LAN_PRINT_135: Ransomware Will Win The War
(LAN_PRINT_86 IT Security)
LAN_PRINT_94 NIST.org
Monday 16 June 2008 - 05:57:58
The well respected Antivirus firm Kaspersky Lab is calling for a massive group effort to break the encryption used by the latest Ransomware. They're asking competitors, governments, and cryptographers to join the effort. But even a massive worldwide computer grid won't win this war.
The malware being battled is called Gpcode. Gpcode is a Trojan that is sent through email or posted on USENET newsgroups. The infected attachment is a MS Word .DOC file and most users still think DOC files are safe to open. When its run it encrypts the users documents.
"The email had an MS word .doc file called anketa.doc attached. (Anketa is the Russian for application form). This file actually contained a malicious program called Trojan-Dropper.MSWord.Tored.a. When the recipient opens the attachment, a malicious macro installs another Trojan - Trojan-Downloader.Win32.Small.crb - on the victim machine." - Virulist.com
Gpcode searches for over 80 different file types on the computer and encrypts them. Besides the normal document files Gpcode also encrypts the users email database files. The program leaves behind a text file instructing the person how to contact the author to purchase the decoder program. The program also deletes references to its self. Gpcode has gone through several revisions, the encryption keys in previous versions was found relatively quickly because of flaws in how the author implemented the encryption. This latest version, first reported on June 4th, 2008, apparently does not have these flaws and all efforts to date to find other such shortcuts to crack the encryption key have failed.
"Different versions of the Gpcode virus encrypt user files of different types (.doc, .txt, .pdf, .xls, .jpg, .png, .cpp, .h etc.) using a strong RSA encryption algorithm with different key lengths. After encrypting files on a computer, the virus automatically generates a message informing the user that the files have been encrypted and demanding payment for a decryption utility." - Kaspersky Lab
Even if Kaspersky manages to find a weakness in the current encryption implementation and finds the encryption key eventually this author (or someone else) will get it right. To date no one has broken a 1024 bit RSA encryption key (what Gpcode currently uses). They have broken a "special" 307 bit key but not a true "proper" 307 bit RSA key. Even that effort took years to accomplish. The last time they broke a proper 155 bit key it took 9 years and quite a bit of computing power. One of the best known cryptanalyst, Bruce Schneier, says that the writing is on the wall for 1024 bit keys and eventually they will be broke. So even if Kaspersky wins this battle they won't win the war against ransomware.
"I hope RSA applications would have moved away from 1024-bit security years ago, but for those who haven't yet: wake up." - Bruce Schneier
If Kaspersky's group can not find a shortcut it will take a massive amount of computing power to accomplish something no one has done before them. In one respect it will be quite an accomplishment, but in reality it really doesn't help much. By the time they break the encryption key the author will have moved on to another key, perhaps one using a 2048 bit key (which is currently well outside the bounds of being able to be broken in our lifetime). Or perhaps the author will switch to AES encryption which is orders of magnitude stronger than RSA. From the ransomware author's point of view switching to a synchronous AES key does present some practical problems with key distribution but they aren't impossible to overcome.
Though there is currently no way to break the encryption used by the Gpcode Trojan Kaspersky does have instructions for restoring some files encrypted by Gpcode. Gpcode currently encrypts a copy of the file and then deletes the original, therefore it may be possible to undelete the original (unencrypted) file. But don't count on getting much back because deleted files will quickly get overwritten by new encrypted files. Your best defense to any unknown threat is a good backup, then you can simply delete the encrypted files and restore them from backup (after removing the infection). Of course keeping MS Office and your antivirus application up to date can help as well.
There are many experts that believe Kaspersky Lab is wildly optimistic in believing that a 1024 bit key can be broken anytime soon. Let us hope Kaspersky is not successful because whenever you visit a SSL webpage it first connects using a RSA 1024 bit key (in order to securely exchange a synchronous RC4 or AES key to encrypt the data). If RSA encryption can be broken quickly anyone using standard SSL certificates will need to upgrade. Previous data transmitted over SSL that may have been recorded will be at risk of compromise.
References:
Kaspersky Lab - Press Release announcing the launch of the Stop Gpcode international initiative.
Schneier on Security - Bruce Schneier's blog. He's 'The Man' when it comes to encryption.
Crypto boffin: writing is on the wall for 1024-bit RSA - The Register: "The largest proper RSA number yet broken was a 200-digit "non-special" number whose two prime factors were identified in 2005 after 18 months of calculations that used over a half century of computer time. The 1024-bit numbers used in RSA encryption are around 100 orders of magnitude bigger than this. The writing may be on the wall for 1024-bit RSA: but as yet, um, nobody can read it."
Virulist.com "Blackmailer: the story of Gpcode" - "Gpcode then scans all accessible directories and encrypts files with certain extensions such as .txt, .xls, .rar, .doc, .html, .pdf etc. It also encrypts mail client databases."
Ransomware resisting crypto cracking efforts - SecurityFocus: "While previous versions have had flawed encryption implementations, the latest version -- Gpcode.ak -- appears to have eliminated the flaws that allowed reverse engineers to find earlier keys."
Kaspersky to try to crack code used in 'blackmailer' virus - CNET.com: "Antivirus software vendor Kaspersky is launching an international effort to try to crack the encryption used in a "blackmailer" virus that locks up data on a victim's computer."
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