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S_SERVER

Section: OpenSSL (1)
Updated: 2003-03-20
Index

NAME

s_server - SSL/TLS server program

SYNOPSIS

openssl s_server[-accept port][-context id][-verify depth][-Verify depth][-cert filename][-key keyfile][-dcert filename][-dkey keyfile][-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][-id_prefix arg][-rand file(s)]

DESCRIPTION

The s_server command implements a generic SSL/TLS server which listensfor 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 optionis not present a default value will be used.
-cert certname: The certificate to use, most servers cipher suites require the use of acertificate 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.
-key keyfile: The private key to use. If not specified then the certificate file willbe used.
-dcert filename, -dkey keyname: specify an additional certificate and private key, these behave in thesame manner as the -cert and -key options except there is no defaultif they are not specified (no additional certificate and key is used). Asnoted above some cipher suites require a certificate containing a key ofa certain type. Some cipher suites need a certificate carrying an RSA keyand some a DSS (DSA) key. By using RSA and DSS certificates and keysa server can support clients which only support RSA or DSS cipher suitesby using an appropriate certificate.
-nocert: if this option is set then no certificate is used. This restricts thecipher suites available to the anonymous ones (currently just anonymousDH).
-dhparam filename: the DH parameter file to use. The ephemeral DH cipher suites generate keysusing a set of DH parameters. If not specified then an attempt is made toload the parameters from the server certificate file. If this fails thena 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 effectivelydisabling the ephemeral DH cipher suites.
-no_tmp_rsa: certain export cipher suites sometimes use a temporary RSA key, this optiondisables temporary RSA key generation.
-verify depth, -Verify depth: The verify depth to use. This specifies the maximum length of theclient certificate chain and makes the server request a certificate fromthe client. With the -verify option a certificate is requested but theclient does not have to send one, with the -Verify option the clientmust supply a certificate or an error occurs.
-CApath directory: The directory to use for client certificate verification. This directorymust be in ``hash format'', see verify for more information. These arealso used when building the server certificate chain.
-CAfile file: A file containing trusted certificates to use during client authenticationand to use when attempting to build the server certificate chain. The listis also used in the list of acceptable client CAs passed to the client whena 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.
-ssl2, -ssl3, -tls1, -no_ssl2, -no_ssl3, -no_tls1: these options disable the use of certain SSL or TLS protocols. By defaultthe initial handshake uses a method which should be compatible with allservers 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 thisoption enables various workarounds.
-hack: this option enables a further workaround for some some early NetscapeSSL code (?).
-cipher cipherlist: this allows the cipher list used by the server to be modified. Whenthe client sends a list of supported ciphers the first client cipheralso included in the server list is used. Because the client specifiesthe preference order, the order of the server cipherlist irrelevant. Seethe ciphers command for more information.
-www: sends a status message back to the client when it connects. This includeslots of information about the ciphers used and various session parameters.The output is in HTML format so this option will normally be used with aweb browser.
-WWW: emulates a simple web server. Pages will be resolved relative to thecurrent directory, for example if the URL https://myhost/page.html isrequested the file ./page.html will be loaded.
-HTTP: emulates a simple web server. Pages will be resolved relative to thecurrent directory, for example if the URL https://myhost/page.html isrequested the file ./page.html will be loaded. The files loaded areassumed to contain a complete and correct HTTP response (lines thatare part of the HTTP response line and headers must end with CRLF).
-engine id: specifying an engine (by it's unique id string) will cause s_serverto attempt to obtain a functional reference to the specified engine,thus initialising it if needed. The engine will then be set as the defaultfor all available algorithms.
-id_prefix arg: generate SSL/TLS session IDs prefixed by arg. This is mostly usefulfor testing any SSL/TLS code (eg. proxies) that wish to deal with multipleservers, when each of which might be generating a unique range of sessionIDs (eg. with a certain prefix).
-rand file(s): a file or files containing random data used to seed the random numbergenerator, 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 : forall 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 receivedfrom the client is displayed and any key presses will be sent to the client.

Certain single letter commands are also recognized which perform specialoperations: 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 shouldcause 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 froma 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 ciphersuites, so they cannot connect to servers which don't use a certificatecarrying an RSA key or a version of OpenSSL with RSA disabled.

Although specifying an empty list of CAs when requesting a client certificateis strictly speaking a protocol violation, some SSL clients interpret this tomean 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 ofthe techniques used are rather old, the C source of s_server is ratherhard to read and not a model of how things should be done. A typicalSSL server program would be much simpler.

The output of common ciphers is wrong: it just gives the list of ciphers thatOpenSSL recognizes and the client supports.

There should be a way for the s_server program to print out details of anyunknown cipher suites a client says it supports.

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