Communication and Network, 2010, 2, 69-72
doi:10.4236/cn.2010.21011 Published Online February 2010 (http://www.scirp.org/journal/cn)
69
Proposed Model for SIP Security Enhancement
Munir B. Sayyad1, Abhik Chatterjee2, S. L. Nalbalwar3
1Technology Innovation Center Reliance Communication, Maharashtra, India
2Electronics Engineerin g of Lok ma nya Tilak College of Engineering,
Mumbai University Maharashtra, India
3Department of Electronics and Telecommunication, Dr. Babasaheb Ambedkar Technological University,
Maharashtra, India
Received October 24, 2009; accepted November 12, 2009
Abstract: This paper aims to examine the various methods of protecting and securing a SIP architecture and
also propose a new model to enhance SIP security in certain selected, specific and confidential environments
as this proposed method cannot be generalized. Several security measures and techniques have already been
experimented with, proposed and implemented by several authors as SIP security is an issue of utmost impor-
tance in today’s world. This paper however, aims to summarize some of the better known techniques and
propose a unique method of its own. It also aims to mathematically represent SIP fitness values graphically as
well via a simulation using the popular Fuzz Data Generation Algorithm. Thus this paper not only aims to
contribute to the already vast field of SIP security in an effective manner but also aims to acknowledge and
represent some of the fail proof methods and encryption techniques that have helped in making SIP a more
secure and less wobbly n e twork for all of us to function in.
Keywords: SIP, SoS, VoIP
1. Introduction
Session Initiation Protocol (SIP) is the Internet Engi-
neering Task Force (IETF) standard for IP Telephony
which is making huge inroads into the Voice-Over-IP
(VoIP) market, previously domineered by implementa-
tions which stuck to the rather difficult H.323 ITU-T
Internet Telephony standard [4]. The apparent reality is
that Voice and Data services are being quickly shifted
from the legacy network to the IPbased network.
The standardization of SIP helped to realize the call
control function. SIP is the present as well the future of
commercial communication systems. SIP is the present a s
well the future of commercial communication systems.
Many carriers and providers are extensively adopting it;
therefore SIP security has become a topic of high impor-
tance and priority [5]. With VoIP, voice can now be trans-
ported on a traditional IP data network, making use of the
vast resources of the Internet and thus drastically lowering
the cost of operation.
However in the recent past, VoIP services have been
plagued and hampered by numerous security threats and
issues. With Internet being the primary carrier, VoIP
networks are exposed to threats and dangers that an IP
data network faces e.g., IP spoofing, denial of service
(DoS) etc. [5].
SIP has become the ef fective standa rd for VoIP services.
It is described as “an application layer control protocol
that can establish, modify and terminate multimedia ses-
sions (conferences) such as Internet telephony calls”. It is
an ASCII/text based request-response based protocol that
works on a client server mode.
2. Security in Sip
SIP security is an issue of pri me im portance. Basically we
can broadly classify the attacks on any type of system into
two categories [2]:
 Passive Attacks: This threatens the confidentiality
of the data/signal being transmitted.
 Active Attacks: This threatens the integrity or
availability of the data/signal being transmitted.
The feasibility of a passiv e network primarily depends
on the physical transm i ssion medi a in use and i ts p hysical
accessibility for any intruder. Fortunately enough, the use
of switching technologies makes it harder and more dif-
ficult for an attacker to passively attack a signal segment.
Now in an active attack, more often than not, the intruder
manipulates the domain name system (DNS) to place
himself bet wee n the sender and recipi ent of a message. In
this situation, the intrud er acts as a man-in-the-mid dle. A
very common form of attack is to spoof signals/messages
on anothe r (or nonexistent) user’s behalf.
These two types of attacks can most probably encom-
pass all the different types of attacks and fo rced attempts
within their broadly diversified branches. The following
diagram will give a clearer picture of a SIP security

M. B. SAYYAD ET AL.
70
Figure 1. Protocol architecture
Figure 2. SIP security breakup
breakup.
Authentication and maintaining the integrity of data/
signaling is a matter of the highest priority. It is also im-
portant to monitor the access control and the availability
of information because it will prevent malformation and
spoofing of dat a .
