Zero-Cost Cold Storage: Turn an Old Phone into an Air-Gapped Wallet⁠

[Son $f Grace]

The buying of hardware wallet like Ledger or Trezor can really be expensive most especially In Nigerian here when you factor in shipping and customs fees.

But also for you to be keeping your Bitcoin savings on the same one phone that you use for everyday activities do also exposes you to malware, phishing and other online risks.

There is this low cost alternative that is really worth understanding. Turning your old spare phone into an offline Bitcoin signing device, using QR codes to transfer transaction data.

What an air gapped wallet?
This a wallet setup where the device that holding your private keys stay offline. This very device doesn’t in any way connect to the internet whether to check balances or send transactions.

Instead make use of two phones.
1.You need an offline phone that will hold your private keys and signs transactions.

2.Your everyday online phone which uses a watch only wallet to check your balance and prepare transactions.

This two devices exchange transaction information through QR codes. With this your seed phrase doesn’t need to leave the offline phone.

Quick setup on how this works

1.Prepare the spare phone
You going to factory reset the old phone you are going to be dedicating for this purpose. So now gree that you are going to download blueWallet from the official source before disconnecting it from the the internet.

2.Disconnecting it from the internet
You are going to remove the SIM card,turn on Airplane More and then of your wifi and Bluetooth. Make sure all this are turned off than also in your BlueWallet also enable Offline Mode on the network settings.

 3.Generating your wallet keys
With the phone offline create a new Bitcoin wallet. Make sure you write down the recovery phrase and store it very securely offline. Then you export the wallet XPUB as a QR code.

After than, you scan that QR code with BlueWallet on your other everyday phone to create a watch only wallet. This will help you veiw your balance and prepare transactions without exposing your private keys.

4. Sign transactions using QR codes
If you want to send Bitcoin:
• your online phone will prepare an unsigned transaction and it will display it as QR code.
• Then next your offline phone scans the QR code and signs the transaction.
•Then this offline phone will display the signed transaction as a QR code.
• Then your online phone scans it and broadcasts the signed transaction to the Bitcoin network.
And note this !!! Before signing make sure you carefully check the recipient address and also the amount on the offline device.

Very important security considerations
This very setup can really reduce your exposure to remote attacks but this not automatically as secure as that of a dedicated hardware wallet. Cause this offline phone can actually still be stolen or even physically compromised and its software must be trustworthy. For your recovery phrase needs a proper offline backup also.

And BlueWallet has an official guide explaining this very setup :
https://bluewallet.io/docs/offline-cold-wallet/

My question for the community
Have you turn your old smart phone into an offline Bitcoin signing device before ? And again do you thing that this a reasonable low cost option for anyone who can’t afford or import a hardware wallet or are we going to still recommend that you save up for a dedicated hardware wallet ?

Let share our opinion

[PostQuantumBTC]

The problem I had with phone is that I was unable to remove the Bluetooth and Wi-Fi, but I needed a device that both the Bluetooth and Wi-Fi can be removed. What I later did was that I used my HP laptop that I bought 2 years ago which was second hand, format it and use it for the airgapped device that I installed Electrum. I wanted to sell it before, but this forum let me know how useful it can be.

[promise444c5]

What if it has an ESIM ? Well most old phones shouldn’t have an ESIM if truly we are trying to follow the standard “old”..

My point is that , you can’t fully turn a mobile device to / trust a mobile phone as - a cold storage but the process can be better than having it on a phone that connects to the internet. But the device connects to the internet once again to download the blue wallet according to your Setup .  

I could have said  a local connection to move the file downloaded on a different device to your device but again you need to trust the other device isn’t screwed either or maybe I’m just being paranoid now ..

You missed the important aspect of verifying the signature [this one is for Electrum though]

[PostQuantumBTC]

What if it has an ESIM ? Well most old phones shouldn’t have an ESIM if truly we are trying to follow the standard “old”..

I am not of the opinion of advising anyone to use phone but esim can be disabled, deactivated or deleted.

My point is that , you can’t fully turn a mobile device to / trust a mobile phone as - a cold storage but the process can be better than having it on a phone that connects to the internet. But the device connects to the internet once again to download the blue wallet according to your Setup . 

You can use type c flash drive or USB stick and do it the traditional way.

I could have said  a local connection to move the file downloaded on a different device to your device but again you need to trust the other device isn’t screwed either or maybe I’m just being paranoid now ..

It is airgapped, no malware can affect it if you let it remain offline. No best way but the chance of having malware is low and the chance of malware affecting you offline is nearly zero if you do not go online. This is the reason I prefer airgapped laptop that can make me achieve the device to be permanently offline.