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Mainframe – AT-TLS Encrypted FTP Client Instructions for zOS Users

This article explains the use of FTP clients to transfer files to the zOS system. University of Chicago mainframes support a protocol called Application Transparent – Transport Layer Security (AT-TLS). This encryption protocol is deemed to be the most secure and resistant to hacking.

Data Center Services examined several SSL enabled FTP clients for use with the zOS systems. These included WS_FTP Professional, Hummingbird Host Explorer, and Core FTP.

OpenText Host Explorer

Ipswitch WS-FTP LE


OpenText Host Explorer

OpenText Host Explorer uses encrypted FTP under the covers to provide a Windows-like view of mainframe files. You can configure a session by clicking on Connection Central and launching (double-clicking) the New FTP Profile icon.

Under the General tab, fill in the blanks as shown below.
Make sure that Connection type is FTP – SSL/TLS Explicit and the port is 21.
Type your mainframe userid in the User name: field and your password in the Password: field.

WARNING: Be sure that you enter your password correctly. If entered incorrectly, there is a good chance your userid will be suspended due to multiple logon errors.

If you want to be shown a directory other than your own userid, select the Other tab and type that directory name in the Initial Directory field.
Note: Leaving this field blank defaults to your own userid.

Select the Advanced tab and under Type of FTP Server: select MVS. Click OK when done.

Save the profile.

You will automatically be connected to your account on the MVS1 mainframe.
The image below is a sample of what an OpenText Connection Central FTP session looks like.

Ipswitch WS-FTP LE (Free)

Ipswitch offers a free version of their FTP client: WS_FTP LE. At the time of this writing, WS_FTP LE could be downloaded from this URL:

Click the Download button to begin.


Fill in required fields and click the Download Now button.

Follow the instructions in the subsequent email.


Save the installation file when prompted.

If the installation does not automatically start, view the downloads (in Firefox it is a green downward arrow on the upper right corner of the browser) and manually launch the install. Click the Run button.

Click the Next button.

Accept the license agreement and click the Next button.

Click the Next button.

Click the Next button.

Click the Next button.

Click the Finish button

Click the Next button.

Enter a name for this connection. In this example UCHIMVS1.UCHICAGO.EDU is used.

For Connection Type, select FTP/SSL (AUTH SSL) and then click the Next button.

In the Server Address field, type in the host name for the MVS1 mainframe: Click the Next button.

Type in your MVS1 userid and password. Click the Next button.

Select the Connect to this site checkbox. Click the Finish button.

If you select the Allow this connection only radio button, you will be prompted again to accept a certificate. If you select Trust this certificate, you will not be prompted again until the certificate expires. Click the OK button.

The image below is an example of a successful FTP session.
Note: If you have used Ipswitch FTP client products in the past, they should work without modification with AT-TLS.


Core FTP LE is a freely available client that has several advanced features and, most importantly, works with SSL/TLSv1 connections to our system. The following are instructions for downloading a copy of this product, installing it, and establishing a connection to uchimvs1. This is not intended to explain the intricacies of file transfer between zOS and a PC. The user is expected to already be familiar with issues such as ASCII vs. EBCDIC and binary mode file transfers.

Navigate to the Core FTP website: The version number may change from what it had been when this screen shot was taken.

Click the Download link. The Core FTP Download page displays. Choose a link to a download site for the most current version of Core FTP LE.

Click the Save File button

You may see a warning. If so, click the Run button.

On the License Agreement, click the I Agree button.

Depending on your operating system, select the components to install and click the Next button.

If you choose to take the default file location, click the Install button.

When the installation is complete, click the Close button.

You may see this flash on the screen.

You may be asked to choose a default file editor for ascii files. Notepad is suitable but you might want to use another word processor.

A Core FTP icon appears on your desktop. Double-click it to launch Core FTP LE.

Use the image below as a guide to defining an FTP session with
Be sure to select AUTH TLS in the Connection area.
Your username and password are optional. You will be prompted for them if not filled in here.
Click the Advanced button for more session options.
Click the Connect button to launch an FTP session.

The first time that you connect to a host (e.g. press the “Connect” button above), you may receive a screen advising you that you are being sent an unknown SSL certificate. You should choose either “Accept Once” or “Always Accept” as you like.
Choosing “Accept Once” means that you will see this dialogue every time you connect to the host.
“Always Accept” means that you won’t see the dialogue until the SSL certificate expires.

Once you are successfully connected you will see a screen that looks something like the one below. The portion of the screen just below the icon “action” bar contains messages pertaining to your FTPsession. A message there about TLS ciphers is a good indication that your session is now encrypted.

For additional information, please refer to the help menu of the program or the Core FTPweb site

Keywords:core coreftp ipswitch   Doc ID:19378
Owner:Todd L.Group:University of Chicago
Created:2011-08-02 18:00 CSTUpdated:2016-07-25 07:50 CST
Sites:University of Chicago, University of Chicago - Sandbox
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