GROUP N
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Transcript of GROUP N
GROUP N GROUP N GROUP N GROUP N Charles BarrassoCharles Barrasso
Carter MayCarter MayChih-Yu (Joey) TangChih-Yu (Joey) Tang
A Survey of Key Management for
Secure Group Communication
A Survey of Key Management for
Secure Group Communication
Sandro RafaeliDavid Hutchison
Goals and Metrics• Storage requirements• Overhead traffic minimization• Backward and forward secrecy
– Messages should remain secure outside of membership changes
• Scalability• Collusion
Approaches1. Centralized group key management
protocols– A single entity (node) is responsible for
directing key management
2. Decentralized architectures– Multiple entities divide the responsibility
3. Distributed key management protocols
– Each of the individual members contribute fairly equally
Decentralized Key Mgmt. Archs.
• More entities may fail before the whole group is affected
• There should not be a central manager that controls the submanagers
• Keys should be independent, but minimize overhead– Usually key changes limited to a single group– Sometimes leads to intercommunication
problems
Distributed Key Mgmt. Protocols
• Each member may contribute, or any single member may generate all keys
• Usually not scalable– Communication time– Each member may have to have
complete member list
Conclusion• No perfect solution• Centralized schemes are easy to
implement but not scalable• Hierarchical schemes hinder
intercommunication between groups• Distributed solutions are even less
scalable
Generic Generic Implementations of Implementations of
Elliptic Curve Elliptic Curve Cryptography using Cryptography using
Partial ReductionPartial Reduction
Generic Generic Implementations of Implementations of
Elliptic Curve Elliptic Curve Cryptography using Cryptography using
Partial ReductionPartial ReductionNils GuraNils Gura
Hans EberleHans Eberle
Sheueling Chang ShantzSheueling Chang Shantz
Elliptic Curve Cryptography
• Uses points where the curve exactly crosses integer (x,y) coordinates to generate group of points.
• These points are ideal for SPEKE, Diffie-Hellman, and other methods and are actually much smaller and faster than those used in traditionally, while providing an equivalent level of security.
http://world.std.com/~dpj/elliptic.html
Reduction• Problem: “The fundamental and most
expensive operation underlying ECC is point multiplication”
• Expensive = Not Good for small devices with limited battery, CPU, etc.
• One step in point multiplication is Reduction
Partial Reduction• They describe a method to short-cut
Reduction and how it can be implemented in both Software and Hardware -> Partial Reduction.
• Partial Reduction allows for smaller operands and smaller number of expensive (clock cycles) multiplication and division operations -> Faster and less “Expensive”
• Partial Reduction allows ECC to be used on small, handheld devices.
Simple and Fault-Simple and Fault-tolerant Key Agreement tolerant Key Agreement
For Dynamic For Dynamic Collaborative GroupsCollaborative Groups
Simple and Fault-Simple and Fault-tolerant Key Agreement tolerant Key Agreement
For Dynamic For Dynamic Collaborative GroupsCollaborative Groups
Yongdae KimYongdae Kim
Adrian PerrigAdrian Perrig
Gene TsudikGene Tsudik
Group Key Management
• In Ad-Hoc networks no centralized servers or key servers
• Could “Elect” a server, but stresses (CPU, Battery, etc) that device too much -> want to distribute load
• People who whish to communicate must then agree on a key and distribute the load on managing the key amongst the devices
Key Trees• Developed a Protocol that Arranges the
group into a Hierarchy (Binary Tree)• Each node has its own key, which it
contributes to the group to form a group key
• Each node knows the keys of a specialized subset of the group from which it can easily generate the group key
Group Key Management Protocol
• As nodes enter/leave the group, the tree is split, merged, etc and computations associated with the structure change are isolated to the affected area
• Result: Simple, secure, fault-tolerant protocol for group key agreement that is more efficient than existing protocols of the same type
Self-Organized Network-Self-Organized Network-Layer Security in Mobile Layer Security in Mobile
Ad HocAd HocNetworksNetworks
Self-Organized Network-Self-Organized Network-Layer Security in Mobile Layer Security in Mobile
Ad HocAd HocNetworksNetworks
Hao YangHao Yang
Xiaoqiao MengXiaoqiao Meng
Songwu LuSongwu Lu
Ad-Hoc Network-Layer• No centralized servers to impose
network topology, members must self-organize
• Need to prevent, discover, and isolate attackers on the Network-layer only.
• Can’t trust anyone.
Self-organized Network Protocol
• Each node needs a token to participate in the network
• Neighbors monitor each other to detect misbehavior
• How long a token is valid depends on how long it has existed in the network and behaved well -> decreasing overhead over time
• Exploits collaboration among local nodes to protect the network without completely trusting any individual node.
A Pairwise Key Pre-A Pairwise Key Pre-distribution Scheme fordistribution Scheme for
Wireless Sensor Wireless Sensor NetworksNetworks
A Pairwise Key Pre-A Pairwise Key Pre-distribution Scheme fordistribution Scheme for
Wireless Sensor Wireless Sensor NetworksNetworks
Wenliang DuWenliang DuJing DengJing Deng
Yunghsiang S. HanYunghsiang S. HanPramod K. VarshneyPramod K. Varshney
Key Distribution• Centralized, Key Agreement, Pre-
distributed• Sensors: Small, Little Memory and CPU;
Deployed w/o Centralized server.• Don’t have resources to agree upon a
key.• Pre-distribute keys, but must be careful
of node keys being compromised -> network communication compromised
Pair-Wise Key Pre-distribution
• Each Node gets a Subset of shared secret keys -> Low memory requirement
• Any two nodes can find at least one common secret key from their set with which to compute a new pair-wise key -> Low CPU requirements
Key Pre-distribution Method
• Developed an improved way to breakdown key space among nodes
• When the number of compromised nodes is less than a given threshold, the probability that any nodes other than those compromised are affected is close to zero
• Requires a significant portion of the network to be compromised -> harder
SPINS: Security Protocols for Sensor Networks
Department of Electrical Engineering and Computer Sciences, UC Berkeley
Sensor Hardware
What are the issues?
• Power: Battery• Computation: 4MHz• Storage: 8 Kbytes instruction flash, 512 bytes of RAM and ROM• Bandwidth: 10 kbps
The characteristics of the Sensor Network restrict its ability to adapt the existing security technologies.
Communication is the big chuck on energy consumption, therefore when developing a security structure for Sensor Network, minimizing the communication overhead is the focus.
Compromised security is inevitable for current Sensor Network.
SPINS: SNEP & μTESLA
SNEP: one to one agreement
• Data confidentiality: who receive msg (encrypted data)• Data authentication: who can do what (MAC)• Data Integrity: not receiving an altered data• Freshness: message must be fresh (counter)
μTESLA: for broadcasting (original TESLA is not for Sensor Networks)
• Authenticated broadcast
Code size: The crypto routines occupies about 20% (2K) of the available code space.
Communication overhead: About 20% more communication
Conclusion
Mobility Helps Security in AdHoc Networks
Laboratory for Computer Communications and Applications (LAC)School of Information and Communication Sciences (I&C)Swiss Federal Institute of Technology Lausanne (EPFL)
Security is usually enforced by a static, central authority.
Ex: Communication Network, Operating System, and the access system to the vault of a bank.
Static, Central Control
Exchange certificates that contain their public keys and establish a security association
Communicate using a Secure Side Channel Ex: Physical contact (wire) or Infrared communication
Adversary cannot modify messages transmitted over the secure side channel
Establishing Security Association: purely mutual agreement between users
Authors’ approach
Friends help establishing security associations faster Friends can help distributing the public-keys (certificate) Direct friends only
Two Models
Fully self-organized ad hoc networks : no central authority
Ad hoc networks with a central authority: a (off-line) central authority
One-way security association Ex: i trusts j (i can relate j’s public key) but j doesn’t trust i
Two-way security association Ex: i trusts j and j trusts i
i can ask a friend to issue a fresh certificate to j
Ex: If a node i possesses a certificate signed by the central authority that binds j with j’s public key, then there exists a one-way security association from i to j.
Authority gives certificates to bind nodes together
Mobility Helps SecuritySimulation shows the higher mobility leads to a faster creation of the security associations
Random walk mobility: nodes move randomly
90% of the desired security associations are established in approximately half of the convergence time.
Experiment result shows Restricted does reduce the time to establish security associations The faster the node’s moving speed the shorter the time it needed to establish security associations (this is why this paper titled mobility helps security)
(Restricted) Random waypoint mobility: choice a destination to move to
Destination Speed of movement The amount of time it pauses at the destination
Factors:
Restricted because users normally choose a destination to go to.Ex: meeting rooms, lounges, and so on.