'End of passwords' predictions are premature - Cambridge boffin

Advances in the power of computers won't automatically make passwords obsolete, according to a top computer science researcher.

Joseph Bonneau, a postgrad researcher at Cambridge University, looked into the perceived wisdom that runs along these lines: "Since computers are getting exponentially faster, yet the human brain is constant, then password crackers will eventually beat human memory."

Remarks such as this are often made when the latest advances in increasingly powerful graphics processors for password cracking or similar stories hit the news. Bonneau doesn't dispute that password cracking is getting faster or that easily guessable or reused passwords are toast. Instead he disputes the idea that well thought out, complex passwords stored using a sufficiently robust hash function with proper salting have had their day.

A hash function is a mathematical process that takes a "message" and forms a message digest or hash from it. Storing plain text passwords as part of an online authentication system is an obviously bad idea. If a website is broken into and the passwords are lifted then even well thought out passwords are exposed.

Instead websites need to store password hashes, protected by salting, in order to prevent brute force attacks using rainbow tables.

A password hash is computationally easy to create but working out the corresponding password from a hash ought to be nearly impossible, given a correctly implemented hash function. Rainbow tables circumvent this snag by creating a large data set of hashes from nearly every possible password. Faster number-crunching chips make it possible to derive and run through an increasing volume of possible passwords, increasing the potency of such brute force attacks.

Bonneau argues however that this points towards an arms race necessitating the development of better hashing algorithms rather than an inexorable move towards the end of days for passwords.

"Password cracking is certainly getting faster," Bonneau explains. "In my thesis I charted 20 years of password cracking improvements and found an increase of about 1,000 in the number of guesses per second per unit cost that could be achieved, almost exactly a Moore’s Law-style doubling every two years.

"The good news though is that password hash functions can (and should) co-evolve to get proportionately costlier to evaluate over time. This is a classic arms race and keeping pace simply requires regularly increasing the number of iterations in a password hash. We can even improve against password cracking over time using memory-bound functions, because memory speeds aren’t increasing nearly as quickly and are harder to attack using parallelism," he adds.

Bonneau cautions against complacency: hashing passwords isn't going to get any more efficient over time and older algorithms will need to be replaced by more complex successors. As well as the brute force problem, hashing algorithms can come under increasing pressure from new types of cryptanalysis.

"Moore’s Law has indeed broken MD5 as a password hash and no serious application should still use it. Human memory isn’t more of a problem today than it used to be though. The problem is that we’ve chosen to let password verification become too cheap," Bonneau argued.

Booneau's remarks come days after Deloitte Canada warned that the password was doomed. It predicted more than 90 per cent of user-generated passwords will be vulnerable to hacking during the course of 2013.

“Passwords containing at least eight characters, one number, mixed-case letters and non-alphanumeric symbols were once believed to be robust. But these can be easily cracked with the emergence of advanced hardware and software,” Duncan Stewart, director, Deloitte Canada Research said. Deloitte Canada made the point while arguing for more widespread use of two-factor authentication using either tokens or mobile phone technology. Password vaults, secured by two-factor authentication, can play a role in driving the wider use of more complex passwords that users don't necessarily have to remember, the management consultancy argues, adding that disaster beckons for continued use of current password choices.

"In a recent study of six million actual user-generated passwords, the 10,000 most common passwords would have accessed 98.1 percent of all accounts," Deloitte Canada adds.

Easily guessable passwords are arguably a lesser problem than password re-use. The average user has 26 password-protected accounts, but only five different passwords across those accounts, according to a recent study by credit reference agency Experian.

Deloitte Canada's prognosis on password problems can can be read on page 11 of a larger report on tech trends here (PDF). ®