Correct Horse Battery Staple: Exploring the usability of system-assigned passphrases

SOUPS 2012: Symposium on Usable Privacy and Security, July 2012. Pittsburgh, PA, USA.

Richard Shay, Patrick Gage Kelley, Saranga Komanduri, Michelle L. Mazurek, Blase Ur, Tim Vidas, Lujo Bauer, Nicolas Christin, and Lorrie Faith Cranor

Carnegie Mellon University
Pittsburgh, PA 15213


Users tend to create passwords that are easy to guess, while systemassigned passwords tend to be hard to remember. Passphrases, space-delimited sets of natural language words, have been suggested as both secure and usable for decades. In a 1,476-participant online study, we explored the usability of 3- and 4-word systemassigned passphrases in comparison to system-assigned passwords composed of 5 to 6 random characters, and 8-character systemassigned pronounceable passwords. Contrary to expectations, system- assigned passphrases performed similarly to system-assigned passwords of similar entropy across the usability metrics we examined. Passphrases and passwords were forgotten at similar rates, led to similar levels of user difficulty and annoyance, and were both written down by a majority of participants. However, passphrases took significantly longer for participants to enter, and appear to require error-correction to counteract entry mistakes. Passphrase usability did not seem to increase when we shrunk the dictionary from which words were chosen, reduced the number of words in a passphrase, or allowed users to change the order of words.

KEYWORDS: Passphrases, System-assigned passwords, Usability, Password composition policies





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