The suggested solution (modular squaring) already reduces to factoring. http://en.wikipedia.org/wiki/One-way_function#Modular_squaring_and_square_roots http://

The suggested solution (modular squaring) already reduces to factoring. http://en.wikipedia.org/wiki/One-way_function#Modular_squaring_and_square_roots http://en.wikipedia.org/wiki/One-way_function#Modular_squari... (And we'd use a cryptographic hash function anyway.)