Rehab K. El Nemr
Computer Science department, Faculty of Media Engineering, German University in Cairo, Egypt
Imane Aly Saroit Ismail, S. H. Ahmed
Information Technology Department, Faculty of Computers and information, Cairo University, Egypt
Keywords: GSM, Authentication, Ciphering, A3/5/8, RSA, Public key and Digital Certificate.
Abstract: Security is a burning issue with intelligent security pausing as the most relevant as it is important in all types
of applications which suffer from security related concerns. Accordingly, Security has become a need rather
than a luxury. GSM Security flaws have been identified several years ago. Some of these flaws have been
mended by the 3GPP but others are left to discussion. In this paper we will integrate a well known technique
in the system; Public-key technique. Yet, we will introduce the solutions in a different point of view; they
are Action-Triggered, meaning; it will work only if the flaw occurs. The original system will work in
normal cases. We will also discuss End-to-End security and propose a mechanism of Key management to
provide the subscribers with private calls’ option. Phone-Dependent technique is conducted to consider
Service provider attacks.
Mobile phones are used on a daily basis by hundreds
of millions of users, over radio links. Fixed phones
offer some level of physical security (i.e. physical
access is needed to the phone line for listening in).
Unlike a fixed phone, with a radio link, anyone with
a receiver is able to passively monitor the airwaves.
Therefore it is highly important that reasonable
technological security measures are taken to ensure
the privacy of user’s phone calls and text messages
(data) as well to prevent unauthorized use of the
service (J.
Quirke, 2004).
Global System for Mobile Communication (GSM)
specification 02.09 (GSM 02.09) identifies three
areas of security that are addressed by GSM as
Authentication of a user: it is the ability for a
mobile phone to prove that it has access to a
particular account with the operator.
Data and signaling confidentiality: this requires
that all signaling and user data are protected against
interception by means of ciphering.
Confidentiality of a user: when the network needs
to address a particular subscriber, or during the
authentication process, the unique IMSI
(International Mobile Subscriber Identity) should not
be disclosed in plaintext. Thus, someone
intercepting communications should not be able to
learn if a particular mobile user is in the area.
A more detailed Security features were specified
by Motorola Corporation (R. Campbell and D.
Mckunas, 2003) in their annual report as follows:
Mutual Authentication: The mobile user and the
serving network authenticate each other
Data Integrity: Signaling messages is protected by
integrity code
Network to Network Security: Secure
communication between serving networks.
User – Mobile Station Authentication: The user
and the mobile station share a secret key, PIN
(Personal Identification Number)
Visibility and Configurability: Users are notified
whether security is on and what level of security is
Multiple Cipher and Integrity Algorithms: The
user and the network negotiate and agree on cipher
and integrity algorithms. At least one encryption
algorithm exported on world-wide basis
K. El Nemr R., Aly Saroit Ismail I. and H. Ahmed S. (2006).
In Proceedings of the International Conference on Security and Cryptography, pages 175-182
DOI: 10.5220/0002101701750182
Lawful Interception: Mechanisms to provide
authorized agencies with certain information about
GSM Compatibility: GSM subscribers roaming are
supported by GSM security context
When a subscriber is added to a home network for
the first time, a Subscriber Authentication Key (Ki)
is assigned in addition to the IMSI to enable the
authentication. Ki must be stored in the user’s SIM
(Subscriber Identity Module). At the network side,
the key Ki is stored in the AuC (Authentication
Center) (Chengyuan Peng,
2003). SIM is the small
smartcard which is inserted into a GSM phone. It
contains all of the details necessary to obtain access
to a particular account. The SIM card contains the
following values: (J. Quirke, 2004)(ETSI TS100
929, November 1999)
IMSI: International Mobile Subscriber Identity
– a unique number for every subscriber in the
world. It is saved in the SIM.
Ki: the root encryption 128-bit key. This key
seeds the generation of all keys and challenges
used in the GSM system. The Ki is highly
protected, and is only known in the SIM and the
network’s AuC.
The SIM itself is protected by an optional PIN; The
PIN is entered on the phone’s keypad, and passed to
the SIM for verification. Algorithms used in GSM
security architecture are: A3 (Used in the
Authentication procedure), A8 (Used to generate the
Private Key Kc), A5 (Used in Ciphering).
