A security researcher has tapped Amazon's cloud computing service to crack Wi-Fi passwords in a fraction of the time and for a fraction of the cost of using his own gear.

Thomas Roth of Cologne, Germany told Reuters he used custom software running on Amazon's Elastic Compute Cloud service to break into a WPA-PSK protected network in about 20 minutes. With refinements to his program, he said he could shave the time to about six minutes. With EC2 computers available for 28 cents per minute, the cost of the crack came to just $1.68.

“People tell me there is no possible way to break WPA, or, if it were possible, it would cost you a ton of money to do so,” Roth told the news service. “But it is easy to brute force them.”

Roth is the same researcher who in November used Amazon's cloud to brute force SHA-1 hashes. Roth said he cracked 14 hashes from a 160-bit SHA-1 hash with a password of between one and six characters in about 49 minutes. He told The Register at the time he'd be able to significantly reduce that time with minor tweaks to his software, which made use of “Cluster GPU Instances” of the EC2 service.

As the term suggests, brute force cracks are among the least sophisticated means of gaining unauthorized access to a network. Rather than exploit weaknesses, they try huge numbers of possible passwords until the right phrase is entered. Roth has combined this caveman approach with a highly innovative technique that applies it to extremely powerful servers that anyone can rent at highly affordable rates.

Roth's latest program uses EC2 to run through 400,000 possible passwords per second, a massive amount that only a few years ago would have required the resources of a supercomputer. He is scheduled to present his findings at next week's Black Hat security conference in Washington, DC. ®