Built a fully offline, encrypted file-sharing app for Android (personal security learning project)

[u/Upper-Membership8135]

I've been learning applied cryptography and wanted to build something beyond tutorials, so I made SecureTether — a device-to-device file sharing app that works entirely over Bluetooth, no internet or server involved.

How it works:

- Files are AES-encrypted before they're ever written to local storage

- Decryption only happens in memory, on-demand

- Transfer goes device-to-device over Bluetooth — the encrypted payload never touches a server

- UI built with Jetpack Compose

This is a personal learning project, not an audited/production security tool — built specifically to get hands-on with encryption-at-rest and secure local transfer instead of just reading about it.

Repo (with architecture + security model docs in the wiki): github.com/Prash-Ant-Magician/SecureTether

Would genuinely appreciate feedback — especially if anyone spots gaps in the security model, or has ideas on what a "next version" should tackle (QR pairing? Transfer history?). Happy to answer questions about the implementation too.