[FoRK] Crypto protocol for only good news?
Matt Jensen <
mattj at newsblip.com
> on >
Tue Aug 15 13:59:15 PDT 2006
I'm looking for a technique for revealing info, but only if the info
has one particular value.
For example: Suppose a couple is pregnant with their second child. The
first kid is a girl, and though the couple will love the second kid
regardless of gender, they'd be extra excited if it turned out to be a
boy. (Plus, they could start outfitting the nursery.)
So, we now want to know if there's some procedure whereby they can
have the sonographer tell them if it's a boy, but not tell them
anything if it's a girl. Obviously, not telling them anything tells
them it's a girl. Anyway around this?
Ideally, you'd like a 100% chance of learning that it's a boy.
However, in order trust an answer like "I can't tell you the result
because our protocol forbids it", it seems you have to accept a lower
chance of getting the good news.
I suppose you could have the sonographer secretly flip a coin, and if
it's heads, she tells the parents the gender. But if it's a girl you
actually have the sonographer lie to you, and tell you she got tails,
so she can't tell you the gender. But even that tells you something:
there are two "tails" outcomes for a girl and only one "tails"
outcome for a boy.
I feel like there's a better answer to this question, but I'm missing
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