3 ms·

Correct me if I'm wrong but that example doesn't seem quite right. If you lift one piece of cardboard the person now sees roughly where Waldo is, right? Sure th

Correct me if I'm wrong but that example doesn't seem quite right. If you lift one piece of cardboard the person now sees roughly where Waldo is, right? Sure the cardboard could be HUGE to obscure the size and position of the book but then asking to lift both pieces will show you the position and size of the book making it immediately obvious where Waldo is.

gbhn 11y ago
Perhaps a good intuition pump is this: after every guess the person claiming to have found Waldo gets to position three things: the book, the waldo mask, and the covering cardboard. This then means the subsequent trials don't reveal any side channels about Waldo's location in the book. (And of course in practice the "pieces of cardboard" are big enough to obscure all book information.)
skj 11y ago
The idea is that some the time, it's not the book, but just a random small picture of Waldo. Since you don't know if it's the book under there or not, you don't know if this example is a "control". The proportion of times that it is the book has to be the same as the odds that you could randomly guess where Waldo is, I think.
- edanm 11y ago
  No, that's wrong. The book always has to be under there, otherwise you aren't proving anything (or at least, the odds are worse). The idea is that your counterparty cannot ever ask for both the book under there and to see Waldo, so they never know where the book is. You can spin the book around under the cardboard to put it in arbitrary locations, therefore just seeing the Waldo doesn't help.
cortesoft 11y ago
Couple of things: 1) It doesn't have to be THAT big. As long as the cardboard has twice the dimensions of the book, having the cutout be in the center ensures that you could reveal a Waldo anywhere on the page without letting the other person see any bit of the book to try to reason which section the book is under. 2) They only get to choose one piece of cardboard to remove per iteration of the game - they don't get to lift one piece and then immediately the other, they only lift one. That means that the person placing the cardboard can't cheat (because they don't know which piece they are going to lift, the one revealing the whole book or the one revealing the waldo), and the other person can't gain any information from the reveal. You can repeat the process many times (moving BOTH pieces of cardboard each time to ensure no gained information), but you can only do one cardboard lift per cycle.
caf 11y ago
The book gets to be repositioned somewhere else under the huge piece of cardboard between each trial.
BinaryIdiot 11y ago
Wasn't sure who to reply to but thanks for all the clarifications!

gbhn 11y ago

Perhaps a good intuition pump is this: after every guess the person claiming to have found Waldo gets to position three things: the book, the waldo mask, and the covering cardboard. This then means the subsequent trials don't reveal any side channels about Waldo's location in the book. (And of course in practice the "pieces of cardboard" are big enough to obscure all book information.)

skj 11y ago

The idea is that some the time, it's not the book, but just a random small picture of Waldo. Since you don't know if it's the book under there or not, you don't know if this example is a "control". The proportion of times that it is the book has to be the same as the odds that you could randomly guess where Waldo is, I think.

edanm 11y ago
No, that's wrong. The book always has to be under there, otherwise you aren't proving anything (or at least, the odds are worse). The idea is that your counterparty cannot ever ask for both the book under there and to see Waldo, so they never know where the book is. You can spin the book around under the cardboard to put it in arbitrary locations, therefore just seeing the Waldo doesn't help.

cortesoft 11y ago

Couple of things: 1) It doesn't have to be THAT big. As long as the cardboard has twice the dimensions of the book, having the cutout be in the center ensures that you could reveal a Waldo anywhere on the page without letting the other person see any bit of the book to try to reason which section the book is under. 2) They only get to choose one piece of cardboard to remove per iteration of the game - they don't get to lift one piece and then immediately the other, they only lift one. That means that the person placing the cardboard can't cheat (because they don't know which piece they are going to lift, the one revealing the whole book or the one revealing the waldo), and the other person can't gain any information from the reveal. You can repeat the process many times (moving BOTH pieces of cardboard each time to ensure no gained information), but you can only do one cardboard lift per cycle.

caf 11y ago

The book gets to be repositioned somewhere else under the huge piece of cardboard between each trial.

BinaryIdiot 11y ago

Wasn't sure who to reply to but thanks for all the clarifications!