So I made my own serial key generation software, using ECDSA, for use in my own applications and it works great so far! To keep the serial key short enough I use a 128 bit EC curve. My final signature (which I use as the product key) ends up containing two BigIntegers, 128-bit each, so the final key ends up being 32 bytes long. This is an ok solution and I can get my final key down to about 50 characters (not counting any delimiters like dashes) by doing some custom base conversion to convert this into a readable string.
Now I found a software called ellipter where the key for a 128 bit key strength only ends up being 30 characters (if you look at the screenshots on their page). Is this even possible? Or are they using a 64-bit curve? I can't understand how they do it. I would love to get my keys shorter also but I can't see how it can be possible?