Turbo-charged cracking comes to long passwords

August 27, 2013 – 1:45 PM

For the first time, the freely available password cracker ocl-Hashcat-plus is able to tackle passcodes with as many as 55 characters. It’s an improvement that comes as more and more people are relying on long passcodes and phrases to protect their website accounts and other online assets.

Until now, ocl-Hashcat-plus, the Hashcat version that can use dozens of graphics cards to simultaneously crack huge numbers of cryptographic hashes, has limited guesses to 15 or fewer characters. (oclHashcat-lite and Hashcat have supported longer passwords, but these programs frequently take much longer to work.) Released over the weekend, ocl-Hashcat-plus version 0.15 can generally accommodate passwords with lengths of 55 characters. Depending on the hash that’s being targeted and the types of cracking techniques being used, the maximum can grow as high as 64 characters or as low as 24. The long sought-after improvement targets one of the last remaining defenses people employ to make their passwords resistant to cracking.

“This was by far one of the most requested features,” Jens Steube, the lead Hashcat developer who also goes by the handle Atom, wrote in the release notes for the new version. “We resisted adding this ‘feature’ as it would force us to remove several optimizations, resulting in a decrease in performance for most algorithms. The actual performance loss depends on several factors (GPU, attack mode, etc.), but typically averages around 15 percent.”

As leaked lists of real-world passwords proliferate, many people have turned to passwords and passphrases dozens of characters long in hopes of staying ahead of the latest cracking techniques. Crackers have responded by expanding the dictionaries they maintain to include phrases and word combinations found in the Bible, common literature, and in online discussions. For instance, independent password researcher Kevin Young recently decoded one particularly stubborn hash as the cryptographic representation of “thereisnofatebutwhatwemake.” Such cracks are known as “offline attacks” because they target the hashes leaked as a result of a database compromise, allowing the person who recovers the hashes to try an unlimited number of guesses until the correct plaintext passwords are found. Once the underlying credentials are revealed, a hacker can use them to compromise the online account they secure.

Yiannis Chrysanthou, a security researcher who recently completed his MSc thesis on modern password cracking, was able to crack the password “Ph’nglui mglw’nafh Cthulhu R’lyeh wgah’nagl fhtagn1.” That’s the fictional occult phrase from the H.P. Lovecraft short story The Call of Cthulhu. It would have been impossible to use a brute-force attack or even a combined dictionary to crack a phrase of that length. But because the phrase was contained in this Wikipedia article, it wound up in a word list that allowed Chrysannthou to crack the phrase in a matter of minutes.


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