I'd guess that (c) refers to the fact that implementation details can expose the algorithm too, e.g. side-channel attacks, leaking timing info, and so on... Thi

I'd guess that (c) refers to the fact that implementation details can expose the algorithm too, e.g. side-channel attacks, leaking timing info, and so on... Things like constant-time comparisons are not generally part of the consideration of the algorithms and proofs (imho).