Category: zWireshark

Tracing encrypted data to z/OS

I had blogged Collecting a wire-shark trace with TLS active for a browser where you could specify an environment variable export SSLKEYLOGFILE=$HOME/sslkeylog.log. OpenSSL would write the key to this file, and Wireshark could decrypt the traffic using this data.

Unfortunately this only worked with RSA keys. I could not get it to work with modern Elliptic Curve keys.

I’ve updated my zWireshark program to capture AT-TLS application data in clear text from the z/OS side. It uses an IBM provided API, and captures the traffic between AT-TLS and the application.

You need to set up security profiles, for example

permit  EZB.TRCSEC.*.*.ATTLS            - 
   CL(SERVAUTH) id(ADCDB) access(READ) 
permit  EZB.TRCCTL.S0W1.TCPIP.DATTRACE  - 
   CL(SERVAUTH) id(ADCDB) access(READ) 
permit EZB.TRCCTL.S0W1.TCPIP.OPEN  - 
   CL(SERVAUTH) id(ADCDB) access(READ) 
permit EZB.TRCCTL.*.*.* CL(SERVAUTH) id(ADCDB) access(READ) 
SETROPTS RACLIST(SERVAUTH) refresh

and change the AT-TLS configuration to include CtraceClearText On

For my web browser traffic it produced (printed with the ASCII switch)

Data trace.  Data length 345.  ATTLS Clear Text.                             
<GPMSERVE  11:01:57.258946 Src 10.1.1.2 Port 8803 Dst 10.1.0.2 Port 45168    
Warning: 199 RMF-DDS-Server SeverityCode(03) Data(0)                         
Content-Location: perform_20250102110157_20250102110157.xml                  
Cache-Control: max-age=30                                                    
Date: Thu, 02 Jan 2025 11:01:57 GMT                                          
Connection: close                                                            
Content-Length: 1468                                                         
Content-Type: application/xml                                                
X-UA-Compatible: IE=edge                                                     
X-Content-Type-Options: nosniff                                              
X-XSS-Protection: 1; mode=block

When the AT-TLS option CtraceClearText was Off, the output was

Data trace.  Data length 0.  PTH_Flag.Confidential.                           
<GPMSERVE  11:27:48.733616 Src 10.1.1.2 Port 8803 Dst 10.1.0.2 Port 52860

So no confidential data was displayed.

The JCL is

//COLINC5    JOB 1,MSGCLASS=H,COND=(4,LE) 
// SET LOADLIB=COLIN.ZWIRESHA.LOAD 
//RUN      EXEC PGM=TCPDATA,REGION=0M,PARMDD=MYPARMS 
//STEPLIB  DD DISP=SHR,DSN=&LOADLIB 
//SYSPRINT DD SYSOUT=*,DCB=(LRECL=200) 
//SYSOUT   DD SYSOUT=* 
//SYSERR   DD SYSOUT=* 
//* MYPARMS needs a / to split LE parms from program parms 
//*         needs a blank before each parm, because trailing blanks removed 
//MYPARMS DD * 
/ 
 --IP   10.1.0.2 
 --WAIT 60 
 --DEBUG 0 
 --DISCARD 1 
 --PRINT A 
/*

Please let me know of any problems or suggestions

zWireshark – capturing TCPIP trace on z/OS and displaying it in wireshark.

For example, a ping to z/OS as seen by z/OS

The TCPTRACE module runs as a batch job. It uses a documented TCPIP interface to collect packet trace data. It writes the trace data to a file which can be downloaded and used as input to wireshark.

Using the TCPTRACE module, you submit the job, run your test. Stop the job, download the file. Simple.

The documented way to collect a trace from z/OS is 

  • Start a CTRACE trace writer
  • Start CTRACE
  • Start TCP trace
  • Run your test
  • Stop TCP trace
  • Stop Ctrace
  • Stop Trace writer 
  • use IPCS to process the trace and create a file to download
  • Download the file

Which is complex and has many steps.

Ive created a github project called zWireshark. You only need the load module, the source is there for example.

Please let me know of any suggestions or improvements.