Extract pre-master keys from memory

Question

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.

Answer 1

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).