bit commitment with hash functions Commitment Alice: generates random ry r2 Alice- Bob: r, and x=h(ry r2 m) x is called a blob Revelation Aice→Bob:rr2m Bob hashes(t1 r2,)and compares it to x Discussion: Bob does not have to send any messages Alice sends a message to commit and a message to reveal Alice cannot find r3 such that h(r1 r3r m)== h(t1 ry m) The value r, is kept secret so Bob cant brute force the message space.11 bit commitment with hash functions Commitment: • Alice: generates random r1 , r2 • Alice → Bob: r1 and x = h(r1 , r2 , m) [x is called a blob] Revelation: • Alice → Bob: r1 , r2 , m • Bob hashes (r1 , r2 , m) and compares it to x Discussion: • Bob does not have to send any messages – Alice sends a message to commit and a message to reveal • Alice cannot find r3 such that h(r1 , r3 , m) == h(r1 , r2 , m) • The value r2 is kept secret so Bob can’t brute force the message space