One-time-use phone numbers

Yesterday, there was an article on HN about the plague of Payday Loan scammers who prey on gullible people. The comments talked at length about how difficult it is to get off a call list once your number is known to these people.

Why do we need publicly accessible phone numbers, i.e. phone numbers that anyone can call?

Prediction Time #

In the future, we’ll have one-use unique identifiers (numbers) that we’ll generate ad-hoc whenever we want to share our contact information with a new person. Met someone at a party, want to exchange numbers? Pull out your phones, touch them together, you’ve generated a public/private key-pair for contact with just that person.

This doesn’t need to be necessarily encrypted, just a way to authenticate that the person is allowed to contact you. That you can also encrypt communications to that person using your public-key cryptography is a bonus.

If it was this easy to exchange “numbers,” you could even use this process for e.g. the dry cleaners- really, anywhere you are giving your number to someone physically present, no matter how trivial.

“What’s your Phone Number?” #

You’ll need some way to exchange “numbers” over the phone, or on the internet. Online, it’s easy to imagine some sort of web standard for exchanging phone identifiers. All you need is to be synced with your phone device

If you’re talking to someone on the phone, you could perhaps give them your “old” phone number, and they can send you a “connect” request in real time, perhaps with a passphrase. You can confirm so your device can execute the exchange.

“This is Bank of America calling” #

One very nice benefit of this system is that you’re authenticating communications on both sides. Scammers can’t call you impersonating your bank- they don’t even have a number to call.

“You guys should definitely talk, I’ll give you her number” #

Alice meets Bob at a party and wants to give him Cindy’s number. Easy. Alice and Bob exchange numbers, then Alice sends him a contact request for Cindy.

Both Bob and Cindy get a notification saying “Alice wants to connect you with [the other].” The system can even remember the referrer. If Alice was a terrible matchmaker, you could delete all contacts referred to you by Alice.

“I lost my number” #

The hardest part of this system is security. I need to make sure my address book is never compromised. Not only would I lose the ability to communicate with my contacts, I don’t even have a recourse for sending them a request to re-connect and “burn” the original compromised identity.

One (half-baked) solution would be to have a “recovery identity account.” Every time a new connection is forged, we generate two trusted key-pairs. The second exchange is made with a second identity account of mine, held in escrow on a trusted server. If my address book were compromised, I’d need to access that escrow account, retrieve my second identity account, and publicly notify the world that the first account was compromised. Easier said than done. We’d need a trusted public “burn” server, which is a rich target. We’d also need a place to store these “escrow” accounts. Perhaps the access to the escrow account needs a physical token that is stored for a fee at local banks.

Even worse than individuals losing their key-pairs would be for a bank to lose its “address book.” A criminal would be able to contact any of the bank’s clients and seem trustworthy.

There are obvious challenges to such a system, but as more and more business happens electronically, we’ll need more elaborate systems to protect and authenticate identities.