Are bitcoin core psbt and electrum psbt cross compatible?

[Joe-Bloggs]

Hi, I would like to understand a little more about the bitcoin core wallet and if it is cross compatible.

Is it possible to create a watch only wallet in electrum . Feed in the public address of a bitcoin core cold wallet.
Create a psbt with the electrum watch only wallet and save to file.   Then where it says load psbt file in bitcoin core v21 just load in that electrum generated file?

Is that dangerous or perfectly fine and long as the change address is the same as the sending address?
Are psbt created with electrum cross compatible? Some people say yes some say no. I don't know who is correct and I can find no mention of importing an electrum watch only wallet generated psbt file into a bitcoin core wallet.

If that is possible and you can sign on the airgapped bitcoin core wallet you can then somehow export the signed tx in hex format and send on the internet enabled full bitcoin node?

I just want some others opinions on feasibility of this process.

Also, this may seem a strange question. But when you create a bitcoin wallet years ago then you also encrypted it with a long password.
If someone only has that password but no access to the wallet.dat file then your coins are safe even if they have the public address?
How can keyloggers steal peoples bitcoins if they can see the password you will type but they can not grab the wallet.dat file?
Or do keyloggers also easily take that wallet.dat file off your machine easily?

Thanks.

[BitMaxz]

I'm also interested to know I haven't tried it yet but someone answered your question in your previous thread.
Check them here https://bitcointalk.org/index.php?topic=5487691.msg63769874#msg63769874

I heard that it only works on the latest version if your current Bitcoin core is v21 you might need to upgrade it to the latest version to make sure the unsigned PSBT generated from Electrum will work on Bitcoin core.

[Joe-Bloggs]

I'm also interested to know I haven't tried it yet but someone answered your question in your previous thread.
Check them here https://bitcointalk.org/index.php?topic=5487691.msg63769874#msg63769874

I heard that it only works on the latest version if your current Bitcoin core is v21 you might need to upgrade it to the latest version to make sure the unsigned PSBT generated from Electrum will work on Bitcoin core.

Perhaps you have now revealed a reason some says yes and some say no.

2 persons have said it is fine to load electrum generated  psbt into bitcoin core.
And 2 have said this can cause problems but didnt say why or what problems.

Maybe that explains the reason.

Those that tried it and said it works fine perhaps only used the very latest version?

I don't want to touch the airgapped machine at all so installing the very latest bitcoin core is not something I can test.
I want to test this on the v21 but I wonder if I can cause some issue that I can then not rectify after.

I suppose I could try it and compare the signed output hex with the hex signing on an electrum wallet produces.
Then if both are exactly identical it is proven to work with zero possible issues?

Or am I still missing deeper potential  issues?

[Zaguru12]

Also, this may seem a strange question. But when you create a bitcoin wallet years ago then you also encrypted it with a long password.
If someone only has that password but no access to the wallet.dat file then your coins are safe even if they have the public address?
How can keyloggers steal peoples bitcoins if they can see the password you will type but they can not grab the wallet.dat file?
Or do keyloggers also easily take that wallet.dat file off your machine easily?

There is no way to that someone without the wallet.dat file can steal your bitcoin but it will be risky to still have bitcoin on a wallet like that when you think one of your security has been compromised. As for public keys they certainly cannot be use d to restore any wallet. Just like the name they are expose even when you broadcast transactions. Aside restoring your wallet from the file only private key or seed phrase can be use to restore your wallet.

[nc50lc]

-snip- I don't know who is correct and I can find no mention of importing an electrum watch only wallet generated psbt file into a bitcoin core wallet.

It's easy to test this with "TestNet" since Electrum wont have to sync the test blockchain to do that and Bitcoin Core will remain offline in your use-case.

To start Electrum in testnet, you either start it using with the command line argument --testnet
or (exclusively in) Windows, create a shortcut and add --testnet after "Target" in the shortcut's 'Properties'.
You can get free test coins in various testnet faucets.

