Hands-on OpenSSL Programming

OpenSSL is an open-source software package which implements general-purpose cryptography and the Secure Sockets Layer (SSL). Learn how to use this tool.

What does that little padlock in your Web browser really mean? How does one set up a secure Web server? How does one implement client and server authentication? What about SSL for non-Web software? We will try to remove the mystique behind such questions.

Participants can passively watch our presentation, or compile along with us. We have several snippets of code:

• Unix programmers can download slightly modified OpenSSL demo code
• Windows programmers should download some modified the OpenSSL demo code. This is a WinZip file with a MSVC++ 6 workspace containing the client and server examples. Also a short readme, and some precompiled library files. It should work out of the box, but probably won't. It needs to be unzipped in its own directory. The code assumes that certificates are in a c:\certs directory.

Agenda

1. Getting started with OpenSSL.
   1. Install OpenSSL 0.9.6

        get openssl
        $ ./config --prefix=/usr/local
        $ make
        $ make test
        $ make install
      

   2. Connect to our server, type a string.

      	openssl s_client -connect snafu.fooworld.org:443 
      	GET / HTTP/1.0
      	

2. Certificate generation
   1. Demo certs.
      1. Sample X509 self-signed server certificate
      2. Sample X509 server certificate issued by Verisign
   2. Generate a key pair:

      	openssl genrsa -out server-key.pem 1024
      

   3. Generate certificate request:

      	openssl req -new -key server-key.pem -out server-req.pem
      

   4. Generate a self-signed cert and key at the same time:

       openssl req -x509 -newkey rsa:1024 -keyout server-key.pem -out server-req.pem
      

   5. Generate CA key pair. Trickier.
3. Authentication
   1. Server authentication. Most common in SSL. Clients will require servers to prove who they claim to be.
   2. Client authentication. Clients can prove identity to a server. Available in SSL, but less common. Used at MIT. Most sites use passwords instead of client certificates.
4. Non-Web SSL Applications
   1. Use our demo code. Compile client.
   2. Modify client to set client certificate.
   3. SSL Analyzer. Decrypt SSL traffic on the fly.
      1. Start the SSL dump program.

             ./ssldump -Ad -k /home/key.pem -p foobar -i eth0 host snafu-beta.mit.edu
         	

      2. Start an SSL client to dump. Note, ssldump requires Kx=RSA.

         	openssl s_client -connect snafu-beta.mit.edu:443 -cipher DES-CBC3-SHA  
         	

   4. SSL on the Web
      1. Apache

         untar apache, openssl, modssl
         install openssl
         cd mod_ssl-2.7.1-1.3.14
         ./configure --with-apache=../apache_1.3.14 \
          --with-ssl=../openssl-0.9.6 \
          --prefix=/usr/local/apache
         
         cd ../apache_1.3.14/
         make
         make certificate
         	[fill in values]
         make install
         
         load httpd.conf to see SSL stuff
         ./bin/apachectl startssl
         [enter cert password]
         

5. Problems related to SSL
   1. Flawed implementation of SSL. E.g., bad random numbers
   2. Demonstrate bug in certificate management of Netscape <= 4.73
      1. Set DNS server to 18.26.4.9. This simulates DNS spoofing. Might need to reboot.
      2. Visit https://snafu.mit.edu/ and click away the warnings
      3. Visit https://www5.etrade.com/etrade.html
      4. Enter the form data. Submit. It's harmless.
      5. technical explanation
   3. Caching on bad parameters. E.g., IP address instead of hostname. Remembering authentication based on certificate, not the hostname.
   4. CA could accidentally certify an inappropriate site. For instance.
   5. Root CA compromised (Sun cert)
   6. What CAs do you trust? Do you know all your CAs?
   7. SSL proxying. Server authentication does not imply content authentication.
   8. Misleading certificate management

Links to software

• OpenSSL for the low-level crypto and SSL libraries. Minimal certificate generation tools.
• Apache and ModSSL to compile an SSL Web Server
• SSL Analyzer to dump SSL negotiation traffic and optionally decrypt traffic.
• OpenCA for a collection of scripts to implement a certificate authority.

Questions/Answers