Will Mt. Gox be offering signing services when multisig is available?

[hannesnaude]

I'm hoping that Mt Gox will convert all their yubikey protected bitcoin accounts to multisig sooner rather than later. The clients private key can be computed from a passphrase using javascript "brainwallet style". Gox will then provide the second signature using their green address. Therefore I can then leave all my coins in a Gox wallet and they will be

- Safe, even if gox is completely pwned by hackers (assuming my passphrase is not password123 or something equally stupid).
- Immediately available for trading at any point without waiting for confirmations.
- Immediately available for spending to a merchant, who will not wait for confirmations if they trust Gox.

Of course anyone can provide this service, but Gox is uniquely well placed to do this since they have allready distributed thousands of  yubikeys to their users. (This model does not really work if you don't have a yubikey or some other 2-factor authentication device, since an attacker can then get all the access they need to your account by just using a keylogger).

Under this model an attacker would either have to compromise my PC AND steal my yubikey or compromise my PC AND hack Mt Gox.

I know the idea is not new (this is what multisig is for after all) I'm just wondering whether there is any official communication from Gox with regards to a roadmap for something like this.

 

[Gaff]

I might not understand this completely but, there's a bit more to consider:

 - If MtGox suffers a data loss or is forcibly shut down by the feds, (depending on how paranoid you feel) your money is lost.
 - If your PC is compromised an attacker may well be able to use social engineering techniques to take the yubikey off your account. (Don't believe me? Email MtGox and tell them you lost your key, see for yourself how hard it is to get it removed).
 - You need to trust that when you enter your password it's not transmitted in plaintext to the serverside, or that MtGox doesn't secretly record your private key in the window when it has access to it. If it does either of these then when MtGox gets hacked you lose your money still. (Don't think this could happen? See here: http://www.wired.com/threatlevel/2007/11/encrypted-e-mai/ ).

What advantage does multisig give you over Blockchain.info where the serverside account is encrypted with a client side password?

[hannesnaude]

- If MtGox suffers a data loss or is forcibly shut down by the feds, (depending on how paranoid you feel) your money is lost.

They only need to back up their private key in several secure locations. In case of a failure for whatever reason, the private key can be released and everyone can move their own money to where they please. Not unfuckupable, I'll grant you that, but nothing is foolproof to the sufficiently talented fool. It is certainly a vast improvement. If the same thing where to happen today, my money would not only be lost., it would actually be under the control of whoever took over Mt Gox.

- If your PC is compromised an attacker may well be able to use social engineering techniques to take the yubikey off your account. (Don't believe me? Email MtGox and tell them you lost your key, see for yourself how hard it is to get it removed).

If this is indeed the case (and it may well be) then it is a seperate issue that needs to be addressed, irrespective of whether Gox uses multisig.

- You need to trust that when you enter your password it's not transmitted in plaintext to the serverside, or that MtGox doesn't secretly record your private key in the window when it has access to it. If it does either of these then when MtGox gets hacked you lose your money still. (Don't think this could happen? See here: http://www.wired.com/threatlevel/2007/11/encrypted-e-mai/ ).

No, I don't. I can easily verify the javascript that is sent to my browser to confirm what will and will not be sent over the wire. Of course I wouldnt want too study the code evry time I want to make a payment, but as long as someone I trust has audited the code since the last version change, and I can reliably detect version changes in my browser, I don't have to. Not only should my private key not be sent in plaintext, it should not be sent at all. All that  is sent to Gox under this model is a half signed 2-of-2 multisig tx. Even if it was plaintext it should be useless to any snoopers.

What advantage does multisig give you over Blockchain.info where the serverside account is encrypted with a client side password?

I don't  have to trust Gox. They are in no position to take my funds (my BTC denominated funds that is, they can have a field day with my fiat). Nor is any hacker that manages to compromise their site in a position to swipe my funds. At the same time I have the ability to trade instantly without waiting for six confirmations, as I would have to do if I chose to keep my funds local and only send to Gox each time I want to trade. Most merchants will accept payments from such an address without waiting for confirmations, since Gox will not sign a double spending transaction. Lastly, my money is safe even if a key-logger is installed on my machine.

[Gaff]

What advantage does multisig give you over Blockchain.info where the serverside account is encrypted with a client side password?

I don't  have to trust Gox. They are in no position to take my funds (my BTC denominated funds that is, they can have a field day with my fiat). Nor is any hacker that manages to compromise their site in a position to swipe my funds. At the same time I have the ability to trade instantly without waiting for six confirmations, as I would have to do if I chose to keep my funds local and only send to Gox each time I want to trade. Most merchants will accept payments from such an address without waiting for confirmations, since Gox will not sign a double spending transaction. Lastly, my money is safe even if a key-logger is installed on my machine.

As shown above with multisig you have to trust:
 - Gox's javascript - Which you must verify each and every time you connect as it could be different from last time.
 - Gox not to dissapear - Sure they should have emergency / backup procedures, but you can't prove they are doing this properly.
 - Your local PC not to be compromised. (As you rightly point out, yubikeys don't really help either way)

This is better than without multisig since without multisig you have to trust all the above, plus:
 - Gox itself doesn't get compromised.


But here's the thing. Blockchain.info keeps server side records encrypted with a client side password. However additionally you can backup your encrypted data locally, so if blockchain.info disappears you can still get your money. In this situation you only need to trust:
 - Blockchain.info's javascript - each and every time.
 - Your local PC not to be compromised. (Again yubikeys don't really help)

Still not perfect, but better than multsig, no?