Offline wallet (Electrum) + Trezor not signing transactions

Question

When I want to make a transaction I follow these steps

• Create order in the ONLINE computer
• Copy transaction to a USB
• Plug USB to OFFLINE computer
• Load transaction from file
• Plug TREZOR
• Sign transaction

But during the signing process an error popups with a message similar to "Unable to connect to servers ". In my opinion it makes no sense, it is supposed to be an offline wallet. There is no need of a server to sign the transaction. ¿Am I wrong?

As far as i know, both computers use the same Electrum version (2.8.3)

Answer 1

Well, yes, sortof. Signing a transaction requires the scriptPubKey from the transactions that funded the source addresses, and if you don't have a copy of the blockchain there's no way to get that information.

I believe Armory handles this by including the necessary information in the data it gives you to take offline, but Trezor apparently does not, and does not considers this use case "redundant."

that's normal. Trezor requires the list of input transactions. your offline wallet did not have them and tried to fetch them.

we will not fix that. the list of previous tx will no longer be needed with segwit.

Electrum issue

If you wanted to work around this issue, you could modify the Electrum plugin to load the necessary info from, e.g., a text file instead of trying to use the internet. The place you would need to change is shown in this post (.../plugins/trezor/plugin.py).