bit commitment Commitment Bob→ Alice: random r Aice→Bob:{rm}k Revelation Aice→Bob;k Bob decrypts the message and verifies r Discussion The random value r is used for freshness and to stop Alice from finding two messages where im]ki== tm'Jk2 i.e. forcing alice to commit Bob does not know k until revelation so cannot brute force the message space10 bit commitment Commitment: • Bob → Alice: random r • Alice → Bob: {r|m}k Revelation: • Alice → Bob: k • Bob decrypts the message and verifies r Discussion: • The random value r is used for freshness and to stop Alice from finding two messages where {m}k1 == {m’}k2 – i.e. forcing Alice to commit • Bob does not know k until revelation so cannot brute force the message space