Exports the underlying key to a binary file securely.
If the key being exported is a symmetric key, ExchangeKey should be
set to a key pair so that the key can be encrypted with the pair's public key,
and BlobType should be set to cbtSimpleBlob.
If you do not wish to encrypt a symmetric key being exported, you should
set the first argument to the special "Exponent 1" key pair.
The Exponent 1 key pair does nothing to information being encrypted. Create an
instance of the Exponent 1 key pair via the CryptoContext's CreateExponentOneKey method.
If the key being exported is a key pair, ExchangeKey should be set
to an symmetric key which will be used to encrypt the key pair, and
BlobType should be set to cbtPrivateKeyBlob.
If the key being exported is a public key, ExchangeKey should be set
to Nothing as no encryption is necessary, and
BlobType should be set to cbtPublicKeyBlob.
Path specifies the file that the key blob will be saved to.
Key.ExportToFile(ExchangeKey, "c:\mykey.key", cbtSimpleBlob )
Related Section: 6.2 OpenContext Method Revisited.