In the literature pertaining to RSA, it has often been suggested that in choosing a key pair, one should use so-called "strong" primes p and q to generate the modulus n. Strong primes are those with certain properties that make the product n hard to factor by specific factoring methods; such properties have included, for example, the existence of a large prime factor of p-1 and a large prime factor of p+1. The reason for these concerns is that some factoring methods are especially suited to primes p such that p -1 or p+1 has only small factors; strong primes are resistant to these attacks.