An Empirical Study of Mnemonic Sentence-based Password Generation Strategies

Mnemonic strategy has been recommended to help users generate secure and memorable passwords. We evaluated the security of 6 mnemonic strategy variants in a series of online studies involving 5, 484 participants. In addition to applying the standard method of using guess numbers or similar metrics to compare the generated passwords, we also measured the frequencies of the most commonly chosen sentences as well as the resulting passwords. While metrics similar to guess numbers suggested that all variants provided highly secure passwords, statistical metrics told a different story. In particular, differences in the exact instructions had a tremendous impact on the security level of the resulting passwords. We examined the mental workload and memorability of 2 mnemonic strategy variants in another online study with 752 participants. Although perceived workloads for the mnemonic strategy variants were higher than that for the control group where no strategy is required, no significant reduction in password recall after 1 week was obtained.