Academic Open Internet Journal

www.acadjournal.com

Volume 16, 2005

 

 

 

SECURED SESSION KEY MANAGEMENT USING DIFFIE-HELLMAN KEY EXCHANGE METHOD

 

* R.K. GNANAMURTHY   ** K.  SANKARANARAYANAN *** T.Arunkumar **** S.N. Sivanandam,

 

 

*  R.K. GNANAMURTHY

   Asst.Professor (PG),

   Department of Computer Science  and Engineering ,

   Kumaraguru College of Technology,
  Chinnavedampatty,

  Coimbatore – 641 006,

  TamilNadu, India.

E-mail: webmaster@kct.ac.in, rkgnanam@yahoo.co.in

 

**  K.  SANKARANARAYANAN,

      Professor (PG),

      Department of Electronics and Communication Engineering

      Sri Krishna College of Engineering and Technology

      Kuniyamuthur

      Coimbatore – 641 008.

      Tamilnadu, India.

 E Mail : kkd_sankar@yahoo.com

 

***  T.Arunkumar

        Asst. Professor

       Department of Computer Science and Engineering

          Sri Krishna College of Engineering and Technology

       Kuniyamuthur

      Coimbatore – 641 008.

      Tamilnadu, India.

E Mail: arunkumar_t@hotmail.com

 

 **** S.N. Sivanandam,

          Professor and Head,

         Department of Computer Science and Engineering,

         P.S.G. College of Technology,

        Coimbatore – 641 004.

       Tamilnadu, India

E Mail: profsns@psgtech.ac.in

 

 

 

 

Abstract - The technology of digital conference has opened up a new area of research and application to computer networks in industry. It can be used in a board meeting, scientific discussion or in virtual classrooms, through the computers connected by IP networks. To protect conversations from eavesdropping, a common conference key agreement protocol is required. Conference key protocol secures the discussion session and data among multiple conferees engaged in common goal of communication. Numerous works have been carried out in providing secured conference, but most of the works concentrate on an efficient key exchange protocol to prevent malicious users to attempt to play the proxy role or delay or destruct the conference environment.

 

  This paper proposes a novel approach of unique dynamic ID based key exchange protocol which possesses the property of fault-tolerance secured session, dynamic ID key generation and key exchange methods.

 

Index Terms : Conference Key , Security  Key  Generation, Fault tolerance  Secured Session.

 

1        INTRODUCTION

 

Secure group communication is an increasingly popular research area which has been receiving much attention in recent years. As a rapid growth of the internet, the group communication has become an important feature of the internet technology. Computer network group communication is a group of people who communicate (or) make a conference in an interactive procedure through the computers connected by networks at distance or discrete location [1]. In order to establish a secured, fault-tolerant communication among groups in an open network, the current internet protocols do not come into needy. 

Conferencing in IP network, through group communication, is actually transmitting data as broadcast through multiple channels. Group communication is more complicated with regard to the concept of security .As the group starts to mutate (members leave and join at any interval of time), the members of group are not a well defined entity. Hence, security services in group communication or multicast groups are complicated issues to be dealt. 

This paper proposes a session based security model SSGCP (Secured Session based Group Communication Protocol), which provides security from establishing a session to the closure (end) of session. Secured session is established for variable time slot dynamically among all conference members, implemented by Common Conference Agreement (CCA) methods. The  conference member here after called as “Conferee” in this paper. Secured group communication among multiple conferees can be established only if a conferee handles the secured key for each session.

Security communication needs to have a conference key agreement [3] for the group communication. Conference key arrangement is a mechanism in which a shared conference key is derived by “conference key engine” which is exchanged among conferee group members who participate in conference. Each conferee member will acknowledge all other conferees, while the conferee “registry” in member system will either accept the key or reject the key. SSGCP protocol follows distributed service architecture, which is designed to be one of the components for secured publish / subscribe and exchange communication infrastructure.

