Quote from: cle on March 13, 2016, 12:10:22 AM

Quote from: Decoded on January 29, 2016, 11:49:46 AM

I use a cold wallet running armory, with multisig. I don't usually withdraw, so this doesn't bother me, only hackers. If I really do need to withdraw, I have a pre signed transaction on Google Drive.

Can you expand on this?

Armory supports cold offline air-gapped signing. Cold and Air-gapped means your computer storing the private keys is never connected to a network, wifi, ethernet, internet.

So you setup a cold offline Armory install (you could use a Raspberry Pi single board computer), you generate the private seed on this computer, and the matching xpub. This cold offline computer does not require a copy of the blockchain. You save this xpub to a brand new factory sealed USB drive (or QR encode it, more later)

You use your laptop/every day computer with a fully connected full node + Armory + xpub. This online computer needs to be online, and have a synced blockchain in order the generate spending transactions. As your online computer has the xpub, it can generate valid spending transactions, but they're invalid until they're signed by the correct private key.

With a few tools you send the unsigned transaction back to your cold airgapped (you could QR encode the unsigned transaction on your online machine, read the QR on your Pi with this this camera), then decode the photographed QR code)

online machine

Code:

$ qr PASTE_UNSIGNED_TRANSACTION_STRING

cold offline Pi

Code:

raspistill -o capture.jpg
zbarimg -d capture.jpg

from here you sign this spending transaction with your private-keys-containing-offline-Pi and then send the signed transaction back to an online device for broadcast to the bitcoin network.

The idea of passing the unsigned/signed transaction back and forth between the cold-airgapped-offline-machine and your everyday-online-machine doesn't appeal (you might choose a one way method like a closed session writable CD-ROM rather than a USB drive) but my advice would be to QR encode the signed transaction on your Pi, scan the QR with your phone, and paste the transaction in a blockexplorer like https://blockchain.info/pushtx via your phone.