Changes in Guesswork over Time 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 exactly describe, assess, and improve the security of computer environments. One existing quantitative security measure is guesswork. Guesswork gives the average number of guesses in a brute force attack to succeed in 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. An intelligent and motivated attacker will however likely use several processors that run in parallel. This paper formally investigates how guesswork changes over time in multi-processor attacks. The result is applied to three probability distributions, the English alphabet, the geometric and the truncated geometric, in order to illustrate some behaviors.