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We implemented five different group key agreement protocols using OpenSSL. All five protocols have similar structure.

Each protocol requires communication facility such as group communication system
Each protocol requires OpenSSL. OpenSSL version should be at least 0.9.4.
Installation information is provided as README file in each gzipped tar file
All APIs have been tested in Linux/x86 and Solaris/Sparc. However it should run on other plataforms without heavy modifications (if any), as long as the other requirements (i.e. openssl) are met.

STR
- Based on A Secure Audio Teleconference System by D. Steer, L. Strawczynski, W. Diffie and M. Wiener presented at Crypto'88
- STR protocol is modified to provide dynamic group operation
- Group Key Structure
- Advantage
  - Low communication overhead(two round for additive operation and one round for subtractive operation)
  - Well-suited for adding new group members(two modular exponentiation)
  - Robustness is easily provided(included in this package)
- Disadvantage
  - Relatively difficult member exclusion(O(n) modular exp.)
BD
- Based on A Secure and Efficient Conference Key Distribution System by M. Burmester and Y. Desmedt presented at EUROCRYPT '94
- BD protocol is modified to provide dynamic group operation
- Group Key Structure
- Advantage
  - Low computational overhead(two modular exponentiations)
- Disadvantage
  - High communication cost(2n broadcast is required)
  - Whenever membership change happens, at least half of session random needs to be refreshed.
GDH
- Based on Key Agreement in Dynamic Peer Groups by M. Steiner, G. Tsudik and M. Waidner presented at IEEE Transaction on Parallel and Distributed Systems, Aug. 2000.
- Group Key Structure
- Advantage
  - High security assurance
- Disadvantage
  - Relatively high computation cost(O(n) modular exponentiation)
  - Relatively hard to provide robustness
CKD
- Centralized key distribution scheme providing same security guarantee as GDH
TGDH
- Based on Simple and Fault-Tolerant Key Agreement for Dynamic Collaborative Groups by Y. Kim, A. Perrig, and G. Tsudik presented at ACMCCS 2000.
- Group Key Structure for 8 users
- Advantage
  - Low communication overhead(requires maximum 2 round except multiple leave)
  - Low computation overhead(maximum 4 log n modular exponentiation)
  - Easy to provide robustness
- Disadvantage
  - Relatively high communication cost for multiple leave(O(log n))