Issue signing transactions with QR code

[leeroyspenken]

Hi everyone, I am trying to use a webcam to sign a transaction using QR codes and I ran into an issue. After reading the first QR code with webcam and signing the transaction on my cold storage device (bootable usb with tails), I displayed the new QR code up so I could load it on to watch-only address and broadcast it.

My watch-only address is currently being ran on Electrum 3.0.6 with Windows 10 and it appears the zbar reader is not installed for me. When I go and try to load from QR code it says "Cannot start QR scanner; zbar not available".

Is there a way I can use zbar on windows 10 or do I need to get another bootable USB with an OS that supports it?

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[leeroyspenken]

1 last thing i want to add, if I use a site like https://webqr.com/ is it safe for me to just get the text file from the signed QR code then load from text in my watch-only address on electrum and broadcast?

[pooya87]

i have never used zbar so i am not sure but according to the readme on their repository https://github.com/ZBar/ZBar/blob/master/README.windows#L72-L76 it shouldn't be a problem to install it on any windows.

1 last thing i want to add, if I use a site like https://webqr.com/ is it safe for me to just get the text file from the signed QR code then load from text in my watch-only address on electrum and broadcast?

as long as the only thing you are giving that website is your transaction hex (signed or unsigned) you are fine because there are no sensitive information in it and you are broadcasting it anyways.
and that tool can not change it or give you a wrong result (for example in case of a bug read the QR wrong) and put you in any kind of trouble because if anything is wrong in a transaction it will become invalid since you have signed it.

[Ayanamirs]

Try with Linux.

[HCP]

My watch-only address is currently being ran on Electrum 3.0.6 with Windows 10 and it appears the zbar reader is not installed for me. When I go and try to load from QR code it says "Cannot start QR scanner; zbar not available".

Did you not see the following note on the Electrum download page?

Note: The QR code scanner is not supported in Windows binaries

Is there a way I can use zbar on windows 10 or do I need to get another bootable USB with an OS that supports it?

zbar is available for download and install, but it doesn't seem to be compatible with Python:

>>> libzbar = ctypes.cdll.LoadLibrary('libzbar-0.dll')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Program Files\Python36\lib\ctypes\__init__.py", line 422, in LoadLibrary
    return self._dlltype(name)
  File "C:\Program Files\Python36\lib\ctypes\__init__.py", line 344, in __init__
    self._handle = _dlopen(self._name, mode)
OSError: [WinError 193] %1 is not a valid Win32 application

...even though you can run zbar just fine from the commandline?!?? Apparently, this is usually indicative of the .dll being compiled for 32bit architecture... and Python being 64bit...  


As for your alternative idea... the QR code should load up fine using a QR Code scanner (like webqr.com)... However, the data in the QR Code is stored as a Base43 encoded string... that is to say, it looks something like:

Code:

E:W-P131.RRM+R91DWWMGE0EQRXD:+879DLKFM.S2C9T/XZP:ZV8RV-*/H*X93O44A+1HS-J1F6:D266RS.Z8O9AYSJ*278CCUQ2H4Z6YWM9CTH66YH6MXFSJ3H7-YBASEABDYWOYGW5K.X0CG4QP6BKDUTWE.1B9MBWT68*B4EGKSWPLPQ2N2/8FW1WCC4:J3/:O7$0+N20QGS*OBXE9:RIQ8U/.MYC.75G*S$6DHA*YEVM3/$VRMT3$/1TNN:.XTN1.Z7:1JZWWTQ7$PG7EOZ:T8O-*PMNUOKN0NBT/CT*.JRU69PYTUI3MQK3-VL.4LCUCM2++YS:

Decoding this to raw hex is not exactly a simple task... by stepping through the Electrum Python code (and a bit of trial and error)... It is possible to get this to convert to:

Code:

0100000001e90bbe1976e7056eca27ea7a280948c17be71cd6f9936c16d4a7afddcb1ac31f010000006b483045022100c4afaa26eecb143927815969f5b409647d7fcbc24f5456f69f80e0ca631a6fa802200f537578611a9d14fb13e37f962a161c6a24ec5a356d26a0db4659d0fc2b77480121028087725567ce3b2395d019b430d9948dd7a91508a32d69d649cc4c1f67cd50b3ffffffff0218b39d00000000001976a91400a99b3e32116afa227b180c26dd03a0fcd7dce588ac319e0a00000000001976a914bcb55f0e60f9859de8a6467f9fcab69745028bf688ac00000000

Honestly, if you're set on using QR codes, for now you'll most likely need to use another OS.

[Saint-loup]

Hello it seems that a dev has just committed a solution yesterday.

But he's now looking for someone able to test the fix.

https://github.com/spesmilo/electrum/issues/6018

It would be good if someone who can reproduce this crash could test with master now.