1. Secure emergency communication of cellular phones in ad hoc mode Authors: Arjan Durresi, Vijay Bulusu, Vamsi Paruchuri, and Leonard Barolli. Sources: Ad Hoc Networks, 5(1), pp. 126-133, 2007. Reporter: Chun-Ta Li ( 李俊達 )

2. 2 22 Outline  Motivation  The proposed mechanism  Comments

3. 3 Motivation  Emergency situation  hurricanes  earthquakes  terrorist attacks  Cell phones  connect to the base station (normal mode)  connect to the ad hoc network (ad hoc mode)

4. 4 Motivation (cont.)  Most of the communications in emergency conditions are broadcasts.  Data confidentiality is not a requirement.  The primary requirement for this situation is broadcast authentication with guaranteed non- repudiation.

5. 5 Motivation (cont.)  Detection and revocation of malicious phones To minimize the damage caused by the malicious phones. Preventing the malicious phones from discrediting non-malicious phones. (DoS attack)

6. 6 The proposed mechanism  Notations : a private/public key pair of PKG PKG: Private Key Generator (each cell) CP: a cell phone BS: a base station : the session key between BS and CP

7. 7 The proposed mechanism (cont.)  Setup phase The base station assigns each phone an ID. The base station generates a private key for each cell phone corresponding to its ID.

8. 8 The proposed mechanism (cont.)  Ad hoc mode in emergency situations

9. 9 The proposed mechanism (cont.)  Key revocation  The normal mode  the base station has all the information of each cell phone  The ad hoc mode  include timestamps in the IDs assigned to each cell phone  the temporary IDs and the corresponding private keys need to be refreshed regularly

10. 10 The proposed mechanism (cont.)  Secure mobility management (k=2) Cell A Cell B Cell C Cell D 1 2 Cell E 3 4 PK pkgA PK pkgB PK pkgC PK pkgD PK pkgE

11. 11 The proposed mechanism (cont.)  Detection and revocation of malicious phones Decision making  maintains a counter for the local revocation messages  Sender must sign the message and broadcasts a local revocation message to neighbors (receives a malicious message)  a network revocation message is broadcasted throughout the network (the counter reaches a threshold value)

12. 12 The proposed mechanism (cont.)  Detection and revocation of malicious phones Decision broadcast the first phone whose local revocation message counter crosses the pre-defined threshold the node which forwards the broadcast message

13. 13 Comments  Forging PKG attacks (a fake private/public key pair of PKG, ) ‘ ‘ Terrorist SK pkg ’ ID [M’, ID] || ID Victim cell Conspirator Normal cell Broadcast Query PK pkg ’ Reply PK pkg ’ Query PK pkg ’

14. 14 Comments (cont.)  Hierarchical structure of cellular networks Administrator PKG 1 PKG 2 PKG 3 PKG N … …… … … …