>cryptographically secure hash function I doubt that would help you. Hash tables take the hash and mod it by the size of the array. That will lead to collision

>cryptographically secure hash function I doubt that would help you. Hash tables take the hash and mod it by the size of the array. That will lead to collisions after the mod even if it's essentially impossible to generate collisions before the mod. What you actually need is a secret hash function, so attackers don't know what the values hash to. This is done using a keyed hash function with a secret key.