Kaspersky Lab succeeded in thwarting previous variants of Gpcode when Kaspersky virus analysts were able to crack the private key after in-depth cryptographic analysis. Their 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.
At the time of writing, Kaspersky researchers are 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 changes the extension of these files to ._CRYPT 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:
In addition, after GPcode encrypts files, it also displays the message shown below:«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»
In this case, Kaspersky researchers recommend that victims try to contact us using another computer connected to the Internet. DO NOT RESTART or POWER DOWN the potentially infected machine.
Kaspersky Lab offers some help:
Kaspersky Lab analysts are continuing to analyze the virus code in search of a way to decrypt the files without having the private key.Contact us by email at email@example.com and tell us the exact date and time of infection, as well everything you did on the computer in the 5 minutes before the machine was infected:
∙ Which programs you have executed,
∙ Which websites you have visited, etc.
We'll try and help you recover any data that has encrypted.