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← 02-35 Coin Tossing Again

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Showing Revision 1 created 04/27/2012 by Amara Bot.

  1. So now we'll assume that we do have such a function.
  2. We'll assume that we have a function H
  3. that acts like a random oracle
  4. that provides the properties of an ideal cryptographic hash function.
  5. Let's try our coin-tossing protocol again.
  6. So, here's our new protocol design.
  7. Alice will pick a number, 0 or 1,
  8. representing heads or tails.
  9. She'll compute using our ideal cryptographic hash function--
  10. the hash of x--and she'll send m to Bob.
  11. Bob will make a guess,
  12. send that guess back to Alice.
  13. Then Alice will send her claimed value of x back to Bob.
  14. Bob can check if the hash of x equals m.
  15. If that's not the case, then Bob suspects that Alice has cheated.
  16. If x is equal to g, Bob wins.
  17. So, do we like this protocol?
  18. We'll assume that H is an ideal hash function,
  19. So which one of the parties, if any--or both--can cheat
  20. with this new protocol that we've defined?