Semantic security and indistinguishability I have two frames f1 and f2 that are each composed of several elements noted e. Note that, an element can fall into one of those two categories: an identifier or a counter.

What I want is to find a property that verifies indistinguishability of elements between frames. For instance, given the element e as an identifier, if f1.e==f2.e the property is not verified while it is verified if f1.e!=f2.e.

For now, I only suppose that such a property includes probabilities and can be obtained via:


semantically secure block cipher for identifier elements;
PRNG for counter elements.
You could use Format Preserving Encryption for either one of the elements. FPE will create a keyed permuation for a specific domain (presuming that this domain can be practically converted to a number representation). That way your identifier can just be a sequential number.

You could see a block cipher as an FPE for a specific domain with $2^n$ elements, where $n$ is the block size in bits. If you can define your domain to have that many elements (even unused ones) then yes, you could use a block cipher. This could be an issue if you cannot handle a relatively large output size (you cannot store $2^{32}$ bits or more, for instance).

You can also create a random nonce, but due to the birthday problem, you will have to generate a pretty large value to avoid collisions in the element itself (and, of course, the encrypted element as well).