There is a whole range of Bitcoin private keys iterated from the beginning to the end. Now how it works: Private key is a simple integer between 1 and 1.157.920.892.373.161.954.235.709.850.086.879.078.528.375.642.790.749.043.826.051.631.415.181.614 inclusive (slightly less than 2²⁵⁶ ). Yes, this is an unfathomably large number.  It is approximately 10⁷⁷ in decimal. The visible universe is estimated to contain 10⁸⁰ atoms. That has a minimal chance, near zero, to repeat randomly.We convert private keys to WIF (Wallet Import/Export Format) for a convenient using. For more details about getting WIF and Bitcoin address, read at About wallet page.