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Alice and Bob share a secret key with Trent.

AliceTrentBobno encryption yetconcat my name + random numbersend (unencrypted)concat Alice's name + Alice's random number + my own random numberencrypt with key shared with Trentsend (encrypted)Create M1:Bob's name + random session key + Alice's random number + Bob's random number.Encrypt with Alice's key.Create M2:Alice's name + random session key + Alice's random number + Bob's random number.Encrypt with Bob's key.send M1 and M2decrypt M1, extract session key, confirm random number matches.send M2send Bob's random numberencrypted with session keyextracts session keyconfirms his random numberAliceTrentBob Have a question⁉ Contact me.