SSL support in Ncat - confusing server parameters and client version issue

[Kristof Boeynaems <kristof.boeynaems () gmail com>]

Hi,

I had a look at the SSL support in Ncat and found the following (I am
using the latest CVS version, Ncat 0.2).

Note that I am using OpenSSL 0.9.8g; I did not test the latest OpenSSL version.

-------------------------------------------------------------------------
1. Ncat as SSL server - confusing parameters
-------------------------------------------------------------------------
The only way I could Ncat get to work as SSL server is by specifying
all the SSL parameters, that is, not only --ssh, but also --ssl-key
and --ssl-cert.
E.g.

  ./ncat --ssl -l 1111 --ssl-cert
/usr/share/doc/libssl-dev/demos/sign/cert.pem --ssl-key
/usr/share/doc/libssl-dev/demos/sign/key.pem

(Note that I am using a certificate and key that comes with libssl-dev)

Now, the fact that the cert and key parameters have to be specified as
well, might sound obvious to SSL experts, but I forgot this in first
instance, and that returns some obscure errors, depending on the SSL
client used to connect to the Ncat server.
These are the Ncat error messages I receive when omitting the cert and
key options, thus running:

  ./ncat --ssl -l 1111

With SSLv2:

  openssl s_client -ssl2 -connect localhost:1111
=> SSL_accept(): error:1406B0C9:SSL
routines:GET_CLIENT_MASTER_KEY:peer error certificate

With SSLv3 and TLSv1:

  openssl s_client -ssl3 -connect localhost:1111
  openssl s_client -tls1 -connect localhost:1111
=> SSL_accept(): error:1408A0C1:SSL routines:SSL3_GET_CLIENT_HELLO:no
shared cipher

I would suggest to provide a user-friendly warning to the user when
she tries to run Ncat with both the "--ssl" and "-l" flags, but not
the "--ssl-cert" and "--ssl-key" flags.

Note that, in theory, there are some ciphers that do not seem to
require certificate nor key. E.g. the "anonymous" ciphers ("openssl
ciphers aNULL") do not seem to require a server certificate. That's
why instead of forcing the user to always use a key/certificate, a
warning might be more appropriate.
However, when I tried to use these anonymous ciphers, this does not
seem to work with Ncat, even when specifying a key and cert:

  openssl s_client -cipher aNULL -connect localhost:1111
=> SSL_accept(): error:1408A0C1:SSL routines:SSL3_GET_CLIENT_HELLO:no
shared cipher

Ncat does not seem to support these ciphers.
I also missed some command line parameters to specify the used SSL
version and supported ciphers in Ncat. Is adding these features
planned?

-------------------------------------------------------------------------------
2. Ncat as SSL client - Not all versions supported?
-------------------------------------------------------------------------------
It seems that Ncat does not support pure TLSv1 or SSLv3 servers.
Starting an OpenSSL SSLv3 or TLSv1 server with following commands:

  openssl s_server -cert /usr/share/doc/libssl-dev/demos/sign/cert.pem
-key /usr/share/doc/libssl-dev/demos/sign/key.pem -ssl3
  openssl s_server -cert /usr/share/doc/libssl-dev/demos/sign/cert.pem
-key /usr/share/doc/libssl-dev/demos/sign/key.pem -tls1

and trying to connect with Ncat as follows:

  ./ncat --ssl localhost 4433

Ncat immediately quits without any error, while at the openssl side
the following error is shown (both in SSLv3 and TLSv1 case):

  3026:error:1408F10B:SSL routines:SSL3_GET_RECORD:wrong version
number:s3_pkt.c:295:

It works fine with an OpenSSL server started without specifying the
version, or using -no_ssl2 or -ssl2:

  openssl s_server -cert /usr/share/doc/libssl-dev/demos/sign/cert.pem
-key /usr/share/doc/libssl-dev/demos/sign/key.pem
  openssl s_server -cert /usr/share/doc/libssl-dev/demos/sign/cert.pem
-key /usr/share/doc/libssl-dev/demos/sign/key.pem -no_ssl2
  openssl s_server -cert /usr/share/doc/libssl-dev/demos/sign/cert.pem
-key /usr/share/doc/libssl-dev/demos/sign/key.pem -ssl2

Am I missing something, or does Ncat indeed not support pure TLSv1 and
SSLv3 servers?

Thank you,

Kristof

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