bitcrypt

Technical Breakdown:

1. File Extension & Renaming Patterns
   • Confirmation of File Extension: Files encrypted by Bitcrypt receive the secondary extension “.bitcrypt” (e.g., budget.xlsx.bitcrypt).
   • Renaming Convention: When Bitcrypt encrypts a file it keeps the original filename and primary extension intact and merely appends .bitcrypt. The overall path is otherwise unchanged, which can help users quickly distinguish encrypted files from originals when offline backups are compared.

2. Detection & Outbreak Timeline
   • Approximate Start Date/Period: Bitcrypt was first documented in underground forums around July 2014 and reached its peak distribution in Q3–Q4 2014.

3. Primary Attack Vectors
   • Key propagation methods observed:
   – Malicious e-mail attachments pretending to be Adobe Flash Player updates or fake invoices.
   – Drive-by downloads from compromised websites serving the “Trojan.Bitcrypt” payload via exploit kits such as Angler and Nuclear.
   – Manual installation by operators via cracked Remote Desktop Protocol sessions (especially when weak or reused credentials are in use).

Remediation & Recovery Strategies:

1. Prevention
   • Disable RDP from public-facing interfaces or enforce IP whitelists + multi-factor authentication.
   • Apply 2014-era Windows patches (MS14-058, MS14-066) and keep Adobe Flash/Java run-times up-to-date; Bitcrypt’s older binaries rely on CVE-2014-6332 in Internet Explorer and Flash CVE-2014-0515.
   • Segment networks and disable SMBv1 (it won’t stop Bitcrypt directly but limits any secondary locker movements often seen by the same actors).
   • Backup strategy: weekly full + daily incremental backups to an offline or immutable repository (Veeam with hardened Linux repo, AWS S3 Object Lock, etc.).

2. Removal (step-by-step)
   a. Isolate the infected host (pull cable / disable Wi-Fi).
   b. Identify and kill the malicious persistence:
   – winlogon.exe, %APPDATA%\Roaming\Updater\csrss.exe (common Bitcrypt filenames).
   – Registry run-keys: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\csrss
   c. Boot into Safe Mode with Networking.
   d. Run a reputable offline scanner (Kaspersky Rescue Disk or Bitdefender BD-LiveUSB) to quarantine Trojan.Win32.Bitcrypt.
   e. Once malware binaries are confirmed removed and quarantined, change all local and domain passwords from a clean machine.

3. File Decryption & Recovery
   • Recovery feasibility: Fortunately, Bitcrypt used a flawed implementation of the AES-256—RSA-1024 hybrid scheme. In 2014, ESET released an official decryptor (still hosted on live ESET servers today).
   – Download “ESET Bitcrypt decrypter” (requires original healthy copy of at least one sample file + matching encrypted version to brute-force the per-victim AES key).
   – Launch from an Administrator command prompt, point to the target directory and the corre­sponding ‘clean’ file; the tool will auto-restore the private AES key and decrypt all .bitcrypt files.
   • There is no paying: the C2 domains seized in late 2014, making ransom notes unreachable; do not attempt to pay.

Crucial Tools/Patches
• ESET Bitcrypt Decryptor (current v1.1.0).
• Microsoft KB3002657v2 (patches the LPE employed by some 2014 bitcrypt droppers).
• Java 7u80 or later / Flash Player 32 or later.

4. Other Critical Information
   • Unique attributes: The ransom note (INSTALL.aes) falsely claimed 256-bit AES encryption, but analysts quickly discovered the insecure padding oracle that enabled key recovery.
   • Broader impact: Primarily targeted home users and SMBs in Europe and the US; considered a precursor to newer ransomware-as-a-service families thanks to its polished payment portal that later inspired copycat operators.