document: Improving computer security for authentication of users : influence of proactive password restrictions Entering a user name-password combination is a widely used procedure for identification and authentication in computer systems . However , it is a notoriously weak method , in that the passwords adopted by many users are easy to crack . In an attempt to , improve security , proactive password checking may be used , in which passwords must meet several criteria to be more resistant to cracking . In two experiments , we examined the influence of proactive password restrictions on the time that it took to generate an acceptable password and to use it subsequently to log in . The required length was a minimum of five characters in experiment I and eight characters in experiment 2 . In both experiments , one condition had only the length restriction , and the other had additional restrictions . The additional restrictions greatly increased the time it took to generate the password but had only a small effect on the time it took to use it subsequently to log in . For the five-character passwords , 75 % were cracked when no other restrictions were imposed , and this was reduced to 33 % with the additional restrictions . For the eight-character passwords , 17 % were cracked with no other restrictions , and 12.5 % with restrictions . The results indicate that increasing the minimum character length reduces crackability and increases security , regardless of whether additional restrictions are imposed
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