AUC
HLR
IS-2001
BTS
BTS
BTS
BSC
BSC
BTS
BTS
MS
MS
BSC
BTS
BTS
IP
AAA
FA PDSN
HA
IWF
MS
VLR
MSC
AN
AT
International Journal of Computer Theory and Engineering, Vol. 1, No. 3, August, 2009
1793-8201
- 218 -
interface frame and an IP end point that may be an
IP-enabled phone, IP based PBX or PC etc [7]-[9].
The circuit switched voice and data services are
arranged in same pattern as CDMA-One (2-G) by MS, BTS,
BSC, MSC, HLR, VLR, AUC and IWF. An IWF
(Inter-Working Function) is configured for converting a
signal into a form compatible with a destination network
receiving the data. While IWF enables circuit switched data
service and BSC carries out mobility management i.e.
controlling hand over or hand off. Additional networks are
provided in 3-G for providing packet switched data service
usually higher speed than that of circuit switched data
service in 2-G.
This packet switched data network [1]-[2], [6]-[9] is
consisting of two parts.
(1) Packet Data Serving Node (PDSN): The PDSN is the
element that provides packet switched data service, like
MSC for circuit switching. It is an internet protocol (IP)
router that switches user data traffic to a public data network
i.e. the internet. It deals with packet switched traffic
(generally data) between the MS i.e. the user and packet
switched network namely Internet or Intranet etc.
(2) Authentication, Authorization and Accounting (AAA):
The AAA is a server that provides three main functions like
authentication, authorization and accounting services for the
packet data traffic connected with PDSN. It ultimately
ensures packet data network connectivity services to the
mobile users.
Authentication requires the user to provide an account
number and password i.e. exchange of logical keys or
certificates between the client and the server. If this
authentication is correct, the MS is permitted for packet data
service by Authorization. Last but not the least, function of
AAA is accounting. It collects information on its usage of
packet data service for billing or tariff calculation.
The CDMA-2000 network is supporting simple IP and
mobile IP functions.
(i) Simple IP: An MS residing in home PDSN is given an
IP address M and the server on the internet has an IP address
S. Using these two addresses, IP packets containing data or
information are exchanged between the MS and different
servers in the same PDSN. A PDSN is consisting of several
servers for routing packets in different directions. These
servers are identified by the assigned address.
(ii) Mobile IP: Two additional network elements are
provided for supporting Mobile IP.
(a) Home Agent (HA): This is a router together with the
foreign agent (FA). This router resides on the MS home IP
network. It serves as a point for communications with the
mobile network.
(b) Foreign Agent (FA): This is another router residing in
other PDSN. When MS travels a foreign IP network, the FA
in the foreign network receives packet forwarded from the
HA and delivers them to the MS. Thus it functions as the
mobile node’s point of attachment when it travels to the
foreign network i.e. the network other than its home
network.
Thus mobile IP uses a tunneling protocol to allow
messages from the PDSN to be directed to the mobile node’s
IP address. This is accomplished by way of routing
messages to the foreign node for delivery via tunneling the
original IP address inside a packet destined for the temporary
IP address assigned to the mobile node by the foreign node.
This method allows for seamless communications between the
mobile node and applications residing on the PDSN,
always-on connectivity for mobile data applications and
wireless computing.
Third Generation mobile service is assured mainly by
two systems like WCDMA and CDMA-2000 [6]-[9]. Some of
the common feature between these two systems i.e.
