Guesswork changes in multi-processor attacks

More and more effort is being spent on security improvements in today´s computer networking environments. However, due to the nature of computer security there is still a lack of good quantitative assessment methods. Inventing and developing new ways of measuring security are therefore needed in order to more exact describe, assess, and improve security of computer environments. One existing quantitative security measure is guesswork. Guesswork gives the average number of guesses in a brute force attack when breaking an encrypted message. In the current definition of guesswork it is assumed that the attacker uses a single processor when breaking an encrypted message. However, an intelligent and motivated attacker will likely use several processors that can work in parallel to break an encrypted message. This paper formally investigates how guesswork changes over time in multi-processor attacks. The result is applied on three probability distributions, the English alphabet, the geometric, and the truncated geometric to illustrate some behaviors.