S_SERVER(1) OpenSSL S_SERVER(1)
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] [-trusted_first]
[-no_alt_chains] [-nocert] [-cipher cipherlist] [-serverpref] [-krb5svc
service] [-keytab filename] [-quiet] [-no_tmp_rsa] [-ssl3] [-tls1]
[-tls1_1] [-tls1_2] [-no_ssl3] [-no_tls1] [-no_dhe] [-bugs] [-hack]
[-www] [-WWW] [-HTTP] [-engine id] [-tlsextdebug] [-no_ticket]
[-id_prefix arg] [-rand file(s)] [-serverinfo file]
[-no_resumption_on_reneg] [-status] [-status_verbose] [-status_timeout
nsec] [-status_url url] [-alpn protocols] [-nextprotoneg protocols]
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.
If the ciphersuite cannot request a client certificate (for example
an anonymous ciphersuite or PSK) this option has no effect.
-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.
-trusted_first
Use certificates in CA file or CA directory before other
certificates when building the trust chain to verify client
certificates. This is mainly useful in environments with Bridge CA
or Cross-Certified CAs.
-no_alt_chains
See the verify manual page for details.
-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.
-ssl3, -tls1, -tls1_1, -tls1_2, -dtls1, -no_ssl3, -no_tls1, -no_tls1_1,
-no_tls1_2
These options require or disable the use of the specified SSL or
TLS protocols. By default the initial handshake uses a version-
flexible method which will negotiate the highest mutually supported
protocol version.
-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.
-serverpref
use the server's cipher preferences, rather than the client's
preferences.
-krb5svc service
the Kerberos service name to use (default "host"). This means
s_server will expect a ticket for the principal
service/hostname@REALM, and will need keys for that principal in
its keytab.
-keytab filename
the Kerberos "keytab" (key table) file, containing keys for the
s_server service principal (Kerberos identity; see -krb5svc).
-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.
-serverinfo file
a file containing one or more blocks of PEM data. Each PEM block
must encode a TLS ServerHello extension (2 bytes type, 2 bytes
length, followed by "length" bytes of extension data). If the
client sends an empty TLS ClientHello extension matching the type,
the corresponding ServerHello extension will be returned.
-no_resumption_on_reneg
set SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION flag.
-status
enables certificate status request support (aka OCSP stapling).
-status_verbose
enables certificate status request support (aka OCSP stapling) and
gives a verbose printout of the OCSP response.
-status_timeout nsec
sets the timeout for OCSP response to nsec seconds.
-status_url url
sets a fallback responder URL to use if no responder URL is present
in the server certificate. Without this option an error is returned
if the server certificate does not contain a responder address.
-alpn protocols, -nextprotoneg protocols
these flags enable the Enable the Application-Layer Protocol
Negotiation or Next Protocol Negotiation extension, respectively.
ALPN is the IETF standard and replaces NPN. The protocols list is
a comma-separated list of supported protocol names. The list
should contain most wanted protocols first. Protocol names are
printable ASCII strings, for example "http/1.1" or "spdy/3".
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)
HISTORY
The -no_alt_chains options was first added to OpenSSL 1.0.2b.
1.0.2k 2023-11-13 S_SERVER(1)
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