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Bartek's avatar
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Jul 20, 2022

Decrypting SSL traffic - PMS and egress

Hi - two questions combined.

Background - trying to catch and decipher tcpdump both for Client -> VIP and F5-> Pool Members traffic 

I'm following this tutorial: Decrypt with tcpdump --f5 ssl

I managed to catch the frontend traffic, but I'm struggling with creating the PMS key. I want to automate it using the provided wireshark cmd command, but I get the error:

C:\Program Files\Wireshark: invalid option -- 'T'
C:\Program Files\Wireshark: invalid option -- 'e'

I'm using Wireshark 3.4.8 - what would be the equivalent options for my version? Unfortunately using a Linux in this environment is out of the question. I can only work on Windows stepping stone and can't send the captures to my PC

Second issue:

Catching the backend traffic does not produce the F5 TLS in the pcap capture... The server ssl profile is present, but I have no idea how to force the --f5 ssl option in tcpdump to catch the keys. 

Will appreciate any advice - It is my second day struggling with the issue

14 Replies

  • This is mostly the case, if:

    • tcpdump has not captured the initial tls handshake
    • HTTP/2 is used (the -p does not capture all http/2 streams)

    Try to add the backend hosts to the filter and always reopen the browser.

  • Bartek  - lots of answers here - did any of them get you where you needed to go? If yes, please make sure to mark it as an Accepted Solution so other users with your issue can quickly find help and the author gets credit. 🙂


  • I have now uploaded my sycript to generate the pms file out of the tcpdump file with enabled sslprovider. This script works for all TLS versions and decrypts clientside and serverside traffic. 

    I use this script in my daily job and I hope it could help other people also!

    • Ichnafi's avatar
      Icon for Cirrostratus rankCirrostratus


      thank you for sharing your script.

      Sorry to bump this old thread.

      For some reason only the client side traffic get's decrypted. Communication between LTM and nodes are still encrypted. I'm using the tcpdump command as mentioned in your github.

      Any idea?

      • David_Larsen's avatar
        Icon for Employee rankEmployee

        One thing to take into account is if you have a OneConnect profile applied to the virtual server the Serverside connections could have established SSL handshakes before you take the capture and not be able to be decrypted.  You have to make sure all connections on the serverside and clientside are deleted before starting the capture otherwise you may not be able to decrypt.  

        You should also use a filter that includes the ServerSide nodes specifically and not rely on the :nnnp to gather that data if you are looking to decrypt the serverside traffic.

  • You have to use the command line tshark.exe.  The other gotcha here is that with Wireshark running you have to have the F5 protocols enabled under Analyze, Enabled Protocols - search for F5 and make sure all the F5 protocols are enabled, otherwise the filters in that commandline will not work properly.  Once you enable the protocols in Wireshark GUI then the tshark.exe commandline has them enabled as well.

  • You must use tshark NOT wireshark to Automate Pre Master Secret File Creation.

    This solution and the solution from CA_Valli does NOT work for TLS 1.3

    To capture backend traffic also you must use the "-i 0.0:nnnp" option for tcpdump.

    But it is possible to decrypt TLS 1.3 also, you must extract following fields from the dump:


    In my tests tshark fails to dump this correctly. My old plan is to create a GitHub repo to upload my script that extracts all pre master secrets for all tls versions.

  • Hello, I usually use an iRule to log and collect secrets which I'm attaching. This saves info in plain text in LTM file, eventually you can force log rotation and manually bulk-delete all lines from this iRule in "ltm.1" file when you're done.

    To retrieve info and create pms file, run this from bash shell. 


    sed -e 's/^.*\(RSA Session-ID\)/\1/;tx;d;:x' /var/log/ltm > /var/tmp/sessionsecrets.pms
    grep -h -o 'CLIENT_RANDOM.*' /var/log/ltm >> /var/tmp/sessionsecrets.pms


     To import PMS file in wireshark, 

    Edit -> Preferences -> Protocols -> SSL => (Pre)-Master Secret log filename [Browse]