BitLocker & Ransomware: Can a Locked Drive be Re-Encrypted?

TL;DR

Generally, ransomware cannot re-encrypt a drive already fully encrypted by BitLocker. However, it can still cause significant damage by encrypting files within the unlocked volume or targeting system boot sectors and other areas outside of the BitLocker protected space. Regular backups are essential.

Understanding BitLocker

BitLocker protects an entire drive (or a partition) at a low level. When enabled, all data written to the drive is encrypted before it’s stored. This means that even if someone physically steals the drive, they can’t access the data without the correct decryption key.

How Ransomware Works

Ransomware typically encrypts files on your computer and demands a ransom payment for their decryption. It targets accessible data – documents, photos, databases, etc. It doesn’t usually try to re-encrypt already encrypted data because it’s redundant.

Can Ransomware Re-Encrypt a BitLocker Drive?

1. Locked State: If the drive is fully locked by BitLocker (e.g., before Windows has booted or after being manually unlocked and then locked again), ransomware cannot access the data to encrypt it. The encryption keys aren’t available, so the ransomware can’t write anything meaningful to the drive.
2. Unlocked State: If the drive is unlocked (e.g., Windows is running and accessing the BitLocker volume), ransomware behaves as normal. It will attempt to encrypt files within that unlocked volume. BitLocker doesn’t protect against this – it only protects data at rest, not while in use.
3. Boot Sector Attacks: Some advanced ransomware strains target the Master Boot Record (MBR) or boot sectors of a drive. This can prevent your computer from starting up even if BitLocker is enabled. This isn’t re-encryption but renders the system unusable.
4. Targeting Unprotected Areas: Ransomware might encrypt files on other drives that aren’t protected by BitLocker, or data in unprotected folders within the same drive (e.g., a network share mounted as a drive letter).

Steps to Protect Yourself

1. Enable BitLocker: Ensure BitLocker is enabled on all drives containing sensitive information. You can do this through the Control Panel or Settings app in Windows.
   • Open Control Panel > System and Security > BitLocker Drive Encryption
   • Select the drive you want to encrypt and click Turn on BitLocker.
   • Follow the on-screen instructions, choosing a strong password or using a smart card. Important: Store your recovery key securely!
2. Keep Windows Updated: Regularly install Windows updates to patch security vulnerabilities that ransomware can exploit.
   • Open Settings > Update & Security > Windows Update and click Check for Updates.
3. Use a Reputable Antivirus/Anti-Malware Solution: A good antivirus program can detect and remove ransomware before it encrypts your files.
4. Regular Backups: This is the most important step! Regularly back up your data to an external drive or cloud storage. If ransomware does manage to encrypt your files, you can restore them from a backup without paying the ransom.
   • Consider using Windows Backup and Restore or third-party backup software.
   • Test your backups regularly to ensure they are working correctly.
5. Be Careful with Emails & Downloads: Avoid opening suspicious emails, clicking on unknown links, or downloading files from untrusted sources.

Checking BitLocker Status

You can check the status of your BitLocker encryption using the manage-bde command in Command Prompt (run as administrator).

manage-bde -status C:

(Replace ‘C:’ with the drive letter you want to check.) This will show whether the drive is encrypted, locked or unlocked.