Bitcoin QT get private key

Bitcoin addresses are at the heart of how bitcoins are transferred. As previously discussed, addresses are essentially public-facing hashes of the public key where you can only spend it if you know the private key. In another post, I discussed how addresses are supposed to be used only once. The reason for it is fairly straightforward, when you sign over some bitcoins to another party, you must reveal the public key of your address as part of the transaction. Reversing the public key to get the private key is called the Discrete Log Problem and while it’s thought to be extremely difficult to solve, there may come some innovation in quantum computing that may render it obsolete and it’s better to be safe against such a possibility than be sorry. So in case you aren’t aware, you should only spend from an address only once. Addresses are really cheap for a computer to make (essentially a random number between 1 and 2^256), so unless you’re trying to get anonymous donations sent to the same address over and over, it’s a good idea to use different addresses every time.

Bitcoin wallet creators have long since tried to make it convenient to do this very thing. The bitcoin-QT client, for example, generates 100 addresses and waits until you’ve used them up to create some more. This can be a bit dangerous, even if you make backups since you may end up with a backup that doesn’t contain the new addresses should you cross the 100 address boundary after your backup.