Password encryption methods

http://news.cnet.com/8301-13578_3-57595529-38/feds-tell-web-firms-to-turn-over-user-account-passwords/

The best practice among Silicon Valley companies is to adopt far slower hash algorithms -- designed to take a large fraction of a second to scramble a password -- that have been intentionally crafted to make it more difficult and expensive for the NSA and other attackers to test every possible combination.

One popular algorithm, used by Twitter and LinkedIn, is called bcrypt. A 2009 paper PDF by computer scientist Colin Percival estimated that it would cost a mere $4 to crack, in an average of one year, an 8-character bcrypt password composed only of letters. To do it in an average of one day, the hardware cost would jump to approximately $1,500.

But if a password of the same length included numbers, asterisks, punctuation marks, and other special characters, the cost-per-year leaps to $130,000. Increasing the length to any 10 characters, Percival estimated in 2009, brings the estimated cracking cost to a staggering $1.2 billion.

As computers have become more powerful, the cost of cracking bcrypt passwords has decreased. "I'd say as a rough ballpark, the current cost would be around 1/20th of the numbers I have in my paper," said Percival, who founded a company called Tarsnap Backup, which offers "online backups for the truly paranoid." Percival added that a government agency would likely use ASICs -- application-specific integrated circuits -- for password cracking because it's "the most cost-efficient -- at large scale -- approach."

While developing Tarsnap, Percival devised an algorithm called scrypt, which he estimates can make the "cost of a hardware brute-force attack" against a hashed password as much as 4,000 times greater than bcrypt.

Bcrypt was introduced PDF at a 1999 Usenix conference by Niels Provos, currently a distinguished engineer in Google's infrastructure group, and David Mazières, an associate professor of computer science at Stanford University.

With the computers available today, "bcrypt won't pipeline very well in hardware," Mazières said, so it would "still be very expensive to do widespread cracking."

Even if "the NSA is asking for access to hashed bcrypt passwords," Mazières said, "that doesn't necessarily mean they are cracking them." Easier approaches, he said, include an order to extract them from the server or network when the user logs in -- which has been done before -- or installing a keylogger at the client.

#encryption - #privacy - #nsa