4.1.2 Individual Uniqueness Analysis To measure the individual uniqueness of keys, we calculated the min-entropyofECGkeysforeachsubject. Themin-entropyshould belargeenoughtoguaranteeresistanceagainstattacks. Consider n subjects,witheachsubjecthavingk keys;k isvariable. Toestimate the min-entropy, we determine the fractional Hamming Weight of key k denoted HW(k) over all subject keys. HW(k) provides an estimate of the probability of key k to be 1. Let pmax denote the most likely outcome of key k as follows: