Norwegian Information Security Laboratory, NISlab, Gjøvik University College, Norway

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Abstract—It is easy for humans to design passwords that are easily remembered. However, such passwords may have a predictable structure, making exhaustive search feasible. We have divided human-generated passwords into three categories: Non-word passwords, Mixture passwords, and Word passwords; depending on their overall structure. Within these categories, we have analyzed the search-space reduction of several common password sub-structures. From this analysis, we have derived guidelines that yield strong passwords within in each password category. Our results contribute towards the goal of achieving both strong and memorable passwords.

Index Terms—Password security, password policy, search space reduction, personnel authentication.

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Cite: Kirsi Helkala, Einar Snekkenes, "Password Generation and Search Space Reduction," Journal of Computers vol. 4, no. 7, pp. 663-669, 2009.