Is it possible to import a private key offline ?

[Erkallys]

The title talks by itself. Is it possible to import a private key into an offline Bitcoin Core/lightwallet ? If it possible there is no risk of fraud, by adding fake bitcoins to an address and then spend it elsewhere ?

[altcoinhosting]

Sure, you can import a private key in an offline bitcoin core client and use it to sign transactions

[Erkallys]

Sure, you can import a private key in an offline bitcoin core client and use it to sign transactions

But how do your computer that is not connected to the internet how much BTC there is on it ? If funds are added, will your balance be actualised ?

[Was]

The network "knows".

When you "send" coins, you're actually just changing the ownership of a previous input, by signing a transaction with your private key and creating/broadcasting an output.

[altcoinhosting]

Sure, you can import a private key in an offline bitcoin core client and use it to sign transactions

But how do your computer that is not connected to the internet how much BTC there is on it ? If funds are added, will your balance be actualised ?

you should create the transaction with an online wallet, then transfer it to your offline machine where you imported the private key, and sign it offline... Afterwards you need to transfer the signed transaction to an online machine to broadcast it...

There are some good step by step guides on this forum on how to achieve this

[DannyHamilton]

The title talks by itself. Is it possible to import a private key into an offline Bitcoin Core/lightwallet?

Yes.  It is possible to import a private key into an offline wallet.

But how do your computer that is not connected to the internet how much BTC there is on it?

It doesn't.

You could copy the blockchain from an online wallet and then your offline wallet could compute the balance as of the time that the blockchain was copied.

or

You could run an online copy of the wallet with bitcoin addresses only (no private keys). This online wallet could calculate balances and allow you to create transactions. Then you could transport the unsigned transaction to the offline wallet to be signed.  Then you could transport the signed transaction back to the online wallet to be broadcast.  This is how Electrum Offline and Armory Offline work.

If funds are added, will your balance be actualised ?

Only on the online wallet (unless you copy the blockchain to the offline wallet).

If it possible there is no risk of fraud, by adding fake bitcoins to an address and then spend it elsewhere ?

It is not possible to spend fake bitcoins.  Bitcoins don't actually exist in a technical sense.  There are only transactions.  When you "spend", you are actually spending the unspent outputs of previous valid transactions.  Therefore, if there isn't a valid previous transaction to spend, then you aren't able to create a valid transaction.

[Was]

Danny comes in for the dunk!

Thanks Danny

[moneyart]

To import a private key offline you have to open the console of your core client and then type:

importprivkey <privkey>

Before that you have to set a password timeout. Most common use of this technique is to redeem the amount on a paper wallet.