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How to know details of generating keying material in openssl library?

kw flag
LUN

I am testing my TLS 1.3 server (it does not use openssl library) using openssl s_client utility. I have found out that s_client can not decrypt encrypted extensions of the server. So I need to know parameters of decryption used by s_client.

Could you tell me:

  1. How can I force s_client to output (if it is possible) keying material.
  2. In which procedures/modules s_client generates keying material - IV, master key - I want to compare it with calculated by the server and understand the reason of differences.
  3. In which procedures/modules s_client updates running hash during handshaking.

I am planning to trace s_client calls in (2) and (3) using debugger to understand the differences. Unfortunately, I couldn't find them myself due to large number of modules.

dave_thompson_085 avatar
cn flag
https://www.openssl.org/docs/man3.0/man1/openssl-s_client.html#keylogfile-file
LUN avatar
kw flag
LUN
@dave_thompson_085, thank you for the link. This (-keylogfile) option allows to get the final result, but unfortunately does not output intermediate data (for example, used hash value of the handshake and others, mentioned in my question). If I would know where to see it in the debugger, I could detect where the openssl results differ from the result of my server.
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