ssl telnet

SSL "telnet"

A common way to debug a network server is to use 'telnet' or 'nc' to connect to the server and issue some commands in the protocol to verify whether everything is working correctly. That obviously only works for ASCII protocols (as opposed to binary protocols), and it obviously also only works if you're not using any encryption.

But that doesn't mean you can't test an encrypted protocol in a similar way, thanks to openssl's s_client:

wouter@country:~$ openssl s_client -host samba.grep.be -port 443
CONNECTED(00000003)
depth=0 /C=BE/ST=Antwerp/L=Mechelen/O=NixSys BVBA/CN=svn.grep.be/emailAddress=wouter@grep.be
verify error:num=18:self signed certificate
verify return:1
depth=0 /C=BE/ST=Antwerp/L=Mechelen/O=NixSys BVBA/CN=svn.grep.be/emailAddress=wouter@grep.be
verify return:1
---
Certificate chain
 0 s:/C=BE/ST=Antwerp/L=Mechelen/O=NixSys BVBA/CN=svn.grep.be/emailAddress=wouter@grep.be
   i:/C=BE/ST=Antwerp/L=Mechelen/O=NixSys BVBA/CN=svn.grep.be/emailAddress=wouter@grep.be
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=/C=BE/ST=Antwerp/L=Mechelen/O=NixSys BVBA/CN=svn.grep.be/emailAddress=wouter@grep.be
issuer=/C=BE/ST=Antwerp/L=Mechelen/O=NixSys BVBA/CN=svn.grep.be/emailAddress=wouter@grep.be
---
No client certificate CA names sent
---
SSL handshake has read 1428 bytes and written 316 bytes
---
New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-SHA
Server public key is 1024 bit
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1
    Cipher    : DHE-RSA-AES256-SHA
    Session-ID: 65E69139622D06B9D284AEDFBFC1969FE14E826FAD01FB45E51F1020B4CEA42C
    Session-ID-ctx: 
    Master-Key: 606553D558AF15491FEF6FD1A523E16D2E40A8A005A358DF9A756A21FC05DFAF2C9985ABE109DCD29DD5D77BE6BC5C4F
    Key-Arg   : None
    Start Time: 1222001082
    Timeout   : 300 (sec)
    Verify return code: 18 (self signed certificate)
---
HEAD / HTTP/1.1
Host: svn.grep.be
User-Agent: openssl s_client
Connection: close

HTTP/1.1 404 Not Found
Date: Sun, 21 Sep 2008 12:44:55 GMT
Server: Apache/2.2.3 (Debian) mod_auth_kerb/5.3 DAV/2 SVN/1.4.2 PHP/5.2.0-8+etch11 mod_ssl/2.2.3 OpenSSL/0.9.8c
Connection: close
Content-Type: text/html; charset=iso-8859-1

closed
wouter@country:~$

As you can see, we connect to an HTTPS server, get to see what the server's certificate looks like, issue some commands, and the server responds properly. It also works for (some) protocols who work in a STARTTLS kind of way:

wouter@country:~$ openssl s_client -host samba.grep.be -port 587 -starttls smtp
CONNECTED(00000003)
depth=0 /C=BE/ST=Antwerp/L=Mechelen/O=NixSys BVBA/CN=samba.grep.be
verify error:num=18:self signed certificate
verify return:1
depth=0 /C=BE/ST=Antwerp/L=Mechelen/O=NixSys BVBA/CN=samba.grep.be
verify return:1
---
Certificate chain
 0 s:/C=BE/ST=Antwerp/L=Mechelen/O=NixSys BVBA/CN=samba.grep.be
   i:/C=BE/ST=Antwerp/L=Mechelen/O=NixSys BVBA/CN=samba.grep.be
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=/C=BE/ST=Antwerp/L=Mechelen/O=NixSys BVBA/CN=samba.grep.be
issuer=/C=BE/ST=Antwerp/L=Mechelen/O=NixSys BVBA/CN=samba.grep.be
---
No client certificate CA names sent
---
SSL handshake has read 1707 bytes and written 351 bytes
---
New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-SHA
Server public key is 1024 bit
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1
    Cipher    : DHE-RSA-AES256-SHA
    Session-ID: 6D28368494A3879054143C7C6B926C9BDCDBA20F1E099BF4BA7E76FCF357FD55
    Session-ID-ctx: 
    Master-Key: B246EA50357EAA6C335B50B67AE8CE41635EBCA6EFF7EFCE082225C4EFF5CFBB2E50C07D8320E0EFCBFABDCDF8A9A851
    Key-Arg   : None
    Start Time: 1222000892
    Timeout   : 300 (sec)
    Verify return code: 18 (self signed certificate)
---
250 HELP
quit
221 samba.grep.be closing connection
closed
wouter@country:~$

OpenSSL here connects to the server, issues a proper EHLO command, does STARTTLS, and then gives me the same data as it did for the HTTPS connection.

Isn't that nice.