 RSA relies on the assumption that it is much easier (that is, more efficient) to perform the multiplication of two (large) numbers formula_22 and formula_124 than to calculate formula_22 and formula_124 (assumed coprime) if only the product formula_177 is known.The Diffie–Hellman key exchange relies on the fact that there are efficient algorithms for modular exponentiation (computing formula_235), while the reverse operation (the discrete logarithm) is thought to be a hard problem.Prime numbers are frequently used for hash tables.