TechFundu

Introduction

The purpose of this article is to create a C# FTP client in Secure mode, so if you don’t have much knowledge of FTPS, I advise you to take a look at this: FTPS.

In the .NET Framework, to upload a file in FTPS mode, we generally use the FtpWebRequest class, but you can not send commands with « quote » arguments, and even if you search on the web, you will not find a concrete example of a secured C# FTP client.

It’s for those reasons I decided to create this article.

SSL Stream:

To send a socket in Secure Socket Layer (SSL) mode, we use the class System.Net.Security.SslStream.

“Provides a stream used for client-server communication that uses the Secure Socket Layer (SSL) security protocol to authenticate the server and optionally the client”.

For more information, refer to MSDN.

Using the Code:

1. Pre-Authenticate

FTPFactory ftp = new FTPFactory();
ftp.setDebug(true);
ftp.setRemoteHost(Settings.Default.TargetFtpSource);

//Connect to SSL Port (990)
ftp.setRemotePort(990);
ftp.loginWithoutUser();

//Send "AUTH SSL" Command
string cmd = "AUTH SSL";
ftp.sendCommand(cmd);

Before connecting to the FTP server in SSL mode, you have to define the 990 SSL port and send the « AUTH SSL » command authentication using SSL.

2. Create SSL Stream

//Create SSL Stream

ftp.getSslStream();

ftp.setUseStream(true);

//Login to FTP Secure

ftp.setRemoteUser(Settings.Default.TargetFtpSecureUser);

ftp.setRemotePass(Settings.Default.TargetFtpSecurePass);

ftp.login();

ftp.getSslStream() creates an SSL stream from client socket which will be used for exchange between the client and the server FTPS. Then, you have to enter a login and password to authenticate on the FTPS server.

Note: if the SSL stream is well established, then I display all the information about the server certificate.

3. Upload File

//Set ASCII Mode
ftp.setBinaryMode(false);

//Send Arguments if you want
//cmd = "site arg1 arg2";
//ftp.sendCommand(cmd);

//Upload file
ftp.uploadSecure(@"Filepath", false);

ftp.close();

Before uploading a file, you have to specify the mode: ftp.setBinaryMode(bool value).

value is false --> ASCII mode
value is true --> Binary mode

By default, it’s binary. Now, you upload the file using:

ftp.uploadSecure(@"Filepath", false)

Note: you can upload in non secured mode using ftp.upload().

Points of Interest

I learned how an SSL stream and the RAW FTP communication works between a client and an FTP server. Searching on the web, I found many who were stuck on the issue of SSL communication with an FTP server, so I hope this article will be of great help.

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