User-generated textual passwords suffer from the conflict between security and usability. System administrators usually adopt password composition policies to help users choose strong passwords. However, users often use predictable patterns to meet the strict password composition policies and to make passwords easy to remember, which in turn reduces the password strength, or write the password down, which may cause the password to be compromised. To overcome the user-generated password security and usability dilemma, we propose Optiwords, which...