Security Market Segment LS
Wednesday, 11 December 2019 09:39

Security firm warns Ryuk ransomware decryption tool may not work

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Security firm warns Ryuk ransomware decryption tool may not work Image by mohamed Hassan from Pixabay

The security firm Emsisoft has warned anyone hit by the Ryuk ransomware that the decryption tool supplied by the malicious attackers behind Ryuk may no longer be able to decrypt files that have been encrypted.

In a blog post, Emsisoft said this was because those behind Ryuk had made changes in the malware within the last fortnight that resulted in data being corrupted or lost while it was being encrypted on a victim's system.

"In one of the latest versions of Ryuk, changes were made to the way the length of the footer is calculated. As a result, the decryptor provided by the Ryuk authors will truncate files, cutting off one too many bytes in the process of decrypting the file," the company said.

Emsisoft's Brett Callow said that the company had devised a method to decrypt files that had been encrypted by Ryuk.

However for this to work, Emsisoft had to use the decryption key from the tool that the ransomware creators supplied. This meant that anyone who was attacked by Ryuk would have to pay the ransom.

"Most of our decryption tools exploit a weakness in the ransomware’s encryption to recover files," Callow told iTWire. "This tool doesn’t, as Ryuk’s encryption doesn’t have any weaknesses.

"What we do, in simple terms, is pull the decryption key from the tool the bad actor supplies (after the ransom is paid) and put it into our tool. The bad actor’s tool causes data loss; our tool does not."

Any victims needed to make back-ups of the files that were encrypted by Ryuk in order for this method to work. "If you’ve paid for a decryptor but have yet to use it, either back up your files before running it or get in touch with us instead," Emsisoft advised.

"Our tool will enable you to safely recover your data whereas the tool supplied by the bad actors will not."

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Sam Varghese

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Sam Varghese has been writing for iTWire since 2006, a year after the site came into existence. For nearly a decade thereafter, he wrote mostly about free and open source software, based on his own use of this genre of software. Since May 2016, he has been writing across many areas of technology. He has been a journalist for nearly 40 years in India (Indian Express and Deccan Herald), the UAE (Khaleej Times) and Australia (Daily Commercial News (now defunct) and The Age). His personal blog is titled Irregular Expression.

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