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Two algorithms are used for encryption: RC4 and RSA. Intimidating Dirty wallpaper File encryptionĭirCrypt doesn't encrypt many types of files, mostly documents and photographs. In version 2.0, at the second stage, the trojan checks the availability of a virtual environment or a sandbox: it searches for processes VBoxService.exe, vmtoolsd.exe or downloaded library sbieDLL.dll. The decrypted resource is the final CryptoWall code. At this stage, the resources encrypted with Base64 are decrypted. The third stage commences with execution transfer to the code, which has been placed in the stack. As soon as this place is determined, the data is decoded to stack.
Decrypt crypto locker code#
The second stage of code decryption starts with the byte array (0x35, 0x5e, 0x74) inside the code saved at the first stage. During the first decryption stage, the trojan reads a large part of the encrypted code, decrypts it and saves it to the buffer. The trojan's code has an elaborate multi-level encryption. All names of command servers are embedded directly in the trojan's body, with the transferred data encrypted by the RC4 algorithm. Connection with the command serverĭepending on the modification, connection with command servers may be established either via Tor (for this, tor.exe is downloaded and installed) or through an anonymous I2P network. The RSA algorithm is rather resource-intensive and creates a big load on the system, which may indirectly indicate CryptoWall infection. In contrast to other lockers, CryptoWall encrypts files using RSA-2048 algorithm, while most others use RSA to encrypt the AES key, which the files were encrypted with. xlsxįirst of all, CryptoWall disables file recovery from shadow copies and recovery points, executing the following commands: vssadmin.exe Delete Shadows /All /Quietīcdedit.exe /set bootstatuspolicy ignoreallfailuresĮncryption starts after the public RSA key is received from the C&C server.
Decrypt crypto locker software#
The list of encrypted files is quite big it's not only owners of MS Office documents and photographs who should be aware of this locker, but also software developers. According to some sources, CryptoWall brought its creators more than 1.1 million dollars in the first 6 months of operation. Version 3.0 (despite losing several capabilities as compared to the previous version) has now almost completely replaced version 2.0. This family is also famous for two versions - CryptoWall 2.0 and CryptoWall 3.0. The massive spread of this malware was recorded in the first quarter of 2014, however, according to some sources, the first samples were identified as early as in November 2013. onion domain extension.Ī part of Tor client inside Critroni (command server address and sent commands are highlighted) CryptoWall In summary, it is impossible to decrypt the files without the master-private key, and this key, as we have explained, is stored on a C&C server in the. Thirty-two bytes of session-public and 16 bytes of service information are written at the beginning of the encrypted file for searching the required master-private key on the command server. Then, the session-shared = ECDH (master-public, session-private) value is computed, SHA-256 hash from which is used as key for file encryption with AES-256 algorithm. Session-public and session-private are generated for each encrypted file. The master-private key is sent to a command server and is not saved on the infected machine (it is also encrypted using ECDH and it is impossible to view it when it is sent). To do this, it takes SHA-256 hash from a 34-byte random number consisting of: 0x14 bytes: value obtained through CryptGenRandom functionĠx08 bytes: value obtained through GetSystemTimeAsFileTime functionĠx04 bytes: value obtained through GetTickCount function the encrypted file gets a "ctbl" extension.ĬTB-Locker uses the so called ECDH (Elliptic curve Diffie-Hellman) algorithm.Īt first, Critroni generates two main keys - master-public and master-private.the information needed for decryption is put at the beginning of the file.the compressed block is encrypted and written on the disk.each read block is compressed using the deflate function of zlib library.this temporary file is read off the disk block-by-block.the file selected for encryption is placed in a temporary file using MoveFileEx API function.Critroni (CTB-Locker) in the register's autorun branches File encryptionĬritroni doesn't encrypt many types of files, mostly MS Office documents, text documents and database files.