We will now define a structure which will include all
the important points mentioned above which are of pri-
mary importance. Authentication, integrity, confidential-
ity, non-re pudiation, access control and avai lability form a
framework upon which the others will be derived.
Authentication is the property by which the correct
identity of an entity, such as a user or a terminal, or the
originality of a message that has been transmitted, is es-
tablished with a required assurance.
Authentication can basically be divided into two
classes, which are peer entity authentication and data
origin authentication. Peer entity authentication assures
that the commun icating parties are who they claim to be.
Data origin authentication assures that a message has
come from a legitimate and authenticated source. Au-
thentication is typically needed to provide safety against
masquerading as well as modification.
Integrity means the avoidance of unauthorized modi-
fication of information. Integrity is an important security
service that proves that transmitted data has not been
tampered with. Authenticating the communicating parties
is not enough if the system cannot guarantee that a mes-
sage has not been altered during transmission.
Confidentiality is the avoidance of the disclosure of
information without the p ermission of its owner. Secrecy
and privacy are terms synonymous to confidentiality.
Confidentiality may be ensured with enciph erment of the
messages.
Non_Repudiation is the property by which one of the
entities or parties in a communication cannot deny having
participated in the whole or part of the communication.
Non-repudiation prevents an entity from denying some-
thing that actually happened.
Access Control is the denial of unauthorized use of a
resource. Access control is closely related to authentica-
tion, which gives the ability to limit and control access to
network systems and applications.
Availability means the accessibility of systems and
information by authorized users. It is closely related to
authentication and access control. An authenticated entity
must have access to a system and on the other hand un-
authorized entity must not prevent the usability of the
system (Denial of service attacks).
3. Some Security Protocols and Applications
for Sip
1) Encryption is a mechanism to secure information so
that only receiver can use it. In encryption, a cleartext
message or plaintext is hidden by using cryptographic
techniques, the resulting message is known as ciphertext.
The receiver recovers the original plaintext by decrypting
the ciphertext.
A key is a mathematical value that modern crypto-
graphic algorithms make use of when encrypting or de-
crypting a message. Cryptographic techniques are not
only used to provide confidentiality, but also other ser-
vices, like authentication, integrity and non-repudiation
may be provided. Cryptographic techniques are typically
divided into two generic types: symmetric key and
asymmetric key techniques.
a) Symmetric Encryption means that the key can be
calculated from the decry ption key and vice versa. In m ost
cases both keys are the same one and the mechanism is
called secret key or single ke y encryption. The security in
symmetric key encryption rests in the key, which must be
agreed before any communication. As long as the com-

M. B. SAYYAD ET AL.
71
munication needs to rem ain secret, the key must be secret,
divulging the key means that anyone could encrypt and
decrypt the messages.
The Data Encryption Standard (DES) is currently the
most widely used symmetric encryption scheme. DE S is a
symmetric block cipher that processes 64-bit blocks of
plaintext producing 64-bit blocks of cipher text The key
length is 64 bits, but since every eighth bit (8, 16, . . . , 64)
is a parity bit for error detection, the effective key length
is 56 bits.
b) Asymmetric Encryption also called public-key
encryption, the key used for encryption is different from
the key used fo r decryptio n and the decryptio n key cannot
be calculated from the encrypti on key. The encryption key
may be publ ished, s o that anyone could us e the encrypti on
key to encrypt the message, but only the receiver with the
corresponding decryption key can decrypt the message.
So the encryption key is also called the public key and the
decryption key is called private key.
The RSA algorithm is perhaps the most popular pub-
lic-key algorithm. It was invented by Ron Rivest, Adi
Shamir and Leonard Adleman in 1977. RSA can be used
for encryption / decryption, providing digital signatures
and key exchange. decrypt the message.
The Diffie-Hellman algorithm was the first ever pub-
lic-key algorithm, invented in 1976 by Whitfield Diffie
and Martin Hellman. The algorithm can be used for key
exchange but not for encryption/decryption, thus the al-
gorithm is typically used for exchanging the secret keys.
2) Message-Digest Algorithms are compact “distil-
late” or “fingerpr ints” of your message or file checksum.
A message-digest algorithm takes a variable length mes-
sage as input a nd pro duces a f ixed len gth di gest as outp ut.
