What is the GDCB file format?
A .gdcb file is a document, photo, or other file that was encrypted by version 1 of the GandCrab ransomware. When the malware runs, it scrambles the file's contents and adds .GDCB to the end of the name, so budget.xlsx becomes budget.xlsx.GDCB. It also drops a ransom note called GDCB-DECRYPT.txt into every affected folder.
GandCrab appeared in late January 2018 and spread through the RIG exploit kit. Version 1 encrypted files with AES-256 and protected the key with an RSA-2048 public key, then demanded payment in Dash cryptocurrency through a Tor site. Only version 1 used .GDCB; later versions switched to .CRAB and .KRAB extensions.
Security & safety
RISK: HIGHA .gdcb file itself is inert encrypted data, but its presence means a machine was compromised by GandCrab ransomware. The malware executable that created it is dangerous and may still be active, so disconnect the device, remove the infection with an anti-malware tool, and only then decrypt. Never pay the Dash ransom; a free decryptor exists for GandCrab v1.
Format details
in a nutshellPrograms that open GDCB files
Windows4 apps
Bitdefender GandCrab Decryption Tool
Free Run the free decryptor to reverse GandCrab v1 encryption and restore the original file from a .gdcb copy; it removes the .GDCB extension once decryption succeeds.
No More Ransom Crypto Sheriff
Free Upload a sample .gdcb file and the GDCB-DECRYPT.txt note to confirm the GandCrab variant and get pointed to the correct free decryptor.
Malwarebytes
Freemium Scan and remove the active GandCrab infection first so files are not re-encrypted before you attempt to decrypt any .gdcb files.
Windows File History / System Restore
Built-in Recover clean copies of affected files from a backup or restore point created before the infection instead of decrypting the .gdcb files. Technical details
deep spec| Encoding | Original file contents encrypted with AES-256 (Cipher Block Chaining) in GandCrab v1; the per-file/per-machine AES key is wrapped with an embedded RSA-2048 public key held by the attackers. |
| Byte order | Not applicable (encrypted ciphertext) |
| Container | The original file is overwritten/replaced with ciphertext and renamed with a trailing .GDCB extension (e.g. photo.jpg becomes photo.jpg.GDCB). |
| Encryption | AES-256 (CBC) for file data plus RSA-2048 to protect the AES key; later GandCrab versions (v4, v5) switched file encryption to Salsa20. |
| Typical size | Roughly the same as the original file plus a small amount of padding/metadata. |
| Structure | Renamed copy of the victim's file containing encrypted bytes; a plain-text ransom note named GDCB-DECRYPT.txt is dropped into every folder that has encrypted files. |
| Integrity | None exposed publicly |
| Platforms | Windows |
| Notes | GandCrab v1 was the first GandCrab release and the only one that used the .GDCB extension. It spread from late January 2018 through the RIG exploit kit via the Seamless malvertising campaign, and demanded payment in Dash cryptocurrency through a Tor payment site. Bitdefender, working with Europol and Romanian police, released a free decryptor for v1 in February 2018. |
| Ransom Note | GDCB-DECRYPT.txt |
| Malware Family | GandCrab (Ransom.GandCrab) |
| Released | January 2018 |
GDCB conversions
Community Q&A
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