computeSkipPath computes a log pattern skip path in reverse e.g., start=100, end=2033 -> ret = {1009, 497, 241, 113, 105, 101} such that ret[i+1] \in computeSkipPointers(ret[i]).

p = HMAC-SHA512-256; (k, v) -> (k, p(p(k, s), v)) where s is a secret unique per Merkle seqno.