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GROUP N. Charles Barrasso Carter May Chih-Yu (Joey) Tang. A Survey of Key Management for Secure Group Communication. Sandro Rafaeli David Hutchison. Goals and Metrics. Storage requirements Overhead traffic minimization Backward and forward secrecy

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group n


Charles Barrasso

Carter May

Chih-Yu (Joey) Tang

goals and metrics
Goals and Metrics
  • Storage requirements
  • Overhead traffic minimization
  • Backward and forward secrecy
    • Messages should remain secure outside of membership changes
  • Scalability
  • Collusion
  • Centralized group key management protocols
    • A single entity (node) is responsible for directing key management
  • Decentralized architectures
    • Multiple entities divide the responsibility
  • Distributed key management protocols
    • Each of the individual members contribute fairly equally
decentralized key mgmt archs
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
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
  • 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 implementations of elliptic curve cryptography using partial reduction

Generic Implementations of Elliptic Curve Cryptography using Partial Reduction

Nils Gura

Hans Eberle

Sheueling 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.

Elliptic Curve Cryptography

  • 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
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 tolerant key agreement for dynamic collaborative groups

Simple and Fault-tolerant Key Agreement For Dynamic Collaborative Groups

Yongdae Kim

Adrian Perrig

Gene Tsudik

group key management
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
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 easilygenerate the group key
group key management protocol
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 layer security in mobile ad hoc networks

Self-Organized Network-Layer Security in Mobile Ad HocNetworks

Hao Yang

Xiaoqiao Meng

Songwu Lu

ad hoc network layer
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
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 distribution scheme for wireless sensor networks

A Pairwise Key Pre-distribution Scheme forWireless Sensor Networks

Wenliang Du

Jing Deng

Yunghsiang S. Han

Pramod K. Varshney

key distribution
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
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
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

Communication is the big chuck on energy consumption, therefore when developing a security structure for Sensor Network, minimizing the communication overhead is the focus.

The characteristics of the Sensor Network restrict its ability to adapt the existing security technologies.

Compromised security is inevitable for current Sensor Network.



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

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)


Static, Central Control

Security is usually enforced by a static, central authority.

Ex: Communication Network, Operating System, and the access system to the vault of a bank.

Authors’ approach

Establishing Security Association: purely mutual agreement between users

  • 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
  • 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

i can ask a friend to issue a fresh certificate to j

  • 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

Ad hoc networks with a central authority: a (off-line) central authority

  • Authority gives certificates to bind nodes together

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.


Mobility Helps Security

Simulation 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.

(Restricted) Random waypoint mobility: choice a destination to move to


  • Destination
  • Speed of movement
  • The amount of time it pauses at the destination

Restricted because users normally choose a destination to go to.

Ex: meeting rooms, lounges, and so on.

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)