Secure Internet Chat

1
Secure Internet Chat

• How to make talking online more secure.

2
Group Key Distribution

• Relation to 2 Party Key Exchange
• Importance
• 4 of 23 Evans Lectures
• Lacking Analysis
• Static/Dynamic Membership

3
Simple System Star

• n Member Keys, Ki
• 1 Common Key, KGroup

1
2
3
8
S
7
4
5
6
4
Star Join

• Establish New Member Key
• Update All Group Keys (Multicast)

E(KGroup, KNewGroup)
1
E(KGroup, KNewGroup)
E(KGroup, KNewGroup)
2
3
8
S
E(KGroup, KNewGroup)
E(KGroup, KNewGroup)
9
E(K9, KNewGroup)
7
4
5
6
E(KGroup, KNewGroup)
E(KGroup, KNewGroup)
E(KGroup, KNewGroup)
5
Star Leave

• n-1 Individual Encryptions

E(K1, KNewGroup)
1
E(K2, KNewGroup)
2
3
S
8
E(K3, KNewGroup)
E(K7, KNewGroup)
9
E(K9, KNewGroup)
7
4
5
6
E(K4, KNewGroup)
E(K6, KNewGroup)
E(K5, KNewGroup)
6
Basic Rekeying Schemes

• N-Party Diffie-Hellman
• MIIA
• Star Graph
• Key Graph

7
Key Graph
SK
K2
K2
K1
K1
K1
K1
K0
K0
8
Key Graph - Member Join
SK
K2
K2
K1
K1
K1
K1
K0
K0
9
Key Graph - Member Leave
SK
K2
K2
K1
K1
K1
K1
K0
K0
10
Several Members Leave
SK
K2
K2
K1
K1
K1
K1
K0
11
Boolean Key Function Minimization
K2
K1
K2
K2
K2
K1
K1
K1
X
K0
1
1
1
0
1
K0
1
1
K2 K1
12
How to Analyze?

• Average Case
• Bandwidth
• Computation
• Storage
• Data Models
• Simulation

13
Data Models

• Simulator calculates more than net gain

14
Sample Output
15
Average Bandwidth/Time
16
Conclusion

• Key Graphs
• Boolean Enhanced
• Periodic Rekeying