as far as I know the current (.NET 2.0 and 3.5) version of FtpWebRequest supports Explicit SSL only.
Actually, .NET 2.0 does not currently
support implicit SSL, only explicit.
We will consider adding this for a
future release.JonCole – MSFTModerator at MSDN forum post
If you need to use both Implict and Explicit TLS/SSL you have to try one of third-party FTP/SSL components. Following code uses our Rebex FTP/SSL and is taken from the tutorial page.
Explicit TLS/SSL
Client connects to FTP server in a usual non-protected way, usually to port 21 was assigned to FTP protocol. When it is desired to protect the connection using SSL, an SSL negotiation is initialized, control connection is secured and all following communication is being protected.
// Create an instance of the Ftp class.
Ftp ftp = new Ftp();
// Connect securely using explicit SSL.
// Use the third argument to specify additional SSL parameters.
ftp.Connect(hostname, 21, null, FtpSecurity.Explicit);
// Connection is protected now, we can log in safely.
ftp.Login(username, password);
Explicit protection means that it is possible to secure the connection at any moment. If you don’t know whether you will need the protection on not at the connection time, you might want to connect using the ordinary unencrypted FTP protocol and secure the connection later.
Ftp ftp = new Ftp();
// Connect to the server with no protection.
ftp.Connect(hostname, 21);
// Upgrade connection to SSL.
// This method also accepts an argument to specify SSL parameters.
ftp.Secure();
// Connection is protected now, we can log in safely.
ftp.Login(username, password);
Implicit SSL protection of the FTP session
FTPS protocol was originally assigned a separate port by the IANA. Upon connection to this port, an SSL negotiation starts immediately and the control connection is secured. All data connections are also secured implicitly in the same way. This is similar to the approach used by HTTPS.
This approach is not favored by the IETF and is deprecated. It is supported by Rebex FTP/SSL for interoperability with older servers, but it is strongly recommended to use the explicit protection instead whenever possible.
Ftp ftp = new Ftp();
// Connect securely using implicit SSL.
// Use the third argument to specify additional SSL parameters.
ftp.Connect(hostname, 990, null, FtpSecurity.Implicit);
// Connection is protected now, we can log in safely.
ftp.Login(username, password);
You may download the component at rebex.net/ftp-ssl.net/