If it would be possible, it would be a very weak protection. Nobody in clear mind won't store non-ciphered passwords anywhere — they are never needed for authentication.
[EDIT]
To understand how to store authentication (it that is what your second question is about), learn Assymetric ciphering:
http://en.wikipedia.org/wiki/Assymetric_key_cryptography[
^], as well as RSA:
http://en.wikipedia.org/wiki/RSA[
^]. It will give you a good idea. Why RSA? One reason is: it is fully implemented in .NET, see
System.Security.Cryptography.RSA
.
—SA