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.\&quot; ========================================================================
.\&quot;
.IX Title &quot;S_SERVER 1&quot;
.TH S_SERVER 1 &quot;2026-06-17&quot; &quot;1.0.2u&quot; &quot;OpenSSL&quot;
.\&quot; For nroff, turn off justification.  Always turn off hyphenation; it makes
.\&quot; way too many mistakes in technical documents.
.if n .ad l
.nh
.SH &quot;NAME&quot;
openssl\-s_server,
s_server \- SSL/TLS server program
.SH &quot;SYNOPSIS&quot;
.IX Header &quot;SYNOPSIS&quot;
\&amp;\fBopenssl\fR \fBs_server\fR
[\fB\-accept port\fR]
[\fB\-context id\fR]
[\fB\-verify depth\fR]
[\fB\-Verify depth\fR]
[\fB\-crl_check\fR]
[\fB\-crl_check_all\fR]
[\fB\-cert filename\fR]
[\fB\-certform DER|PEM\fR]
[\fB\-key keyfile\fR]
[\fB\-keyform DER|PEM\fR]
[\fB\-pass arg\fR]
[\fB\-dcert filename\fR]
[\fB\-dcertform DER|PEM\fR]
[\fB\-dkey keyfile\fR]
[\fB\-dkeyform DER|PEM\fR]
[\fB\-dpass arg\fR]
[\fB\-dhparam filename\fR]
[\fB\-nbio\fR]
[\fB\-nbio_test\fR]
[\fB\-crlf\fR]
[\fB\-debug\fR]
[\fB\-msg\fR]
[\fB\-state\fR]
[\fB\-CApath directory\fR]
[\fB\-CAfile filename\fR]
[\fB\-trusted_first\fR]
[\fB\-no_alt_chains\fR]
[\fB\-nocert\fR]
[\fB\-client_sigalgs sigalglist\fR]
[\fB\-named_curve curve\fR]
[\fB\-cipher cipherlist\fR]
[\fB\-serverpref\fR]
[\fB\-krb5svc service\fR]
[\fB\-keytab filename\fR]
[\fB\-quiet\fR]
[\fB\-no_tmp_rsa\fR]
[\fB\-ssl2\fR]
[\fB\-ssl3\fR]
[\fB\-tls1\fR]
[\fB\-tls1_1\fR]
[\fB\-tls1_2\fR]
[\fB\-no_ssl2\fR]
[\fB\-no_ssl3\fR]
[\fB\-no_tls1\fR]
[\fB\-no_dhe\fR]
[\fB\-no_ecdhe\fR]
[\fB\-bugs\fR]
[\fB\-hack\fR]
[\fB\-www\fR]
[\fB\-WWW\fR]
[\fB\-HTTP\fR]
[\fB\-engine id\fR]
[\fB\-tlsextdebug\fR]
[\fB\-no_ticket\fR]
[\fB\-id_prefix arg\fR]
[\fB\-rand file(s)\fR]
[\fB\-serverinfo file\fR]
[\fB\-no_resumption_on_reneg\fR]
[\fB\-status\fR]
[\fB\-status_verbose\fR]
[\fB\-status_timeout nsec\fR]
[\fB\-status_url url\fR]
[\fB\-alpn protocols\fR]
[\fB\-nextprotoneg protocols\fR]
.SH &quot;DESCRIPTION&quot;
.IX Header &quot;DESCRIPTION&quot;
The \fBs_server\fR command implements a generic \s-1SSL/TLS\s0 server which listens
for connections on a given port using \s-1SSL/TLS.\s0
.SH &quot;OPTIONS&quot;
.IX Header &quot;OPTIONS&quot;
.IP &quot;\fB\-accept port\fR&quot; 4
.IX Item &quot;-accept port&quot;
the \s-1TCP\s0 port to listen on for connections. If not specified 4433 is used.
.IP &quot;\fB\-context id\fR&quot; 4
.IX Item &quot;-context id&quot;
sets the \s-1SSL\s0 context id. It can be given any string value. If this option
is not present a default value will be used.
.IP &quot;\fB\-cert certname\fR&quot; 4
.IX Item &quot;-cert certname&quot;
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 \s-1DSS\s0 cipher suites require a certificate containing a \s-1DSS\s0
(\s-1DSA\s0) key. If not specified then the filename \*(L&quot;server.pem\*(R&quot; will be used.
