The somewhat surprising move this week by the operators of the TeslaCrypt ransomware sample, to cease operations and publicly release the universal master decryption key for it, is good news for victims of the malware.
It now means that they have a way to unlock data that might have been encrypted by TeslaCrypt. But the move, welcome as it is, doesn’t necessarily mean that the group won’t simply release another sample or start afresh with a new malware campaign altogether, security researchers warned.
Slovakia-based ESET, which has been tracking TeslaCrypt for the past several months, recently noticed an announcement from the group behind the malware of its decision to cease operations. A security researcher at ESET reached out anonymously to the group via its support channel for victims, and asked for the master decryption key. “Surprisingly, they made it public,” the company announced on its blog.
ESET has released a free decryption tool based on the master key that it says can unlock files that were encrypted by any variant of TeslaCrypt. The company has provided instructions on how to use the tool at its ESET Knowledgebase website.
In comments to Dark Reading, ESET security researcher Lysa Myers says it’s unclear what prompted the change of heart within the TeslaCrypt group. “While it’s possible that the authors felt remorse, it’s also possible that they’ve decided to shut down this codebase in favor of starting fresh,” she says.
At the same time though, it does not necessarily mean that the group has suddenly decided to give up writing malware or even that they have abandoned ransomware campaigns, she cautions.
Similar things have happened in the past, she says. As one example, Myers pointed to an incident last year where someone purporting to be the creator of the Locky ransomware sample, apologized for activating the tool and publicly released a decryption key for the malware on PasteBin. Interestingly enough, a year later, Locky continues to be active and is actually the most widely distributed ransomware sample in circulation.
Importantly, releasing the master decryption key does not mean the threat actors behind TeslaCrypt have abandoned malware altogether.
“The most likely scenario is that authors could start fresh with a new codebase, learning from their previous efforts, and then begin infecting people again,” Myers says. “People who were previously infected with the older variant would be an obvious target, as they’ve [shown themselves] to be vulnerable.”
Engin Kirda, co-founder and chief architect at cybersecurity firm Lastline says that without direct information from the group behind TeslaCrypt, it is only possible to speculate on their motives.
“In reality, it could be anything,” he says. “It might be that they are moving to a new, illegal online business, or it might be because they are concerned that the authorities have some concrete evidence against them.”
According to Kirda, the mere fact that the master key was publicly released does not mean that TeslaCrypt’s operators cannot resume their operations using new keys and new infectors. “Typically, it is easy to shut down an operation by malware authors, and just as easy to restart it.”
It is also possible that the TeslaCrypt group could start using multiple encryption keys for locking data, so while some data can be released other data might remained encrypted.
“Whatever happens is only limited by the imagination of the malware authors and what they really plan to do,” Kirda says. “We have also seen cases in the past where malware authors have done things just to have fun with security professional such as choosing easily guessable passwords and providing wrong information.”
Recap On TeslaCrypt
TeslaCrypt was one of those that first added PayPal My Cash cards as a payment method, in addition to Bitcoins.
TeslaCrypt became known because it not only encrypted the usual document and image files, it also targeted video game-related files associated to Call of Duty, Minecraft, League of Legends, and Steam among others.
So far, there has been four versions of TeslaCrypt. It was first discovered in February 2015, and the latest one identified in March 2016.
In the first version, although it said it used RSA-2048, it was in fact using AES encryption. The encrypted files will have the .ECC extension in their filenames.
The second version of TeslaCrypt, TeslaCrypt 2.0, came out sometime in July 2015. This version claimed to still use the RSA-2048 algorithm, even if it used AES. The extensions for the encrypted files were changed to, for example, .VVV or .ABC. The ransom demand also changed. It came up in three different formats: an HTML page, text file, and an image within a wallpaper or in photo gallery. The difference between these two versions were visible in the text and also look of the ransom message. It added the titles and chapters to make reading easier. The new ransom demand also removed the countdown payment.
TeslaCrypt 3.0 was discovered in January 2016. TeslaCrypt 3.0 claimed it used RSA-4096 for encryption, but still uses AES. However, this version used a different encryption key exchange algorithm which made the encryption more difficult to break. Another difference in this version was the use of extensions such as.MP3, .XXX, .TTT or .MICRO for the encrypted files. The HTML ransom message was the same as in TeslaCrypt 2.0, but the text file format had some slight changes as seen below. Version 3.0 included the link to Google Translate and the “What does this mean” line was removed.
TeslaCrypt 4.0 is the latest version of the TeslaCrypt ransomware family. It was first seen sometime in March 2016. One of the biggest differences between this version and the older ones is that 4.0 doesn’t use file extensions like .VVV or .MP3 for the encrypted files. Also, in the older versions, there was a bug that encrypting files over 4GB of size ended up being corrupted. In this version that bug has been fixed. It also tries to search for more information about the victim’s computer and send that information back to the criminal network.
TeslaCrypt 4.0 again claims that it uses RSA-4096 encryption, but still uses AES. The look of these ransom demands has not changed but the text underwent quite a lot of changes between this version and TeslaCrypt 3.0. For example, 4.0 uses “What’s the matter with your file” whereas 3.0 used “What happened to your files”. TeslaCrypt 4.0 also added back the “What does this mean” line from version 2.0.