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Using Unsniff to analyze SSL and TLS streams
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Version "Using Unsniff to analyze SSL / TLS " (694 kb)
 A number of
applications today use SSL and TLS as a security
layer. Unsniff allows authorized users to analyze these
applications by decrypting the SSL/TLS streams in real time. This is
done without interrupting the SSL streams in any way. Unsniff can also
strip out the SSL/TLS layer completely and analyze the application
protocols as if the security layer never existed. If you
are working with a secure web
server,
you can analyze the HTTPS protocol,
including the ability to reconstruct complete web pages.
References : RFC2246
(TLS 1.0), RFC2459
(X.509v3), PKCS Standards (RSA Website)
Feature
overview
Working
with PDUs and Streams
Decrypting
SSL/TLS
Analyzing
upper
layer protocols
Howto
: Analyzing a secure
Microsoft IIS web server
Howto :
Analyzing a secure Apache web server
Howto : Analyzing protocols tunneled via stunnel
FAQ
Feature
Overview
| SSL
records |
Unsniff
shows SSL/TLS records as
separate entities in the PDU sheet irrespective of how they were
carried at the link layer. |
| Stream
analysis |
Monitor entire SSL / TLS
sessions in real time via the Streams sheet. |
| Decryption |
Provided
you have the
servers private
key material you can decrypt SSL / TLS sessions in real time. Most of
the popular ciphers are supported. |
| Advanced
Decryption |
Unsniff supports SSL / TLS
features such as session reuse and cipher renegotiation. |
| Upper
layer decryption |
SSL/TLS
only acts as a
transport layer
for higher layer protocols. Ultimately we are interested in the
analysis of higher layer protocols such as HTTP, LDAP etc. Unsniff does
not just stop at showing you the decrypted text, it actually strips off
the security layer and performs full analysis of the upper layer
protocol. This allows you to do things like view complete web pages
transferred via HTTPS. |
| Scripting |
Like all other
protocols, SSL/TLS
is completely scriptable. You can write tools in Ruby or VBScript to
scan through a capture file looking for weak ciphers or untrusted
certificates. |
Working
with PDUs and Streams
Use
PDU and Stream analysis to perform more efficient and
accurate analysis
PDU Analysis
SSL/TLS is a record oriented protocol that runs on top of TCP. These
SSL/TLS records (or PDUs) can be upto 16K bytes in length. They also do
not respect link layer packet boundaries. You can have multiple SSL/TLS
records per ethernet packet or a single record spread over multiple
packets. Unlike older protocol analyzers, Unsniff analyzes
PDUs (protocol data
units) as first class entities. This means that you do not have to dig
through ethernet (or other link layer) frames while trying to locate
SSL / TLS records.
To view entire SSL/TLS records switch to the PDU sheet
Stream Analysis
Unsniff also allows you to monitor entire SSL / TLS streams as first
class entities. You can see entire SSL/TLS sessions
being established and completed in real time in the Streams sheet. The
main advantage of stream monitoring is you can instantly zone in on
the exact stream you want. You can even copy-paste entire streams into
another capture file or iterate through streams via the scripting
interface.
To view SSL/TLS streams switch to the "Sessions" sheet
Decrypting
SSLv3.0 / TLS 1.0
How it works ?
 |
Only
legitimate users who have access to the servers private key
such as system administrators can use this feature. Unsniff has no
mechanisms to decrypt SSL / TLS sessions without legitimate server
private key material. |
The servers digital certificate plays a pivotal role in
the authentication and encryption of data. The SSL client and
server quickly agree on a shared secret (the master secret) using
public-key cryptography. When provided with the servers keying
material, Unsniff can decrypt the data transferred. Unsniff has built
in full stream and PDU analysis which are able to support the SSL / TLS
record layer very well.
When the right keying material is available
- For every encrypted record (PDU), Unsniff
shows a
corresponding clear text record. This helps you analyze encrypted SSL
records such as alerts.
- For every encrypted SSL stream, Unsniff shows a
corresponding clear text stream.