.IP &quot;\fB\-certform format\fR&quot; 4
.IX Item &quot;-certform format&quot;
The certificate format to use: \s-1DER\s0 or \s-1PEM. PEM\s0 is the default.
.IP &quot;\fB\-key keyfile\fR&quot; 4
.IX Item &quot;-key keyfile&quot;
The private key to use. If not specified then the certificate file will
be used.
.IP &quot;\fB\-keyform format\fR&quot; 4
.IX Item &quot;-keyform format&quot;
The private format to use: \s-1DER\s0 or \s-1PEM. PEM\s0 is the default.
.IP &quot;\fB\-pass arg\fR&quot; 4
.IX Item &quot;-pass arg&quot;
the private key password source. For more information about the format of \fBarg\fR
see the \fB\s-1PASS PHRASE ARGUMENTS\s0\fR section in \fBopenssl\fR\|(1).
.IP &quot;\fB\-dcert filename\fR, \fB\-dkey keyname\fR&quot; 4
.IX Item &quot;-dcert filename, -dkey keyname&quot;
specify an additional certificate and private key, these behave in the
same manner as the \fB\-cert\fR and \fB\-key\fR 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 \s-1RSA\s0 key
and some a \s-1DSS\s0 (\s-1DSA\s0) key. By using \s-1RSA\s0 and \s-1DSS\s0 certificates and keys
a server can support clients which only support \s-1RSA\s0 or \s-1DSS\s0 cipher suites
by using an appropriate certificate.
.IP &quot;\fB\-dcertform format\fR, \fB\-dkeyform format\fR, \fB\-dpass arg\fR&quot; 4
.IX Item &quot;-dcertform format, -dkeyform format, -dpass arg&quot;
additional certificate and private key format and passphrase respectively.
.IP &quot;\fB\-nocert\fR&quot; 4
.IX Item &quot;-nocert&quot;
if this option is set then no certificate is used. This restricts the
cipher suites available to the anonymous ones (currently just anonymous
\&amp;\s-1DH\s0).
.IP &quot;\fB\-dhparam filename\fR&quot; 4
.IX Item &quot;-dhparam filename&quot;
the \s-1DH\s0 parameter file to use. The ephemeral \s-1DH\s0 cipher suites generate keys
using a set of \s-1DH\s0 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.
.IP &quot;\fB\-no_dhe\fR&quot; 4
.IX Item &quot;-no_dhe&quot;
if this option is set then no \s-1DH\s0 parameters will be loaded effectively
disabling the ephemeral \s-1DH\s0 cipher suites.
.IP &quot;\fB\-no_ecdhe\fR&quot; 4
.IX Item &quot;-no_ecdhe&quot;
if this option is set then no \s-1ECDH\s0 parameters will be selected, effectively
disabling the ephemeral \s-1ECDH\s0 cipher suites.
.IP &quot;\fB\-no_tmp_rsa\fR&quot; 4
.IX Item &quot;-no_tmp_rsa&quot;
certain export cipher suites sometimes use a temporary \s-1RSA\s0 key, this option
disables temporary \s-1RSA\s0 key generation.
.IP &quot;\fB\-verify depth\fR, \fB\-Verify depth\fR&quot; 4
.IX Item &quot;-verify depth, -Verify depth&quot;
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 \fB\-verify\fR option a certificate is requested but the
client does not have to send one, with the \fB\-Verify\fR option the client
must supply a certificate or an error occurs.
.Sp
If the ciphersuite cannot request a client certificate (for example an
anonymous ciphersuite or \s-1PSK\s0) this option has no effect.
.IP &quot;\fB\-crl_check\fR, \fB\-crl_check_all\fR&quot; 4
.IX Item &quot;-crl_check, -crl_check_all&quot;
Check the peer certificate has not been revoked by its \s-1CA.\s0
The \s-1CRL\s0(s) are appended to the certificate file. With the \fB\-crl_check_all\fR
option all CRLs of all CAs in the chain are checked.
