Karl Bonenberg

Electronic Safe

How to make your passwords really secure? How to protect your precious bitcoins?

Technologies: #Android #Tasker #Bash #GPG

About

Let’s say you have some really precious data : passwords, crypto, sensitive documents. You don’t want to keep them on your PC. You don’t trust encrypted cloud storage. You don’t even trust the popular electronic wallets. You don’t want to use pen and paper for obvious reasons.

Well, it’s time to get to the next level: turn your old mobile phone into a custom made electronic safe. *


Process

Things you will need:

  • An old mobile phone with full disk encryption
  • A sturdy phone case, preferrably a wallet type
  • Heat-resistant epoxy glue (to prevent malicious desoldering)
  • A universal wireless charging receiver with USB input to block the phone’s port
  • Mini jack cable for encrypted backups to your PC (optional)
  1. Turn on the phone’s encryption, set up a password. I recommend diceware.
  2. Download a password manager e.g. Keepass2Android
  3. Create a new password database (kdbx), set up a different password.
  4. Turn on airplane mode (it will stay on for ever)
  5. Remove phone’s case
  6. Mount a wireless charging receiver and glue the USB input to the phone’s port
  7. Put lots and lots of glue around the phone before you put the case back on
  8. Mount the case, wait for the glue to dry

Here you go, the build is almost complete. The device is protected from an evil maid attack, mobile forensics devices, and makes desoldering difficult due to heat-resistant epoxy resin. If you want to be able to make backups via the only port left available (mini jack!) you need to do a bit more.

First of all, I recommend to download tasker app. You can then create an automated task that will detect a jack cable plugged in and then additionally encrypt your kdbx database with gpg, zip it, and start transmitting to other device using Quiet for Android. Maximum transfer speed with this method is about 64kbps so it may take a while.

* While it is never impossible to hack anything, the amount of time and effort required to get into this safe is colossal. Overall, it is a very cost efficient solution to keep your data secure.