CDMA-2000 1X and WCDMA are the followings:
Direct sequence spread spectrum multiple access
(CDMA-2000 1X uses 1.25 MHz bandwidth, WCDMA uses 5
MHz bandwidth), Orthogonal (Walsh) code division multiple
access (mitigates interference), Random access, Fast uplink
power control, Rake receivers, Soft handoff (between BTSs),
Softer handoff (between BTS sectors), Soft hand off (SHO)
active set (seamless service with increased spectral
efficiency), Single frequency reuse, QPSK (Quadrature
Phase Shift Keying) modulation, Downlink slotted paging,
Blind rate detection, Down link reference channel (share
common pilot), Downlink channel structure (separating
channels with Walsh codes), Scrambling (for uniform
interference and communication privacy), Speech regulated
vocoder (increased system capacity) etc. In case of packet
switching, variable length orthogonal codes are a mandatory
feature for both CDMA-2000 and WCDMA for managing the
mix of voice and non voice (data, multimedia)
communications. Packet switching can afford different
services like data, VoIP, Push to Talk, Video Telephony,
Multimedia communications etc. These include enhanced
downlink and uplink packet access techniques. High speed
packet data communications is done in identical features like
CDMA 2000 1X EV-DO (Evolution-Data Optimized) and
WCDMA HSUPA (High Speed Uplink Packet Access),
HSDPA (High Speed Downlink Packet Access).
At the same time there is existing some difference also
between these two systems such as, (i) Both WCDMA and
CDMA-2000 use separate coding scheme.
(ii) Both use control channels to manage the network.
(iii) WCDMA and CDMA-2000 are not compatible from
the perspective that they have different chip rates like 3.84
Mcps for WCDMA vs. 1.2888 Mcps for CDMA-2000.
WCDMA uses a 5 MHz channel (bandwidth) initially,
CDMA-2000 1X uses only a 1.25 MHz channel, but
CDMA-2000 3X, three 1.25 MHz channels combine to form 5
MHz bandwidth.
There are three modes of operation for WCDMA or
CDMA-2000
• Direct sequence (DS) WCDMA in UMTS for
frequency Division Duplex (FDD).
• W-CDMA Time Division Duplex (TDD).
• CDMA 2000 Multicarrier FDD
International Journal of Computer Theory and Engineering, Vol. 1, No. 3, August, 2009
1793-8201
- 219 -
III. AUTHENTICATION IN MOBILE COMMUNICATIONS 2-G NETWORK
GSM (2-G) networks utilize authentication for verifying
authenticity of subscriber [3]-[5]. Each subscriber is
identified with a unique IMSI (International Mobile
Subscriber Identity) number. He has a unique subscriber
authentication key (Ki).The authentication algorithm used in
the GSM system in 2-G is known as the A3 algorithm. The
SIM (Subscribe Identity Module) contains the IMSI, Ki and
A3 algorithm. The AUC (Authentication Center) contains
the A3 algorithm as well as a database of authentication
information about the subscriber. A3 actually generates 128
bits of output. The first 32 bits of those 128 bits form the
Signed Response. The A3 algorithm is implemented in the
SIM (Subscriber Identity Module).
Authentication in the GSM network utilizes following
Challenge/Response mechanism,
1. The HLR (Home Location Register) generates a
128-bit RAND (Random Challenge).
2. The HLR sends RAND to the MSC (Mobile Switching
Center).
3. The MSC sends it to the BTS (Base Transceiver
Station).
4. The BTS sends it to the MS (Mobile Station).
5. The MS receives it and generates 32-bit SRES*
(Signed Response) utilizing RAND and the 128-bit Ki from
the SIM (Mobile Station's Subscriber Identity Module)
utilizing the A3 algorithm.
6. The MS sends the SRES* to the BTS.
7. The BTS sends the SRES* to the MSC.
8. The MSC checks whether SRES = SRES* or not. If
they are same, MS is authentic.
This process authenticates the MS (Mobile Station) to the
GSM or CDMA-One network. One known security
limitation of 2-G networks is that the network is never
authenticated by the MS (Mobile Station). This one-way
authentication makes it possible for an attacker to pretend to
be a network provider. As 2-G mobile authentication
mechanism is only one way, therefore the user is not given
the assurance that they have established a connection with
an authentic serving network.
IV. AUTHENTICATION FOR MOBILE
COMMUNICATIONS 3-G NETWORK
In 3-G mobile communication, voice communication is
held by MSC and its accessories. In packet switching,
authentication is done separately by PDSN servers [6]-[9].