.IP &quot;\fB\-CApath directory\fR&quot; 4
.IX Item &quot;-CApath directory&quot;
The directory to use for client certificate verification. This directory
must be in \*(L&quot;hash format\*(R&quot;, see \fBverify\fR for more information. These are
also used when building the server certificate chain.
.IP &quot;\fB\-CAfile file\fR&quot; 4
.IX Item &quot;-CAfile file&quot;
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.
.IP &quot;\fB\-trusted_first\fR&quot; 4
.IX Item &quot;-trusted_first&quot;
Use certificates in \s-1CA\s0 file or \s-1CA\s0 directory before other certificates 
when building the trust chain to verify client certificates.
This is mainly useful in environments with Bridge \s-1CA\s0 or Cross-Certified CAs.
.IP &quot;\fB\-no_alt_chains\fR&quot; 4
.IX Item &quot;-no_alt_chains&quot;
See the \fBverify\fR manual page for details.
.IP &quot;\fB\-state\fR&quot; 4
.IX Item &quot;-state&quot;
prints out the \s-1SSL\s0 session states.
.IP &quot;\fB\-debug\fR&quot; 4
.IX Item &quot;-debug&quot;
print extensive debugging information including a hex dump of all traffic.
.IP &quot;\fB\-msg\fR&quot; 4
.IX Item &quot;-msg&quot;
show all protocol messages with hex dump.
.IP &quot;\fB\-nbio_test\fR&quot; 4
.IX Item &quot;-nbio_test&quot;
tests non blocking I/O
.IP &quot;\fB\-nbio\fR&quot; 4
.IX Item &quot;-nbio&quot;
turns on non blocking I/O
.IP &quot;\fB\-crlf\fR&quot; 4
.IX Item &quot;-crlf&quot;
this option translated a line feed from the terminal into \s-1CR+LF.\s0
.IP &quot;\fB\-quiet\fR&quot; 4
.IX Item &quot;-quiet&quot;
inhibit printing of session and certificate information.
.IP &quot;\fB\-psk_hint hint\fR&quot; 4
.IX Item &quot;-psk_hint hint&quot;
Use the \s-1PSK\s0 identity hint \fBhint\fR when using a \s-1PSK\s0 cipher suite.
.IP &quot;\fB\-psk key\fR&quot; 4
.IX Item &quot;-psk key&quot;
Use the \s-1PSK\s0 key \fBkey\fR when using a \s-1PSK\s0 cipher suite. The key is
given as a hexadecimal number without leading 0x, for example \-psk
1a2b3c4d.
This option must be provided in order to use a \s-1PSK\s0 cipher.
.IP &quot;\fB\-ssl2\fR, \fB\-ssl3\fR, \fB\-tls1\fR, \fB\-tls1_1\fR, \fB\-tls1_2\fR, \fB\-dtls1\fR, \fB\-no_ssl2\fR, \fB\-no_ssl3\fR, \fB\-no_tls1\fR, \fB\-no_tls1_1\fR, \fB\-no_tls1_2\fR&quot; 4
.IX Item &quot;-ssl2, -ssl3, -tls1, -tls1_1, -tls1_2, -dtls1, -no_ssl2, -no_ssl3, -no_tls1, -no_tls1_1, -no_tls1_2&quot;
These options require or disable the use of the specified \s-1SSL\s0 or \s-1TLS\s0 protocols.
By default the initial handshake uses a \fIversion-flexible\fR method which will
negotiate the highest mutually supported protocol version.
.IP &quot;\fB\-bugs\fR&quot; 4
.IX Item &quot;-bugs&quot;
there are several known bug in \s-1SSL\s0 and \s-1TLS\s0 implementations. Adding this
option enables various workarounds.
.IP &quot;\fB\-hack\fR&quot; 4
.IX Item &quot;-hack&quot;
this option enables a further workaround for some some early Netscape
\&amp;\s-1SSL\s0 code (?).
.IP &quot;\fB\-client_sigalgs sigalglist\fR&quot; 4
.IX Item &quot;-client_sigalgs sigalglist&quot;
Signature algorithms to support for client certificate authentication
(colon-separated list)
.IP &quot;\fB\-named_curve curve\fR&quot; 4
.IX Item &quot;-named_curve curve&quot;
Specifies the elliptic curve to use. \s-1NOTE:\s0 this is single curve, not a list.
