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Flipping a coin over the phone: Solution

  1. Alice chooses a string that ends with either heads or tails

  2. She checksums this string

  3. She sends the checksum to Bob


4. Now Bob chooses heads or tails and tells his choice to Alice

5. Alice divulges the original string


6. Bob calculates the checksum for this string

7. Bob verifies that the checksum matches what Alice sent before

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