The following content was written by krogothmanhattan on December 26, 2020, 06:38:43 PM in the thread Offline signing your paper wallet using air gapped phone via Electrum. It was archived as part of the Informative Bitcointalk Posts Initiative. All content is owned by the author of the bitcointalk.org post. (original)
One of my most favorite ways of storing bitcoin is on a paper wallet. Paper wallets if done right are one of the most secure ways of storing bitcoin especially if done on an air gapped computer which in my opinion is a must.The tricky part is when the time comes to sweep the wallet and that is where screwups can happen. If your computer or phone has a malware or virus infecting it, then chances are you can lose your bitcoin.
One way to prevent this from happening is to never expose your private key to a hot wallet or the internet, but rather have it signed using an airgapped device with a wallet on it.
We will be using Electrum and to make sure you have the right Electrum, you can read about it on this thread I wrote on another way of siging a BTC transaction where people brought up ways to make sure your electrum download is not tainted in anyway. https://bitcointalk.org/index.php?topic=5106013.0 www.electrum.org
I will use cell air gapped cold wallet to cell hot wallet
So in this setup we will have a cellphone and a computer both installed with the latest version of Electrum.
These are the steps I took….
Wipe out all data on cellphone and have it reboot with factory reset, thus cleaning it of any malware or viruses.
Install Electrum and then place it in Airplane mode, disable wifi, disable bluetooth, remove sim card and also remove the antenna thus making it air gapped.
Creating new wallet as follows…..
Click NEXT then name your wallet
Next create new password
The select type of wallet you are creating..in our case we are importing a public or private key.
So up to this point you can use for both the air gapped and live hot phone electrums.
Click on the camera tab to scan the qr code.
Here I will be importing the private key for the air gapped wallet phone
You can do the same for the HOT LIVE Cell phone wallet, BUT, ONLY IMPORT THE PUBLIC KEY!
On the air gapped phone the OFFLINE will show as there is no connection with any internet signal. Thats exaclty what we want to see.
When clicking receive on both phones, and then request, the public address matching THAT particular private key will show.
The Air gapped and the Hot phone Public addresses should both match!
On the HOW LIVE phone, click click scan and scan qr code of public address you want to send the paper wallet funds to
Then Click amount and send MAX. Always sweep a paper wallet fully!
You can set the mining fees on the app,
Change the method to “Static”, you will be able to set the transaction fee to lower amounts.
Look at the image below. The fee is only 1 sat/byte.
Next click PAY and the following information will show. Here you can check amount of BTC sent, mining fee and most importantly BTC address where bitcoin is being sent
to.
Next click on QR tab and the following RAW UNISGNED TRANSACTION QR code comes up.
Now with your air gapped phone click on SCAN and scan the QR code from your live phone.
This will take your raw unsigned transaction into your cold air gapped phone with the private key to be able to be signed!
This is what will show on your air gapped phone after scanning the QR code from the LIVE HOT phone wallet.
Next click on the sign TAB and the following will come up confirming you want to sign the unsigned transaction.
Once you click on yes, the new window coming up will show you a signed BTC transaction with the address the btc is going to also the amount!
This way you can be sure the btc is going to the BTC address you want it to goto and not some malware altered BTC address!! Also the TX data is also present and
showing.
Now for the final steps of transferring this to your hot phone by clicking on the QR tab on the air gapped phone which will produce a QR code.
Take your live HOT Wallet phone and click on Scan, then scan the QR code from the Air gapped wallet.
The following will show up, and again you can confirm and the information. Once you are satisfied, click on Broadcast and the raw transaction will be broadcast on blockchain and the bitcoin will be transferred from your paper wallet to the BTC addy of your choice.
I hope this helps people understanding how a paper wallet can be swept without ever having to expose the private keys to a HOT wallet.
Again test with a very small amount of BTC until you have it nailed down and feel comfortable in doing this.
Made another visual aid to make it even easier to understand.
or full version here
The following content was written by krogothmanhattan on October 19, 2018, 04:57:14 AM in the thread Offline signing your paper wallet using air gapped phone via Electrum. It was archived as part of the Informative Bitcointalk Posts Initiative. All content is owned by the author of the bitcointalk.org post. (original)
THIS OFFLINE WALLET SWEEP WILL BE USING AN AIR GAPPED PHONE AND A PC ELECTRUM.
Again create the same steps you did with the air gapped wallet as we did in the example above.
Next for the hot wallet on the PC, install Electrum….
STEP 1 NAME YOUR WALLET
STEP 2 CREATE NEW WALLET…SELECT IMPORT BITCOIN ADDRESS
On the hot live PC wallet, we will be importing the public address ONLY
STEP 3 Click on camera tab and scan in front of pc camera
the Public address part of your paper wallet. HIDE THE PRIVATE WALLET, MAKE SURE NOT TO EXPOSE IT TO CAMERA!!
As you notice, if bitcoin word is in front of the address then you need to delete the word otherwise the next button will be greyed out.
STEP 4 Once the public address is on their click on next, a password option is given, if you want to add you can otherwise hit next.
STEP 5 Watch only wallet created meaning the paper wallet public address is on the electrum with no private key which is EXACTLY WHAT YOU WANT! Click OK and the click on the send tab
STEP 6 Click on camera tab on the pay to box, this will activate your computer camera. SCAN the QR code for the public address you want to send all the funds from your paper wallet to. Then click on MAX on the amount line. You should see the full amount of the balance minus miner fees in this box. Then click PAY
STEP 7 You can see you have an unsigned transaction in the highlighted box top left. Also I adjusted the miners fee down to 2 sats in the middle highlighted box.
In the outputs boxe, you can find the public address where the funds will be sent to. SO double check to confirm it is correct, with the amount to be sent as well.
Click FINALIZE
STEP 8 You now have an UNSIGNED transaction ready to be signed on your air gapped phone. Click on export and then show as QR code.
Once the QR raw transaction pops up, scan with you are gapped wallet and the following will come on the screen…
STEP 9 The unsigned transaction scanned into your air gapped phone will be shown. Click SIGN
STEP 10 Confirm signing transaction…Click OK
STEP 11 You can now see on top it says signed and also the transaction ID is shown as well. This is ready to be broadcast as the button is available as well, but since this is an air gapped phone you cannot, so we need to click on the QR code and take back to the live wallet on the PC. Also you can double check amount and pub address where the funds are to be sent to to confirm nothing has changed!!
STEP 12 On laptop Electrum, On top where the tools tab is click on load transaction and then select QR code. This will activate camera, the scan the QR code raw transaction from your air gapped phone.
STEP 13 You will see the identical information you have in your air gapped phone come up. Again double check to confirm all is correct! Once ready, click broadcast and your raw transaction has been sent to the blockchain! The payment sent TX id will pop up as well!
Hope this helped you all, any questions ask!!
To recap…
Cover Image by Erdenebayar Bayansan from Pixabay