Take note that you may have to finalize the (fully signed) PSBT in Bitcoin Core using finalizepsbt command for it to be converted into raw transaction to be compatible with other broadcasting tool/sites/wallets.
If to another online Bitcoin Core, the fully signed PSBT in the GUI will work.

Is it possible to create a watch only wallet in electrum . Feed in the public address of a bitcoin core cold wallet.
Create a psbt with the electrum watch only wallet and save to file.   Then where it says load psbt file in bitcoin core v21 just load in that electrum generated file?

As I've said in the other thread, yes:

Here's a demonstration:
(I've used RegTest Bitcoin Core and TestNet Electrum so the bech32 address' format is different but keys and transactions are compatible)

In watch only Electrum that contains an address from Bitcoin Core, create a transaction and export it as file in the next window, "Share->Save to file".
(don't use 1sat/vB if legacy, this is just a demo)


Load the psbt file to Bitcoin Core, Sign it with "Sign Tx" and then Export it using "Save...".


Load the signed PSBT file to Electrum and you should be able to broadcast it.


But as my note above implies, some script types may require you to finalize it first using the said command.

[Joe-Bloggs]

Thanks nc50lc for taking time to make this excellent guide.
I hope other people who want to move funds from their offline wallets and dont know exactly how to make the descriptors code can also find this guide very simple way to spend some of their funds.

Using electrum watch only to make the correct inputs outputs and fees for a tx
Then input to bitcoin core ( so dont need to go through all the dump priv key or even install electrum on offline machine if they dont want to.
Then sign with offline core wallet. Export signed tx and can spend on watch only electrum or on a synced up bitcoin core.
Sounds good.

I

I may do another experiment using clipboard and not using files with bitcoin core.
Because I notice with electrum when you use clipboard outputs and not save to files.
This keeps everything in hex. Which is just numbers and letters.
When you save to files instead it adds extra symbols like//++ other stuff I think psbt is an unsigned tx but with some different way to code it.

The nice thing about just hex is that if you break that long hex string in 3 and fit on one page without sideways scroll.
You can take a picture on your phone and depending which phone you have it can turn that picture into a text file.
So you dont need to transfer anything physical off from the offline machine.
Just a photo. Then use phone to turn back to hex file with built in OCR.

So you can then type decoderawtransaction in bitcoin core to check all the details
If it looks good then sendrawtransaction.

This could be a reasonable solution for the novice who wants to move some btc from offline machine that just has bitcoin core but no electrum already installed there.
 
This process only requires the skill to download electrum to an internet connected machine and copy in the address you want to send from to make the watch only wallet. Then make a send tx and save to psbt file. Take that on usb to you offline machine and load psbt into core.
Sign it and save as file, to transport back to the online full node to broadcast, or broadcast on electrum watch only to broadcast.

Some people say it is unsafe to USB files on and off a airgapped machine. Because sometimes inside the usb bios can be a virus. You can't even see it on the files of the usb. Even formatting cant always remove it.

So perhaps 2 ways to mitigate this I have been thinking about.

1. You can usb on to the airgapped machine the psbt from electrum but then format that usb or even chuck it away if it is just a couple dollars small usb.  Then take a photo and OCR on phone of the signed raw hex output, to test by decoderawtransaction. Before sending.

2. If you're great at touch typing of have a lot of bitcoins then you may even consider
If it is possible for you to export the unsigned tx you made in electrum not by a file but by clipboard and get in raw hex.
Then copy it by just typing it all into your offline machine. Dont make a mistake though.

That is if you really dont want any single physical contact with usb or anything with the airgapped machine.

I have not tried 2. I'm not to great at typing without looking at the keyboard.

Also Zaguru12

Thanks it's good to know they need password and dat file.

