Speaking at PasswordsCon 2016 last week, Federal Trade Commission Chief Technologist Lorrie Cranor spoke about her own surprise when she left Carnegie Mellon University to work at the FTC. Cranor discovered that not only did the agency tell employees to encourage friends and family to change passwords often, she herself now had six new government passwords that she was required to change every 60 days.
Cranor told FTC information and security officers that changing passwords often can lead to weaker security because users make predictable changes hackers can detect with algorithms. Asked for proof of this unexpected assertion, Cranor got it.
In 2010, researchers from the University of North Carolina at Chapel Hill studied 10,000 expired university accounts for which they were able to trace password history. The account holders had been required to change passwords every three months. Most commonly, the users made only minimal changes to their passwords, using detectable patterns. For example, a user might progressively capitalize one letter in a password, advancing to the next letter with each change, for example, “Pumpkin77!,””pUmpkin77!,” and “puMpkin77!.” Another common pattern was to increase a digit when changing, such as “Pumpkin1!,” “Pumpkin2!,” and “Pumpkin3!.” The researchers developed algorithms that could crack accounts before lockout 17 percent of the time.
Additional studies from Canada’s Carleton University, the National Institute of Standards and Technology, and the U.K.’s CESG (Communications-Electronics Security Group) all showed that frequent and mandated password changes inconvenienced users to the point that the users created detectable passwords. In other words, conventional wisdom backfired.
Cranor reported that as a result of her research, the FTC is gradually changing internal procedures away from required password changes.
The advice to change passwords makes sense if all users create long, complex passwords with, for example, more special characters than letters or digits. Most people, however, take the easier route and use easy to remember passwords and change them when required in detectable patterns.
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