The two main security features offered by GSM
and the role of the above algorithms are discussed in
the following subsections.
a. Authentication
Authentication is needed in a cellular system to
prevent an unauthorized user from logging into the
network claiming to be an authorized mobile
subscriber. If this were possible, it would be easily
possible to “hijack” someone’s account and
impersonate that person (or simply making that
person pay for the services) (J. Quirke, 2004).
Authentication is a function which is triggered
by the network when a subscriber applies for a
change of subscriber-related information (location
updating) element in the VLR (Visiting Location
Register) or HLR (Home Location Register). These
work together as a database of user information for
all people in the network and the immediate location
area. While the HLR stores the user records
permanently, the VLR dynamically stores the user
records of people in their location area to save time
connecting to the HLR. Also it is triggered when a
subscriber accesses to a service (call setup,
terminating calls, activation or deactivation of a
supplementary service) or when a subscriber
accesses to the network for the first time after
restarting of MSC (Mobile Service Switching
Center) or a VLR. Finally it is triggered when the
cipher key sequence number mismatch (Chengyuan
2003). In order to authenticate a user to the
network, the SIM card should prove knowledge of
the correct K
but it will be highly insecure to send
the K
as a plaintext to the network for
authentication. The K
in this case can be
intercepted. Instead the procedure works as
following (O. Benoit1& N. Dabbous, 2004):
1. A connection is attempted between the phone
and the network. The phone submits its identity.
Where possible, it avoids sending its IMSI in
plaintext (to prevent eavesdroppers knowing the
particular subscriber is attempting a
connection). Instead, it uses its TMSI
(Temporary Mobile Subscriber Identity).
2. The network generates a 128-bit random
number, known as the RAND and uses the A3
algorithm to mathematically generate an
authentication token known as the SRES.
3. The network sends the RAND to the phone to
do the same.
4. At the SIM side, a 32-bit SRES is generated
which is returned to the network for
comparison. If the received SRES matches the
network’s generated SRES, then the K
’s must
be the same (to a high mathematical
probability), and the phone has proved
knowledge of the K
and is thus authenticated.
The RAND must obviously be different every
time. Otherwise, an attacker could impersonate the
user by sending the same SRES. If authentication
fails the first time, and the TMSI was used, the
network may choose to repeat the authentication
with the IMSI. If this fails, the network releases the
radio connection and the mobile should consider that
SIM to be invalid (O. Benoit1& N. Dabbous, 2004).
b. Ciphering
Ciphering is highly important to protect user
confidentiality. It is done to protect both data and
signaling information. The purpose of this function
is to avoid an intruder to identify a subscriber on the
radio path by listening to the signaling exchanges.
This function can be achieved by protecting the
subscriber’s IMSI and any signaling information
elements. Therefore, a protected identifying method
should be used to identify a mobile subscriber
instead of the IMSI on the radio path. The signaling
information elements that convey information about
the mobile subscriber identity must be transmitted in
ciphered form (Chengyuan Peng, 2003).
The GSM system uses symmetric cryptography -
the data is encrypted and decrypted using the same
ciphering key – the Kc. The idea is that the Kc
should only be known by the phone and the network.
If this is the case, the data is meaningless to anyone
intercepting it. The Kc should also frequently
change, in case it is eventually compromised (J.
Quirke, 2004). Whenever the A3 algorithm is run (to
generate SRES), the A8 algorithm is run as well.
The A8 algorithm uses the RAND and K
as input to
generate a 64-bit ciphering key, the Kc, which is
then stored in the SIM and is readable by the phone.
The network also generates the Kc and distributes it
to the Base Station handling the connection.
At any time, the network can then order the
phone to start ciphering the data (once authenticated)
using the Kc generated. The network can pick from
a number of algorithms to use, as long as the phone
supports the one chosen. It can choose from up to 7
different ciphering algorithms (or no ciphering),
however it must choose an algorithm the phone
indicates it supports. Currently there are 3
algorithms defined – A5/1, A5/2 and A5/3. It should
be noted that A5/0 (no encryption) is available for
use in countries where there may be political
obstacles in supplying cryptographic hardware, such
as Middle Eastern or certain former Soviet countries.
This allows roaming to continue to work, and also
offers these countries the ability to use modern GSM
handsets (Bruce Potter, May 2004).
