To start with, try to understand how digital signature works.
See this:
http://en.wikipedia.org/wiki/Digital_signature[
^].
You also need to understand the idea of
public-key cryptography:
http://en.wikipedia.org/wiki/Public-key_cryptography[
^].
You should understand the main idea:
using two keys; encrypting using one key and decrypting with another one. Implications of this thing in security needs
thorough thinking.
You cannot really proceed until you get it.
This all is based on the notion of one-way function:
http://en.wikipedia.org/wiki/One-way_function[
^].
To best of my knowledge, the existence of one-way function is not strictly proven yet, but most specialists in the related field of mathematics believe it does exist. One candidate for a one-way function is RSA algorithm:
http://en.wikipedia.org/wiki/RSA[
^].
It is fully implemented in .NET, see
http://msdn.microsoft.com/en-us/library/system.security.cryptography.rsa.aspx[
^].
You have everything to get started now.
Good luck,
—SA
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