Encrypt files and folders on Android with a password

To protect private photos, documents or videos on your Android phone with a password, select them in Solid Explorer and tap Encrypt. Solid Explorer encrypts them with AES-256 using a key derived from your password, and turns them into a .sec file or an encrypted .sec folder. To open them, you tap them in Solid Explorer and type the password (or use your fingerprint). Encrypted files can be copied to another phone, an SD card or cloud storage and opened there with Solid Explorer and the same password. There is no desktop app for them, and a forgotten password can't be recovered by anyone, including us. Creating encrypted files and folders is a Pro feature; opening and decrypting them is free.

Before you start

• Choose a password you won't forget. There is no password hint, no reset and no recovery. If you forget the password, the files can't be opened.

• Keep it under 100 characters. Longer passwords aren't accepted.

• Encrypting needs Solid Explorer Pro (holders of the older one-time license have it too). Opening, browsing and decrypting existing .sec files works in every version of the app, without Pro.

Encrypt files or a folder

1. In Solid Explorer, long-press a file or folder to select it. Tap more items to add them to the selection.

2. Open the selection menu and tap Encrypt.

   • The File Encryption window opens. Fill in:

     Password and Repeat password.

   • Remove source files. Check this to delete the original, unencrypted files after they're encrypted. Leave it unchecked to keep both.

   • Use biometrics. Shown only if a fingerprint or face is set up on your phone. Check it to open these files with your fingerprint or face later, on this phone (see "Open with your fingerprint instead of the password" below).

3. Tap Encrypt.

The progress is shown like any other copy or move. When it's done, the encrypted item appears next to the originals with a lock icon.

One file becomes a single encrypted file with .sec added to its name, next to the original. For example, photo.jpg becomes photo.jpg.sec. The file name itself is not hidden: anyone who sees the file can read photo.jpg in its name.

Several items, or a folder, become an encrypted folder whose name ends in .sec. Inside it:

• every file is encrypted separately,

• every file and folder name is encrypted too, so nobody can see what's inside without the password,

• your folder structure is kept.

Encrypted files show a lock icon instead of a thumbnail. Solid Explorer doesn't create previews of them, so no image of their content is stored anywhere.

Open encrypted files

A .sec file: tap it and enter your password when you see Please enter the password. The file opens decrypted on the fly. Nothing decrypted is written to your storage.

A .sec folder: tap it and enter the password. The folder opens and you can browse it like any other folder: open, copy, rename and delete files inside it.

Encrypted videos play in Solid Explorer's own player or can be streamed to other video player apps as long as the container is open.

Decrypt files

To turn encrypted items back into normal files, select the .sec file or folder and tap Decrypt, then enter the password.

• The decrypted copy is created in the same folder as the .sec item.

• The encrypted original is kept. Delete it yourself if you no longer need it.

• A single file loses its .sec ending, so photo.jpg.sec becomes photo.jpg again.

Open with your fingerprint instead of the password

When you check Use biometrics (in the File Encryption window or in the password prompt), Solid Explorer stores the password securely on this phone only, so you can open the files with your fingerprint or face from then on.

This is a convenience, not a second key:

• It works only on the phone where you turned it on. On another phone, or after reinstalling Solid Explorer, you have to type the password.

• Solid Explorer can't show you the stored password.

• If you change your fingerprints or face unlock, Android may invalidate the stored password, and you'll need to type it again.

So you still need to remember the password.

Move encrypted files to another phone, SD card or the cloud

The key is calculated only from your password and data stored inside the encrypted file or folder itself. Nothing is tied to your phone. You can:

• copy .sec files and folders to an SD card, a USB drive, a PC, cloud storage (Google Drive, Dropbox, OneDrive…) or a backup,

• open them on another Android phone with Solid Explorer and the password,

• open them again after reinstalling Solid Explorer or resetting your phone.

A few things to keep in mind:

• Copy an encrypted folder completely, including any hidden files in it. Don't copy only some of its contents.

• Moving or renaming the whole .sec folder with other apps (or on a PC) is fine. So is moving or renaming files inside it, as long as you don't change their encrypted names. A file whose encrypted name was changed (for example a sync app's conflict copy such as name (1)) shows up as unreadable.

• Keep Solid Explorer up to date on every device that opens your encrypted files. Files and folders encrypted with the current version can't be opened by older versions, which report "The password is incorrect". Adding files to a folder that was encrypted with an older version updates the folder, and after that older versions can't open it either.

• Use biometrics doesn't move with the files. Type the password on the new device.

Can I decrypt the files on my PC?

There's no official desktop app for .sec files. They can only be opened with Solid Explorer on Android.

If you need the files on a computer, decrypt them on your phone first and then transfer them:

• Decrypt first, then transfer: select the .sec items and tap Decrypt. Then move the decrypted files to your computer in any way you like, for example with WebFS (your phone's files in a web browser) or the FTP server. These two serve the files exactly as they're stored on the phone, so a .sec file or folder sent through them stays encrypted. Decrypt it first.

• Copy straight out of an open encrypted folder: if your PC has a shared folder added in Solid Explorer, open the .sec folder in one panel and the shared folder in the other, and copy. Files copied out of an open encrypted folder are written decrypted.

If you want them encrypted again afterwards, delete the decrypted copies and keep only the .sec original. Remember that decrypted copies on a PC are no longer protected by Solid Explorer.

If you forget the password

The password can't be recovered or reset. There is no hint, no backdoor and no master key, and NeatBytes support can't open your files for you. That's what makes the encryption meaningful, but it also means a lost password means lost files.

One exception: if you turned on Use biometrics for those files, you can still open them on that phone with your fingerprint or face. Do this right away, while it still works:

1. Open the files with your fingerprint.

2. Either Decrypt them, or create a new encrypted folder with a new password and move the files into it.

What encryption protects, and what it doesn't

Encryption keeps the content of your files private: without the password, nobody can read them, even if they copy them off your phone or out of your cloud storage.

It doesn't hide everything:

• File sizes are visible. An encrypted file is 36 bytes larger than the original.

• Names of single encrypted files are visible. For example, photo.jpg.sec shows the original name. To hide names, put the files in an encrypted folder instead.

• Changes aren't detected. Encryption protects confidentiality, but it doesn't check whether someone modified or damaged an encrypted file. A damaged file decrypts to damaged content, without an error. Keep backups of important files.

• Removing source files is a normal delete. It's not a secure wipe. On the flash storage of phones and SD cards, deleted data may still be recoverable with special tools. For very sensitive files, avoid storing them unencrypted in the first place: move them straight into an open .sec folder.

• Open files are decrypted in memory while you use them, as with any encryption app. Close them when you're done.

Troubleshooting