Researchers urge ransomware victims to try file-recovery app

No progress yet on cracking 1,024-bit RSA key

The security company that two weeks ago said it would lead a group effort to crack an encryption key used in a "ransomware" scam today offered victims more practical advice as it published instructions on how to recover data thought lost to the extortionists.

Moscow-based Kaspersky Lab added the instructions, which rely on an open-source file-recovery utility, to its writeup of Gpcode.ak, the Trojan horse that it first warned users about on June 8.

At the time, Kaspersky said that Gpcode.ak encrypted 143 different file types on compromised Windows PCs and deleted the original unencrypted files before displaying a message telling users that they could ransom the data by purchasing a decrypting tool. A week ago, Bulgarian security researcher Dancho Danchev reported that the hackers were demanding $100 to $200 for the unlocking program.

Today, Kaspersky said users might be able to recover the Gpcode.ak-deleted files without paying the ransom. "It is possible to restore a deleted file as long as the data on disk has not been significantly modified," noted a Kaspersky researcher identified as VitalyK on the company's blog. VitalyK then recommended that users download PhotoRec, an open-source file-recovery utility that runs on Windows and other operating systems.

Kaspersky Lab's analysis of Gpcode.ak has been expanded to include step-by-step instructions on how to recover files the Trojan horse deleted but that actually remain on the drive. The company also crafted a second utility, dubbed "StopGpcode," that finishes the work PhotoRec starts by restoring the filenames and folder organization of recovered files.

More than a week ago, Kaspersky proposed a community project that would use distributed computing -- parceling out the work to a large number of PCs -- to try to crack the 1,024-bit RSA public key used to encrypt the files. The company also created a special forum dedicated to the project where researchers and users can trade information.

Some researchers, including Danchev, have criticized Kaspersky's talk of cracking the key. Today, for example, Danchev called the job "futile" in a blog entry of his own, but he applauded Kaspersky's new approach of recommending file recovery as "reasonable."

Kaspersky's VitalyK acknowledged that his company had made no progress in cracking the encryption key. "It's not possible to decrypt files encrypted by Gpcode.ak without the private key," he said.

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