Debugging TLS connections with Wireshark?

On 10.07.2020 13:18, Hannu Hartikainen wrote:
> I logged some traffic between my own client and server last night with
> Wireshark. Obviously the data is encrypted, but I was surprised to not
> be able to decrypt the data even when I have the private key for the
> server (it would work for some TLS 1.2 setup, apparently). Fortunately I
> found the bug hindering my progress just by looking at the code. Eventually.
> 
> Does anyone know how to log TLS session keys and later use them to
> decrypt the logged traffic? Does some client perhaps already support?this?

The (asymmetric) keys in the certificates are only used to exchange a
(symmetric) session key, which would need to be logged in order to be
able to decrypt the traffic.

You would typically log the session keys to a file which then is read by
Wireshark to decrypt the TLS traffic, see [0] for an example using Firefox.

To have an idea of how to do it in your own application you might want
to have a look at the answers at [1].

Cheers, J.

[0] https://wiki.wireshark.org/TLS#Using_the_.28Pre.29-Master-Secret
[1]
https://security.stackexchange.com/questions/80158/extract-pre-master-keys-
from-an-openssl-application

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