This information makes me think signing with core on airgapped machine is safer than importing priv key to electrum.
Because even if a keylogger could sneak the private key out of the airgapped machine or the password encrypting the dat file on a qr code. I dont think it can sneak the wallet.dat off this way.

If anyone can notice any problems with my process then please say.

[Pmalek]

I have never been a fan of overcomplicating things and trying to come up with non-traditional systems. It's one thing to be interested in learning and experimenting. That's ok. But creating an unorthodox setup increases the risk that you took a wrong step somewhere which could prove costly. Both Electrum and Bitcoin Core can run as hot or cold wallets. All the user has to do is to pick one or the other. There really is no increase in security to combine the two. And perhaps it can cause compatibility issues of some sort in the future.

[nc50lc]

Because I notice with electrum when you use clipboard outputs and not save to files.
This keeps everything in hex. Which is just numbers and letters.

That only applies to exported fully signed raw transactions.
Even the file export (.txn) shows the same hex characters when opened as text.

If unsigned, Electrum will export it in PSBT format, via save to clipboard (base64) or file export (.psbt).

If anyone can notice any problems with my process then please say.

Cold-storage Electrum setup supports QR Code export and scan,
That essentially fulfills your main goal to eliminate the usage of flash drive in your setup.

Is there any particularly reasonable explanation why you must use Bitcoin Core in your Air-Gap machine instead of another offline Electrum?

[Joe-Bloggs]

Thank you yes .


That only applies to exported fully signed raw transactions.
Even the file export (.txn) shows the same hex characters when opened as text.

If unsigned, Electrum will export it in PSBT format, via save to clipboard (base64) or file export (.psbt)


Ah yes you are correct it only works on the signed tx. Thanks.



Cold-storage Electrum setup supports QR Code export and scan,
That essentially fulfills your main goal to eliminate the usage of flash drive in your setup

Yeah I'm confused why I get a warning that qr code can not contain all the data of the psbt unsigned tx.
When I scan it on the airgapped machine it gives a warning yellow triangle says cant put the fees and it can be maliciously changed.

When I transfer on usb it works fine and no warning.

Is there any particularly reasonable explanation why you must use Bitcoin Core in your Air-Gap machine instead of another offline Electrum?

Well only that I was wondering if I could avoid doing a dumprivkey to core to put that into electrum. The wallet.dat was made in core and even a key logger could only see my passphrase to sign at the moment and I think if it could slip out a passphrase hopefully it could not slip out a wallet.dat

I'm able to scan qr code for signed as it seems all the info can easily fit inside.

So I can use the airgapped electrum but at the moment I still have to bring the unsigned psbt with usb so I guess there is some danger something slips in to the airgapped machine.  

I probably shouldn't use that usb again even though I do format it straight away as soon as I used the psbt from it  

Someone suggested to me you can break the unsigned data into parts and make several qr codes but I got lost on his idea.

Thanks for pmalek also for warning about possible issues in the future I will work on a way for electrum only until broadcast rawtx at then end from full node.

[Pmalek]

Yeah I'm confused why I get a warning that qr code can not contain all the data of the psbt unsigned tx.
When I scan it on the airgapped machine it gives a warning yellow triangle says cant put the fees and it can be maliciously changed.

I think it's telling you that there is a possibility that someone could change and try to manipulate the transaction. That doesn't mean it will happen. After all, it's you creating it and you broadcasting it afterwards. Why don't you try the entire process with a small amount of a few dollars to see if it will work. Create a $5 BTC transaction on your online machine, bring it over to your airgapped computer for signing, and finally broadcast it on the online computer. 

I probably shouldn't use that usb again even though I do format it straight away as soon as I used the psbt from it

Good idea. Use it only as a communication medium between your hot and cold wallet and format it every time on either end if you are worried about catching malware.  

Someone suggested to me you can break the unsigned data into parts and make several qr codes but I got lost on his idea.

That's again adding new complexities to the transaction creation process that don't need to be there.

