What can you do with the private key?

Question

I am trying to understand all security regarding blockchain and bitcoins.

Let's say you have a bitcoin wallet which is secured, only you know the private key. This bitcoin address was created on one of the bitcoins wallet provided by bitcoin.org What if a person has your private key? I know it's difficult but let's say he knows the 54 letters private key from hacking a database. How can that person interact with your wallet? Does he have to know which wallet you use as well or can he use just the private key to 'log in'?

Answer 1

Anyone who knows the private key will have full access and control of any coins stored at the corresponding address.

When you put a password on a wallet or login account, that password is only for unlocking that instance of the wallet (it is possible to create another instance, that is not locked by your password). Once unlocked, the wallet will use the private key to sign transactions that move the coins, etc. But without the password an attacker can not unlock the wallet if it the wallet alone is found.

However, having the private key itself means you don’t need to unlock the wallet, because you already have the key. You can import the key into just about any other wallet software, and then use that wallet instance to move the coins, etc.

There is BIP38, which allows you to password protect a private key itself, but this is different, and a less common set up.

Answer 2

What if a person has your private key?

Then they have independent control over all the unspent Bitcoins associated with that private key. Once they have the private key there is nothing you can do to rescind their control (other than moving the Bitcoin into a new wallet before the other person does)

How can that person interact with your wallet?

They don't need to.

The only valuable thing in your wallet are the private keys.

Bitcoins are "stored" as unspent transaction outputs (UTXOs) in the blockchain - but the blockchain is completely public. Every full node (wallet, miner etc) has a copy of the blockchain.

Does he have to know which wallet you use as well ...

No, the other person doesn't need to know anything else.

... or can he use just the private key to 'log in'?

They don't use the private key to log in.

They can import the private key into any wallet software and use the private key to prove to all other bitcoin nodes that they have the right to spend any unspent bitcoin associated with that private key.

Knowing the private key allows them to construct a transaction spending your Bitcoins, they then broadcast that transaction to miners who add the transaction to the blockchain thus spending the Bitcoins (i.e. moving Bitcoins into another wallet which has a different private key)

Answer 3

You can secure your private keys using the Hardware Wallet such as Trezor https://cryptototem.com/trezor-wallet/. Such wallets are used for storing your coins and secure them from different interventions. The developers of such wallets ensure us that will not have any troubles with loss of coins and leakage of your personal data.