Cold wallet for android

Question

Android

At the moment, there are a lot of hardware crypto wallets - trezor, ledger, coolwallet s, etc. Among them, a very good option caught my eye - Ellipal ( https://www.ellipal.com/pages/coldwallet ), it's something like a smartphone, but without bluetooth, Wi-Fi and Internet access. Those. a private key is stored on the device, and transactions are signed using QR codes. Because the device is proprietary, it is very difficult to say if there is a backdoor there - perhaps a hidden radio module has been introduced, perhaps hidden information is transmitted through QR codes ... So, there is an idea to do something like the same, but opensource based on a cheap android smartphone - in- the first is cheaper, and secondly there is at least some control. For this you need:
1) A library for working with various cryptocurrencies (using a BIP39 phrase to generate private keys, a public list of addresses, a transaction signature) - who knows if there is something ready? It seems that there is a list of disparate modules for nodejs, but it is not clear which of them is better and more reliable.
2) A library for generating and reading QR codes - there are standard ones, there seems to be no problems with this ..
3) We need a way to disable the radio module on the smartphone at the iron level - bluetooth, wifi, lte, 3g, etc. - I have not found this yet either ... if only to disconnect the antenna, but this is unreliable.
By the way, this idea is also for signing transactions of ordinary online banks such as Sberbank, VTB, etc. - now it's all too unreliably implemented through SMS codes ...

Answer 1

I’m doing exactly what you haven’t thought of yet (there are interesting solutions to emerging problems)
1) yes
2) yes
3) I’ll hint - why do you need modules at all if you are going to disable them?

Answer 2

The Electrum wallet has ready-made tools for working offline and broadcasting a signed transaction, for example, using sound. I'm not sure though that all these charms work on the android version, but yes on the desktop.