Using really big numbers!

Hi,

I'm working on several projects in C++ that require the use of very large numbers. One of these projects is a RSA encrypter. Using this encryption method, one must use prime numbers that are over 'one-hundred-thousand' digits long. How would one go about preforming standard mathmatical functions in C++ with such large numbers?

Also, is it possible for a user to input a number as large as this, using scientific notation, in the 'cin' function?

Your help would greatly be appreciated.

regards,

machewy