title: Decrypt data using an RSA public key
body: <p>First off, that is not a typo, I want to <em>decrypt</em> using a <em>public</em> key.  The purpose for doing this is to challenge a third party to ensure they do, in fact, have the private key that corresponds to the public key.  Basically, I would send some random data, they would encrypt it with their private key, I would decrypt it using the public key and compare the decrypted value to the random data that I sent.  I believe this is a pretty standard procedure in public key crypto but for some reason decrypting with a public key seems to be taboo.</p>
  
  <p>I am simply using the <code>RSACryptoServiceProvider</code> in .NET 2.0.  However, when I call <code>Decrypt</code> it throws a <code>CryptographicException</code> with message <code>Bad Key</code>.  The key is not bad (I can <code>Encrypt</code> with no problem), but it appears as though it will not let me decrypt with just the public key.  What gives?  This must be possible to do.</p>