"You can trivially reverse them by iterating through every phone number and computing the hash." Well yes and no. What exactly is your understanding of a phon

"You can trivially reverse them by iterating through every phone number and computing the hash." Well yes and no. What exactly is your understanding of a phone number 8) Not everyone is blessed with the NANP. I'm a Brit and we have an eye wateringly complicated nonsense of a numbering plan and our's isn't the worst. What do you hash? Perhaps the standardised international representation or one of them (no that is not a joke - telephony is weird). For a laugh you could try one of the many colloquialisms. For example a UK number might be 00441395112233 or 441395112233 or +44 (0)1395 112233 - the final part might be displayed as 112 233 or 112-233. Imagine if the database works by operating on all numbers in locally correct colloquial mode and hashes that! Now let's really get silly: There are hashes that are nasty to compute but easy to check and vv. We'll use whatever is indicated. Anyway this is all a very well researched problem, there is no need for silly games: passwords.