Sorry, messed up on that part, heard a while ago that someone was working on implementing Niederreiter and didn't fact check it. Seems to not be the case after all. Allegedly, with some sort of error correction was used to prevent the reconstruction of private keys which usually taunts McEliece and its implementations.
@goldstein Regarding how we can tell, whether an encryption is safe against QC, it's actually quite easy and doesn't need any sort of simulation.
You see, the QC operation we are most concerned about at the moment is called "Shor's algorithm", which is a quite advanced system for the integer factorization of large numbers. In regards to the technology of QC, it just has a few limitations. One of them is the fact that for a QC to use this method to factor a number, the resulting numbers must be lower than the amount of Qubits the used QC has. At the moment, for Shor's algorithm, the official record lies at 21 using a seven qubit system which factored the numbers 3 and 7 out of it (3*7=21). With this, we can do a small thought experiment.
Think of two numbers with the following properties:
1.) They are both prime numbers.
2.) At least one of them is bigger than seven.
Now multiply them. You have created a simple encryption solution which at the moment can't be attacked by Shor's algorithm, whose main job it is to factor (i.e. guess back) the two prime numbers your result is made out of.
What this means is that, at least for Shor's algorithm, because of these mathematical limitations imposed on such a system, there are actually multiple things we can do to protect against QC based attacks. For one, looking for new, longer prime numbers is a good start. That's the reason the EFF pays anyone up to 250,000$ who finds new, long prime numbers. Regarding McEliece and other "postqantum encryption candidates", as far as I can tell, what they do is use far more complex mathematical systems over simple factorization and other solutions, though I'm not sure, I wasn't able to follow this document detailing it in it's entirety: http://tuvalu.santafe.edu/~moore/mceliece-waterloo.pdf
Furthermore, allegedly the so called "adiabatic quantum computation" used in the famous D-Wave QC's is capable of circumventing this problem which, if true, could be a massive problem as it would allow to crack encryption much faster then initially predicted. It has been said that this algorithm has factored numbers as high as 200099, though evidence is supporting this is rare.
Have a nice day,