I am currently trying to solve an exercise where I should look at a TLS 1.2 handshake trace while having access to pre and both randoms (server random and client random).

In order to decrypt application data, I need to rebuild the master key.

But I am struggling with finding the section where it is negotiated how this master key is actually built from pre and randoms.

How does TLS 1.2 handle that? Is there maybe a default handling?


1 Answer 1


At the end, I didn't had to rebuild it manually. I used wireshark and its automatic decryption tools to build the master key and extract the desired information.

  • This might have ended up working for you, but it's not an answer to what you asked. You asked how it was done in the protocol. Your answer is "I didn't need to know, I just clicked a button in this tool."
    – schroeder
    Jan 23, 2020 at 13:53

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