Hello,

I and a friend are trying to develop an exchange, at last to learn how it works.
At moment, we are using bitcoinjs-lib.

1) An exchange creates a wallet per user ? Or does it have a single wallet which makes all transactions ?
2) If the exchange keeps a wallet per user, how can it protect the user's private key in case  of unauthorised access in database ? Crypt and decrypt it with user's password is an option, but it implies in ask for password every transaction.

Regards,