Tuesday, July 01, 2008

Decrypting and Restoring GPcode Encrypted Files

The futile attempt to directly attack the encryption algorithm used by the GPcode ransomware, is prompting Kaspersky Labs to invest in a more pragmatic solutions to the problem, with a new version of the StopGpcode tool released last week. More info :

"It turns out that if a user has files that are encrypted by Gpcode and versions of those same files that are unencrypted, then the pairs of files (the encrypted and corresponding unencrypted file) can be used to restore other files on the victim machine. This is the method that the StopGpcode2 tool uses.

Where can these unencrypted files be found? They may be the result of using PhotoRec. Moreover, these files may be found in a backup storage or on removable media (e.g., the original files of photographs copied to the hard disk of a computer that has been attacked by Gpcode may still be on a camera’s memory card). Unencrypted files may also have been saved somewhere on a network resource (e.g., films or video clips on a public server) that the Gpcode virus has not reached."

As the customer support desk behind GPcode pointed out in an interview, the malware is prone to evolve, and the simplistic file deletion process will be replaced by secure file deletion in order to render all data recovery tols useless, unless of course backups of the affected data are available. They often aren't, and depending on the importance of the files encrypted, the successful ransom is all a matter of the momentum.

"A person, presumably the author of Gpcode, contacted at one of the e-mail addresses left behind by the program stated that future development efforts will likely increase the key size to 4,096 bits, "if AV companies or other (people) crack the current key, but (that's) impossible. The self-proclaimed author, who used the name "Daniel Robertson," also said that other standard techniques to defeat antivirus will be added, including polymorphic encryption, anti-heuristic features and the ability to self propagate, turning the program into a computer virus. It well pays back itself," he said"

There are even more pragmatic approaches to dealing with this problem, next to backups undermining their business model. Try following the virtual money for instance.

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