Currently the pex address book uses double sha256. However this is essentially distributing buckets for a hashmap. It should instead be like typical hashmaps and use AESHash (this is in the stdlib so can just be copy pasta'd) or use high way hash #2187, it definitely doesn't need the overhead of two cryptographic hashes. (If we really wanted a cryptographic hash, then lets use a fast hash here, like blake2{b,s})