1. Multi-party Authentication in Web Services
Madhumita Chatterjee
Dt :28th October 2004
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2. Overview Web Services Architecture Typical Scenario Security Threats
Challenges and issues
Need for Session Authentication
Two Approaches—an analysis
Proposal
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3. Web Service Components
Internet based modular applications
Program to program communication
XML
WSDL
SOAP
UDDI
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4. Web Service Architecture
Implementation of Services
(components)
UDDI
Interface Description with WSDL
1. Request
4. Request
Service requester
Service Broker
Web
Server
For SOAP S E R V I C e
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5. Web Service Workflows Dynamic composition Multiple instances
Workflow involves service instances belonging to different Web services
Multiple parties belong to a flow.
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6. Typical Web Service Scenario
Buyer
Govt service
Financer
Provider
Shipper
B.1
G.1
P.2
S.1
P.1
F.2
Service
Instance
Insurance
I.1
F.1
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7. Threats…. Unauthorized access Parameter manipulation
Network eavesdropping
Message replay
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8. Challenges Dealing with un-trusted clients.
Application internals are exposed.
SOAP messages are not point to point
Challenge is to preserve security of SOAP message from initial SOAP sender to ultimate SOAP receiver.
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9. SSL is inadequate SSL provides point-to-point security
Web Services need end-to-end security
SSL does not support
End-to-end confidentiality
Element wise signing and encryption
Non-repudiation
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10. Need for session Authentication
TA-1
TA-2
Hotel
Flight
Car#1
Car#2
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11. Maruyama’s protocol
Session Authenticator component responsible for distributing keys and authenticating messages
Each instance belonging to a session gets the shared key
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12. Maruyama’s protocol….cont
Message authentication protocol
transports authentication information between session participants
Session management protocol
responsible for starting, running and ending a particular session.
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13. Message Authentication
Session Authenticator
Allows service instances to mutually verify transient membership
Service Authenticator
Protocol for sending Web service to send MACed SOAP envelope to receiving Web Service
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14. Session Authenticator
Sending instance prepares SOAP envelope
Optionally uses XML encryption
Adds authentication to SOAP header
Using SOAP-DSIG applies MAC to envelope under session key.
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15. Session Auth….cont… Receiver checks for session key.
Else obtains key from session manager.
Validates MAC and accepts SOAP envelope.
Decrypts encrypted message.
Receiver now has authenticated mesg and session handle.
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16. Service Authenticator
Sending service prepares SOAP envelope.
Adds authentication header.
Uses SOAP-DSIG to digitally sign mesg.
Optionally uses XML encryption.
Receiver decrypts, validates signature, verifies its own sign and accepts.
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17. Session Management Initiator of session could be SA
Assigning session Ids.
Creating session secrets.
Maintaining status information for each session.
Keeping participants informed of the status.
Shutting down sessions.
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18. Online session Management
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19. Drawbacks .. SA cannot measure the validity of service instance
Anyone who has session ID can contact SA.
An attacker who has compromised an instance can request to join session
No unique identifier for each instance
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20. Multi-Party Auth Protocol
Each instance has unique identifier
Based on Diffie Hellman Key exchange to compute shared secret key.
Session Manager manages a given Web Service session
Manager instance’s identifier is unique for one session.
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21. Notations….. p: a large prime number g: a primitive root of p
R: random no. chosen by a service instance of the
session
gR: gRmod p is the unique identifier used by the
instance.
Kx,y: security key shared by service instance x and y.
MACx,y(M): MAC code for msg M under key Kx,y.
U(R, gR): Service Instance U with pvt msg R and identifier gR.
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22. Example Scenario User instance (UI (x, gx).
UI contacts session manager
Manager invokes service instance (MI(y, gy)).
MI and UI exchange identifiers and a session is initialized.
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23. Multi-Party Auth Protocol
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24. Cont…. UI wants to contact service # 1
New instance (NI(z, gz)) invoked
UI and NI exchange identifiers gx and gz
UI sends <Introduction-of-new-Instance> message to MI
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25. Cont….
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26. Cont….. NI needs to contact another service #2.
NI2(n, gn ) is invoked by NI and recommended to MI
NI2 sends MI an <identifier-query> message to check UI’s identity
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27. Cont….
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28. Strengths of Protocol Each service instance has a unique identifier
Attackers cannot get key shared in an instance from plain text and MAC code
Any new instance wanting to join session must be recommended by session participant.
Malicious instance will be detected by SA
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29. Mathematical Model
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30. Model…cont… 4xi +1 xi Ttotal,i   ( Tm(j,i)) + Tkey-pair(j,i)
j= j =1
2(xi + 1)
 ( Tsec(j,i) ) + T inst,I …………….(1)
j=1
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31. Cont……
n 4xi xj
Tn-total = Ttotal,i   (  ( Tm(j,i)) + Tkey-pair(j,i) )
i= j= j =1
n 4xi xj
 (  ( Tm(j,i) )+ Tkey-pair(j,i)
i= 1 j= j=1
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32. Cont………….. 2(xi +1) +  ( Tsec(j,i) ) + T inst,I j=1
== [4(x1 + x2 + x3 +….. xn ) + n](Tmessage) + (x1 + x2 + x3 +….. xn ) + n](Tkey-pair)
+ 2[(x1 + x2 + x3 +….. xn ) + n](Tsecret) + n Tinstant … ……………………………….(2)
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33. Cont…… n 4xj + 1 where Tmessage =  (  ( Tm(j,i) )) i= 1 j=1
______________ n
 ( 4xi + 1 )
i=1
n xi
Tkey-pair =  (  ( Tkey-pair(j,i) ))
i= 1 j=1
 xi
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34. Cont…… n 2xi + 1 Tsecret =  (  ( Tsec(j,i) )) i= 1 j=1
______________ n
 (2xi + 1)
i=1
Tinstance =  ( Tinst,i )
i= 1
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35. Analysis Assume that key space is large.
Prob that two partners within same session chose same private key is small
For every i in {1,2,3….n} xi  1.
(x1 + x2 + x3 + …….xn)  n.
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36. Cont…. Tn-total = 5n (Tmessage) + n(Tkey-pair ) + 4n (Tsecret ) +
n Tinstance
= n [5(Tmessage) +(Tkey-pair ) + 4 (Tsecret ) + Tinstance]
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37. Result of Analysis
In worst case time consumption of introducing service instances into session increases linearly with amount of session partners.
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38. Drawbacks Message overheads due to Diffie Hellman exchange
Time consumption to compute so many key pairs
Diffie Hellman also prone to attacks
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39. Issues not considered What if Session Manager is malicious??
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40. A Proposal….Adaptive approach
Requirements of users may vary.
Is there need for stringent measures uniformly to every node and transaction
Can we apply as much security as a particular transaction requires?
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41. Sophisticated Web Services
E.g order for aircraft engine
Spawns multiple supporting transactions
Orders to individual parts
Orders for shipping containers
Etc
Involves handling huge volumes of traffic
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42. Adaptive approach ….cont
For Simple Web services existing security measures may suffice.
For sophisticated Web Services involving long transactions trusted third party model desirable.
Can an adaptive/hybrid approach be implemented???
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43. References
1. S. Hada and H. Maruyama, “Session Authentication Protocol for Web Services,”
Proc IEEE Symposium on Application and the Internet, pp , Jan
2. Dacheng Zhang and Jie Xu, “Multi-Party Authentication for Web Services:
Protocols, Implementation and Evaluation,” Proc IEEE Symposium on
Object Oriented Real-time Distributed Computing.
3. M.Hondo, N. Nagaratnam, A.Nadalin, “Securing Web Services,” IBM Systems Journal,
Vol 41, No. 2, 2002.
4. David Geer, “Taking Steps to Secure Web Services,” IEEE Computer, Vol 36,
Oct 2003.
5. V Vasudevan, “A Web Services Primer”,
April 2001.
6. Y. Nakamur, S. Hada and R. Neyama, “Towards the Integration of
Web Services Security on Enterprise Environments,” Proc Symposium on
Applications and the Internet, pp , Jan
7. W3C NOTE, Simple Object Access Protocol (SOAP) 1.1,
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44. References 8. W3C NOTE, SOAP Security Extensions: Digital Signature,
9. Web `Services Security(WS-Security),
10. Web Services Security Threats and Countermeasures,
Microsoft Corporation, Jan 2004.
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45. Acknowledgements
Prof Bernard M
Prof G.Sivakumar
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