Decrypting a file in Windows allows you to access data that has been encrypted and transformed into unreadable ciphertext. There are a few different ways to decrypt files on Windows depending on the encryption method used. In this comprehensive guide, we’ll walk through the steps for decrypting files encrypted with BitLocker, EFS, ransomware, zip/archive files, and VeraCrypt.
Decrypting BitLocker-Encrypted Files
BitLocker is the built-in full-disk encryption tool included in certain versions of Windows. It is used to encrypt entire drives to protect data in case a device is lost or stolen. If you need to access BitLocker-encrypted files on a drive, you’ll need to provide the correct decryption key.
Requirements for BitLocker Decryption
- The encrypted drive must be connected and recognized by Windows
- You must have the 48-digit recovery key used to encrypt the drive
- BitLocker must be turned on for the drive (it cannot be suspended or off)
Decrypting the Drive with the Recovery Key
If you have the recovery key, decrypting the drive is straightforward:
- Open the BitLocker control panel (search for it or find it in System and Security)
- Click “Manage BitLocker” and select the encrypted drive
- Click “Unlock Drive”
- Enter the 48-digit recovery key and click Unlock
Once unlocked with the recovery key, the drive will be fully decrypted and accessible. All files on the drive will be readable.
Decrypting without the Recovery Key
If you don’t have the recovery key, decryption is still possible but more complex. Here are a few options:
- Use the recovery password if you set one up during encryption
- Unlock the drive from another user account that has permission
- Take the drive to a tech professional for specialized decryption
- Perform a full system restore to a time before encryption was enabled
As you can see, not having the recovery key makes decryption very difficult. This is intentional to prevent unauthorized access.
Decrypting EFS Encrypted Files
The Encrypting File System (EFS) is another encryption method built into Windows. It encrypts files and folders individually rather than full drives.
Requirements for EFS Decryption
- The encrypted files must be on an NTFS-formatted drive
- You must have access to a private key or recovery agent certificate to decrypt the files
- The EFS feature must be enabled on the Windows machine
Using Your Private Key to Decrypt
If you encrypted the files with your own Windows user account, you can decrypt with your private key:
- Navigate to the encrypted file/folder in File Explorer
- The icons will appear with a lock symbol indicating encryption
- Double-click to open – Windows will use your private key for transparent decryption
You can also right-click, select Properties, and click “Advanced” to explicitly unlock EFS files.
Using a Recovery Agent Certificate
If you don’t have the original user’s private key, you can still decrypt by obtaining a recovery agent certificate. This special certificate is created explicitly for decrypting files when keys are lost.
To decrypt with a recovery agent certificate:
- Obtain the .PFX certificate from the recovery agent
- Import it into your Personal certificate store
- Right-click the encrypted file, Properties, Advanced, select your certificate, and click OK
The files will then decrypt with the recovery agent’s private key.
Decrypting Ransomware-Encrypted Files
Ransomware is malware that encrypts your personal files and demands payment for the decryption key. There are several ways you may be able to decrypt ransomware encrypted files without paying the ransom:
Restore from Backup
If you have an unencrypted backup from before the infection, you can restore your files from there. This is the best and simplest option if you have backups available.
Use Antivirus Decryption Tools
Many antivirus vendors have released free decryption tools for popular ransomware strains. Tools are available from Kaspersky, Avast, McAfee, and others. Run a tool to check if it works on your files.
Find a Decryptor Online
Third-party decryption tools are also available online for many types of ransomware. Sites like NoMoreRansom.org offer tools for ransomware victims.
Unlock with a Recovery Key
For some ransomware infections, security researchers are able to find flaws in the encryption algorithms used by the malware authors. This allows them to retrieve the master decryption keys. These may be made publicly available for free decryption.
Do a System Restore
On Windows, doing a system restore to a date before the infection will restore your files to an unencrypted state. Only possible if System Restore was enabled.
As you can see, options are available for decrypting ransomware files without paying. But restoring from backup is by far the most reliable method.
Decrypting Encrypted Zip/Archive Files
Encrypted zip or archive files like 7zip, RAR, and WinZip files can also be decrypted on Windows. This works much like decrypting EFS files.
Requirements
- The zip/archive software used to encrypt the contents
- The original password or encryption key used to encrypt the archive
Steps to Decrypt
- Locate the encrypted archive file
- Open the zip software and select the file
- Enter the encryption password when prompted
- The archive will decrypt with the provided password
If you get the password wrong, the archive will fail to decrypt. Only with the proper encryption password will the contents unlock.
Decrypting VeraCrypt Encrypted Volumes
VeraCrypt is a popular open-source disk encryption tool. It lets you create encrypted containers or encrypt entire drives. Here’s how to decrypt VeraCrypt volumes on Windows.
Requirements
- VeraCrypt installed on your Windows machine
- Access to the encrypted volume file or drive
- The original passphrase used to encrypt the volume
Steps to Decrypt a VeraCrypt Volume
- Open the VeraCrypt application
- Click Select Device and choose the encrypted volume
- Click Mount and enter your decryption passphrase
- The volume will mount decrypted as a new drive letter
If you enter the wrong passphrase, mounting will fail and encryption will be maintained. The correct passphrase is required for decryption.
How to Recover Encryption Passwords and Keys
In many cases, decryption is only possible if you have the original encryption key or password used to encrypt the files. If you’ve lost the key, these tips may help you recover it:
- Search old emails – encryption keys are often emailed for backup
- Check password manager apps like LastPass
- Look for written backups like sticky notes or notebooks
- Try recalling context around when it was created
- Use password cracking/recovery software (caveat – this is very difficult)
Preparing backups of encryption keys is crucial to avoid losing access to encrypted data. Store them somewhere secure like a password manager or physical safe.
When You Cannot Decrypt
In some cases, decryption is simply not possible unless the original key or password can be recovered. If you cannot find the key through any means, here are your options:
- Keep trying password guesses if you have some ideas what it may be
- Use data recovery specialists who may have capabilities beyond consumer tools
- Accept the data as lost if encrypted with strong methods like BitLocker
Encryption provides very robust protection when the keys are properly secured and managed. This makes recovery extremely difficult by design if keys are ever lost.
Conclusion
Decrypting encrypted files in Windows is possible if you have the proper keys, passwords, recovery agents, or backups available. Understanding the encryption method used, whether BitLocker, EFS, ransomware, VeraCrypt or others, will guide you to the proper decryption steps. While challenging at times, decryption is nearly always feasible with the right information and techniques.
