Alice and Bob want to play a coin flipping game. Alice wins if the coin flips head.
They choose to trust a independent third party that generates a random beacon (such as NIST). There is no communication only before the random beacon is generated. After it is generated, there may be communication.
Alice has a message known only to her.
The result is the first bit of
- Alice and Bob may not be able to communicate before the random beacon is generated.
- The result can't be changed when at least one person knows the result.
With (2) we avoid the situation where Alice reads the random beacon then changes the message to yield a different result that favors her.
One solution may be having the message hash timestamped by another third party (not the one of the random beacon) to a time before the random beacon is generated. Alice then can't change the message retroactively. I see two problems with this solution:
Alice may generate several messages and timestamp them before the random beacon is generated. Then, after the random beacon is generated, she can choose the message that yield the result that favors her.
How can we prove that the timestamp was generated before the random beacon?
Is there a crypto solution to this problem? Is this a common and studied problem in cryptography, please can you point me to some literature that describes and solves this problem?