cloned from https://git.lekensteyn.nl/peter/wireshark-notes/

The repo contains loads of other stuff, but I needed only the sslkeylog for now

sslkeylog

Dumps master keys for OpenSSL clients to file. The format is documented at https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Key_Log_Format

Capture the traffic with wireshark,
right click on a TLS packet line
select Protocol Preferences... -> (Pre)-Master-Secret log filename... and
enter the full path to the premaster.txt

Building

Linux

    cc sslkeylog.c -shared -o libsslkeylog.so -fPIC -ldl

OSX

    cc sslkeylog.c -dynamiclib -o libsslkeylog.dylib -I$(brew --prefix openssl)/include -L$(brew --prefix openssl)/lib -lssl

Usage

Linux

    SSLKEYLOGFILE=premaster.txt LD_PRELOAD=./libsslkeylog.so openssl ...

OSX

    SSLKEYLOGFILE=premaster.txt DYLD_FORCE_FLAT_NAMESPACE=1 DYLD_INSERT_LIBRARIES=./libsslkeylog.dylib openssl ...