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CS6204, Spring 2005
CS6204, Spring 2005
A survey of Key Management for Secure Group Communication Sandro - - PowerPoint PPT Presentation
A survey of Key Management for Secure Group Communication Sandro - - PowerPoint PPT Presentation
A survey of Key Management for Secure Group Communication Sandro Rafaeli and David Hutchison Presented By: Anil Bazaz CS6204, Spring 2005 Intro: Group Communication Uses IP multicast to transmit data Does not limit access to data No
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CS6204, Spring 2005
Intro: Basic Solution
♦ Encryption
– Encryption using a group key – Selective Key Distribution
♦ Challenges
– Rekeying Group Key with membership changes – Backward Secrecy – Forward Secrecy
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CS6204, Spring 2005
A simple scheme
♦
A secret key for all members
♦
Group key distributed using secret keys
♦
Problems:
– Requires extensive computation – Size of message containing group key
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CS6204, Spring 2005
Categories of key management schemes
♦ Centralized key management protocols ♦ Decentralized key management protocols ♦ Distributed key management protocols
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CS6204, Spring 2005
Centralized Key Management
♦ Single Entity Controls the group (KDC) ♦ Single point of failure ♦ Scalability Issues ♦ Measuring Efficiency
– Storage Requirements – Size of Messages – Backward & forward Secrecy – Collusion
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CS6204, Spring 2005
Logical Key Hierarchy
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CS6204, Spring 2005
Logical Key Hierarchy
Join Operation Leave Operation
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CS6204, Spring 2005
Centralized Flat Table
♦ Table has one entry for TEK ♦ 2w entries for KEKs (w = No. of Bits in member
ID)
♦ ID determines KEKs held by members
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CS6204, Spring 2005
Centralized flat table
♦ Rekeying:
– {TEKnew} unchanged KEKs – {KEKsnew}KEKsold, TEKnew
♦ Susceptible to collusion attacks
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CS6204, Spring 2005
Decentralized Architecture
♦ Large group split into smaller groups ♦ Controllers for subgroups ♦ More fault tolerant ♦ Measuring Efficiency
– Key independence – Decentralized controller – Local Rekey – Key vs. Data – Backward & forward secrecy – Type of Communication (1 to n or n to n)
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CS6204, Spring 2005
Intra-Domain Group Key Management
♦ DKD: Domain Key Distributor ♦ AKD: Area Key Distributor ♦ Single key for everybody ♦ Single point of failure
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CS6204, Spring 2005
MARKS
♦ Applies to time lengths (TV transmission) ♦ Keys changed as function of time
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CS6204, Spring 2005
Distributed Key Management
♦ No group controller ♦ Group key generation: contributory or
single member
♦ Evaluating efficiency
– Number of rounds – Number of messages – Processing during setup – DH key
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CS6204, Spring 2005
Group Diffie-Hellman Key Exchange
♦ Group agrees on public Values q and α ♦ Upflow:
– First member calculates αx1, passes it along – Subsequent members receive set, raise it, pass it along – Example:
- Fourth member receives set: {αx1, αx1x2 ,αx1x2x3 }
- Sends set: {αx1, αx1x2 ,αx1x2x3, αx1x2x3x4}
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CS6204, Spring 2005
Group Diffie-Hellman Key Exchange
♦ Member n calculates key using : αx1x2x3…Xn mod
q
♦ Downflow:
– Each member calculates Key – Each member provides intermediate values to lower index members – Example (n = 5)
- Fourth member recieves: {αx5, αx1x5 ,αx1x2x5, αx1x2x3x5}
- Fourth member sends: {αx5x4, αx1x5x4 ,αx1x2x5x4}
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CS6204, Spring 2005
Distributed Logical Key Hierarchy
♦ Key Hierarchy generated among members ♦ Subtrees agree on mutual key ♦ Left subtree: leader ml, key kL ♦ Right subtree: leader mr, key kR ♦ Protocol
– ml chooses kLR, sends it to kR – ml encrypts kLR with kL sends it to subtree L – mr encrypts kLR with kr sends it to subtree R
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CS6204, Spring 2005
Distributed Logical Key Hierarchy
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CS6204, Spring 2005