Isn't it possible to use an offline PC to sign the transaction using electrum+trezor and broadcast the transaction on a online PC
I too thought that was possible, but it's not.
It is not necessary. The point of the trezor is to be the offline computer.
Thanks, but I know. Offline Trezor usage is not what I'm interested in, protecting the chain of public keys is. My bad, I didn't leave the quotes for the whole discussion in the post.
Why are so keen in protecting your Extended Public key? Please educate me. I was under the impression that only protection of the Private keys was important.
Yep, privacy.
1. The 3rd parties who broadcast your Trezor transactions for you necessarily know the xpub (and possibly the entire public key seed too). That information could be used to discover all the money you have/had with that Trezor seed.
2. If you want to use "Sign in with Trezor", depending on the way that scheme is implemented, could also reveal xpub or public key seed to the services you use it to sign in with. That provides a possible way to link your website profiles together (and the email, real name, real address, other real world info etc), and also to link those profiles with all the money you have/had with that Trezor seed.
I realise there are good reasons to trust MyTrezor.com, an Electrum server or a miner you resolve your Multibit SPV transactions with. But that doesn't account for hacks/mistakes at their end. My preference would be to eliminate the need to trust those people with the xpub information altogether. Rule #1 of keeping information off the internet: don't even make the information available to begin with.
