Troubleshooting
Problem
You want to set up SSL (Secure Socket Layer) communications for an application that uses CICS. You attempt to secure the communications on the TCP/IP port using Application Transparent Transport Layer Security (AT-TLS). You are unable to get SSL communications to work.
Cause
CICS can not use AT-TLS.
Diagnosing The Problem
AT-TLS came out in z/OS V1R7. Part of its goal was to allow applications to use SSL security without any application code changes. In that way, it is transparent to the application. However, if the application has already been modified to use its own SSL security, AT-TLS is not needed and will most likely cause a problem because you will have double SSL being done, and neither side will be able to handle it. In this scenario, CICS is considered an "application". CICS enabled its own support for SSL many releases ago.
Resolving The Problem
Enable SSL security within CICS using the documented steps in the CICS information center section Configuring CICS to use SSL.
Product Synonym
CICS/TS CICS TS CICS Transaction Server
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Document Information
Modified date:
05 January 2026
UID
swg21621769