Bitcoin QT show private key
Change addresses are an important part of most bitcoin clients. They are used to store change and to enhance a user’s privacy. Let’s see what change addresses are all about.
Change and change addresses explained
A change address is an address where change from a transaction is sent. Bitcoin transaction outputs can only be spent whole. So, if you want to send someone a portion of a bitcoin transaction output you have to spend the whole lot and send some of it back to an address you own. For example, if you have 2.00 in an address and want to send someone 1.00 you will have 1.00 change that will come back to you. Depending on your bitcoin client this change will go to a new unused address or one of the input addresses.
The privacy aspect of change addresses
Bitcoin transactions are all public. You can view any and all bitcoin transactions that have ever taken place on a block explorer site like blockchain.info. This means that if someone associates your bitcoin address with you they can view all your transactions! To help you maintain some semblance of privacy two approaches are taken:
- You are discouraged from reusing bitcoin addresses. Use a separate address for every transaction.
- Change is sent to a different address than the address you are spending from.
So, the use of change addresses that are different from the input addresses is a good thing from a privacy point of view. It is not perfect – people can still infer that you are the owner of the change address too – but it helps.
How different wallets deal with change
At the time of writing this is how different wallets deal with change:
- Bitcoin-QT: QT does use different addresses for change than the input address(es). It picks an unused address from its address pool to use as a change address.
- Electrum: Electrum too uses a different address for change than the input addresses. It maintains a separate branch of deterministic addresses for change.
- Armory: Armory also uses a different deterministic address to send change to. It also allows you to control where change is sent to in expert mode.
- Multibit: Multibit sends change back to the second address in the wallet if it is available. If it is not available all change goes to the very first address in the wallet.
- Blockchain.info MyWallet: According to their FAQ they send all change to the very first address in your wallet. However, users have reported that other addresses, including ones from imported private keys, are also sometimes used.
