You can use Bitcrack to Brute-force Bitcoin private keys,
What is Bitcrack?
Bitcrack is an open-source set of tools used for cracking Bitcoin Private Keys. It needs CUDA GPU to perform its functions. The main purpose of Bitcrack is to solve the Bitcoin puzzle transaction: A transaction with 32 addresses which becomes difficult to crack.
Here is the Official Git Repository and full command-line usage – Bitcrack
In my opinion, your thought of hacking bitcoin private keys is useless because you may not achieve to the point of breaking encryption as it requires a lot of processing power to hack the bitcoin network. Mining will be more profitable as compared to stealing bitcoins. if possible it may take some years for a successful brute-force attack