Strong RSA keys

A simple method is given for finding strong primes for use in conjunction with the RSA Public Key Cryptosystem. A strong prime p is a large prime satisfying the following: (a) p = 1 mod r; (b) p = s?1 mod s; (c) r = 1 mod t; where r, s and t are all large, random primes. It is shown that the problem of finding strong, random, large primes is only 19% harder than finding random, large primes.