Bitcoin Forum

If you're wanting to use an older version of electrum (like me) this guide will be helpful..

First install electrum on your android device.
Make a new watching only wallet using the master public key from wallet>information>qr. On the phone use standard wallet and master key (not what I did the first time)....
Then get your recipient whoever it is and make an invoice on your phone once its synced.
Back on the computer, press send and click the qr code scanner
load up a qr on your phone to scan.
Once scanned, click preview on your computer then click sign and click the qr
Now scan that qr code onto your phone and hit broadcast.

(my webcam stopped working so I couldn't test this).


If you use the playstore to download apps then what you're going to want to do is go to your files on android and find the apps section and there'll be a section called something like "installers" or "not installed" click that and wait for it to load and find the installer of the corresponding version of your computer.

I'd suggest you use versions beyond 3.1.0 on android to ensure it's compatible with the new servers.

(android can't display the phishing message I don't think it usually doesn't fit error messages on very well and they're not formatted)...

Why would you want to keep using an older version of Electrum?

I don't like upgrading straight away and I'd like to keep that computer offline.

Funny thing is that I created my BitcoinTransactionTool project for the same reasons on top of other things. Basically you are looking for a way to make an unsigned transaction and give it to your cold storage for signing.
I haven't had time to work on it anymore ever since I made it and Electrum has changed a lot, but I'll probably fix its bugs and release the new version this month if I can get the script part of my library finished :P
Feel free to take a look at the code to get the idea (you can find it in my signature).

I remembered of your script and then thought you wouldn't support what I'm trying to do as it's native segwit and a multisig... So it isn't exactly the easiest thing. Although I managed to make a transaction so big it couldn't be represented in a qr code (I think anyway).

It isn't that hard either. I just never knew how scripts worked when I started that project and never gotten around to upgrade it until now.
As for the size, there are certain small changed that can help create a smaller QR code. For example making the hex uppercase would make a big difference. Or you can do what Electrum does and use the Base-43 encoding on it before you turn it into QR.
Base-43 is exactly the same as Base-58 but with these character:

Base43? That's a weird base to use. It's a prime number which means it'll take ages to compute. Saying that we use base58 isn't exactly easy to optimise also...

But multisig with segwit sounds difficult I'm not looking forward to when I start trying to program with it.

that only matters if you are about to do millions of conversions and want them to only take a second. but when you are doing only 1 encoding and do it with a small size byte array (hundreds of bytes not even 1 kB) the speed of such process does not matter.