Choose a very random number from a very big set of numbers. This is the private key.
Hi Danny, many thanks. I thought private keys are generated by online wallets? Sorry not quite get how to generate private keys automatically here. Could you explain a bit more? Thanks!
A private key is just a very random number from a very big set of numbers.
Specifically, every number from 1 to 115792089237316195423570985008687907852837564279074904382605163141518161494336 is a valid private key.
When an online wallet, or offline wallet "generates a private key", all they are doing is picking a random number in that range.
What is important when "generating a private key" is that the number that is chosen is
random enough. In maths, the word that is used to describe the amount of "randomness" is entropy. So, you will often hear people state that you need to make sure you use enough entropy when choosing the private key.