Include in the function RSAKeyGen an additional check to ensure that the primes p and q that it generates are not too close, so that the modulus cannot be factored by Fermats method. This is largely unnecessary when generating keys of realistic size but may serve to exclude extreme cases, such as the primes being equal, when generating very small toy examples. Of course, these toy examples might also be banned altogether by including in the function an instruction requiring a minimum value for k.