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ssltrace

ssltrace hooks an application's SSL libraries to record keying data of all SSL connections. By default, this data is outputted on stderr in a Wireshark-compatible format.

Supported SSL libraries:

  • OpenSSL
  • NSS [1]
  • GnuTLS

[1] Recent versions of NSS also support the SSLKEYLOGFILE environment variable, which might be easier to use.

Building

Build dependencies:

  • libdw
  • OpenSSL headers
  • NSS headers
  • NSPR (Netscape Portable Runtime) headers
  • GnuTLS headers

For example, on Debian or Ubuntu based systems: sudo apt-get install libdw-dev libssl-dev libgnutls-dev libnss3-dev libnspr4-dev

After installing the dependencies, run make.

Running

Run dependencies:

  • libdw
  • NSS/GnuTLS debug symbols

For example, on Debian or Ubuntu based systems: sudo apt-get install libdw1 libgnutls28-dbg

NSS and GnuTLS internal structures are not defined in public headers. If you want to trace programs that use these libraries, you'll need to have the debugging symbols installed. Mozilla products such as Firefox have been known to ship with its own version of the NSS libraries.

After installing the dependencies, run LD_PRELOAD=/path/to/ssltrace.so child-program.

Configuring output

If the environment variable SSLTRACE_LOG is set, ssltrace will try to use it as a filename to open for append and log there. If opening the file fails, ssltrace will print a message on stderr and exit.

If the file /etc/ssltrace.d/logfile exists, ssltrace will try to use the contents as a filename to open for append and log there. If opening the file fails, ssltrace will print a message on stderr and exit.

Otherwise, ssltrace will log on stderr.

Note that ssltrace won't try to open any files until it actually has to log something (which is usually when the first SSL connection gets initiated).

Testing OpenSSL

We can just use the openssl command-line utility.

Use s_client to make an SSL connection as a client:

LD_PRELOAD=./ssltrace.so openssl s_client -connect SOME_HOST:SOME_PORT

To run an OpenSSL server, you first need to generate a public/private key pair:

openssl req -newkey rsa:2048 -nodes -new -x509 -keyout KEY_FILE -out CERT_FILE

Run the s_server SSL server:

LD_PRELOAD=./ssltrace.so openssl s_server -accept SOME_PORT -key KEY_FILE -cert CERT_FILE

Testing NSS

We will use the NSS tools certutil, tstclnt and selfserv. These might or might not come with your distribution's NSS package [2].

First, you need to create a certificate database in some directory:

certutil -N -d /PATH/TO/YOUR/NSS/DB

Now, run tstclnt to make an SSL connection as a client:

LD_PRELOAD=./ssltrace.so nss/tstclnt -o -V ssl3: -h SOME_HOST -p SOME_PORT -d /PATH/TO/YOUR/NSS/DB

To run an NSS SSL server, you first need to generate a public/private key pair:

certutil -t P,P,P -x -S -d /PATH/TO/YOUR/NSS/DB -s "o=SUBJECTNAME" -n AN_IDENTIFIER

Run the selfserv SSL server:

LD_PRELOAD=./ssltrace.so selfserv -v -n AN_IDENTIFIER -p SOME_PORT -d /PATH/TO/YOUR/NSS/DB

[2]: On Ubuntu (and probably Debian-flavored distributions), certutil is in libnss3-tools, but for tstclnt and selfserv do;

apt-get source nss
apt-get build-dep nss
cd nss-*
debuild -i -us -uc -b

Find your binaries in mozilla/dist/bin/. Don't ask me why they're not included in the package while they obviously do get built by default.

Testing GnuTLS

We can just use the gnutls-cli and gnutls-serv command-line utilities.

Use gnutls-cli to make an SSL connection as a client:

LD_PRELOAD=./ssltrace.so gnutls-cli --insecure -p SOME_PORT SOME_HOST

The GnuTLS server uses the same type of keys as OpenSSL, see above on how to generate them.

Run the gnutls-serv SSL server:

LD_PRELOAD=./ssltrace.so gnutls-serv -p SOME_PORT --x509keyfile KEY_FILE --x509certfile CERT_FILE