All the ideas are explained here:
http://en.wikipedia.org/wiki/Public-key_cryptography[
^]. Please read very carefully.
As you want to make the decryption key public, your data can be decrypted by anyone. So, what's the use? Here is what it is: it can be used to protect the source document from faking using the
digital signature schemes:
http://en.wikipedia.org/wiki/Digital_signature[
^].
In turn, digital signatures can be use in digital certificates:
http://en.wikipedia.org/wiki/Digital_certificate[
^].
With .NET FCL, a lot of encryption stuff is already implemented for you. As you are interested in asymmetric algorithms (and public-key cryptography) in particular, you can start here:
http://msdn.microsoft.com/en-us/library/system.security.cryptography.asymmetricalgorithm%28v=vs.110%29.aspx[
^].
—SA