- If enabled, for every SSL stream, Unsniff shows a
corresponding
application layer stream with the SSL / TLS layer completely stripped
off.
Supported
Cipher Suites
Unsniff supports the following cipher suites. If you want support for a
cipher not listed below, please post a request in our forum.
- RC4_128_WITH_MD5
- RC4_128_EXPORT40_WITH_MD5
- RSA_WITH_AES_256_CBC_SHA
- RSA_EXPORT1024_WITH_RC4_56_SHA
- RSA_EXPORT1024_WITH_DES_CBC_SHA
- RSA_WITH_RC4_128_MD5
- RSA_WITH_RC4_128_SHA
- RSA-WITH-3DES-EDE-MD5
Note
: Ephemeral Diffie Hellman is not supported nor
are export ciphers less than 1024 bits in length.
This section explains how you can setup Unsniff to decrypt SSL/TLS if
you have access to the right keying material.
Step by step
instructions
This section contains detailed instructions for setting up Unsniff to
decrypt SSL / TLS.
- Enable the SSL/TLS decryption feature
- Obtain the server private key
- Enter the key information into Unsniff
- Start capturing and analyzing SSL / TLS
Enable the SSL/TLS decryption
feature
You must first ensure that you have enabled SSL/TLS decryption. This
option is enabled by default.
Click on Plugins->Customize or the
Customize Plugins
toolbar icon. Ensure that the “Decrypt SSL/TLS”
option is
set to “True”
Obtaining the server private key
If you are developing or testing protocols you can request the private
key file from the system administrator. Unsniff expects the server
private key to be in "unencrypted PKCS #8" format. You may have to
convert your key to this format; Click on these links for specific
instructions for Apache,
Microsoft
IIS, STUNNEL
Private
Key Formats
There are three main key formats :
- OpenSSL Traditional (this is a format that has been in use
in OpenSSL and its predecessor SSLeay)
- PKCS#8 : This is a standard format for storing private keys
(Unsniff requires keys to be in this format)
- PKCS#12: This is a combined file format for keys and
certificates (used by web browsers)
(Public Key Cryptography Standards. These standards are issued by RSA
and can be found on the web at http://www.rsasecurity.com/rsalabs/pkcs )
Using OpenSSL to convert between private key formats
To convert the private key into PKCS#8 format you need
to
use OpenSSL.
Enter the private key information for the server into
Unsniff
Collect information about the IP address and TCP port on which your
SSL / TLS enabled server is running. Now you are ready to enter this
information into Unsniff.
Enter the server information into
Unsniff
Select Tools->TLS->Manage
Private Keys from the
main
Unsniff menu. This opens the “SSL/TLS Key Manager”
Dialog.
Select New
to open the “Enter New
Key” dialog.
Specify the IP Address, Port and the PKCS#8 private key file in this
dialog and click OK.
Start capturing and analyzing SSL / TLS
Now you are ready to start analyzing SSL / TLS. Just click on the
"Start Capture" button or import a capture file in tcpdump format.
Unsniff will automatically decrypt and present you with clear text
protocol data in real time.
Flags
mark decrypted packets and PDUs
Decrypted packets and PDUs are flagged with special icons in the packet
sheet. Observe the
"key" icons on the
left side of the packets sheet.
Analyzing
upper layer protocols
An exciting new feature of Unsniff Network Analyzer is the ability to
analyze upper layer protocols of SSL / TLS. This allows you
to go beyond the clear text of the higher layer protocols and actually
continue the analysis as if the security layer never existed. For
example, when analyzing SSL/TLS web sessions, Unsniff can reconstruct
the entire HTTPS session including the web pages as seen by the browser.
Enable the application analysis feature
You must
first ensure that you have enabled the "SSL/TLS Application Analysis"
feature. This feature is disabled by default due to the overheads
involved with this feature.
- Click
on Plugins->Customize or the
Customize Plugins
toolbar icon.
- Scroll
down
and locate the TLS group.
