But how do you make sure the user actually runs your component without any modification?
You must ask for each number in the interval the two primes and a Primality certificate for each prime. https://en.wikipedia.org/wiki/Primality_certificate
The idea is that it's very hard to find the two primes and it's very hard to prove that they are actually primes. But if the client send you both primes and send you each primality certificate, then the verification is very fast. Also, you can store that info so people can see it.