blockchain.info most certiantly DOES NOT need to know your private key...
They use normal 1... bitcoin addresses right? Then how can it be possible that its impossible for them to know the private keys? The wallets are on their servers, which means one way or another they, or at least an employee has to be able to get the keys.
Maybe i did not think it through how it could be done otherwise.
Your browser on your computer encrypts/decrypts your blockchain.info wallet.
Blockchain.info only holds and stores your encrypted wallet and sends it to you.
In theory, they do not know your private keys.
Here is their explanation:
https://blockchain.info/wallet/how-it-worksThats interesting and i hear that the first time.
So the only thing that could compromise that would be when blockchain info somehow could achieve the passwords. Maybe by fetching them from the start or getting them with a compromised script, delivered by a corrupt employee, to the customer.
I couldnt check the image on my current internet so maybe they used an encryption that someone negates that chance. Though it have a hard time imagining how.