There are still some potential threats posed in the
GSM system although of these security measures
(GSM 02.09)(R. Campbell & D. Mckunas, 2003)(
Yong LI, Yin CHEN& T. MA, 2002)(L. Ertaul and
B. Kasim, June 2005) summarized as follows:
Limited encryption scope (Encryption
terminated at the base station)
Insecure key transmission (Cipher keys and
authentication parameters are transmitted in
clear between and within networks).
Security through Obscurity- Authentication and
encryption algorithms were never made public.
The whole security model developed in secret
which rises suspicion that cryptographic
algorithms are weak. Although never published,
ciphering algorithm A5 has been reverse
engineered by authors in (A. Biryukov and A.
Shamir, 2000). Authentication algorithms are
also reversed engineered (J. Rao, P. Rohatgi, H.
Scherzer and S. Tinguely, 2002).
End to end security is not provided.
If track of TMSI is lost then the mobile needs to
transmit the IMSI, this can be done by the false
base station.
Using the knowledge of IMSI and using
repeated authentication requests, the Ki can be
Network does not authenticate itself to the
phone, making it possible for an attacker to set
up false base station.
Ciphering is optional and is turned on by the
base station.
It is believed that GSM is secure for average
users. However it is not secure for high security
In our proposed integration system, public key
technique is the main factor. Public-key algorithms
are based on number theory. It is asymmetric,
involving the use of two separate keys, in contrast to
the symmetric conventional encryption, which uses
only one key (RSA Labs). Each one of the
communicating parties has a pair of keys, “Public
Key” and “Private Key”. Those keys are used in both
Encryption and Authentication (digital signature)
(William Stallings)(Limor Elbaz, 2002).
In this section we will emphasize on some of the
above problems and highlight the solutions in our
proposed system. Of course, using Public-key
technique in mobile communication is not un-
explored before but it was not used due to its high
computations that cause a delay. But our solutions
based on an Action Triggered mode, meaning, if a
flow occurs, like losing the IMSI for example, the
use of public key system is triggered.
System to be proposed is based on the idea of
obtaining a digital certificate from a third trusted
party i.e: a CA. A digital certificate is an electronic
identity, constructed of a public key and an
identification of the owner of the corresponding
public key. Digital certificates are issued, managed
and revoked by a CA (Limor Elbaz, 2002). Problems
attached to the existence or the extinction of a CA is
mostly political. Issues like selecting the Certificate
Authority (CA) or selecting a certain public-key
algorithm that is most suitable for GSM are out of
our scope. Proposed system requirements are:
The SIM/HLR/AuC/VLRs should have Digital
certificates along with their public keys.
The Digital Certificate of the home network
should be distributed when a new SIM card is
issued to a customer.
A public key Algorithm should be mounted on
the Mobile Station.
The files in AuC and HLR should be protected
against attacks using highly secure procedure of
“Password-locking” mechanism in order to
protect the users’ data (Keys and IMSI).
Problem 1: IMSI sent in a plain text
The GSM specifications have gone to great length to
avoid phone’s being addressed (i.e. paged) or
identifying themselves in plaintext by their IMSI.
This is supposed to prevent an eavesdropper
listening in, on the initial plaintext stage of the radio
communication, learning that a particular subscriber
is in the area (and what they are doing). Thus where
possible the network pages users by their TMSI and
maintains a database mapping TMSIs to IMSIs. If
the network somehow loses track of a particular
TMSI, and therefore cannot determine who the user
is, it must then ask the subscriber for his IMSI over
the radio link. Obviously, the connection cannot be
ciphered if the network does not know the identity of
the user, and thus the IMSI is sent in plaintext (J.
Quirke, May 2004).
Triggered Action 1
When this flaw is identified, SIM extracts the HLR
public key from its certificate. In SIM-VLR
communication, the public key of the VLR is
distributed in the initiation process. SIM then
encrypts the IMSI using the public-key and sends it
to the HLR/VLR. The VLR decrypts the ciphered
data using the correspondent private key. This
process is illustrated in figure 1.
Problem 2: Network does not authenticate
itself to a phone
This is the most serious fault with the GSM
authentication system. The network does not have to
prove its knowledge of the K
, or any other
authentication context to the phone. Thus it is
Figure 1: IMSI retreival mechanism.
possible for an attacker to setup a false Network
node. Since the authentication procedure initiation is
up to the network’s discretion, the false network
may choose not to authenticate at all, or simply send
the RAND and ignore the response. It does not have
to activate ciphering either (J. Quirke, May 2004).
