Obfuscating an ID

Question

I\'m looking for a way to encrypt/obfuscate an integer ID into another integer. More precisely, I need a function int F(int x), so that

• x<->F(x

Answer 1

Not sure how "hard" you need it to be, how fast, or how little memory to use. If you have no memory constraints you could make a list of all integers, shuffle them and use that list as a mapping. However, even for a 4 byte integer you would need a lot of memory.

However, this could be made smaller so instead of mapping all integers you would map only 2 (or worst case 1) byte and apply this to each group in the integer. So, using 2 bytes a integer would be (group1)(group2) you would map each group through the random map. But that means that if you only change group2 then the mapping for group1 would stay the same. This could "fixed" by mapping different bits to each group.

So, *(group2) could be (bit 14,12,10,8,6,4,2,0) so, adding 1 would change both group1 and group2.

Still, this is only security by obscurity, anyone that can feed numbers into your function (even if you keep the function secret) could fairly easily figure it out.