Hi,

According to the wiki:

Nearly every 256-bit number is a valid private key. Specifically, any 256-bit number between 0x1 and 0xFFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFE BAAE DCE6 AF48 A03B BFD2 5E8C D036 4141 is a valid private key.

The range of valid private keys is governed by the secp256k1 ECDSA standard used by Bitcoin.

So, how would one go about generating a random private key? I just use some random number generator or a hash of some text (in the case of brain wallet keys), make sure that it fits in the range, and if it does, it's good. If not, make a new random one, or if it's a hash, increment a nonce for that hash. Then check to make sure that it fits in the range. Repeat until you get a good private key.

For the randomly generated keys, I understand that using regular PRNGs are not a good idea, but used together with SHA256, along with other inputs (time? mouse movements? keyboard timing entries, or even what is actually typed, external files that you are sure no one else has, or external files that are randomly generated by a trusted PRNG), it might be "acceptable".

I could also use OpenSSL RNG, but that might be more difficult.

From there, it's a matter of following the logic to create the WIF private key, the public key, and to make them with the compressed flag.

As a personal project, I'd like to create a program that does this in basic (visual basic or power basic) for Windows. I know and I've seen there are C versions for Linux and pre-compiled binaries for Windows (vanitygen) and even java (bitaddress, brainwallet).