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Unformatted text preview: Bit Commitment, Fair Coin Flips, and OneWay Accumulators Matt Ashoff 11/9/2004 Cryptographic Protocols Outline Bit Commitment Definition Properties Applications Implementations Fair Coin Flips Definition Implementations OneWay Accumulators Definition Example Motivation Applications References Definition Bit Commitment Goal is to ensure bit commitment. Simplest example: Decide who goes first in a game If Bob guesses correctly, he goes Alice picks a bit (0 or 1) and locks it in a box Bob guesses a bit The box is opened to see if he is right Two parts: Commitment Unveiling Must ensure that: Alice cannot change her bit after Bob guesses Bob cannot know what Alices bit is until she unveils it Assume no trusted thirdparty Properties Bit Commitment Ideally, bit commitment has two interesting properties: It is unconditionally secure if implemented correctly As opposed to computationally secure, which is a requirement for most algorithms It requires only a noisy channel However, implementing the algorithm ideally is the key Applications Bit Commitment ZeroKnowledge Protocols Identification Schemes Multiparty Computation Fair Coin Flips Electronic Voting Implementations Bit Commitment Symmetric Cryptography Alice encrypts her bit with a random key Sends to Bob At a later time, she sends Bob the key He can then verify the bit Disadvantage: Alice may be able to generate another key so that the bit is changed once she knows the result....
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 Fall '08
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