[Joe-Bloggs]

Yeah, I'm not certain what it means about the fees being later maliciously adjusted.

Seems strange.

Does it mean.

A. If you had 10 bitcoins in your wallet someone could charge the entire 10btc in fees
Even though only want to send 0.01btc to the recipient and want to spend 0.0002 in fees.

B. That when you have signed it to allow 0.01 btc out of your wallet then it could just use up that entire amount in fees.

I dont actually know what it means.

I dare not test it with a small tx because it may mean it can absorb the entire balance and use it as fees.

When you look at a raw signed hex in bitcoin core wallet with the decoderawtransaction command.
Where do you see the fees?

I can only see the vout for the recipient and change.
I don't see on the bitcoin console where it shows the fees.

I believe someone said you can just calculate that when you take the recipient and change from the balance.
But on electrum it shows the fees in the console expressly.

I'm not sure why but the yellow triangle just seems to be worrying.
It says it can only be maliciously changed until signed. But I'm signing it straight away.

[fasttimes]

Is there any particularly reasonable explanation why you must use Bitcoin Core in your Air-Gap machine instead of another offline Electrum?

not answering for OP, but i would prefer to use only btc core for a cold wallet. is there a a straightforward and secure way to do this? having to use electrum or sparrow or any other software/hardware with btc seems to add surface area and complexity to the process.

[nc50lc]

Is there any particularly reasonable explanation why you must use Bitcoin Core in your Air-Gap machine instead of another offline Electrum?

not answering for OP, but i would prefer to use only btc core for a cold wallet. is there a a straightforward and secure way to do this?

Certainly, but not as straightforward as Electrum Cold-Storage but not too complex either.
The procedure are: create the offline wallet, export the descriptors, create the online watching-only wallet, import the descriptors.

You can refer this post for the steps: http://bitcointalk.org/index.php?topic=5392824.0
If you're using v26.0, the first step to select "descriptor" isn't unavailable due to being selected by default; the rest of the steps are still applicable.
But instead of selecting only one script type, I'd suggest to import all 4 script types to the watching-only wallet, that's a total of 8 descriptors.

[Pmalek]

Yeah, I'm not certain what it means about the fees being later maliciously adjusted.

Seems strange.

Does it mean.

A. If you had 10 bitcoins in your wallet someone could charge the entire 10btc in fees
Even though only want to send 0.01btc to the recipient and want to spend 0.0002 in fees.

I have never heard of such an attack or read about someone suffering from it. I remember seeing mentions of maliciously altered fees, but that's all. I don't know how it's possible to modify a transaction that was already signed by a private key that only you have access to. Wouldn't such a modification require access to the signing keys because it's different transaction data @nc50lc? In that case, you would need to ask yourself who has got your private keys?

[fasttimes]

Certainly, but not as straightforward as Electrum Cold-Storage but not too complex either.
The procedure are: create the offline wallet, export the descriptors, create the online watching-only wallet, import the descriptors.

You can refer this post for the steps: http://bitcointalk.org/index.php?topic=5392824.0
If you're using v26.0, the first step to select "descriptor" isn't unavailable due to being selected by default; the rest of the steps are still applicable.
But instead of selecting only one script type, I'd suggest to import all 4 script types to the watching-only wallet, that's a total of 8 descriptors.

thank you. is having a watching only wallet not a security risk?

[nc50lc]

-snip-

thank you. is having a watching only wallet not a security risk?

No, as long as you don't compromise even a single private key from your air-gap wallet.
Otherwise, the only risk is your privacy in case the watching-only wallet's extended public keys are compromised.

As a heads-up, Bitcoin Core already taken the necessary precaution against that by disallowing the exportation of individual private key from a descriptor wallet.
There are workarounds to do so but be aware that the "extended private key" pair of the watching-only wallet's "extended public key" can be computed from any of its child private key.
So if you ever require to export a key for whatever reason, do everything exclusively in the same air-gap machine where the offline Core is installed.