Use an OS that predates Bitcoin. Windows XP or some old Linux distribution. Obviously install the vanilla version and don't update it.

The QR code method you propose also works. I believe that JustDice uses this method for transfers out of its cold wallet.

I would point out that every OS install image is assumed to be a compile of the source, largely on trust. Of course, the whole development team would not need to be complicit to allow this to happen, as only certain members are involved with the build process.

The best you could do to work around that issue today is to create a build of the source yourself, which is not a small task. Suggestions of pre-bitcoin OS make sense, but you'd have to be very disciplined about maintaining the airgap, as the threat is just less specific in that circumstance.

I think using linux os would be safe for now.

If you want to store something and have it really secure or you want an unplugged computer to use for generating keys or such look into a free software linux distro.

Free software is not to be confused with open source, Free software is anti-proprietary where open source may be open but proprietary too.

Use a distro like GNUsense or trisquel etc.

http://www.gnu.org/distros/free-distros.html

These should be free of any backdoors, An unplugged computer running one of those distros should be pretty darn secure.

Someone already made this solution for Armory.

If you want to get down to the bottom of it, no code that you don't personally authored can be trusted. http://cm.bell-labs.com/who/ken/trust.html

This is exactly the issue we solved with Bitalo, where you can create a multisignature wallet that will be safe even if your computer is compromised when setting it up. To achieve that we use MePIN 2-factor authentication, which unline Google 2FA talks directly from our servers to your mobile device, so your computer never sees the secret key for 2-factor.

So now to move your funds from your Bitalo wallet you have to:

- know your account password (which also acts as a key to unlock your part of private key) - this will be known to the attacker because your computer is compromised
- have your mobile device with MePIN app, that will confirm that the transaction is legit. Again, your computer doesn't take any part in it - you just press a button in the MePIN app and their servers send a message to ours that this request is OK.

Only after BOTH of these steps completed we proceed to sign your transaction with our private key and only then it gets submitted to the network and accepted.

The good thing about our approach is that you don't have to take my word for it. All of the code that handles Bitcoin is in uncompressed Javascript for everyone to inspect. You can also check network requests to see exactly what's happening. Of course you need to have some knowledge to perform this kind of audit, but if you don't, someone else will. We couldn't possibly try to do anything fishy here that would go undetected.

I know it's hard to understand because systems like Mt. Gox created a mindset in people that you are totally blind regarding your Bitcoins. That's not the case with multisignature-based services though!

Problem: People STILL don't know what happened to Mt.Gox coins. Whose hands they are now, when exactly they were transfered, what addresses the cold storage was on, etc., etc.
Solution: In a multisig service you can monitor your wallet in real time on the blockchain. If we somehow stole coins from you, you would know that immediately. We would have no excuse.

Problem: When a centralized service fails, often all users lose money. That was the case for Mt. Gox, inputs.io, Flexcoin and others.
Solution: You cannot steal from all users in a multisig service, unless Bitcoin itself has some fatal flaw (in which case we're all doomed). It could be possible to plant malicious javascript to the website, but that would be detected quite quickly and only a handful of users that were using the site at that specific time could be harmed. The "reward" is much, MUCH lower for a thief, so there's less incentive to risk a criminal act.

Sample scenario: let's say that at some point we have 10,000 BTC in our wallet (hint: we have *much* less at this moment). Most users only store few BTCs in their wallet, and only 5% of Bitcoins is in active usage at any given moment. So if we're lucky, we're get 500 BTC out before people find out. Is ~250,000 EUR worth risking jail time? For an individual, maybe. For a trade registered AG company with 75,000 EUR founding capital, not so much I think.

@jubalix: When setting up two-factor, you usually have an option to remember some kind of recovery code, that you can use later should you ever lose your phone. Even if you don't have it, we would get you through the user verification procedure again to make sure it's not a hacker who tries to access your account, and if everything's fine we would disable 2-factor temporarily so you could sign in and set it up again.