In circuit switching, the authentication for establishing
voice path is done by the following procedure,
1. Mutual authentication where MS and MSC are
confirmed identity individually.
2. Assure that the authentication information and keys are
not being re-used (key freshness).
Additional parameters and cryptographic checks are
introduced in 3-G network to provide mutual entity
authentication between the USIM at the user side and the
AUC at the network side. This technique uses symmetric
key or code using a secret subscriber authentication key K
which is shared between and available only to the USIM and
the AUC in the user’s HE (Home Environment). In addition,
the AUC entrusts with track of a counter SQNHE and at the
same time USIM controls track of a counter SQNMS. It also
stores additional data to support network authentication
providing the user with assurance by key freshness.
This scheme is assembled of a challenge/response protocol
identical to the 2-G mobile subscriber authentication with an
additional feature of network authentication. The HE, which
manages both the AUC and the USIM, possesses some
technique in the management of sequence numbers.
In 3-G mobile communication, voice communication is
held by MSC and its accessories. In packet switching,
authentication is done separately by PDSN servers [6]-[9].
In circuit switching, the authentication for establishing
voice path is done by the following procedure,
1. Mutual authentication where MS and MSC are confirmed
identity individually.
2. Assure that the authentication information and keys are
not being re-used (key freshness).
Additional parameters and cryptographic checks are
introduced in 3-G network to provide mutual entity
authentication between the USIM at the user side and the
AUC at the network side. This technique uses symmetric key
or code using a secret subscriber authentication key K which
is shared between and available only to the USIM and the
AUC in the user’s HE (Home Environment). In addition, the
AUC entrusts with track of a counter SQNHE and at the same
time USIM controls track of a counter SQNMS. It also stores
additional data to support network authentication providing
the user with assurance by key freshness.
This scheme is assembled of a challenge/response protocol
identical to the 2-G mobile subscriber authentication with an
additional feature of network authentication. The HE, which
manages both the AUC and the USIM, possesses some
technique in the management of sequence numbers.
This scheme is assembled of a challenge/response protocol
identical to the 2-G mobile subscriber authentication with an
additional feature of network authentication. The HE, which
manages both the AUC and the USIM, possesses some
technique in the management of sequence numbers.
2.4. Computes an expected response XRES = f2K (RAND),
where f2 is a (possibly modified) message authentication
function;
2.5. Computes a cipher key CK = f3K (RAND), integrity
key IK = f4K (RAND) and anonymity key AK = f5K (RAND),
where f3, f4, f5 are key generating functions.
2.6. Computes the concealed sequence number SQN AK.
2.7. Assembles the authentication token AUTN =
SQN [ AK] || AMF || MAC-A and the quintet Q = (RAND,
XRES, CK, IK, AUTN) and updates the counter SQNHE.
3. AUC sends that ordered array of n quintets to the VLR.
4. When the VLR initiates the authentication scheme it
selects the next quintet from an array held in the VLR and
International Journal of Computer Theory and Engineering, Vol. 1, No. 3, August, 2009
1793-8201
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sends the parameters RAND and AUTN to the user.
5. After receiving of a (RAND, AUTN) from the VLR,
USIM in MS computes the following procedure:
5.1 If the sequence number is concealed, the USIM
computes the anonymity key AK = f5K (RAND) and
retrieves from AUTN the unconcealed sequence number
SQN = (SQN AK).
5.2 The USIM then computes XMAC-A = f1K (SQN ||
RAND || AMF) and compares XMAC-A with MAC-A
which is included in AUTN.
5.3 If they are not matching i.e. MAC-A ≠ XMAC-A, the
USIM directs the MS to fail a user authentication response
with indication of integrity failure to the VLR and cancels
the further execution.
If they are matched i.e. MAC-A = XMAC-A, the USIM
computes the following:
5.4 The USIM verifies that the received sequence number
SQN is acceptable or not.
5.5 If the sequence number SQN is not acceptable, the
USIM computes the re-synchronization token AUTS and
directs the MS to fail a user authentication response, with an
indication of synchronization failure, including the
re-synchronization token AUTS and abandons the
procedure.