For a list of all possible curves, use:
.Sp
.Vb 1
\&amp;    $ openssl ecparam \-list_curves
.Ve
.IP &quot;\fB\-cipher cipherlist\fR&quot; 4
.IX Item &quot;-cipher cipherlist&quot;
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 \fBciphers\fR command for more information.
.IP &quot;\fB\-serverpref\fR&quot; 4
.IX Item &quot;-serverpref&quot;
use the server's cipher preferences, rather than the client's preferences.
.IP &quot;\fB\-krb5svc service\fR&quot; 4
.IX Item &quot;-krb5svc service&quot;
the Kerberos service name to use (default \*(L&quot;host\*(R&quot;). This means s_server
will expect a ticket for the principal \fIservice\fR/hostname@REALM, and will
need keys for that principal in its keytab.
.IP &quot;\fB\-keytab filename\fR&quot; 4
.IX Item &quot;-keytab filename&quot;
the Kerberos \*(L&quot;keytab\*(R&quot; (key table) file, containing keys for the s_server
service principal (Kerberos identity; see \-krb5svc).
.IP &quot;\fB\-tlsextdebug\fR&quot; 4
.IX Item &quot;-tlsextdebug&quot;
print out a hex dump of any \s-1TLS\s0 extensions received from the server.
.IP &quot;\fB\-no_ticket\fR&quot; 4
.IX Item &quot;-no_ticket&quot;
disable RFC4507bis session ticket support.
.IP &quot;\fB\-www\fR&quot; 4
.IX Item &quot;-www&quot;
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 \s-1HTML\s0 format so this option will normally be used with a
web browser.
.IP &quot;\fB\-WWW\fR&quot; 4
.IX Item &quot;-WWW&quot;
emulates a simple web server. Pages will be resolved relative to the
current directory, for example if the \s-1URL\s0 https://myhost/page.html is
requested the file ./page.html will be loaded.
.IP &quot;\fB\-HTTP\fR&quot; 4
.IX Item &quot;-HTTP&quot;
emulates a simple web server. Pages will be resolved relative to the
current directory, for example if the \s-1URL\s0 https://myhost/page.html is
requested the file ./page.html will be loaded. The files loaded are
assumed to contain a complete and correct \s-1HTTP\s0 response (lines that
are part of the \s-1HTTP\s0 response line and headers must end with \s-1CRLF\s0).
.IP &quot;\fB\-engine id\fR&quot; 4
.IX Item &quot;-engine id&quot;
specifying an engine (by its unique \fBid\fR string) will cause \fBs_server\fR
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.
.IP &quot;\fB\-id_prefix arg\fR&quot; 4
.IX Item &quot;-id_prefix arg&quot;
generate \s-1SSL/TLS\s0 session IDs prefixed by \fBarg\fR. This is mostly useful
for testing any \s-1SSL/TLS\s0 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).
.IP &quot;\fB\-rand file(s)\fR&quot; 4
.IX Item &quot;-rand file(s)&quot;
a file or files containing random data used to seed the random number
generator, or an \s-1EGD\s0 socket (see \fBRAND_egd\fR\|(3)).
Multiple files can be specified separated by a OS-dependent character.
The separator is \fB;\fR for MS-Windows, \fB,\fR for OpenVMS, and \fB:\fR for
all others.
.IP &quot;\fB\-serverinfo file\fR&quot; 4
.IX Item &quot;-serverinfo file&quot;
a file containing one or more blocks of \s-1PEM\s0 data.  Each \s-1PEM\s0 block
must encode a \s-1TLS\s0 ServerHello extension (2 bytes type, 2 bytes length,
followed by \*(L&quot;length\*(R&quot; bytes of extension data).  If the client sends
an empty \s-1TLS\s0 ClientHello extension matching the type, the corresponding
ServerHello extension will be returned.
.IP &quot;\fB\-no_resumption_on_reneg\fR&quot; 4
.IX Item &quot;-no_resumption_on_reneg&quot;
set \s-1SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION\s0 flag.
.IP &quot;\fB\-status\fR&quot; 4
.IX Item &quot;-status&quot;
enables certificate status request support (aka \s-1OCSP\s0 stapling).
