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Generating Custom SSL Certificates for WebScarab

Revision as of 10:15, 9 January 2009 by RoganDawes (talk | contribs) (Fix up some phrasing, removed the embedded copy of the script, make sure that the link always points to the latest version in the repo)

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When using WebScarab to proxy SSL conversations, you may want to avoid the somewhat annoying warnings for an unrecognized certificate. You can generate a custom SSL certificate to remove these warning messages and it's rather straight forward if you have a sufficiently recent version of WebScarab (initial support was added on 2008/08/05). Read on to see how.


Below is an illustration of what happens when WebScarab is used as a intercepting proxy for SSL connections.

 --------           -----------           ---------
| server |<--[1]-->| WebScarab |<--[2]-->| browser |
 --------           -----------           ---------

For [1], you are using the "real" SSL certificate from the website you are browsing to. That SSL certificate is signed by a recognized certificate authority (CA). The thing that makes those CA's special is that browsers know about them and trust them. For example in Firefox:

  1. Open Edit -> Preferences -> Advanced -> Encryption
  2. View Certificates button
  3. Authorities tab

to see a list of built-in trusted CA's. The only thing that needs to trust this certificate is WebScarab, which trusts all certificates, whether valid or not.

For [2], you are using the the self-signed server.p12 certificate which comes with WebScarab. The difference between [1] and [2] is that the CA which signed that certs is NOT built into browsers so they do not trust them by default. Additionally, the domain name of this certificate will not match the domain your browser is accessing. The default is the webscarab CA and a host name of webscarab.

Generating a Certificate

Since your browser doesn't trust the CA which signed server.p12 in [2] above, you've got two choices:

  1. Instruct the browser to trust the certificate. This will work for the CA part but not for the host name. You will still be prompted by the browser so this doesn't really help much, and is not advised anyway, due to the fact that lots of people have this CA cert, and could use it to create SSL certificate for arbitrary sites. I know that you can have Firefox trust the CA used in [2] permanently - though it's a bunch of clicks in Firefox 3 - about 6 or 7 clicks and you still have the host name mis-match issue.
  1. Use a .p12 file & CA certificate. You'll have to have WebScarab use the new .p12 file and install the CA certificate into your browser.

There is a script to do this in the WebScarab Git repository. You can get it here.

The script will create a server-specific key and certificate for the site provided as a parameter on the command line. If this is the first time the script is being run, it will also create a CA cert which you can then import into your browser(s).

If you called that script like:

$ ./

It will generate a bunch of output and create a file for WebScarab and a ca_cert.pem file (this is the CA used to sign The script will run fine on Linux (I just tried it) and possibly OS X but will only work on Windows under Cygwin.

Take the (assuming you ran the script like above) and let WebScarab know about it. To do this you will need to place it in ${WEBSCARAB_HOME}/certs/. WebScarab checks in that directory whenever a request is made for an SSL site, for a file <sitename>.p12, and will use it in preference to the default server cert if one is found.

Take the ca_cert.pem file and configure your browser to trust that CA. For Firefox:

  1. Open Edit -> Preferences -> Advanced -> Encryption
  2. View Certificates button
  3. Authorities
  4. Click the Import button and navigate to the ca_cert.pem file

Make sure you at least check the box "Trust this CA to identify web sites." option when you are importing - it will bring up a window with that information.

For IE, I don't know off the top of my head. Try this link except for instead of downloading it you can right-click on the ca_cert.pem file and select "Install Certificate"

FYI: Firefox and IE will both need to be configured if both are used as they keep their lists of trusted CAs in different places.

Added Bonus If you keep the working directory for (recommended!), you can create new custom SSL certificates and not need to import a new CA cert. If you know all the domains you'll be testing, you can run multiple times and just restart WebScarab once to get them all recognized.

For the curious, this is the directory structure the script creates:

|-- sslcerts
|   |-- ca_cert.pem
|   |-- certindex.txt
|   |-- certindex.txt.attr
|   |-- certindex.txt.old
|   |-- certs
|   |   `-- 100001.pem
|   |-- openssl.cnf
|   |-- private
|   |   |-- ca_key.pem
|   |   `--
|   |-- serial
|   |-- serial.old
|   |--
|   `--

3 directories, 14 files 


  1. I was not precise in terms and used SSL and HTTPS loosely in the above. This process would also applies to TLS - I just didn't want to type SSL/TLS over and over.
  2. Matt Tesauro was the author of this document. If you have corrections, feel free to make them yourself (its a Wiki after all) or contact Matt at mtesauro (at)