Securing Ad Hoc Networks Richard Lawrence Gordon 2007 Introduction • An ad hoc network describes a network which is formed in a spontaneous manner so as to meet an immediate communication need between mobile nodes. They do not rely on a fixed network infrastructure for. • Unique properties provide network security challenges, pre- dominantly within the area of key management. • Before ad hoc networks will experience large scale development, within both the military and commercial world, the issue of security needs to be resolved. Ad Hoc Network Challenges • Lack of Infrastructure – A fixed entity structure such as a base station or central administration is crucial for security mechanisms, defining security services, and manages and distributes secret keying information which allows secure communication of data through encryption and decryption techniques. • Connectivity – Networks are created spontaneously and nodes are mobile. Therefore connectivity between the nodes is sporadic. • No prior relationship with Nodes – It can not be assumed that pairwise secrets exist between nodes which is the assumption of many of existing routing protocols have such as ARAN, SEAD, SRP, and Ariadne • Physical Vulnerability – A higher possibility of mobile node capture or compromised nodes. Security Solution • Public Key Encryption Scheme – Public key systems are recognized as the most effective mechanism for providing security services to a dynamic network. This is due to their superiority in distributing keys, providing authentication and achieving integrity and non-repudiation. • Employing: – Distributive Key Management Scheme – Proactive Active Refreshing Scheme – Physical Secure Threshold Scheme Distributive Key Management • Threshold Cryptography: – (t-out-of-n) threshold scheme allows n nodes to share the cryptographic capability, but requires t nodes, from the n node set, to successfully perform the CA’s functionality jointly. • Distributed CA Key’s k an1 .... an2 .... ann K1/k1 K2/k2 Kn/kn Distributive Key Management • Group signature: – (2-out-of-3) threshold scheme, message m is signed by the CA, two partial signatures (PS) are accepted while the third (an2) was corrupted. The partial signatures are combined at c and applied to the message. an1 PS(m,an1) m an2 c an3 PS(m,an2) Proactive Security • Share refreshing: – Protect against all nodes becoming compromised. – New key shares created. 1. Each authority node ani an1n … an1n … an1n ann’ generates subshares (ani1, ani2, … , anin) an (t-out-of-n) . . . . sharing of 0 (ith column) . . . . 2. subshares anij is sent to . . an … . an … . an 1j ij nj authority node anj. anj’ . . . 3. all subshares (an1j, an2j , … , . . . . annj), (jth row) used to . an11 … . . ani1 … ann1 . genterate new share an1’ . an1’ an1 … ani … ann Physically Securing Threshold Scheme • CA Nodal Selection: – Most existing ad hoc network schemes assume a homogeneous network. – Heterogeneous selection protocol creates a more physically secure network. – Authority Nodes selected based on a certain criteria: • Purpose • Physical Security • Computationally more powerful • Position • …etc Conclusion • Unique Challenges faced • The illusion of a Trusted Third Party • Securing that illusion through: – Heterogeneous Selection patterns – Proactive key refreshing • What the future holds?