Password security: a case history
Communications of the ACM
Proofs of Work and Bread Pudding Protocols
CMS '99 Proceedings of the IFIP TC6/TC11 Joint Working Conference on Secure Information Networks: Communications and Multimedia Security
The domino effect of password reuse
Communications of the ACM - Human-computer etiquette
Fast dictionary attacks on passwords using time-space tradeoff
Proceedings of the 12th ACM conference on Computer and communications security
Password security: an empirical study
Journal of Management Information Systems
A large-scale study of web password habits
Proceedings of the 16th international conference on World Wide Web
A future-adaptive password scheme
ATEC '99 Proceedings of the annual conference on USENIX Annual Technical Conference
Password Cracking Using Probabilistic Context-Free Grammars
SP '09 Proceedings of the 2009 30th IEEE Symposium on Security and Privacy
Testing metrics for password creation policies by attacking large sets of revealed passwords
Proceedings of the 17th ACM conference on Computer and communications security
Popularity is everything: a new approach to protecting passwords from statistical-guessing attacks
HotSec'10 Proceedings of the 5th USENIX conference on Hot topics in security
Of passwords and people: measuring the effect of password-composition policies
Proceedings of the SIGCHI Conference on Human Factors in Computing Systems
The Science of Guessing: Analyzing an Anonymized Corpus of 70 Million Passwords
SP '12 Proceedings of the 2012 IEEE Symposium on Security and Privacy
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Password-based authentication is widely used today, despite problems with security and usability. To control the negative effects of some of these problems, best practice mandates that servers do not store passwords in clear, but password hashes are used. Password hashes slow down the password verification and thus the rate of password guessing in the event of a server compromise. A slower password hash is more secure, as the attacker needs more resources to test password guesses, but at the same time it slows down password verification for the legitimate server. This puts a practical limit on the hardness of the password hash and thus the security of password storage. We propose a conceptually new method to construct password hashes called "useful" password hashes (UPHs), that do not simply waste computing cycles as other constructions do (e.g., iterating MD5 for several thousand times), but use those cycles to solve other computational problems at the same time, while still being a secure password hash. This way, we are convinced that server operators are willing to use slower password hashes, thus increasing the overall security of password-based authentication. We give three constructions, based on problems from the field of cryptography: brute-forcing block ciphers, solving discrete logarithms, and factoring integers. These constructions demonstrate that UPHs can be constructed from problems of practical interest, and we are convinced that these constructions can be adapted to a variety of other problems as well.