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I know it is generally a very bad idea to share one wallet.dat between many clients on different machines because public/private key sets start divirging after some time if all the clients are allowed to recieve and spend money and this leads to a possibility of a dangerous collision.

However, what if I introduce a constarint that, say, of 5 machines with shared copies of wallet.dat, only one particular machine can both recieve and spend bitcoins while the rest of 4 machines are only allowed to recieve payments.

Would this be a safe setup or would there still be a risk of losing coins?

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The risk is if you have shared private keys on multiple computers. Even if you maintain a personal discipline that you won't spend from those other 4 wallets, the risk is still there. With those private keys still on the other computers, you have opened up 4 additional vectors of attack on your keys, as well as given yourself 5 times the workload securing it all.

You should only have the private keys for your addresses on the one machine that you say you want to spend from.

On the other 4, you should only use "watch only" clients, such as the online wallet at blockchain.info or Armory. There are others as well. Both of those wallets will let you set up public keys to watch, but not spend from, because they don't also have the associated private keys.

Watch only wallets can receive funds just like any other wallet -- you're just watching the balance on the blockchain.

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    Thanks for "watch only" clients. This really seems to be solving my case without additional risks. – src091 Mar 3 '14 at 12:54
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    You're welcome. By the way, there is no collision risk whatsoever even if you did spend from multiple clients with the same bitcoin addresses and private keys. What will happen is (depending on the wallet) your change will eventually end up in the generated address of a spending wallet. If you continued to willy-nilly spend from multiple wallets like this your change would be spread out across multiple addresses in multiple wallets. It's no big deal, you still have access to all the coin, but the wallets are severely diverged, as you noted in your original post – Brian Onn Mar 4 '14 at 3:05
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To be truly secure you're going to want as little .dat sort of files on any machine you use -much less Five of them.

By storing your coins in these files you unnecessarily expose yourself to various forms of attacks. Instead of increasing the chances of your coins security being compromised 1x - you're using hot storage (cold wallets are the safest option known to date) practices on 5x vulnerable machines!

NOT a good idea if you're interested in safely keeping your bitcoins.

So the simple answer to your question is a resounding ***No. They are highly vulnerable.

  • I mostly was interested in technical risk i.e. some collisions that might arise from such a setup or whatever that I'm not aware of. But the info you've provided is still important and I see this way of sharing is a bad idea. Thanks. – src091 Mar 3 '14 at 12:53
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    My pleasure. If you want more detail on how to stay secure just shout. Clearly you've got passion for the bitcoin protocol. Id hate to see it get blitzed by a simple hack draining all your coin – TheGenesisBloke Mar 3 '14 at 19:37

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