Another solution - drop numeric phone numbers all together and switch to alphanumeric or verified contact only. With numeric, sequential phone numbers you can just robocall all the numbers until you find a victim. Making the search space significantly larger should solve that attack vector. Of course, this will effectively be the same as transitioning from IPv4 to v6 - with all the same associated pain
It'll help with so many things: - in contact syncing systems you can't rainbow table your way to decrypting numbers - numbers can be permanently burned once they're released or deemed as spam. This means every service could ban spammers safely without fear of burning a real user. - people could more easily have alt numbers, non-voip numbers for untrusted services.
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