Open Wireshark, go to Edit > Preferences > Protocols > SSL > RSA Keys list > Edit > New. Location will vary depending on your OS or set-up Using it Quite simple here in that you just copy the private key (being aware you are copying a private key?! :) you can export it with a pass phrase) to a file on your Wireshark machine then tell Wireshark where it is. The biggest benefit here is that its easier to decrypt old captures you may not have necessarily prepared for and its easy to decrypt lots of traffic sourced from multiple clients. So let’s see how to use each option Private Key Access Its worth noting some SSL chipers/key exchanges are do not work with all these options e.g when using ECDH key exchanges, but apart from that they work very nicely. Thanks to chisight in the comments for noting this Unfortunately, dumping the premaster secret was removed in FireFox 48 and later, it is now only available if you compile with a non-default build option.

Access to the client machines and its (pre)master secrets (also need Firefox or Chrome).

Wireshark has some very nice SSL/TLS decryption features tucked away although you need either of the following two:

Decrypt https wireshark