A private key is random 256 bit number stored in the wallet (not the key to access it) and are used by it to sign transactions. The private key is part of a key pair, the other part being a public key, a number calculated from the private key using elliptic curve algorithm.
The bitcoin address is a base58check encoded RIPEMD-160 hash of a SHA-256 hash of the public key. If you don't know what a hash is, it's a mathematical function.
Private key > Public Key > address
Those functions are not reversible (or at least it is not computationally feasible to calculate the private key when you have only the public key and the public key when you have the address), so you can disclose the address without fear of your public key being calculated. But if you have a private key, you can calculate all the rest and therefore spend every bitcoin associated with that address.
The identifier requested by blockchain, it's simply a login identifier for blockchain, like your login account for any other service. It's not connected in any way with your private key.
Thanks for the detailed explanation
If I have backed up my BTC blockchain.info wallet do I need to use this in anyway, or just make sure my back up is protected as the private key is a means to hack my account and not needed by myself for the operation of my wallet? many thanks
You still confuss 2 things.
Privat Key=Wallet
and
blockchain.info=Wallet Software
(that is also not 100% accurat)
If someone has your Privat Key, he doesn't need your blockchain account.
You can Import a privat key in any wallet-software(e.g. Bitcoin Core/Bitcoin QT) and just spend the Bitcoin as you like.
A privat key is the Thing you have to Keep most secure.
Your blockchain.info-credentials just gives you acces to the private key and the functionality to use your wallet.
I hope, that helped.
Thanks, yes I was slightly confused as to whether they would need access to my blockchain.info account if they were able to get my private key from my wallet. I have backed up my wallet on a couple of usb sticks but will look into cold storage once I have done alot more research.
You can also choose (like I do) to keep most of your bitcoins in a paper wallet and load it on blockchai as a "watch only" address, which means that you don't provide BC with your private key, but your address only. Even if BC is hacked or they shut down, you don't loose anything since you never gave them your private key.
If you need to actually "use" some coins, just keep that small amount "loaded" with the private key on BC and keep all the rest in cold storage.
I chose the email wallet option, I know its not as secure, but I have deleted the backup attachment email from blockchain.info and will go ahead and download a paper back up now for added security. Thanks for the advice