This work is quite different from the work carried out by other researchers. Mostly the work carried out by Tzeng [15] would be suitable only for honest group of users but not for malicious users or who intentionally attempt to delay or destruct the conference. Similarly Yongdae Kim’s [16] work adds communication overhead for peer group overhead on a global network setup like internet. An active attack (malicious participant) tries to disturb establishment of a common conference key among the group of honest participants. Passive attacks are carried out on gathering the conference key by listening to the communication of participants.

This protocol works on the basis of only proper secret keys agreed between honest conferees. If any malicious user, who may destruct the conference or delay the operation, is found or suspected, then the malicious user’s port is blocked for further operations. Hence, this work is efficient in secret key generation and operations among honest conferees.

The paper is organized as follows: Section 2 discusses on identifying an efficient security key by group key agreement method. Existing research works carried out in this area are also discussed. Section 3 focuses on the model and design, that have been developed using simple key exchange “Diffe-Hellman” algorithm. This work suggests a simple scheme of 2-way Diffe-Hellman (2DH) method and against n-party Decisional Diffe-Hellman (nDH) problem. The efficiency of group communication using Common Agreement based on Diffe-Hellman secured key algorithm is proved. Section 4 discuss on the architecture and implementation of SSGCP on IP based network. Section 5 analyses the performance of SSGCP and conclude with the need for future work. 

 

2. RELATED WORK

The literature survey finds good number of recent interesting research works that have been carried out on group key agreement by XunYi[17], M.Steiner and M. Waidner  [12]. A most all group key agreement protocol can be directly adapted to conference key agreement. However, most of them operate only when all conferees are honest but do not work when some conferee is malicious and attempts to delay (or) destructs the conference.

      Most of entity conference key agreement protocols operate only when all conferees are honest, but do not work when some conferees are malicious and attempt to delay (or) destruct the conference. Sometimes the conferees may cause severe damage to the conference setup or break the session in use.

      The problem of common key agreement [13] schemes, in dynamic group key agreement, especially in creating a group, has been the steppingstone for all the other securely service schemes. Several schemes on group key agreement have been done in centralized manner [16], where one dedicated party (typically leader of peer group) has to select the group key which will be distributed among other peer groups in a distributed fashion. This method is actually a key distribution or key transfer among the groups and not Key Agreement. This method can be suitable only for static groups not for dynamic groups. Dynamic peer groups require not only the initial key agreement (IKA) but also auxiliary update key agreement (AKA) operations such as member addition, member deletion and other internal group functions.

        CLIQUES ,a concrete protocol [13] which is based on multiparty extension of the well known Diffie- Hellman key exchange protocol and Tzeng [15] explained in control based on authenticated broadcast channel model by  the honest participant under the assumption of variant Diffie-Hellman problem.

       Xun Yi [17] explained his research work in novel fault tolerant conference key agreement protocol. in which each conferee only needs to send one message to a semi trusted conference bridge and receives one broadcast message . The identity based key agreement is based on elliptic curve cryptography (ECC). It is resistant to the different key attack from malicious conferee and needs less communication cost than Tzeng protocol[15].Comparatively, the conference key agreements are having disadvantages and our new protocol give an efficient way of conference session key agreement.

 

3        DESIGN AND MODEL

This section provides a detailed overview of notable features of reliable group communication and session key agreement methods. This work adopts the following assumptions and notations.

 

G     = Peer Group { G1, G2, .. Gi,… Gn}, Gi è ith group where i Î [1,..n]

M    = Conferee members in group,

Mi è ith member in a group where i Î [1,… n]

M*  = All group members

K    =  Group key generated

Ki è ith   group key where i Î [1,..n ]

Kn   = Group key shared among all ‘n’ members

a       = exponentiation base ; generator in algebraic group G delimited by ‘q’

q  =  prime number, order of algebraic group.

W =  secret exponent of  key  agreed by Mi and generated by Conference Manager

H  = sub-set of  Wi  { W1, … Wn}

S  = Conferee Session to hold secret key Si { S1,…Sn} 

S*= Multiple sessions with {M1,..Mi}, {Mi+1,…Mk}, {Mk+1,..Mn} conferees

Session is created when at least two conferees accept a secured key to establish a communication path. Session can be established among multiple conferees ( who can be distributed locations ) engaged in communication. Session is a virtual communication path established among one or more conferees with a secured key as an entry point.