Triggered Action 2
The SIM should have the option to initiate the
authentication process, for both Home Network and
a Visiting Network as follows:
1. Authenticating the Home Network: two
scenarios can be presented (illustrated in figure 2):
Scenario A: SIM generates a new RAND and
sends it to the Network. The Network encrypts it
using its Private Key and then sends the ciphered
data to the SIM. The SIM then decrypts the
ciphered data using the extracted Network Public
key and compares the two codes. If the two codes
do not match then the SIM sends a
connection fails.
Scenario B: authenticity can be proven also by
proving the knowledge of K
, in this case the
procedure is the following: SIM sends a RAND to
the Network and the network produces the
correspondent SRES and sends it back to the SIM.
But this procedure is not safe because an attacker
can obtain both SRES and RAND and perform a
“Known-plaintext attack” to retrieve the K
Therefore RAND should be sent encrypted by the
Network public key; in this case the attacker can
not obtain both RAND and SRES together.
2. Authenticating a foreign network: two scenarios
can be presented
Scenario A: As we mentioned before, authenticity
can be proven by proving the knowledge of the K
2. IDENTITY Response (E
But If the Mobile Station is authenticating a
foreign VLR, the Home Network will not send the
of the specified SIM in plain. A proposed
scenario is to do the following:
SIM sends a new RAND along with the TMSI
encrypted using the VLR public key.
VLR decrypts the message and extracts the
RAND then encrypts it using the home Network
public key and sends it to the HLR/AuC.
The HLR checks the “Chain of trust” of the
VLR and checks its validity. If it is valid, the
HLR computes the SRES using RAND and K
The Kc is computed as well.
The Kc and SRES are sent to the VLR
encrypted using the VLR public key.
The VLR decrypts the message and obtains
SRES and Kc, encrypts SRES using Kc and
sends it to the phone.
At this stage the SIM has calculated the Kc and
uses it to decrypt the message and compares the
two SRESs then sends either Accept or Reject
Since the SIM can not keep all the public keys of
the VLRs dealt with, SIM and the VLR should
exchange public Keys for future use in the
initiation phase.
Scenario B: another scenario to reduce the
computation overhead in the SIM is to change the
first step in scenario A to the following:
SIM sends the RAND in plain form to the VLR.
The rest of the steps are repeated.
These processes are illustrated in figures 3, 4 and 5.
Advantages of these two approaches are:
The VLR authentication relies on the HLR
validation procedure now. Note that there is a
list of Forbidden Network operators in the HLR.
Also the HLR checks the validity of the VLR by
sending its information to the CA.
will never be sent in plain or even encrypted
RAND and SRES are not sent in plain form. So
attacks of getting both SRES and RAND to
calculate the K
is not possible now.
Problem 3: Kc is sent in plain form in
Roaming is defined as the ability for a cellular
customer to automatically send & receive data when
traveling outside the geographical coverage area of
the home network, by means of using a visited
network. When a VLR connects to a user, it requests
the Kc from the HLR. HLR sends the Kc of a user in
plain form to the VLR.
Triggered Action 3
HLR identifies the last Kc being used by the user
and encrypts it using VLR public key and sends it to
the VLR. The VLR then decrypts it using the
correspondent private key. This procedure can be
Figure 2: Mobile Station – Home Network Authentication
Figure 3 VLR/ HLR connection to get SRES and Kc.
applied also if Kc is lost from the VLR. If the last
Kc used is not updated in the HLR, then a new
RAND should be sent to the SIM to calculate a new
Kc taking into consideration that RAND in this case
should not be transmitted in plain form. The HLR,
however, sends the Kc to the VLR encrypted using
VLR public key.
Problem 4: End-to-End security is not
Although GSM focuses on some of the security
aspects addressed by the 3GPP standards but still
there is no defined procedure to initiate end-to-end
secure communication between two users. This is
acceptable for average users where speed is the most
important factor, but some subscribers will sacrifice
this in favor of getting higher security level.
SPC and Phone-Dependent Key
SPC: Special Private Calls” where a certain
subscriber has the ability to transfer data or make
calls in a private mode. The data is transferred in
an encrypted form between the two users. This
option will delay the transfer of data but still will
give subscribers, who prefer security over speed,
the ability to increase the security level. It should
1. E
2. Response (E
3. Reject/ Accept registration
2. Auth_ Response (E
be optional to the customer to subscribe in this
Use a built-in key in the phone:
If MS-A would like to communicate with MS-B in
a secure manner then the procedure will be
partitioned into 2 phases:
Figure 4: Mobile Station –Visiting Network authentication
procedure (Scenario A).
