Quote from: coastermonger on September 24, 2013, 10:04:20 AM

Let's imagine a challenge with 4 facts:

1.) There is a merchant out in the world who is offering something you want, (something truly amazing, like an Enzo Ferrari) for 1,000 BTC.

2.) Fortunately, I'm about to give you 1,000 BTC because I owe ya.

3.) Using a wallet of your design, your job is to create a new address to receive this bitcoin into your wallet, and then subsequently spend this bitcoin into the merchant's 3rd party address.

4.) Unfortunately, the computer you are using is infected with undetectable and unremovable keylogging Malware and screencapture technology. It's designed to immediately intercept and re-spend bitcoins to a thief's address. You don't even know its infected. In other words, as soon as the malware is able to see either your password or your private key, any funds in your wallet will immediately be stolen.

So how can you receive this bitcoin onto the computer's wallet and spend it again without the thief intercepting ANY of it? AND without changing the current bitcoin protocol?

(Hint: easier than you think, don't spend too much time on it, I will reply with the correct solution in about 12 hours time.)

iirc it is possible to send the coins to me using a multisig transaction (CHECKMULTISIGVERIFY), requiring 2 signatures to spend them: Mine and the merchant's.
The malware only knows my key so it can't steal the(se) coins!

Geddi

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