The peer group communication semantics is defined as follows:  

1).A group Gi is an entity, which depicts various conferees engaged in communication using a single communication session / channel.

2).All conferees engaged in conference / communication require independent security key.

3).A group may consist of minimum two conferees at least.

4).Any conferee in a group may leave the group or join the group or rejoin the group at any time of communication process for a session.

Group Key Agreement – It is defined as a comprehensive group key solution which should handle the adjustments to group key secrets. Subsequent to all membership change operations in the underlying group communication system, the following conferee memberships are considered:

i)   The system distinguishes among single and multiple group conferee operations.

ii)   Keys are defined and invoked

independently for single ( one-to-one )

conferee sessions and multiple group ( many-to-many ) conferee operations.

iii) The keys assigned to session are  unique and dynamic in nature, where type of key and  its hierarchy carry importance.

iv). Key generated for each session is entirely new and remains out of reach of former group members

Secure Key Ki ( such that K is the unique key id and ‘i’ is the order of group ) is   generated by “conference server engine” which is basically random in generation. The generated key Ki is agreed by both the conferees who negotiated to communicate. Ki is exchanged by conferee members {M1… Mn} to establish the conference.

 

 3.1 PROOFS ON SECURITY MODEL

       The key agreement protocol belongs to family of n-party DH scheme, which is an extension of 2-party DH key exchange [17]. The work adopts n-party DDH method among multiple groups Mn who agree a priori on a cyclic group G. Each key Ki, generated randomly from the generator engine ‘a’ can belong to Wi Î q. The group key K =  a W1,…Wn

This protocol works only when conferees are honest, and will break the operation (by blocking user’s port ) if user is found to be malicious.

 

A.  SINGLE SESSION COMMUNICATION

In 2-party DH scheme, Ki is computed by exchanging aW1 for conferee M1 and aW2 for  conferee M2. Key Ki can be computed as  (aW1) W2   = ( aW2 ) W1.

W1 represents the secure key selected with r1 being the key of conferee M1 and cr1 being the agreed group key assigned for a group.

W1 = R1  CR1  and W2 = R2CR2

The generated key Ki is assigned to session Si.

 

B.  GROUP SESSION  COMMUNICATION

In case of multiple group communication where conferee members {M1,…Mn } of  Gi, 2-party DH  cannot be implemented, hence n-party DH scheme is used. In n-party DH key exchange scheme, a subset of Si = {a P(H) | HÌ{W1,…. Wn}} is exchanged among conferees. This set includes random number values aW1 ….Wn, which can compute Ki. Hence Ki is the secret key agreed by conferee members M1,…Mn belonging to Gi.

Wi = Ri  CRi,  also Wn = Rn  CRn   

Session based security key Ki is an extension of n-party DH. The key Ki is assigned for session Si.

The key assigned for a session is dynamic. Hence for any random small interval of time the key may be used. Any update of session for change in intervals new key is generated and assigned to session Si.

 

 4.            SESSION BASED SECURED CONFERENCE KEY SCHEME

 4.1 Model and Architecture

        SSGCP model setup is as shown in Fig-1. Architecture basically consists of three main procedures “Conference Key Generation Engine”, “Conference Session Manager” and “Conference Registry” procedures which reside on Conference Server.                            

1)      Key Generation Engine is a trusted key generator which generates the “secured common session key” (CRi) for each session based on DES Scheme [2 ] and  generates individual conferee key (conf_keyi) or multiple group key (gp_keyi) based on Diffie-Hellman Scheme [12 ]. 

2)      Session Manager manages various sessions among conferees in group session or single session as well handles Key Agreement.

3)      Registry procedure maintains the complete information of each conferee,that is, their session in use, network port in use and key generated.

