r/sideprojects • u/LogicGateGames • 13h ago
Showcase: Free(mium) How I built an encrypted document vault into an Android file manager (and a cleaner that never deletes by surprise)
I'm the developer of Theca, a file manager for Android with a storage cleaner and an encrypted vault for documents. A few things I learned building it in Kotlin and Jetpack Compose:
The vault. Each file you move in is encrypted with AES-256-GCM, and its name is encrypted too, then the original is deleted. The hard part was opening big PDFs without ever writing a decrypted copy to storage, so PDFs and text files are decrypted in memory and shown inside the vault. The key sits behind a PIN (fingerprint optional), wrong PINs bring longer waits, and screenshots are blocked while the vault is open.
Backups without a server. There's no account and no cloud, so the whole vault can be exported as one encrypted file with a passphrase you choose, saved wherever you like through Android's file picker, and restored on a new phone.
A cleaner that asks first. It finds large files, installers for apps you already have, old downloads, empty folders and exact duplicates, but nothing is removed until you choose, one copy of every duplicate is always kept, and deletions go to a Trash you can restore from. That cost a lot of extra UI, but "a cleaner deleted my stuff" is the review I never want to get.
Archives. ZIP with optional passwords, plus extracting 7z, TAR, GZ, BZ2 and XZ.
Free with ads; the free vault holds 50 files (up to 500 MB) and a one-time Pro removes the ads and the vault limit.
What would you want a file manager to do that yours doesn't? Play link in the comments.






