However, these can be on different devices. Transactions can be signed on an off...

		Geee on March 5, 2014 \| parent \| context \| favorite \| on: Peter R’s Theory on the Collapse of Mt. Gox However, these can be on different devices. Transactions can be signed on an offline machine. Also, you need just the unspent transactions to sign a new transaction, not the whole blockchain. Bitcoin Trezor works this way, http://www.bitcointrezor.com/