Wallet keys should be stored in a hardware wallet, but hardware wallets are difficult to use, especially with mobile devices. So, we came up with a solution to use the SIM card as the hardware wallet.
An overlay SIM card with a custom Java SIMGap applet as the hardware wallet, it stores the keys and signs transactions.
An APP (MetaMask fork) as the user interface to show it can be integrated and work with existing software.
See the video demo at the bottom.
As mentioned, the APP is forked from MetaMask to show how existing software can work with the SIMGap hardware wallet with only minor changes. The APP does not store or access keys, it obtains user input for the transaction and sends the transaction details to the SIMGap hardware, the wallet keys are stored in the SIMGap and the SIMGap wallet does the signing.
APP used in video: GitHub - TaisysTeam/metamask-mobile