BIP32 derivation is vastly superior. In order to figure out all of your private keys, an attacker would need to know the master private key and the derivation paths. This means that if one of your private keys were compromised, your whole wallet isn't compromised. It is far easier to protect one key than it is to protect billions of keys.
BIP32 seems too complicated, I am looking for something I can calculate in mind without effort. Then can easily obtained by hand, without additional code I may not have access to, and still secure (i.e. not technically exploitable).
What if we change the way its range is obtained to a less obvious one, like this. The good thing is that we can set our own simple customized rules:
Random key:
Random mask:
In this case, valid range would be:
Not sure if one would even bother try the same thing you did with the other to figure out near keys, that is in case any of my keys are stolen.
Or we can try more tricky things, yet without loosing simplicity and portability (i.e. can be write down in a piece of paper, easily remembered, easy to execute).
Thank you for reading!
You can always write up a BIP and implement something with your proposal and see if there is demand for it knowing the strengths and weaknesses.