NAME¶
s_server - SSL/TLS server program
SYNOPSIS¶
openssl s_server [
-accept port] [
-context id] [
-verify depth] [
-Verify depth] [
-crl_check] [
-crl_check_all] [
-cert filename] [
-certform DER|PEM] [
-key keyfile] [
-keyform DER|PEM] [
-pass arg] [
-dcert filename] [
-dcertform DER|PEM] [
-dkey keyfile] [
-dkeyform DER|PEM] [
-dpass arg] [
-dhparam filename] [
-nbio] [
-nbio_test] [
-crlf] [
-debug] [
-msg] [
-state] [
-CApath directory] [
-CAfile
filename] [
-nocert] [
-cipher cipherlist] [
-quiet]
[
-no_tmp_rsa] [
-ssl2] [
-ssl3] [
-tls1] [
-no_ssl2] [
-no_ssl3] [
-no_tls1] [
-no_dhe] [
-bugs] [
-hack] [
-www] [
-WWW] [
-HTTP] [
-engine id] [
-tlsextdebug] [
-no_ticket] [
-id_prefix
arg] [
-rand file(s)]
DESCRIPTION¶
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
- additional 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.
SEE ALSO¶
sess_id(1),
s_client(1),
ciphers(1)