Conference key agreement (CKA) is the method of certification of acceptance made by each conferee engaged in conference for a session. The certificate of agreement will be registered in “Conference Server” and in “Registry”. CCA method provides the simplicity and flexibility of assigning a common key among conferees which is generated by Conference Key Generation engine and negotiated among all conferees. Conference key agreement method is more secure than Conference Key Distribution (CKD), since the possibility of a malicious user obtaining the secured key is possible. The possibility of deriving the secured key is also possible since, the key generated can be a combination of all conferees engaged in conference.

Fig-2 shows Stack architecture of SSGCP. Session manager implemented at Conference Server in Conference network enables a secured-session management, start a session and end a session. Registering the conferees for each session as well maintaining a proper synchronization among conferees through session serialization is handled by Registry. Initially each user or a group, is authenticated by logging into conference room. A User can be a conferee only if secured key is allotted by Key-Generator based on key generation and CKA procedures. Conferees can establish communication path with another single conferee or group conferee to form a session. The session established at multiple conferee’s end or host of the network manages the secured-session key.

 

     

 

 

 

 

 

 

 

 

 

 

 

On mutual agreement session is established with other conferee members or groups.  SGGCP protocol assumes that server is a computer network server or server module executing in any network nodes, while the conferees or groups reside in multiple end-nodes. Multiple requests and acknowledgements on the network backbone may be altered, blocked, delayed due to various latency effects.

 

4.2 Security Key Generation

Various types of security keys used in SSGC Protocol are discussed in Table-1. Usage of   keys is based on type of session requested and number of conferees requested to communicate. The secured keys of conference key protocol generated possess the following properties.

i). Key is unique for a particular group of participants in a pre-distributed  conference key protocol.

ii).Secured key will be changed dynamically at unequal time intervals for sessions.

iii).Secured Key generated will be changed for each session update or new session.

iv).The pre-distributed conference key protocol provides lack of flexibility.

      SSGCP uses various keys at each session to maintain uniqueness and independency. In order to increase security for conferees and session, two keys are assigned to conferee for each session or any session update.

1. A common key is allocated ( CRi ) by Key Generator, which is generated by DES scheme, which will be used by all conferees in a session, but unique to a session. Each session in Registry is identified by CRi.

2. Each individual conferee is assigned a key (Ri) by Key Generator. This key is generated by Diffe-Hellman Scheme.

Hence each conferee is assigned a session key Si (discussed in Section-3) to be agreed by another conferee with session key Sk to establish a communication path in a session.

 

1. Session_Request

To request for a conference to conferee initially.

2. Session_Ack

To acknowledge request (True / False ), with request for conference type.

3. Session_Key_Register

To acknowledge type of conference and session key to Conference Manager.

4. Session_Establish/

    Update

To establish session for conference with conferees.

5. Session_Negotiate

To check and negotiate on keys for existing conference.

6. Session_Expiry

To indicate that conference session is broken , and key has to be generated.

7. Session_Alert

To indicate that session can be broken, due to an intruder malicious use.

8. Session_Close

Bye.  { To end conference }

9. Session_Key _Update

Conferee check on Server as request to update session.

 10. Issue_Session_State

To identify the state of a conferee session at a time interval and inform as well update on conference.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table1- Session Procedures

 

4.3              Secure Keys Used In SSGCP

        Public Key pb_key is assigned to all users who have joined the conference room. User holding this key can view the list of conferees who are actively in live communication but they cannot participate nor view the contents. Both “conferees”, “check” required a key to “establish” a connection. Each move at random time interval, “session-negotiation” and “session–key–update” is carried out. If the expected key state is not identified, then “session-expires” and a “session-reconnect” has to be requested.

 

conf_key

Conference key for individual conferee engaged in conference.

ss_key

Session conference key for each group or individual conferee engaged in conference. Involves multicasting / broadcast

gd_key

Conference key generated for multiple peer groups

dgp_key

Distributed group key on conference. Engages various groups of members

 in multiple groups on conference.

pb_key

Public key assigned for all members not engaged in conference.

Table2- List of Security Keys

 

4.4  Session Protocol Operations

4.5        SSGCP Protocol

       The protocol runs in four different phases ie., Join / Leave Conference Server, Key Generation,  Session Registry in Server and Create – Establish - Manage session as shown in Fig-3.

