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9.2 Invoking gnutls-serv

Server program that listens to incoming TLS connections.

This section was generated by AutoGen, using the agtexi-cmd template and the option descriptions for the gnutls-serv program. This software is released under the GNU General Public License, version 3 or later.

gnutls-serv help/usage (--help)

This is the automatically generated usage text for gnutls-serv.

The text printed is the same whether selected with the help option (--help) or the more-help option (--more-help). more-help will print the usage text by passing it through a pager program. more-help is disabled on platforms without a working fork(2) function. The PAGER environment variable is used to select the program, defaulting to more. Both will exit with a status code of 0.

gnutls-serv - GnuTLS server
Usage:  gnutls-serv [ -<flag> [<val>] | --<name>[{=| }<val>] ]...

   -d, --debug=num            Enable debugging
                                - it must be in the range:
                                  0 to 9999
       --sni-hostname=str     Server's hostname for server name extension
       --sni-hostname-fatal   Send fatal alert on sni-hostname mismatch
       --alpn=str             Specify ALPN protocol to be enabled by the server
                                - may appear multiple times
       --alpn-fatal           Send fatal alert on non-matching ALPN name
       --noticket             Don't accept session tickets
   -g, --generate             Generate Diffie-Hellman parameters
   -q, --quiet                Suppress some messages
       --nodb                 Do not use a resumption database
       --http                 Act as an HTTP server
       --echo                 Act as an Echo server
   -u, --udp                  Use DTLS (datagram TLS) over UDP
       --mtu=num              Set MTU for datagram TLS
                                - it must be in the range:
                                  0 to 17000
       --srtp-profiles=str    Offer SRTP profiles
   -a, --disable-client-cert  Do not request a client certificate
   -r, --require-client-cert  Require a client certificate
       --verify-client-cert   If a client certificate is sent then verify it.
   -b, --heartbeat            Activate heartbeat support
       --x509fmtder           Use DER format for certificates to read from
       --priority=str         Priorities string
       --dhparams=file        DH params file to use
                                - file must pre-exist
       --x509cafile=str       Certificate file or PKCS #11 URL to use
       --x509crlfile=file     CRL file to use
                                - file must pre-exist
       --x509keyfile=str      X.509 key file or PKCS #11 URL to use
                                - may appear multiple times
       --x509certfile=str     X.509 Certificate file or PKCS #11 URL to use
                                - may appear multiple times
       --srppasswd=file       SRP password file to use
                                - file must pre-exist
       --srppasswdconf=file   SRP password configuration file to use
                                - file must pre-exist
       --pskpasswd=file       PSK password file to use
                                - file must pre-exist
       --pskhint=str          PSK identity hint to use
       --ocsp-response=file   The OCSP response to send to client
                                - file must pre-exist
   -p, --port=num             The port to connect to
   -l, --list                 Print a list of the supported algorithms and modes
       --provider=file        Specify the PKCS #11 provider library
                                - file must pre-exist
   -v, --version[=arg]        output version information and exit
   -h, --help                 display extended usage information and exit
   -!, --more-help            extended usage information passed thru pager

Options are specified by doubled hyphens and their name or by a single
hyphen and the flag character.

Server program that listens to incoming TLS connections.

debug option (-d)

This is the “enable debugging” option. This option takes a number argument. Specifies the debug level.

sni-hostname option

This is the “server’s hostname for server name extension” option. This option takes a string argument. Server name of type host_name that the server will recognise as its own. If the server receives client hello with different name, it will send a warning-level unrecognized_name alert.

alpn option

This is the “specify alpn protocol to be enabled by the server” option. This option takes a string argument.

This option has some usage constraints. It:

Specify the (textual) ALPN protocol for the server to use.

require-client-cert option (-r)

This is the “require a client certificate” option. This option before 3.6.0 used to imply –verify-client-cert. Since 3.6.0 it will no longer verify the certificate by default.

verify-client-cert option

This is the “if a client certificate is sent then verify it.” option. Do not require, but if a client certificate is sent then verify it and close the connection if invalid.

heartbeat option (-b)

This is the “activate heartbeat support” option. Regularly ping client via heartbeat extension messages

priority option

This is the “priorities string” option. This option takes a string argument. TLS algorithms and protocols to enable. You can use predefined sets of ciphersuites such as PERFORMANCE, NORMAL, SECURE128, SECURE256. The default is NORMAL.

Check the GnuTLS manual on section “Priority strings” for more information on allowed keywords

x509keyfile option

This is the “x.509 key file or pkcs #11 url to use” option. This option takes a string argument.

This option has some usage constraints. It:

Specify the private key file or URI to use; it must correspond to the certificate specified in –x509certfile. Multiple keys and certificates can be specified with this option and in that case each occurrence of keyfile must be followed by the corresponding x509certfile or vice-versa.

x509certfile option

This is the “x.509 certificate file or pkcs #11 url to use” option. This option takes a string argument.

