I have been tasked with implementing a PKI library in C# for a company project, and have been unable to find a good implementation of it. There appear to be multiple libraries, and many broken links pointing to MSDN libraries that have been removed. I've seen people using Crypt32.dll, people building their own libraries, people using P/Invoke to access system certificate stores, people extending the built-in libraries, examples that simply don't apply to C# (e.g. Java examples), and commercial libraries.
My question is, which implementation/library is most recommended for simple encryption/decryption of data?
As some background for what I plan to do with it, I simply need to encrypt messages using a private key (.pfx), and decrypt with public keys (.cer). Message signing and authentication isn't required at this level of the project, although it may be in future. I have seen reference to encryption lengths which make me uneasy. We need to be able to encrypt any length message (within reason, of course!). Is this something I need to worry about, and if so, is there a way to deal with it?
I would prefer not to store public/private keys in the windows certificate manager if at all possible, but if it makes implementation significantly simpler, so be it.
I realize PKI and encryption is a large and complex subject, but I'm hoping for a relatively simple library anyway... (one can hope, right?)