Shit I got it!!

[mik3cap]

Okay, so here's the solution. Stupid, but it would work.

Both parties get web cams. They show the unscratched cards to each other on cam. They then simultaneously scratch the tickets, and then simultaneously show the codes to each other.

Now where am I going to get a web cam? And does Party B have a web cam?

Comments

[bluegargantua]

I fake-scratch the last number or two on my card, then do the big reveal. Screen-cap the other guy's numbers and walk away chortling.

no dice
Tom

[mikecap.livejournal.com]

Okay granted, it's not perfect, but I think it's about as near as I can get. The reveal has to be simultaneous. You'd have to do the whole thing on camera, and reveal as much as the other person does and watch it carefully.

Like Chef says; "You! And me! And her! Simultaneous!!"

My daddy want's to know

[timothy-tim.livejournal.com]

Why you trust them to give you the right number at all?

If you trust them to give you the right number and you get at least two tries w. the device you are unlocking then you can convert the number to binary and tell each other the thing bit by bit. If they don't give you the last bit then you only need to tries to get it.

-ben

Re: My daddy want's to know

[timothy-tim.livejournal.com]

Oh, and see also chapter 5 of Scheneier's "Applied Crypto, 2nd ed." -- "Simultaneous Exchange of Secrets". I'd summarize but I don't have my copy here.

-ben