How to Install an SFTP server on a Windows Server

Many people have heard of FTP - File Transfer Protocol. This protocol is used in FTP applications to transfer files between two locations. The unfortunate thing about the traffic between the two FTP endpoints (Client and Server) is that traffic between the two is not encrypted. There is a thing called the Secure FTP protocol, which as it's name implies, the traffic between the client and server is secured i.e. encrypted. There is also FTPS (FTP Secure), which is an extension to FTP which uses SSL but is not compatible with SFTP which uses SSH. This article will show you how to install SFTP (Secure FTP) on a Windows server.

Before we start installing SFTP, let's find out a little bit about Cygwin and Open SSH which makes all this possible on Windows.

Cygwin ( https://www.cygwin.com ) is a collection of Open Source tools which provide functionality similar to a Unix distribution on Windows.

One of the many tools which comes with Cygwin is OpenSSH.

OpenSSH ( http://www.openssh.org ) is a collection of free communications programs which provides encrypted sessions over a network using the SSH (Secure Shell protocol). The Secure Shell protocol was developed by SSH Communications Security Corporation (www.ssh.com) in Helsinki . The SSH Communications Security Corporation offers SSH based commercial products.

Cygwin comes with a collection of OpenSSH communications programs such as SFTP and the SSH Server. To make our Windows server and SFTP server, it is necessary to install the SSH Server. In the past, there is an OpenSSH for Windows distribution which one could easily install. It comes with an install wizard and it would put the necessary folders on your system and install the SSH Server service. That development have been discontinued, and the last version seemed only to work with Windows 2003, but not Windows 2008 and later.

However, Cygwin is still continually being developed and maintained and it is possible to use the OpenSSH tools from Cygwin to make any of the Windows Server operating system to have the SFTP functionality. What this means is that Cywgin will need to be installed first, and from within Cygwin the SSH Server application need to be installed and configured.

First, go to www.cygwin.com and download the installation package for your system. We will be using the 64 bit version for our tutorial as we will be installing this on a Windows Server 2008R2 operating system.

You need to select the following packages to install. It's obvious why we need the openssh and openssl-dev packages, but the reason you need the unzip and zip packages is that those packages will install necessary dependencies which are required by OpenSSH. Without them, you will have trouble installing the SSH Server.

- unzip: Info-ZIP decompression utility
- zip: Info-ZIP Compression utility
- openssh
- openssl-dev

Once Cygwin is installed, there will be a Cygwin Terminal icon on the desktop. Right-click on this icon and select Run As Administrator.

Now that the SSH Server is installed, we can start creating SFTP login accounts for clients to use to connect.

It is good practice to create a "parent" folder which will contain the folders for the SFTP accounts "home" folders. This parent folder can be called anything meaningful i.e. sftproot. Each login will then have a folder with the same name as the login account inside this parent (sftproot) folder.

Note: The Windows "Users" group need to have read access to the sftproot folder.

Creating a Windows User Account

The SFTP login is actually a Windows account. For this tutorial, we will talk about local user accounts.

Right click on "Computer" , and select Manage. Create a local Windows user account.

Once the Windows account is created, create a home folder with the same name as the user account.

Assign appropriate NTFS security permissions to this folder. My suggestion is to add the below and remove anything else :

SYSTEM - Full

Administrators - Full

user account (above) - Modify

In Unix, users are authenticated against the passwd file. Since Cygwin is really about having the Unix experience on Windows, we need to add the Windows account we created into the passwd file so that the client can authenticate to the SSH Server (aka SFTP server). While the authentication requires the user account to be present in the passwd file, the password for the account is still validated from Windows. Therefore, if it is required to change the password for the SFTP account, you just need to change it in Windows even after the account has been added to the passwd file.

Assuming we have installed Cygwin to the C:\Cygwin folder and the home folder
for the client is located in D:\clients\SFTPRoot

• Make a backup of the c:\Cygwin\etc\passwd file.
  
  
• Go to the command prompt and navigate to the c:\Cygwin\bin folder.
  
  
• Type in mkpasswd -l -u sftplogin >> ..\etc\passwd
  (-l stands for “local” as opposed to domain account. –u stands for user as oppose to group name.)
  The mkpasswd command will now add the username and the default home directory of the user (sftp.pyramid in our example) to the passwd file
  
  
• Now you need to modify the passwd file to point to the SFTP home directory for this user as created in step3.
  In our example, replace /home/sftp.pyramid with /cygdrive/d/clients/sftproot/sftp.pyramid. As you can see, the real path is D:\clients\SFTPRoot\sftp.pyramid. However, you need to use the notation above.
  
  
• Save the file.
  
  
• You should now be able to log in via an SFTP client

Now that the SSH Server (SFTP Server) is installed and the user accounts created, you are ready to test connecting into the SFTP server.

You need to make sure that TCP Port 22 is allowed for incoming in Windows Firewall if it is enabled. You need to make sure TCP Port 22 is opened up in your Internet Firewall if you are accessing the SFTP server via the internet and configure any NATing or port forwarding if required on your firewall.

You need to use an SFTP compatible client such as FileZilla, WinSCP, or an SFTP program from another Cygwin installation.

Once an SFTP server is created, you can now begin to use it to receive and even send files securely across the internet. Files that are transferred this way include files that contain payroll and personnel information which you do not want hackers to get their hands on.