If SQN is acceptable, the USIM progresses through the
following procedures:
5.6 The USIM then computes the response RES =
f2K(RAND) and directs the MS to send back a user
authentication response back to the VLR, with an indication
of successful receipt of the signed challenge and including
the response RES.
6. The VLR compares the received RES with XRES. If
they identical, the VLR confirms that the MS (USIM) is
authentic and therefore authentication proceeding is
successfully completed.
B. Authentication for Packet Switching in 3G network:
Authentication for packet switching is done by AAA
(Authentication, Authorization and Accounting) server [2],
[6]-[9]. Authentication requires the user to provide an
account number or identifier and password i.e. exchange of
logical keys or certificates between the client (MS) and the
server in PDSN. If this authentication is correct, then MS is
permitted for packet data service by Authorization.
An AAA server is a server program that handles user
requests for access to network resources. The AAA server
typically interacts with network access and gateway servers
and with databases and directories containing user
information.
V. PROPOSED AUTHENTICATION SCHEME FOR
PACKET SWITCHED NETWORK
The entire packet switched mobile network
authentication and improvements provide only one-way
authentication i.e. only Servers in PDSN can check the
authenticity of a user. The user can not check whether he is
communicating with a correct server in PDSN or not. It is a
vital gap where a potential adversary can spoof the servers in
PDSN and get valuable user information. This motivates to
construct an authentication scheme for packet switched
mobile network that provides user and server authentication
and the user gets access to the network resource only if <user,
server>’s authenticity is passed correctly. The authenticity of
user can be checked by different entities as in following
procedures:
(i) Using log identifier with password for authentication of
mobile subscriber.
(ii) Certified authority server checks the authenticity of
subscriber (MS).
(iii) Different biometric authentication is a technique to
check a valid user by user physical characteristic. Human
physical characteristics are called Biometric property such as
Fingerprint, Voiceprint, Retinal scan and Face recognition etc.
Out of these biometric characteristics, we emphasis on
following areas:
(A) Acoustic Recognition: In this process, sound detecting
from ear of the mobile subscriber (MS) is done by biometric
authentication method. Ear not only senses sound but also
makes signals of its own called OAEs (Otoacoustic Emission).
These OAEs are produced by the motion of hair cells within
the outer part of the spiral shaped cochlea lying in the inner
ear. Hearing is an active process where the ear actually puts
energy into the incoming sound waves to replace energy lost
as sound which is absorbed by the ear’s function. Due to this
process some of the energy added by the hair cells escape as
OAEs. These OAE signals are detectable by supersensitive
(ultra low noise) microphone. These signals prove unique to
each individual including male, female etc. Thus this can be
used as an authenticity marker for a caller or set of callers
using MS to the network either in circuit or packet switching
cases. Hence the use of stolen mobile can be automatically
disabled in case of the users are not legitimate owner by
simply matching the stored specimen of OAEs.
(B) Face recognition: Face images of the mobile equipment
(MS) users are stored either in AUC or PDSN server. The MS
(mobile caller) is authenticated by matching the face image of
actual user with that of the notified users in MSC or PDSN
database. If these two images are completely matched, the call
will be progressed, otherwise not.
Authenticity of the network or server (MSC or PDSN) is
identified by MS through the following procedure:
(i) Response and throughput time of the server.
(ii) Shared secret key pairs between the user and the server.
(iii) Received power level from the server.
VI. CONCLUSION
3-G mobile network is completely described above with
the present authentication scheme. It is seen that wireless
communication is enhanced in packet switching technology,
as a result high speed secured data as well as voice
transmission-reception is possible. Our future work is to
invent new efficient mutual authentication technique using
entities like Password, Identifier, Certified Authority,
Biometric Property etc. of the subscriber in both circuit
International Journal of Computer Theory and Engineering, Vol. 1, No. 3, August, 2009
1793-8201
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switching and packet switching mobile communications.
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