Researchers crack ransomware encryption

Posted by   Virus Bulletin on   Feb 21, 2014

'Bitcrypt' authors confused their bytes and digits.

Two French researchers have found a serious vulnerability in a new piece of ransomware that has allowed them to crack the keys used by the malware to encrypt the victim's files.

CryptoLocker has become known as the unfortunate crypto success story of 2013. While stories about broken cryptography implementations made the headlines throughout the second half of the year, no one has yet been able to find a serious weakness in this piece of ransomware. Victims who find their files encrypted by CryptoLocker and who do not have a backup of the files are forced either to pay the ransom, or to consider their files lost forever.

Unsurprisingly, CryptoLocker's success has been noted by other criminals, and other pieces of ransomware are trying to use the same method to extort money from their victims. Thankfully, not all of them have the cryptography skills of the CryptoLocker developers.

Fabien Perigaud and Cedric Pernet, two researchers working for Airbus in France, found a friend's computer infected with 'Bitcrypt', a new kind of ransomware. While the ransomware had encrypted all the important files on the computer, a message pointed to a website where a 'recovery application' could be purchased for 0.4BTC.

  When we accessed the page through its .onion domain today, the price had increased to 0.5BTC

When they looked at the malware sample, the researchers found it was using 1024-bit RSA encryption. While this kind of encryption might be crackable by NSA-like agencies, it is beyond the capabilities of ordinary researchers. In any case, the cost of cracking the key would far exceed the ransom demanded by the malware.

However, it turns out that the malware authors did not pay attention during cryptography lessons. While they meant to use a key of 128 bytes (or 1024 bits), they actually used a key of 128 decimal digits. This is equivalent to around 426 bits. Keys of this length were first cracked 20 years ago and these days can be cracked by a standard PC within a day.

As a result, the researchers were able to restore all the encrypted files. More details can be found at their Cassidian CyberSecurity blog here, where they've also made a Python script available that can be used by others to crack Bitcrypt keys.

Of course, authors of other kinds of ransomware are likely to have a better understanding of cryptography. Making sure ransomware has little chance of making it to your computer, and keeping offline backups in case it does, remains as important as ever.

Posted on 21 February 2014 by Martijn Grooten

twitter.png
fb.png
linkedin.png
hackernews.png
reddit.png

 

Latest posts:

First 11 partners of VB2019 announced

We are excited to announce the first 11 companies to partner with VB2019, whose support will help ensure a great event.

VB2018 paper: Fake News, Inc.

A former reporter by profession, Andrew Brandt's curiosity was piqued when he came across what appeared at first glance to be the website of a small-town newspaper based in Illinois, but under scrutiny, things didn’t add up. At VB2018 he presented a…

Paper: Alternative communication channel over NTP

In a new paper published today, independent researcher Nikolaos Tsapakis writes about the possibilities of malware using NTP as a covert communication channel and how to stop this.

VB2019 conference programme announced

VB is excited to reveal the details of an interesting and diverse programme for VB2019, the 29th Virus Bulletin International Conference, which takes place 2-4 October in London, UK.

VB2018 paper: Under the hood - the automotive challenge

Car hacking has become a hot subject in recent years, and at VB2018 in Montreal, Argus Cyber Security's Inbar Raz presented a paper that provides an introduction to the subject, looking at the complex problem, examples of car hacks, and the…

We have placed cookies on your device in order to improve the functionality of this site, as outlined in our cookies policy. However, you may delete and block all cookies from this site and your use of the site will be unaffected. By continuing to browse this site, you are agreeing to Virus Bulletin's use of data as outlined in our privacy policy.