In the first phase, user can join the conference server through a simple user authentication method. During login process, user generates a random value, which may be obtained from keyboard buffer. The generated value with login time, port selected for communication from random available ports together is considered as combination of secured conferee key CK1, CK2 (conf_key) as shown in Fig-4.

 

In second phase, conference server generates a random key (ss_key) CRi. CKA method negotiates with Registry module in Conference Server and registers the session conference key. Third Phase focuses on creating the session Si, and managing the session among various conferees( C1, C2, .. Cn ). Session update is performed at frequent time intervals of few milliseconds, invariably time interval is not consistent.  Fourth phase deals with virtual connection establishment among multiple conferees or multiple groups.

 

Session Update

Faulty Session Handler

5  IMPLEMENTATION

         Performance measures of SSGCP were carried out by testing on four different 100Mpbs LAN based Ethernet network. The deployment comprises of four servers running on separate domains, so the system was capable of tolerating a single compromised server. The measurements were gathered separately on client systems and server of LAN network. Round-trip times for ICMP echo packets typically measured within 100ms, such that network delays are observable. The hosts and network are relatively quiescent during the experiment; client was executed on separate machine and its signal processing and latency times are also observed.

Experimental test-bed helps to identify the mean execution times between various three conference groups created for test purposes. TCP based signal methodology for Conference_Request and Conference_Reply procedures have been implemented in Java based EJB development. The setup has helped to identify the fatigue property of conference session manager due to malicious user or intruder trying to disturb the conference setup. Malicious user calls from five network stations have been tested to attempt access rights for conference server and disturb conferencing.

Fig-8 SSGCP Session Implementation

Two tests were conducted to determine the overhead of using secure session key generation / control and dynamic certificate agreement in SSGCP. These test procedures include raw processing time per routing packet for varying key sessions established and measurements of average route acquisition latency. The RTT time between establishments of conference between multiple conferees and group conferees have discussed. Table-3 shows our results. Results were conducted over two Ethernet of 10Mbps LAN networks.

     Multiple call sessions were handled at an instant over three different groups. Test was carried out over Microsoft’s NetMeeting installed over Java modules SSGCP_Client and SSGCP_Server. Java modules reside at each client (SSGCP_Client) and server machines (SSGCP_Server). Java module creates secured key, assigns to user session and maintains the secured session. Table-2 shows call established between two different LAN networks. Calls were established over SSGCP scheme and Microsoft’s Net Meeting Scheme. SSGCP handles better secured session management, number of sessions established at a time is higher compared to Net-Meeting where only maximum of five sessions were allowed. Security method is common in Net Meeting. The time taken to establish a call is comparatively less as shown from Fig-9.

Fig-9 Secured Session Establishment time

Fig-10 Group Conference User Session Call Conference – In Progress

Fig-11 Call Conference Status

Sl No

Sender IP Address

Receiver IP Address

Ave No of Bytes Send / Session

Type Of Conference   Call

SSGCP with NetMeeting

NetMeeting

No of Sessions  

handled

Time taken to  

establish / call (ms)

No of Sessi

ons handled

Time  to

establish / call (ms)

1

192.168.67.34

192.168.65.30

106,352

Individual Audio

22

190

1

320

2

192.168.67.30

192.168.65.31

111,120

Group Audio

20

178

5

486

3

192.168.67.31

192.168.65.32

106,184

Group Video

18

186

5

310

4

192.168.67.32

192.168.65.33

107,384

Group Video

22

223

3

354

5

192.168.67.33

192.168.65.34

107,032

Group Video

24

187

4

323

6

192.168.67.36

192.168.65.35

107,848

Group Video

23

203

3

329

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table-Table-3 Call Conference Setup

6.      CONCLUSION

SSGCP scheme, implemented based on Diffie-Hellman key exchange algorithm, achieves secure and efficient key agreement in the context of one-to-one conference scheme and group conference communication. The scheme works well for small groups as well for number of groups not greater than 100. For very large groups of intentionally large the scheme may not appropriate in selecting unique key distributions.

