CHAPTER 6 Robust Wireless Infrastructure against Jamming Attacks 133 6.4. RESILIENCY TO INSIDER CROSS-LAYER ATTACKS Many communication schemes that provide resiliency against adversarial interference (e.g., spread spectrum) require the use of a pre-shared secret between the communicating nodes. This makes such schemes vulnerable to insider attacks by compromised nodes or traitors. In this sec- tion, we describe several schemes that achieve resiliency against insider attacks. users by assigning each a unique polynomial over (j ) GF (q) with degree c. Let u j (x) = c =0 s k x k k denote the identifying polynomial of user j , (j ) (j ) (j ) and s j = (s 0 , s 1 , . . . , s c ) be its coefficient vector. Evaluating u j (x) over {0, 1, . . . , p - 1} gives p val- ues in GF(q), and the values are used by the sys- tem for key assignment to user j . Algorithm 1: PBK-T Setup: N , key pool F Result: a N × p key-distribution matrix K (j ) noted K ji or K i begin Initialize K [0] N ×p S = { (c+1)-vector in GF(q) } for j = 0 to N - 1 do Pick unique s j S for i = 0 to p - 1 do (j ) c k 6.4.1. Polynomial Key Assignment for Robust Broadcast and Insider Attackers Identification In Section 6.2, we outlined the vulnerabilities of broadcast control channels to attacks. Cryp- tographically randomizing the mapping of logi- cal broadcast channels to physical channels (i.e.,