.IP &quot;\fB\-status_verbose\fR&quot; 4
.IX Item &quot;-status_verbose&quot;
enables certificate status request support (aka \s-1OCSP\s0 stapling) and gives
a verbose printout of the \s-1OCSP\s0 response.
.IP &quot;\fB\-status_timeout nsec\fR&quot; 4
.IX Item &quot;-status_timeout nsec&quot;
sets the timeout for \s-1OCSP\s0 response to \fBnsec\fR seconds.
.IP &quot;\fB\-status_url url\fR&quot; 4
.IX Item &quot;-status_url url&quot;
sets a fallback responder \s-1URL\s0 to use if no responder \s-1URL\s0 is present in the
server certificate. Without this option an error is returned if the server
certificate does not contain a responder address.
.IP &quot;\fB\-alpn protocols\fR, \fB\-nextprotoneg protocols\fR&quot; 4
.IX Item &quot;-alpn protocols, -nextprotoneg protocols&quot;
these flags enable the 
Enable the Application-Layer Protocol Negotiation or Next Protocol
Negotiation extension, respectively. \s-1ALPN\s0 is the \s-1IETF\s0 standard and
replaces \s-1NPN.\s0
The \fBprotocols\fR list is a
comma-separated list of supported protocol names.
The list should contain most wanted protocols first.
Protocol names are printable \s-1ASCII\s0 strings, for example \*(L&quot;http/1.1\*(R&quot; or
\&amp;\*(L&quot;spdy/3\*(R&quot;.
.SH &quot;CONNECTED COMMANDS&quot;
.IX Header &quot;CONNECTED COMMANDS&quot;
If a connection request is established with an \s-1SSL\s0 client and neither the
\&amp;\fB\-www\fR nor the \fB\-WWW\fR option has been used then normally any data received
from the client is displayed and any key presses will be sent to the client.
.PP
Certain single letter commands are also recognized which perform special
operations: these are listed below.
.IP &quot;\fBq\fR&quot; 4
.IX Item &quot;q&quot;
end the current \s-1SSL\s0 connection but still accept new connections.
.IP &quot;\fBQ\fR&quot; 4
.IX Item &quot;Q&quot;
end the current \s-1SSL\s0 connection and exit.
.IP &quot;\fBr\fR&quot; 4
.IX Item &quot;r&quot;
renegotiate the \s-1SSL\s0 session.
.IP &quot;\fBR\fR&quot; 4
.IX Item &quot;R&quot;
renegotiate the \s-1SSL\s0 session and request a client certificate.
.IP &quot;\fBP\fR&quot; 4
.IX Item &quot;P&quot;
send some plain text down the underlying \s-1TCP\s0 connection: this should
cause the client to disconnect due to a protocol violation.
.IP &quot;\fBS\fR&quot; 4
.IX Item &quot;S&quot;
print out some session cache status information.
.SH &quot;NOTES&quot;
.IX Header &quot;NOTES&quot;
\&amp;\fBs_server\fR can be used to debug \s-1SSL\s0 clients. To accept connections from
a web browser the command:
.PP
.Vb 1
\&amp; openssl s_server \-accept 443 \-www
.Ve
.PP
can be used for example.
.PP
Although specifying an empty list of CAs when requesting a client certificate
is strictly speaking a protocol violation, some \s-1SSL\s0 clients interpret this to
mean any \s-1CA\s0 is acceptable. This is useful for debugging purposes.
.PP
The session parameters can printed out using the \fBsess_id\fR program.
.SH &quot;BUGS&quot;
.IX Header &quot;BUGS&quot;
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
\&amp;\s-1SSL\s0 server program would be much simpler.
.PP
The output of common ciphers is wrong: it just gives the list of ciphers that
OpenSSL recognizes and the client supports.
.PP
There should be a way for the \fBs_server\fR program to print out details of any
unknown cipher suites a client says it supports.
.SH &quot;SEE ALSO&quot;
.IX Header &quot;SEE ALSO&quot;
\&amp;\fBsess_id\fR\|(1), \fBs_client\fR\|(1), \fBciphers\fR\|(1)
.SH &quot;HISTORY&quot;
.IX Header &quot;HISTORY&quot;
The \-no_alt_chains options was first added to OpenSSL 1.0.2b.
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