Secure Socket Layer (SSL)

Transport Layer Security (TLS) provides security in the communication between two hosts. It provides integrity, authentication and confidentiality. It is used most commonly in web browsers, but can be used with any protocol that uses TCP as the transport layer.

SSL is the former version of the TLS protocol. These names are often used interchangeably which can lead to some confusion:

Protocol dependencies

Some well known TCP ports for TLS traffic are

SSL dissection in Wireshark

The SSL/TLS dissector is fully functional and even supports advanced features such as decryption of TLS if appropriate secrets are provided. TLS decryption requires Wireshark to be built with Libgcrypt (mandatory since Wireshark 2.4). Support for RSA private key files requires GnuTLS. The official Wireshark binaries have both dependencies.

Preference Settings

Go to Edit -> Preferences. Open the Protocols tree and select SSL. Alternatively, select a SSL/TLS packet in the packet list, right-click on the SSL layer in the packet details view and open the Protocol preferences menu.

RSA keys list

The RSA keys list button opens a new dialog with the following fields:

IP address

The IP address of the SSL server in IPv4 or IPv6 format, or the following special values: any, anyipv4, anyipv6, 0.0.0.0 (this field is ignored since Wireshark 2.0)

Port

The port number, the special value start_tls or 0. Ignores since Wireshark 2.0.

Protocol

A protocol name for the decrypted network data. Popular choices are http or data. If you enter an invalid protocol name an error message will show you the valid values.

Key File

path to the RSA private key.

Password

Leave it empty for PEM-encoded private key files or provide it for encrypted PKCS#12 key files.

The RSA key file can either be a PEM format private key or a PKCS#12 keystore. If the file is a PKCS#12 keystore (typically a file with a .pfx or .p12 extension), the password for the keystore must be specified in the Password field.

Starting with Wireshark 2.0, the RSA key file is automatically matched against the public key as found in the Certificate handshake message. Before Wireshark 2.0, it relied on the user to enter a valid Address and Port value. Note that only RSA key exchanges can be decrypted using this RSA private key, Diffie-Hellman key exchanges cannot be decrypted using a RSA key file! (See "SSLKEYLOGFILE" if you have such a capture.)

Key File format conversion

The file format needed is 'PEM'. Note that it is common practice on webservers to combine the public key (or certificate) and the private key in a single PEM file. In that case - locate this PEM file and cut and paste the section headed by 'PRIVATE KEY' (including header and footer) into a new 'file.key' file which should look like:

-----BEGIN RSA PRIVATE KEY-----
MIIEpAIBAAKCAQEAtIvaDmeOGleYuxT01GfAmgugHVlqCOFfGYqy3gxMWt/fxO/7
s7BJzqnhAFOWBjmBAdj7hHmPyCoJM7/MdCDJt1y7d20BJAGxD0ZQ4kxzGZDCjc5z
....... some 20-100 lines of base64 encoded data ...............
Jh2kZkKoVG3Qr+66IlBDuVllIbwQU0F1fYy2FTjZL4vbmdupwHUyTnPK57vP8RJ7
cpc1qwLZxfurxZfhI9gxXOO5eUg1WBupw029SSoSafYBqO4a9wg1OA==
-----END RSA PRIVATE KEY-----

If the PEM file is encrypted, it will appear as:

-----BEGIN RSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-EDE3-CBC,CB7BE7B5A318ACE6

ScuaEtGA1xy7iVvvntc4hZ9Kl0VOKmA9sOcfP1CnrUVpAuLoHPEXTsc10smlXwsl
[...]
yy7ANfGCZTWaWP89uOIwlXK0n8hHZjTjw5axBuWXvgWHNbvein7tsg==
-----END RSA PRIVATE KEY-----

Such key files are currently not supported by Wireshark, so they have to be decrypted first:

openssl rsa -in encrypted.key -out new.key

On Windows keys are often stored in PKCS7/DER format (locally) or in NET format (from any directory server). Use the following to convert:

# for PKCS7/DER keys (as held on disk)
openssl pkcs8 -nocrypt -in derfile.key -inform DER -out key.pem -outform PEM
# for NET keys (from the directory server)
openssl pkcs8 -nocrypt -in file.ick -inform NET -out key.pem -outform PEM

On OS X and Solaris, around Oracle and various other systems the file format used is often PKCS#12. Convert with:

openssl pkcs12 -nodes -in file.p12 -out key.pem -nocerts

Example capture file

See also SampleCaptures#SSL_with_decryption_keys.

dump.pcapng TLSv1.2 capture with 73 cipher suites, you need this premaster.txt file for decrypting the traffic. (linked from https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=9144)

Display Filter

A complete list of SSL display filter fields can be found in the display filter reference

Show only the SSL based traffic:

Capture Filter

You cannot directly filter SSL protocols while capturing. However, if you know the TCP port used (see above), you can filter on that one, for example using tcp port 443.

