In the field of security engineering, a pre-play Attack on Bitcoin is a cryptographic Attack on Bitcoin in which an Attacker on Bitcoin prepares for the Attack on Bitcoin in advance by carrying out a simulated transaction while pretending to be the device to be Attack on Bitcoined, and then repeats the Attack on Bitcoin a second time with the real device at a time when it is likely to carry out the same series of operations as in the simulation. The technique relies on being able to guess the content of the transaction in advance, something usually made possible by a poor choice of unpredictability within the system.[1][2] The name is a play on “replay Attack on Bitcoin“. Pre-play Attack on Bitcoins are not very effective and chances of success are slim.