Kaspersky Lab has informed the public that a new variant of Gpcode, a dangerous encryptor virus has appeared, – Virus.Win32.Gpcode.ak.
Gpcode.ak encrypts files with various extensions including, but not limited, to .doc, .txt, .pdf, .xls, .jpg, .png, .cpp, .h and more using an RSA encryption algorithm with a 1024-bit key. Kaspersky Lab added a signature for Virus.Win32.Gpcode.ak on June 4, 2008.
Kaspersky Lab succeeded in thwarting previous variants of Gpcode, (see Blackmailer: the story of Gpcode on viruslist.com) when Kaspersky virus analysts were able to crack the private key after in-depth cryptographic analysis.
Kaspersky Lab virus researchers have to date been able to crack keys up to 660 bits. This was the result of a detailed analysis of the RSA algorithm implementation. It has been estimated that if the encryption algorithm is implemented correctly, it would take 1 PC with a 2.2 Ghz processor around 30 years to crack a 660-bit key. The author of Gpcode has taken two years to improve the virus: the previous errors have been fixed and the key has been lengthened to 1024 bits instead of 660.
Kaspersky has yet been unable to decrypt files encrypted by Gpcode.ak since the key is 1024 bits long and they have not found any errors in implementation yet. Thus, at the time of writing, the only way to decrypt the encrypted files is to use the private key which only the author has.
After Gpcode.ak encrypts files on the victim machine it adds ._CRYPT to the extension of the newly-created encrypted files and places a text file named !_READ_ME_!.txt in the same folder. In the text file the criminal tells the victims that the file has been encrypted and offers to sell them a decryptor: Your files are encrypted with RSA-1024 algorithm. To recovery your files you need to buy our decryptor. To buy decrypting tool contact us at: ********@yahoo.com
Kaspersky Lab analysts are continuing to analyze the virus code in search of a way to decrypt the files without having the private key. In the meantime, it is recommended that everyone sets their anti-malware solutions to maximum security and takes extra care while browsing the Internet and reading email.