Appendix C. Using the GNU GMP Library

As explained in Chapter 4, public key cryptography involves a mathematical function that is relatively easy to calculate in the forward direction, but the inverse function is extremely costly to calculate in the reverse direction unless a secret backdoor (i.e., key) is provided. All such mathematical functions suitable for use in public key cryptography require the use of arbitrary precision arithmetic.

Since the .NET Framework currently has no explicit support for such arithmetic, we must look elsewhere if we want to experiment with asymmetric algorithm implementations . There are numerous multiprecision libraries available; however, the most obvious choice is probably the GNU MP library, also known as GMP, from the open -source world. You can learn more about this library at http://www.gnu.org/directory/gnump.html.

The GNU GPL (General Public License) covers the GMP library. This means that you can freely copy the library source code and distribute your programs that use it, but you are required to make your own source code available under the GPL. For more information on GPL, see http://www.gnu.org/.