HEXSecure

To get much more features and more advanced security, check out HEXSecure Full! It includes hash/checksum algorithms, password safe and AES file encryption. This app might not receive more updates!
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If you like this app, please buy HEXSecure Full, which allows you to encrypt larger files (>2MB) and disables the ads! HEXSecure Full is much smaller, doesn't use the internet permission, has hash algorithms and contains a password safe and many more!
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This application is designed to encrypt smaller files or simple text. It is the improvement of the old app TXTEncrypt, with better algorithms, and more user-friendly and modern interface. This app uses non-standard, algorithms, which makes it suitable for encrypting sensitive data. Though the strength of these algorithms is not officially tested, they seem to be quite strong.
You can choose between 5 algorithms, which have similar bases. The strongest one is "Threedog2", which is also used for the encryption of the files. A pro version is available from now, it disables the ads, and enables the encryption of larger files (>2 MB) If you would like to enjoy the more advanced features like the password safe and the checksum algorithms, buy HEXSecure Full version.
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Usage:
If you encrypt a text, the result will be copied to the clipboard of your device, which means, that you have to go to the desired place, (for example open the SMS application, Messenger or Notebook) and paste the text. (long-press on the field, and choose the paste button in the "floating" menu)
If you decrypt a text, paste it to the text-field, or write there manually, and enter the correct key, then press the decrypt button.
If you encrypt or decrypt a file, first, press the file chooser button. In the opened window, navigate to the file, which you'd like to en/decrypt, and click on it. Automatically, the file will be saved to the same place with the same name, but a ".encrypted" extension will be added. If the output file already exists, check the overwrite box, to replace it with the new one.
You can share the encrypted text with other app, such as SMS app, Messenger, Email, etc. without having to copy-paste. Just press the share button (next to encrypt) and choose the app you'd like to use. In the free version, you can only use this option only three times! If you buy HEXSecure Pro or HEXSecure Full, you can use this function unlimited times. To decrypt the received encrypted text, press the share button in that app (if there is) and choose HEXSecure (Decrypt text) in the list.
The android.permission.INTERNET is used only by the ads.