Phase 1 Key Management phase
MS-A asks the network to send a “secret session
key” in order to start a secure session between
A and B
The network generates a secret key, encrypts it
using the A-Kc then sends it to A. Also it
encrypts the secret key using B-Kc and sends it
to B.
At this point A and B can communicate securely
using the secret key sent by the network
Key- deletion procedure should be triggered
immediately in the AuC, where Secret Session
Key is deleted.
Phase 2 Exchanging of Phone-dependent sub-
For further security (considering the case that
there is an attacker exists inside the Service provider
Network or attack the service provider Data base),
MS-A sends MS-B a phone-dependent Key that is
encrypted using the secret session key obtained from
the network. Some will argue that an attacker can
clone a user and initiate a session with MS-A in
order to have the Key P to intercept any future
communication for MS-A. This can be solved by
changing the key P for each session. A sub-key P
created each time the session is initiated – creating
sub-keys from the original P-key:
= SUB(P)
, where SUB is the function performed over the root
P-Key to get a new P
each time. Now, A and B can
encrypt their data using both the Session Key S and
the P
key or by using P
key only. It is up to the
network operator to use either A5 or another
symmetric key algorithm as the encryption
Figure 5: Mobile Station –Visiting Network authentication
procedure (Scenario B).
Our Proposed system has the following advantages:
Our main advantage that our system is action
triggered due to flaws occurrences.
A new key parameter is presented that is
independent of the SIM and the Network
operator; Built-in Key. The Built-in key is the
root of other sub-keys.
IMSI and Kc are not sent in plain form
Secure communication between HLR and VLR
can be implemented.
End-to-End secure communication, for non-
average users, can be implemented.
Mutual Authentication is possible.
Known Security algorithms can be used such as
RSA or Elliptic Curves.
In order to apply our system, the SIM components
must change to include user certificate, home
network public key and a public key algorithm. New
SIMs can be provided for the new users of any
network or this system can be applied in future
Mobile Communication systems.
The simulation is implemented in JAVA. Server side
and Client side modules are implemented by J2SE
5. Accept/ Reject registration
3. E
4. E
.. Contact HLR
.. Validation process
.. Get SRES and Kc
2. E
3. Accept/ Reject registration
.. Contact HLR
.. Validation process
.. Get SRES and Kc
v1.5. The codes run on Intel Centrino 1.7 Ghz
machine with 512MB RAM. We have implemented
the RSA as our public key system for its popularity.
Time taken for Encrypting/Decrypting: IMSI,
RAND, Kc and a 64bit session key is measured to
evaluate the delay that will be caused by applying
the RSA algorithm.
System parameters like RANDs and K
s are real
test data taken from 3GPP technical specification
(3GPP TS 55.205 V6.1.0) to test our system. We run
the simulation for 100 times and computation times
are recorded for 512, 1024 and 2048 bit RSA keys.
We recorded the standard Authentication time
(Creating both SRES and Kc). We also recorded the
time taken to Encrypt/Decrypt data (84 and 160
bytes) using A5. Algorithms are seeded using 20
different RANDs and 20 different K
For an efficient security system to work in a
mobile environment, the time taken to generate a
new public key pair, key generation process, should
be minimized as much as possible. The process of
selecting the primes and generating the
corresponding encryption and decryption keys is
large, but it is worth mentioning that Key Generation
in our system is done for each run. This is conducted
for the sake of testing our system versus several
public key values. Table 1 illustrates the average
time in milliseconds taken to select p, q, e, d and n.
Table 1.
Key size 512 bit 1024 bit 2048
Time 164.4334 1120.894 11333.304
As JAVA calls the garbage collector in
undefined periods, which will affect the time
records, we eliminated the best and the worst results.
In the following, the results are summarized.
Table 2: describes the time taken in m-seconds to
encrypt/ decrypt an IMSI (10 and 15 digits) using
RSA algorithm.
Table 2.
RSA (average processing time in msec)
512 bit key 1024 bit key 2048 bit key
Enc Dec Enc Dec Enc Dec
10 3.19 6.65 28.7 46.48 264.2 383.12
15 4.46 6.7 29.9 46.92 266.12 383.24
Table 3 describes the time taken in m-seconds to
encrypt/decrypt a 64 bit Kc using RSA algorithm.
