Quote from: 20kevin20 on April 03, 2021, 09:19:33 PM

The security of your chosen method depends on your habits. Most people have bad habits and generally practice bad security and based on my experience, the more critical your thinking is and the more paranoid you are, the higher the security you'll be looking for.

I'll leave here what I would personally do, since I really think you should always keep a good security practice. The more you don't, the higher your risks of messing up are.

If you want to sweep a paper wallet, the most secure way to do it is on an offline, airgapped PC. For the setup, you basically need three things: two computers (one as the cold, airgapped wallet and one as the online wallet to broadcast your sweeping transaction) and an address to which you want to sweep your BTC.

Take an older PC of yours, remove any wireless modules from it and install a clean Linux distro on it. I'd personally recommend Debian or Ubuntu. If you don't want to install it, then you could use it as a Live CD instead (Live CD means everything you do is wiped upon shutdown/reboot). For Live CDs, I'd recommend Parrot OS which comes with Electrum preinstalled (or Tails). (bonus: I also recommend encrypting your HDD; bonus x2: if your future airgapped PC is old or you want it to run a lightweight distro, install Debian with XFCE). Make sure you verify your install file upon downloading it (Ubuntu verification tutorial; Debian verification depends on the type of download you prefer.

After installing Linux on this offline PC, it's time to download Electrum. Download it from here and verify it.

Installing Electrum
Now you have to install Electrum on both of your PCs (cold and online). If you want extra security, after verifying the file, you can (in descending order based on security as I see it):
- Write the file (and signature, if it has one) onto a CD from your online PC and plug the CD into your now-airgapped computer;
- Plug an SDHC/SDXC card (or a microSD with a SDHC/SDXC adapter if you have one around) into your online PC, put the file on it (and signature, if it has one), unplug it and flip the read-only switch so that your file/card never gets modified. Now plug it into your airgapped PC and copy the file there;
- Plug an USB stick into your online PC (preferably a stick with a read-only switch), put the file (and signature, if it has one) on it, unplug it, flip the read-only switch and put the file onto your now-airgapped PC.

As soon as you have Electrum installed on both PCs, this is what you have to do next:

Step 1. You have to work on your airgapped PC to import the private key or seed into Electrum.
Step 1a. From your airgapped PC, if you have a paper wallet containing a private key:
1. Open up Electrum and, as soon as you're asked what kind of wallet you want to create, check "Import Bitcoin addresses or private keys"
2. Insert your private key in the textbox. Move on to Step 2.

Step 1b. From your airgapped PC, if you have a paper wallet containing a seed:
1. Open up Electrum and, as soon as you're asked what kind of wallet you want to create, check "Standard wallet"
2. Continue by checking the "I already have a seed" option and input your seed into the textbox.
3. After importing your seed, go to Wallet > Information and look for the Master Public Key. It should look something like this:

Code:

zpub6nXwKjUbuUY8BE2ETiErVgkSJZv5F5Ekz76dDFVzsmhNi26sm2WSkgNX4hmLE1c22q3prLJCcgCrkHyijEXsRb5SfNX5HAezmLVdinX1mTh

4. Scan the code using a barcode scanner or, the traditional way I like, write it down on a piece of paper

Move on to Step 2.

Step 2. You have to work on your online PC to import the private key public address or the seed's Master Public Key into Electrum.
Step 2a. From your online PC, if you just imported a private key into your airgapped computer:
1. Open up Electrum. During the Install Wizard, select "Import Bitcoin addresses or private keys".
2. If you have a paper wallet, chances are you have a public address on it. So, depending on this:
2a. If you have the public address, insert it into the textbox.
2b. If you do not have the public address, go back to your airgapped PC's Electrum and click the Receive tab. On the right side of your window, the public address is shown. Write it down somewhere or scan the QR Code (click the QR Code tab for this) and insert the address into the online PC's Electrum textbox. Move on to Step 3.

Step 2b. From your online PC, if you just exported your Master Public Key from your airgapped computer:
1. Open up Electrum. During the Install Wizard, select "Standard wallet" followed by "Use a master key".
2. Insert the Master Public Key into the textbox. Move on to Step 3.

Step 3. Still working on the online PC, you have to create the sweeping transaction and export it:
1. Now you should see your balance in your online Electrum. Go to the Send tab, insert the address you want to send your BTC to and push the "Max" button. Do NOT leave it unchecked or you risk losing part of your funds! Press "Pay...", change the fee rate if you will and then press "Send".
2. In the bottom-left corner of the Transaction window, you have an "Export" button. Click Export > Export to file. After exporting it, either:
- Write the file onto a CD and insert the CD into your now-airgapped computer;
- Plug an SDHC/SDXC card (or a microSD with a SDHC/SDXC adapter if you have one around) into your online PC, put the file on it unplug it and flip the read-only switch so that your file/card never gets modified. Now plug it into your airgapped PC and copy the file there;
- Plug an USB stick into your online PC (preferably a stick with a read-only switch), put the file on it, unplug it, flip the read-only switch and put the file onto your now-airgapped PC.

Step 4. From your airgapped PC, you have to import the transaction and sign it:
1. In Electrum, go to Tools > Load transaction > From file and select the transaction you just copied.
2. Press "Sign" and export the transaction to File again (Export > Export to file..). Copy the file back to your online PC safely. Move to Step 5.

Step 5. Moving back to the online PC, you need to import the signed transaction and finally broadcast it:
1. In Electrum, go to Tools > Load transaction > From file and import the signed transaction file.
2. Press "Broadcast".

There you go. Quite complicated for a newbie, but it's the safest way you can go. From here on, you could safely use the airgapped PC as a cold wallet. Practice good security. It's worth it in the long run.

Thanks. So on the online PC I create a watch-only wallet?