SSGCP proves confidentiality of conference shared and authentication.  In general this architecture elucidates on secure key generation, key management, control, session control and fault tolerant aspects. Hence data is secured with transaction and processing parameters. The future work stresses on the need for a secured session system for large conference networks, which should be extended to scalability and load balancing. 

 

References

(1)    D.Reed. “ A Discussion on Computer Network Conferencing” RFC:1324.Network working group May 1992.

(2)    FIPS PUB 197, “Advanced Encryption Standard”, Federal Information Processing Standard Publications” US Dept. of commerce/N.I.S.T, Nov 2001.

(3)    C.E Shannon “Communication Theory of Secret systems “Bell systems Technical.J.,        Vol 28 No:4 PP: 656-715. 1949.

(4)    A.J. Menezes P.C vanOorschot and S.A.Vanstone Handbook of Applied Cryptography CRC Press ,Oct 1996.

(5)    S.Berkovits “How to broadcast a  secret “ proc. Advance in cryptology-Eurocrypt  ’91 PP553-541, 1991.

(6)    C.C.Chang, T.C Wu and C.P.Chen , “The Design of a conference key Distribution systems” proc Advances in cryptology -  Auscrypt’ 1992 ,PP 459-466,1992 .

(7)    C.C.Chang and C.H.Lin, “How to converse securely in a Conference,” Proc.IEEE  30th Ann. Int’l carnahan conf., pp 42-45, 1996.

(8)    R.Blom, “An Optimal class of Symmetric Key Generation Systems,”” Proc. Advances in cryptology  -  Eurocrypt ’84,  pp. 335-338, 1985.

(9)    C.Blundo, A.D. Santis, A. Herzberg, S.Kutten U.Vaccaro, and M.Yung, “Perfectly Secure Key Distribution for Dynamic Conferences,” Proc. Advances in Cryptology –Crypto ’92,pp. 471-486,1993.

(10)      T.Matsumoto and H.Imai “On the Key Predistribution System: A Practical Solution to the Key Distribution Problem,” Proc. Advances in cryptology –Crypto ’87, pp 185-193, 1988.

(11)      D.Steer, L. Strawczynski, W. Diffie and M.Wiener, “A secure Audio Tele conference system,” Proc.  Advances in cryptology (CRYPTO ’88), pp.520-528, Aug 1988.

(12)      M. Steiner, G. Tsudik, and M. Waidner, “Diffie-Hellman Key     Distribution Extended to Groups” Third ACM Conf. Computer and Comm. Security , PP 31-37 ,      March -  1996 

(13)      Michael steiner, Gene Tsudik “Key agreement in Dynamic peer groups” IEEE, Transactions  on parallel and distributed systems vol 11 No :8 August 2000.

(14)      G. Ateniese ,  M. Steiner and G.Tsudik, “ New Multiparty Authentication Services and Key Agreement Protocol,” IEEE.   J,  Selected Area in Comm. Vol.18, no.4, pp:628-629 Apr 2000.

(15)      W.G.Tzeng, “A Secure Fault Tolerant Conference Key agreement Protocol,” IEEE Trans. Computers, Vol. 51, No 4. pp. 373-379 Apr 2002.

(16)      Y.Kim, A. Perig, and G. Tsudik, “Group Key Agreement Efficient in Communication,” IEEE Trans. On Computers, vol 53, No.7,pp.905-921, July 2004.

(17)       “Identity Based Faulty-Tolerant Conference Key Agreement”,      Xun Yi, IEEE Trans. on Dependable and Secure Computing, Vol.1, No 3 , July-Sep 2004.

 

Correspondence Author:

 

R.K. GNANAMURTHY

Asst.Professor (PG),

Department of Computer Science  and Engineering ,

Kumaraguru College of Technology,
Chinnavedampatty,

Coimbatore – 641 006,

TamilNadu, India

E-mail: webmaster@kct.ac.in, rkgnanam@yahoo.co.in

 

 

 

 

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