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Secure and efficient key management in mobile ad hoc networks

Authors: Bing Wu, Jie Wu, Eduardo B. Fernandez, Mohammad Ilyas, and Spyros Magliveras

Sources: Journal of Network and Computer Applications, 30(3), pp. 937-954, 2007.

Reporter: Chun-Ta Li (李俊達 )

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Outline Motivation Secure and Efficient Key Management (SEKM) Comments

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Motivation Key management (PKI)

CA (certificate authority)

Secret sharing (distribute the central trust to multiple entities)

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Motivation Secure and Efficient Key Management (SEKM)

Share updating Certificate updating Certificate expiration/revocation

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Secure and Efficient Key Management Notations

Structure of a certificate

6

SEKM scheme (cont.) Server group substructure snapshot in SEKM

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SEKM scheme (cont.) Group creation {IDi, SEQi, TTL, [h(IDi, SEQi)]Ki

-1

||(TTL)Ki-1

}JoinServeReq

JoinServeReq

Server node 1 14, 20

{ID1, SEQ1, TTL, [h(ID1, SEQ1)]K1-1

||(TTL)K1-1

}

Forwarding node 20 9, 21

{ID1, SEQ1, TTL-1, [h(ID1, SEQ1)]K1-1

||(TTL-1)K20-1

}

JoinServeReply

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SEKM scheme (cont.) Server group mesh and table snapshot

Group maintenance (soft state) JoinServerRequest and JoinServerReply

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SEKM scheme (cont.) Share updating (k, m)

Selects k active servers to perform the share update phase Each active server i generates a (k-1)-degree polynomial

Server i broadcasts the witness for polynomial coefficient and its hashed signature to the server group

Each active server i computes a share for server j with Sij=gi(j) mod p and sends {[Sij]

Kj} to the corresponding server j (1< j < k)

Server j’s new share k

i jijj SSS1

'

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SEKM scheme (cont.) Certificate updating

k=3, node 1 receives a certificate updating request from regular node 14 or itself

• Regular node 14 1 CertUpdateReq m’

CertUpdateReq = {ID14, SEQ5, [h(m’)]K14-1

}

• Server node 1 20 (2 tickets)

• Server node 1, 16 and 22 produces a partial certificate for regular node 14 by computing Certj=1,16,22i=14 = (K14)Sj*lj(0) mod p

• Server node 1 combines 3 partial certificates into one certificate by computing

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1 14

)0(*

14)0(*

14

3

1 1414

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1 mod)(mod cajjjj KlSlSj KpKpKCertCert

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SEKM scheme (cont.) Handling certificate expiration and revocation

Expired certificate off-line or in-person reconfiguration

Certificate revocation Refuse to issue certificates Issues wrong partial certificates Any misbehavior or malicious attacks

Accusation (signature of initiator) CRL (Certificate Revocation List)

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Comments Group communications

N1 N2 N3 N4

<{1}, {g}, gN1>

<{1,2}, {gN2,gN1}, gN1N2>

<{1,2,3}, {gN2N3,gN1N3,gN1N2}, gN1N2N3>

N4 multicasts <{1,2,3,4}, {gN2N3N4,gN1N3N4,gN1N2N4,gN1N2N3}> to the group

The group key = gN1N2N3N4

Attacker intercepts the packets and multicasts <{1,2,3,4}, {gN2N3N4’,gN1N3N4’,gN1N2N4’,gN1N2N3}> to the group

For N1, N2 and N3, the group key = gN1N2N3N4’

For N4, the group key = gN1N2N3N4 Signature

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Comments (cont.) Solutions

Group key validation process

Symmetric encryption

N1 N2 N3 N4

EDH12{<{1}, {g}, gN1>}

EDH23{<{1,2}, {gN2,gN1}, gN1N2>}

EDH34{<{1,2,3}, {gN2N3,gN1N3,gN1N2}, gN1N2N3>}

N1, N2 and N3 send EGK{IDi, T} to N4