- Ensure
that
the “Application Analysis”
option is
set to “True”
Specify the SSL / TLS ports used by the application
Unsniff
can analyze any application that uses SSL/TLS. If you want to perform
application analysis, you must tell Unsniff what port number
corresponds to your secure application. You have to use the Access
Point Manager for that purpose. For example : HTTPS (secure HTTP based
on SSL/TLS) runs on TCP port
443. You can specify addition ports or new protocols If the
upper layer protocol is not supported by Unsniff, you need not have an
entry.
To customize SSL/TLS ports:
- Open the
Access Point Manager via Manage->
Access Points
- Scroll
down
and locate the SSL/TLS group
- Click on
the SSL/TLS entry
- Click
on the New Access Point button at the top of the window
- Now you can create a new SSL/TLS to application layer
port
mapping
View
application streams and user objects
Once
everything is in place, Unsniff will automatically generate a new
stream in the Streams Sheet that represents a real-time stripped
version of the encrypted stream. You can expand the stream and view
packets, or view the user objects in that stream and so forth.
Example:
Capture a HTTPS session and view the reconstructed web
page. Read more about Unsniff powerful HTTP analysis capabilities here.
Howto
: Analyzing Microsoft IIS web server
The IIS server allows you to export the private and the server
certificate in a PFX format. This tutorial explains how to export the
key and convert it into unencrypted PKCS #8 format as expected by
Unsniff.
Export
the servers private key to PFX format
Microsoft
Windows allows you to export your IIS private key and digital
certificate in a format called PFX. It is roughly equivalent to the
PKCS#12 format used by apache.
To export your servers private key follow the step-by-step instruction
provided by Microsoft in this Technet article. Remember the password
you used to export the private key. You will need it later !
How
to back up a server certificate in Internet Information Services 5.0
Convert
the PFX format private key to PKCS #8
Once
you have the key material in PFX format, you must convert it into
PKCS#8 format required by Unsniff.
First convert PFX to PEM
openssl
pkcs12 -in MyCert.PFX -nocerts -nodes -out MyCert.PEM
* You will have to enter the password used to protect
the
server private key.
Next convert
PEM to PKCS#8
openssl
pkcs8 -in MyCert.PEM -topk8 -nocrypt -out MyCert.PK8
The file MyCert.PK8 is the key file you must use with Unsniff.
Howto
: Analyzing a secure Apache web server
The apache web server stores its private key in a PEM format. You need
to convert it to PKCS#8 format.
Locate
the apache SSL certificate key (private key) file
- Open httpd.conf , this is usually located in
/etc/httpd/conf
- The SSLCertificateKeyFile line tells you the name and
location of the private key file
- By convention the private key file is placed in
/etc/httpd/conf/ssl.key (You can then ask your administrator for help)
Convert
the apache PEM format to PKCS#8
You
need the secure webserver password to proceed. This is the password
used to protect the server private key.
openssl
pkcs8 -in myapachekey.pem -topk8 -out outkey.pk8 -nocrypt
* You will have to enter the password used to protect
the
server private key.
Howto
: Analyzing protocols tunneled via STUNNEL
STUNNEL is an
excellent piece of software that allows you to secure
arbitrary TCP connections inside a secure SSL tunnel. It is widely used
to provide security to client-server systems that do not have it built
in. Unsniff can look into these encrypted tunnels and provide complete
visibility to the protocols that are carried inside them.
Locate
the server private key
Stunnel
can be started with the private key specified on the command line or
reading the private key location from the stunnel.conf configuration
file. The private key is in PEM format.
Convert
the PEM format to PKCS#8
Use
the following command to convert the private key to PKCS#8 format
required by Unsniff.
openssl
pkcs8 -in stunnel.pem -topk8 -out outkey.pk8 -nocrypt
* You will be asked for the password if the stunnel.pem
key is password protected
FAQ
How can I debug errors encountered during SSL/TLS
analysis ?
Any error encountered during SSL/TLS analysis such as invalid key
material or unsupported cipher is sent to the Unsniff Log Window. You
can view the log window, via the "View->Log
Window" menu. By
default
the log window only shows Major and Critical error messages. You can
adjust the setting via "Tools->Configure->Miscellaneous",
then
select from the logging options.
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