“…Despite the research efforts over the recent years, it remains a significant challenge to design a robust SUA-WSN scheme that carries a formal proof of security in a widely-accepted model. As summarized in Table 1 , most of the published schemes either provide no formal analysis of security [ 3 , 12 – 14 , 16 , 20 – 22 , 24 – 26 ] or fail to achieve important security properties, such as mutual authentication, session-key security, user anonymity, two-factor security and resistance against various attacks [ 3 , 13 – 16 , 19 , 21 – 27 , 30 , 31 ]. Some schemes [ 2 , 17 – 19 , 23 , 27 ] have been proven secure using a computer security approach, which, as mentioned above, suffers from intractability and undecidability and could possibly give a false positive result.…”