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

        7b93c6b134ce346d211cefb4a473061f

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

5. Alice divulges the original string

        sezvvamredfkpkpvsgccidzgvtxfolzlobivdenz:tails