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I want to get pre-master key from OpenSSL application (in order to decrypt traffic). Details:

  • OpenSSL version: 1.0.2l, statically linked, no debug symbols
  • I'm able to debug the application (hit breakpoint inside SSL_connect(SSL *s) method)

Is there any way to get the pre-master key from there? I'm using x64dbg.

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  • Can you modify OpenSSL and link with the modified version?
    – ambiso
    Nov 21, 2020 at 22:57

1 Answer 1

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From https://stackoverflow.com/questions/36240279/how-do-i-extract-the-pre-master-secret-using-an-openssl-based-client

I recommend using the master key, which is easier to get at. To the best of my knowledge the pre-master key only exists ephemerally on the stack in OpenSSL. The master key is available in ssl_session_st (defined in ssl.h in the 1.0.2 branch but moved to ssl_locl.h in a later version). The SSL member variable session is a pointer to its ssl_session_st (aka SSL_SESSION).

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