The s_server command implements a
generic SSL/TLS server which listens for connections on a given port
using SSL/TLS.
OPTIONS
-accept port
the TCP port to listen on for connections. If not specified
4433 is used.
-context id
sets the SSL context id. It can be given any string value. If
this option is not present a default value will be used.
-cert certname
The certificate to use, most servers cipher suites require
the use of a certificate and some require a certificate with
a certain public key type: for example the DSS cipher suites
require a certificate containing a DSS (DSA) key. If not
specified then the filename "server.pem" will be used.
-certform format
The certificate format to use: DER or PEM. PEM is the
default.
-key keyfile
The private key to use. If not specified then the certificate
file will be used.
-keyform format
The private format to use: DER or PEM. PEM is the default.
-pass arg
the private key password source. For more information about
the format of arg see the
PASS PHRASE ARGUMENTS
section in openssl(1).
-dcert filename, -dkey keyname
specify an additional certificate and private key, these
behave in the same manner as the -cert and -key options except there is no
default if they are not specified (no additional certificate
and key is used). As noted above some cipher suites require a
certificate containing a key of a certain type. Some cipher
suites need a certificate carrying an RSA key and some a DSS
(DSA) key. By using RSA and DSS certificates and keys a
server can support clients which only support RSA or DSS
cipher suites by using an appropriate certificate.
-dcertform format, -dkeyform format, -dpass arg
addtional certificate and private key format and passphrase
respectively.
-nocert
if this option is set then no certificate is used. This
restricts the cipher suites available to the anonymous ones
(currently just anonymous DH).
-dhparam filename
the DH parameter file to use. The ephemeral DH cipher suites
generate keys using a set of DH parameters. If not specified
then an attempt is made to load the parameters from the
server certificate file. If this fails then a static set of
parameters hard coded into the s_server program will be used.
-no_dhe
if this option is set then no DH parameters will be loaded
effectively disabling the ephemeral DH cipher suites.
-no_tmp_rsa
certain export cipher suites sometimes use a temporary RSA
key, this option disables temporary RSA key generation.
-verify depth, -Verify depth
The verify depth to use. This specifies the maximum length of
the client certificate chain and makes the server request a
certificate from the client. With the -verify option a certificate is
requested but the client does not have to send one, with the
-Verify option the client
must supply a certificate or an error occurs.
-crl_check, -crl_check_all
Check the peer certificate has not been revoked by its CA.
The CRL(s) are appended to the certificate file. With the
-crl_check_all option all
CRLs of all CAs in the chain are checked.
-CApath directory
The directory to use for client certificate verification.
This directory must be in "hash format", see verify for more information. These are
also used when building the server certificate chain.
-CAfile file
A file containing trusted certificates to use during client
authentication and to use when attempting to build the server
certificate chain. The list is also used in the list of
acceptable client CAs passed to the client when a certificate
is requested.
-state
prints out the SSL session states.
-debug
print extensive debugging information including a hex dump of
all traffic.
-msg
show all protocol messages with hex dump.
-nbio_test
tests non blocking I/O
-nbio
turns on non blocking I/O
-crlf
this option translated a line feed from the terminal into
CR+LF.
-quiet
inhibit printing of session and certificate information.
-psk_hint hint
Use the PSK identity hint hint when using a PSK cipher suite.
-psk key
Use the PSK key key when
using a PSK cipher suite. The key is given as a hexadecimal
number without leading 0x, for example -psk 1a2b3c4d.
-ssl2, -ssl3, -tls1, -no_ssl2, -no_ssl3, -no_tls1
these options disable the use of certain SSL or TLS
protocols. By default the initial handshake uses a method
which should be compatible with all servers and permit them
to use SSL v3, SSL v2 or TLS as appropriate.
-bugs
there are several known bug in SSL and TLS implementations.
Adding this option enables various workarounds.
-hack
this option enables a further workaround for some some early
Netscape SSL code (?).
-cipher cipherlist
this allows the cipher list used by the server to be
modified. When the client sends a list of supported ciphers
the first client cipher also included in the server list is
used. Because the client specifies the preference order, the
order of the server cipherlist irrelevant. See the ciphers command for more information.
-tlsextdebug
print out a hex dump of any TLS extensions received from the
server.
-no_ticket
disable RFC4507bis session ticket support.
-www
sends a status message back to the client when it connects.
This includes lots of information about the ciphers used and
various session parameters. The output is in HTML format so
this option will normally be used with a web browser.
-WWW
emulates a simple web server. Pages will be resolved relative
to the current directory, for example if the URL
https://myhost/page.html is requested the file ./page.html
will be loaded.
-HTTP
emulates a simple web server. Pages will be resolved relative
to the current directory, for example if the URL
https://myhost/page.html is requested the file ./page.html
will be loaded. The files loaded are assumed to contain a
complete and correct HTTP response (lines that are part of
the HTTP response line and headers must end with CRLF).
-engine id
specifying an engine (by its unique id string) will cause s_server to attempt to obtain a
functional reference to the specified engine, thus
initialising it if needed. The engine will then be set as the
default for all available algorithms.
-id_prefix arg
generate SSL/TLS session IDs prefixed by arg. This is mostly useful for testing
any SSL/TLS code (eg. proxies) that wish to deal with
multiple servers, when each of which might be generating a
unique range of session IDs (eg. with a certain prefix).
-rand file(s)
a file or files containing random data used to seed the
random number generator, or an EGD socket (see RAND_egd(3)). Multiple
files can be specified separated by a OS-dependent character.
The separator is ; for
MS-Windows, , for OpenVMS,
and : for all others.
CONNECTED COMMANDS
If a connection request is established with an SSL client and neither
the -www nor the -WWW option has been used then normally any
data received from the client is displayed and any key presses will
be sent to the client.
Certain single letter commands are also recognized which perform
special operations: these are listed below.
q
end the current SSL connection but still accept new
connections.
Q
end the current SSL connection and exit.
r
renegotiate the SSL session.
R
renegotiate the SSL session and request a client certificate.
P
send some plain text down the underlying TCP connection: this
should cause the client to disconnect due to a protocol
violation.
S
print out some session cache status information.
NOTES
s_server can be used to debug SSL
clients. To accept connections from a web browser the command:
openssl s_server -accept 443 -www
can be used for example.
Most web browsers (in particular Netscape and MSIE) only support RSA
cipher suites, so they cannot connect to servers which don't use a
certificate carrying an RSA key or a version of OpenSSL with RSA
disabled.
Although specifying an empty list of CAs when requesting a client
certificate is strictly speaking a protocol violation, some SSL
clients interpret this to mean any CA is acceptable. This is useful
for debugging purposes.
The session parameters can printed out using the sess_id program.
BUGS
Because this program has a lot of options and also because some of
the techniques used are rather old, the C source of s_server is
rather hard to read and not a model of how things should be done. A
typical SSL server program would be much simpler.
The output of common ciphers is wrong: it just gives the list of
ciphers that OpenSSL recognizes and the client supports.
There should be a way for the s_server program to print out details of any
unknown cipher suites a client says it supports.