This fixed length output is called the message digest, a
digest or a hash of the message. The digest, which is
typically shorter than the original message, acts as a fin-
gerprint of the inputted message. The message digest
verifies your message and makes it possible to detect any
changes made to the message by a forger.
4. Novel Proposed Method to Enhance Sip
Security in Specific Confidential Sectors:
TOUCH ME NOT
In some secure and confidential sectors such as the army
(for e.g.) data and signaling leakage is highly volatile and
potentiall y very da ngerous. In such cases signal ta pping is
neither lawful nor desirable. Thus a new security archi-
tecture termed TOUCH ME NOT is being proposed in-
order to avoid signal tapping. This proposed model is
currently under test and development. Its source code has
been written in Tu rbo C++. The testing activity has been
carried out using freely available evaluation copies of
several popular SIP soft phone clients. Since our testing
activity is not complete, we have not informed the ven-
dors about our produced results. Hence, in this paper we
Figure 3. TOUCH ME NOT architecture
Figure 4. N vs deviation factor
are refraining from using client names.
In this process, there will be present a main security
master which will be consisting of a continuous key
jumbler whose task will be to rando mly jumble and reas-
sign key values in order to prevent key cracking by an
intruder.
The security master will also be consisting of a list of
predefined attack cycles and algorithms so that it can
detect and reco gnize the m ost com m on and di f ficul t ty pes
of attacks if any.

M. B. SAYYAD ET AL.
72
The entire signaling route from the sender to th e sender
to the receiver will be divided into several checkpoints. If
the attacker attempts to access or tap the signal at any
point, on or between the checkpoints, a pre programmed
delay generator which may be an exe file will appear as a
non removable pop up, displaying random gibberish
values or a blank screen.
This will act a cover for the signal to self destruct, in
other words the signal will be auto terminated at that point
and a signal informing the sender and receiver of the
interception or attempted attack on the sent signal will
reach the sender as well as the receiver in due time. This
will prevent the signal from being tapped with, examined
or malformed. This method cannot however be general-
ized in all sectors as tapping is lawful in several govern-
ment as well as private sectors.
5. Fuzz Data Generation
We are already aware of the Fuzz Data Generation Algo-
rithm. Fuzz testing or fuzzing is a software testing tech-
nique used to find implementation defects using mal-
formed or semi malformed input data [1]. We have to
define a set of parameters that contribute to the overall
fitness value of a given data. All these parameters need
not always be used: a subset of them can be used de-
pending on the input population and the application being
fuzzed. They can be for e.g. Native size, Native type,
Parent’s Fitness etc. [1] The challenge will be to define
more and more criterion to define a fitness value. The
more the value of N, the better the fitness value. This can
be verified from the graph given below as well as the set
of relations provided [1].
Let N be the n umber of param eters chose n to contrib ute
to the fitness value.
Calculate the deviation factor DF+1/N (We can also
calculate a weighted DF, i f some of the parameters need t o
be given more weight compared to the others).
Calculate the deviation contribution DC=A*DF, for
each parameter, where A is the deviation percentage.
Calculate total deviation contribu tion TDC=SUM(DC)
for all N.
Final Fitness Value F= Ceiling [TDC*10]
6. Conclusions
Thus we have analyzed some of the methods which make
SIP a more secure network. The proposed TOUCH ME
NOT architecture is an effective way to prevent illegal
tapping in selected confidential setups. Fuzzing data
generation along with the simulation can be used to de-
termine fitness values. Th ese steps will hopefully help in
making SIP a stronger and a more secure network.
REFERENCES
[1] IEEE Paper: A SIP Security Testing Framework: Hemanth
Srinivasan and Kamil Sarac.
[2] Applied Cryptography-Second Edition-Protocols, algo-
rithms and Source code in C: Bruce Scheneier.
[3] SIP Tutorial: Daniel-Constantin Mierla.
[4] IEEE Paper: SIP Security Issues: The SIP Authentication
Procedure and its Processing Load: Stefano Salsano, Luca
Veltri, Donald Papalilo.
[5] IEEE Paper: Security Challenges for Peer-to-Peer SIP:
Jan Seedorf.