3 ms·
The first approach protects against a global lookup table attack but doesn’t help with the root issue that a 10 digit phone number isn’t enough entropy and you
by bri3d 7y ago
The first approach protects against a global lookup table attack but doesn’t help with the root issue that a 10 digit phone number isn’t enough entropy and you could still brute force the number (depending on the hash algorithm) in seconds to hours.
The second approach isn’t how AirDrop works as a product: when you open the Share dialog, you see a list of eligible recipients (either people with open permissions OR you in their contacts list). The recipient is the one doing the identity check, so their phone number isn’t known upfront.
- stordoff 7y agoI'm unfamiliar with AirDrop, but is there any reason it _has_ to work with phone numbers? Would sending nonce+hash(AppleID+nonce) work? I suspect an email address would have significantly more entropy than a phone number (36^6 * 4 ~= 10^10, so six alphanumerics plus four common email domains has about the same entropy (assuming random distribution-you could make better guesses)). One downside is that it may be make targeted attacks easier (if you can guess the approximate form of someone's email address, you can easily confirm it), but that doesn't seem like much of a leak if you can already guess sufficiently closely. Sending hash(nonce+AppleID+phone number) might be an option, but that feels more limiting.
- phs318u 7y ago> is there any reason it _has_ to work with phone numbers? Would sending nonce+hash(AppleID+nonce) work? I would suggest it's because phone number is (should be) device specific, while AppleID's can be shared across devices. But now that I think about it, does anyone know if AirDrop works with iDevices that don't have a SIM? Such as the iPod Touch?
- Nemo157 7y agoThe email address I use for Apple ID is not the same one my contacts would have.