I'm not surprised that no suggestions have been offered so far, because as I have mentioned, I've done lots of searching and have come up with nothing, myself.
I'm willing to consider an alternative: does anyone know of an Android text editor or file manager that allows the editing of encrypted files, and whose encryption (not necessarily GNUPG-based) is also manageable (decryption and encryption) by software that runs under Linux? I want to be able to edit encrypted files under Linux and to edit those same files under Android (after I have transferred them to Android). And I want to perform the same function in the opposite direction: i.e., edit encrypted files under Android and edit those same encrypted files after transferring them to Linux.
I want this to be file-by-file encryption, not filesystem encryption such as encfs. And the files must be encrypted and decrypted locally without any access to anything in the cloud.
I know how to incorporate any encryption/decryption mechanism under Linux into emacs, so the Linux-based encryption doesn't need to be part of an existing text editor. However, on the Android side, I need the encryption/decryption to be built into a text editor or file manager.
Thank you for any suggestions.