if your n isn’t a power of two,
it may produce numbers larger
than n
The others are not such big problems as I don't need strong resemblence to real randomness.
I can’t look into your use case, but I’m not sure you realize how spectacularly bad xoring with a fixed value is as a way to generate a ‘random’ permutation.
For example, it will still alternate odd and even numbers.
Also, an adversary can derive the xor key from a single sample, and predict the entire sequence from it.
- xoring will only produce permutations that have period two, and every element will be part of a 2-cycle.
- if your n isn’t a power of two, it may produce numbers larger than n
The set of 2-cycles will have a lot of structure, too (for example, if your magic constant is even, all cycles will have either two even numbers or two odd numbers; if it is odd, all cycles will have an even and an odd number), but the above should already be bad enough to drop that idea.