How to Decrypt SSL using Chrome or Firefox and Wireshark in macOS
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Created On 04/27/21 00:18 AM - Last Modified 10/21/24 20:36 PM
Objective
Capture SSL session keys from encrypted web-browsing or other web application traffic in Chrome or Firefox and use it to decrypt packet captures in Wireshark.
Environment
- macOS 10.15 or newer
- Chrome 85 or newer, or Firefox 81 or newer
- Wireshark 3.2.7 or newer
- SSL/TLS sessions using RSA, DHE or ECDHE key-exchange algorithms.
Procedure
1. Close Chrome or Firefox completely. Make sure all instances are closed by using the Force Quit option (right click in the web browser's icon down in the Applications Dock, hold down the Option key, and select Force Quit).
2. Open a Terminal window and set the SSLKEYLOGFILE environment variable using the following command.
export SSLKEYLOGFILE="/Users/$USER/sslkey.log"
| Do not close the terminal window. |
3. Launch Wireshark, and start the packet capture.
4. Launch Chrome or Firefox using the terminal window that was used to set the environmental variable in step 2. (The environment variable is set only for that specific Terminal session).
For Chrome:
open /Applications/Google\ Chrome.app
For Firefox:
open /Applications/Firefox.app
5. Use the terminal to verify that the sslkey.log file is created.
file /Users/$USER/sslkey.log
The expected output if the file is properly created will be:
/Users/user1/sslkey.log: ASCII text
6. Browse to the website or web application that is being tested and run all actions that need to be captured.
In our example we download the malware test file from the EICAR secure site.
7. Check in Wireshark to confirm that the activity was properly collected, and stop the capture.
8. In Wireshark go to [ Preferences > Protocols > TLS ]. Under (Pre)-Master-Secret log filename, select the sslkey.log file created in Step 5, and click on OK.
9. The decrypted packet capture is displayed in Wireshark.
10. (Optional) Follow the HTTP Stream to visualize the decrypted contents.
Note1: The steps may change when MAC OS or Chrome gets updated.
Note2: This article is written for informational purposes only. Palo Alto Networks does not support any third-party operating systems.
Additional Information
Use tshark to decrypt and export packets
There is currently no way to export the decrypted packet captures from Wireshark in PCAP format, however, this task can be achieved using tshark, which is the command-line counterpart of Wireshark. It allows you to extract and save the decrypted data.
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Ensure you have the (Pre)-Master-Secret keys available.
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Run
tsharkwith the TLS key log and appropriate decryption settings:tshark -r original.pcap -o tls.keylog_file:/path/to/your/tls_keys.log -o tls.desegment_ssl_records:TRUE -o tls.desegment_ssl_application_data:TRUE -w decrypted.pcap-r original.pcap: Your original PCAP file with encrypted TLS packets.-o tls.keylog_file: Path to your TLS key log file.-o tls.desegment_ssl_records: Ensures proper segmentation of SSL/TLS records.-o tls.desegment_ssl_application_data: Ensures the SSL/TLS application data is properly reassembled.
The
-w decrypted.pcapflag will write the decrypted packets to a new output file.