Complete SSL decryption walk through

Ensure you have a version of Wireshark with GnuTLS support:

$ wireshark --version
wireshark 1.0.0

Copyright 1998-2008 Gerald Combs <gerald@wireshark.org> and contributors.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Compiled with GTK+ 2.12.9, with GLib 2.16.3, with libpcap 0.9.8, with libz
1.2.3, without POSIX capabilities, with libpcre 7.4, with SMI 0.4.7, with ADNS,
without Lua, with GnuTLS 2.2.2, with Gcrypt 1.4.0, with Heimdal Kerberos,
without PortAudio, without AirPcap.

Running on FreeBSD 7.0-RELEASE, with libpcap version 0.9.8.

Built using gcc 4.2.1 20070719  [FreeBSD].

Specifically check for the with GnuTLS 2.2.2 in the output.

Next create an RSA key and certificate pair with:

openssl req -new -x509 -out server.crt -nodes -keyout server.pem -subj /CN=localhost

Now run a server using above:

openssl s_server -www -cipher AES256-SHA -key server.pem -cert server.crt

and test that the server works by going to https://localhost:4433/ (use the flag -accept 443 to bind above to the normal https port).

Now start Wireshark - add above privkey.pem in the SSL preference pane:

http://people.apache.org/~dirkx/settings.png

This should result in a config snipped in the file ~/.wireshark/preferences

ssl.desegment_ssl_records: TRUE
ssl.desegment_ssl_application_data: TRUE
ssl.keys_list: 127.0.0.1,4443,http,/home/dirkx/xx/privkey.pem
ssl.debug_file: /home/dirkx/.wireshark-log

and configure the capturing:

http://people.apache.org/~dirkx/config.png

and then do a test request; for example with the command

printf 'GET / HTTP/1.0\r\n\r\n' | openssl s_client -ign_eof

Then stop your capture. The screen should look like attached:

http://people.apache.org/~dirkx/dump.png

And the TCP connection like

http://people.apache.org/~dirkx/tcp.png

and analyze the SSL shows you:

http://people.apache.org/~dirkx/ssl.png

Or if you want to observe authentication with a client cert; try the following:

# Generate self signed cert
openssl req -new -x509 -nodes -out client.crt -keyout client.key -subj /CN=Moi/O=Foo/C=NL

# Start a server
openssl s_server -cipher AES256-SHA -accept 4443 -www -CAfile client.crt -verify 1 -key server.pem -cert server.cert

# And test
printf 'GET / HTTP/1.0\r\n\r\n' | openssl s_client -connect localhost:4443 -ssl3 -cert client.pem -key client.key -ign_eof

# tshark commands
tshark -o "ssl.desegment_ssl_records: TRUE" -o "ssl.desegment_ssl_application_data: TRUE" -o "ssl.keys_list: 127.0.0.1,4443,http,/home/dirkx/xx/privkey.pem" -o "ssl.debug_file: /home/dirkx/.wireshark-log" -i eth0 -R "tcp.port == 4443"

The log should look like http://people.apache.org/~dirkx/wireshark.log. Or, a more realistic example with Firefox is at http://people.apache.org/~dirkx/wireshark-firefox.log (from 10.11.0.200->10.11.0.111, port 4433).

Using the (Pre)-Master-Secret

Decoding an SSL connection requires either knowledge of the (asymmetric) secret server key and a handshake that does not use DH or the (base of) the symmetric keys used to run the actual encryption. Support was added to Wireshark with SVN revision 37401 to do this, so it became available with Wireshark 1.6. For instructions look at this question on ask.wireshark.org

Since SVN revision 36876, it is also possible to decrypt traffic when you do not possess the server key but have access to the pre-master secret. For more details, see this security.stackexchange.com answer or this step-by-step walkthrough. That answer also contains some suggestions on finding out why SSL/TLS sessions do not get decrypted. In short, it should be possible to log the pre-master secret to a file with a current version of Firefox, Chromium or Chrome by setting an environment variable (SSLKEYLOGFILE=</path/to/private/directory/with/logfile>).

Applications using OpenSSL could use a GDB or a LD_PRELOAD trick to extract the secrets. If you do not mind recompiling Qt4/Qt5 with a patch, then see this blog with details. For Java programs, pre-master secrets can be extracted from the SSL debug log, or output directly in the format Wireshark requires via this agent. Python scripts can be edited to dump keys as well.

External links


SSL (last edited 2018-03-30 12:23:49 by PeterWu)