Table 3.
RSA (average processing time in msec)
512 bit key
1024 bit
2048 bit key
Enc Dec Enc Dec Enc Dec
4.55 6.69 28.7 46.5 265.31 367.643
Table 4 describes the time taken in m-seconds to
encrypt/ decrypt a 64 bit Session Key using RSA
Table 4.
RSA (average processing time in msec)
512 bit key 1024 bit key 2048 bit key
Enc Dec Enc Dec Enc Dec
2.93 6.56 21.2 46.59
306.77 352.623
Table 5 describes the time taken in m-seconds to
encrypt/ decrypt a 64 bit Session Key using A5.
Table 5.
A5 (average processing time in msec)
Encryption Decryption
64 bit
0.298 0.224
Table 6: describes the time taken in m-seconds for
authentication by signing a generated RAND, where
Network encrypts the RAND using its Private Key/
SIM decrypts RAND using Network Public Key.
Table 6.
RSA (average processing time in msec)
512 1024 2048 bit key
Enc Dec Enc Dec Enc Dec
6.67 4.46 47.15 28.7
387.91 294.54
Table 7: describes Authentication Scenario A with
additional step; where row 1 denotes that SIM
encrypts a 128 bit RAND using network Public key/
Network decrypts RAND using network Private
Key. Row 2 denotes that Network encrypts RAND
using network private key /SIM decrypts RAND
using network public key.
Table 7.
RSA (average processing time in msec)
512 bit key 1024 bit key 2048 bit key
Enc Dec Enc Dec Enc Dec
4.48 6.66 28.6 46.62
264.88 363.23
6.71 4.46 46.7 28.87 350.761 297.24
Table 8.1: describes the time taken in m-seconds for
Authentication by proving knowledge of Ki; where
SIM encrypts RAND using Network Public Key/
Network decrypts RAND using Network Private
Key. Table 8.2 Row 1 denotes the time taken to
encrypt/decrypt SRES using A5. Row 2 denotes the
time taken to create SRES using RAND and Ki.
Table 8.1.
RSA (average processing time in msec)
512 bit key 1024 bit key 2048 bit key
Enc Dec Enc Dec Enc Dec
4.52 6.75 28.56 46.6 265.50 360.392
Table 8.2.
Average Time in Milliseconds
Encryption Decryption
0.2888 0.2537
In this paper we discussed some of the flaws occur
in the existing GSM security system. We also
presented an application for Public Key techniques.
Action-Triggered Public Key Security System
(ATPKSS). It is a way to solve some of the flaws
occur in GSM security system without overloading
the system with a whole public key technique. Our
approach presents a hybrid system; where the
original system works in normal conditions and only
when a flaw occurs, the ATPKSS is triggered. RSA
is implemented as our public key technique. Time
(in milliseconds) is recorded for using RSA with
three key lengths; 512 bit, 1024 bit and 2048 bit. By
analyzing our results for 512 bit key; the highest
delay that will be caused by using ATPKSS is 6.75
milliseconds in average which is a very few price to
pay in terms of ensuring security. For 1024 bit key
the highest delay will be 47.15 milliseconds and for
2048 the delay is .
Also we presented a new end-to-end approach
where a key agreement phase takes place between
the network and the two users first, then in the
second phase, the initiating user sends a built-in
phone sub-key. The original built in phone key is the
root of the sessions’ sub-keys. Each time a new
session is opened, a function is applied to the root
key to obtain a sub-key. The data is transferred
between the two users afterwards encrypted by this
key only or a combination key between the phone
key and the network session key. This will address
the problem of attacking the Service provider itself.
Since in reference (Julio Lo`pez and Ricardo
Dahab) the authors states that ECC is preferable in
mobile systems due to the use of smaller key, we
suggest as a further research that an ECC
implementation is tested instead of RSA and see
whether the time measured is decreased or not.
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GSM 02.09 - Digital cellular telecommunications system
(Phase 2+); Security aspects (GSM 02.09 version 8.0.1
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Telecommunications Software and Multimedia
Laboratory, Helsinki University.
ETSI TS 100 929.Digital Cellular Telecommunication
System (Phase 2); Security related network functions.
European Telecommunications Standards Institute.,
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O. Benoit1, N. Dabbous, 2004. Mobile Terminal Security,
Report in the International Association for Cryptologic
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