This option has some usage constraints. It:

Specify the certificate file or URI to use; it must correspond to the key specified in –x509keyfile. Multiple keys and certificates can be specified with this option and in that case each occurrence of keyfile must be followed by the corresponding x509certfile or vice-versa.

x509dsakeyfile option

This is an alias for the x509keyfile option, see the x509keyfile option documentation.

x509dsacertfile option

This is an alias for the x509certfile option, see the x509certfile option documentation.

x509ecckeyfile option

This is an alias for the x509keyfile option, see the x509keyfile option documentation.

x509ecccertfile option

This is an alias for the x509certfile option, see the x509certfile option documentation.

ocsp-response option

This is the “the ocsp response to send to client” option. This option takes a file argument. If the client requested an OCSP response, return data from this file to the client.

list option (-l)

This is the “print a list of the supported algorithms and modes” option. Print a list of the supported algorithms and modes. If a priority string is given then only the enabled ciphersuites are shown.

provider option

This is the “specify the pkcs #11 provider library” option. This option takes a file argument. This will override the default options in /etc/gnutls/pkcs11.conf

gnutls-serv exit status

One of the following exit values will be returned:

0 (EXIT_SUCCESS)

Successful program execution.

1 (EXIT_FAILURE)

The operation failed or the command syntax was not valid.

gnutls-serv See Also

gnutls-cli-debug(1), gnutls-cli(1)

gnutls-serv Examples

Running your own TLS server based on GnuTLS can be useful when debugging clients and/or GnuTLS itself. This section describes how to use gnutls-serv as a simple HTTPS server.

The most basic server can be started as:

gnutls-serv --http --priority "NORMAL:+ANON-ECDH:+ANON-DH"

It will only support anonymous ciphersuites, which many TLS clients refuse to use.

The next step is to add support for X.509. First we generate a CA:

$ certtool --generate-privkey > x509-ca-key.pem
$ echo 'cn = GnuTLS test CA' > ca.tmpl
$ echo 'ca' >> ca.tmpl
$ echo 'cert_signing_key' >> ca.tmpl
$ certtool --generate-self-signed --load-privkey x509-ca-key.pem \
  --template ca.tmpl --outfile x509-ca.pem

Then generate a server certificate. Remember to change the dns_name value to the name of your server host, or skip that command to avoid the field.

$ certtool --generate-privkey > x509-server-key.pem
$ echo 'organization = GnuTLS test server' > server.tmpl
$ echo 'cn = test.gnutls.org' >> server.tmpl
$ echo 'tls_www_server' >> server.tmpl
$ echo 'encryption_key' >> server.tmpl
$ echo 'signing_key' >> server.tmpl
$ echo 'dns_name = test.gnutls.org' >> server.tmpl
$ certtool --generate-certificate --load-privkey x509-server-key.pem \
  --load-ca-certificate x509-ca.pem --load-ca-privkey x509-ca-key.pem \
  --template server.tmpl --outfile x509-server.pem

For use in the client, you may want to generate a client certificate as well.

$ certtool --generate-privkey > x509-client-key.pem
$ echo 'cn = GnuTLS test client' > client.tmpl
$ echo 'tls_www_client' >> client.tmpl
$ echo 'encryption_key' >> client.tmpl
$ echo 'signing_key' >> client.tmpl
$ certtool --generate-certificate --load-privkey x509-client-key.pem \
  --load-ca-certificate x509-ca.pem --load-ca-privkey x509-ca-key.pem \
  --template client.tmpl --outfile x509-client.pem

To be able to import the client key/certificate into some applications, you will need to convert them into a PKCS#12 structure. This also encrypts the security sensitive key with a password.

$ certtool --to-p12 --load-ca-certificate x509-ca.pem \
  --load-privkey x509-client-key.pem --load-certificate x509-client.pem \
  --outder --outfile x509-client.p12

For icing, we’ll create a proxy certificate for the client too.

$ certtool --generate-privkey > x509-proxy-key.pem
$ echo 'cn = GnuTLS test client proxy' > proxy.tmpl
$ certtool --generate-proxy --load-privkey x509-proxy-key.pem \
  --load-ca-certificate x509-client.pem --load-ca-privkey x509-client-key.pem \
  --load-certificate x509-client.pem --template proxy.tmpl \
  --outfile x509-proxy.pem

Then start the server again:

$ gnutls-serv --http \
            --x509cafile x509-ca.pem \
            --x509keyfile x509-server-key.pem \
            --x509certfile x509-server.pem

Try connecting to the server using your web browser. Note that the server listens to port 5556 by default.

While you are at it, to allow connections using ECDSA, you can also create a ECDSA key and certificate for the server. These credentials will be used in the final example below.

$ certtool --generate-privkey --ecdsa > x509-server-key-ecc.pem
$ certtool --generate-certificate --load-privkey x509-server-key-ecc.pem \
  --load-ca-certificate x509-ca.pem --load-ca-privkey x509-ca-key.pem \
  --template server.tmpl --outfile x509-server-ecc.pem

The next step is to add support for SRP authentication. This requires an SRP password file created with srptool. To start the server with SRP support:

gnutls-serv --http --priority NORMAL:+SRP-RSA:+SRP \
            --srppasswdconf srp-tpasswd.conf \
            --srppasswd srp-passwd.txt

Let’s also start a server with support for PSK. This would require a password file created with psktool.

gnutls-serv --http --priority NORMAL:+ECDHE-PSK:+PSK \
            --pskpasswd psk-passwd.txt

Finally, we start the server with all the earlier parameters and you get this command:

gnutls-serv --http --priority NORMAL:+PSK:+SRP \
            --x509cafile x509-ca.pem \
            --x509keyfile x509-server-key.pem \
            --x509certfile x509-server.pem \
            --x509keyfile x509-server-key-ecc.pem \
            --x509certfile x509-server-ecc.pem \
            --srppasswdconf srp-tpasswd.conf \
            --srppasswd srp-passwd.txt \
            --pskpasswd psk-passwd.txt

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