Fix Data Encryption Module Failure 0x80071771

Quick answer: Run certmgr.msc → Personal → Certificates. If your EFS certificate is missing or expired, back up any encrypted files then delete and reissue the certificate via cipher /rekey. Then restart.

This error shows up when you try to open an encrypted file or folder and Windows can't find the encryption key it needs. What's actually happening here is the Encryption File System (EFS) uses a certificate tied to your user account to encrypt and decrypt files. If that certificate gets deleted, corrupted, or the user profile gets rebuilt (common after a domain rejoin or Windows reinstall), the system throws 0x80071771: Data Encryption Module Failure. You'll see this most often when opening a folder you encrypted years ago, or after IT rolled back your domain account.

Fix Steps

Check your EFS certificate
Press Win+R, type certmgr.msc, hit Enter. Expand Personal → Certificates. Look for any certificate with File Encryption or EFS in the Intended Purposes column. If you see one, skip to step 3. If it's missing or shows Expired, continue to step 2.
Back up encrypted files
Before touching certs, copy any files you can't open to an external drive. Use robocopy /MIR or just drag them—they'll copy as-is. If they're encrypted, the copy won't help, but it's a safety net.
Reissue your EFS certificate
Open an admin Command Prompt (cmd as Administrator). Run:
```
cipher /rekey
```
The /rekey switch tells Windows to generate a new EFS certificate and re-encrypt any files that can still be accessed. This command works because EFS stores a backup of the file's encryption key in the file header—if the key is still readable, the new cert can decrypt it. It won't help if the original key is gone, but it's the first thing to try.
Restart and test
Reboot your machine. Try opening the encrypted file again. If it works, you're done. If not, move to the alternative fixes.

Alternative Fixes If the Main One Fails

Use the Data Recovery Agent (DRA)
If you're on a domain, your admin might have a DRA certificate set up. Only they can decrypt the file. Contact IT and ask them to use EFS DRA to recover the file. This is the only way if the original cert is completely gone and no backup exists.
Restore from an EFS certificate backup
If you ever backed up your EFS cert (you'd have a .pfx file), double-click it, select Current User, and import it into the Personal store. Make sure to check Mark this key as exportable for future backups.
Decrypt using a different user account
Log in as another user with admin rights. Run cipher /rekey from that account—it won't decrypt files from the original user, but it lets you at least access the folder structure. Then use takeown and icacls to reset permissions, then delete the encrypted files if they're unreadable.
Last resort: format and restore from backup
If the files aren't critical, delete them. If they are, you need a backup from before the cert went missing. EFS is tied to the user SID and cert—once corrupted, data recovery tools won't help because the encryption is key-based, not password-based.

Prevention Tip

Back up your EFS certificate the day you first encrypt anything. Run certmgr.msc, find your EFS cert, right-click → All Tasks → Export. Choose Yes, export the private key, set a strong password, save the .pfx file to a USB drive or password manager. Store that drive somewhere safe—if you lose that cert and the file key, those files are gone forever. Also, regularly run cipher /rekey every 6 months to refresh the cert and re-encrypt files with the latest key.