s_server (1)

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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] [-no_alt_chains] [-nocert] [-cipher cipherlist] [-serverpref] [-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)] [-serverinfo file] [-no_resumption_on_reneg] [-status] [-status_verbose] [-status_timeout nsec] [-status_url url] [-nextprotoneg protocols]

DESCRIPTION

The s_server command implements a generic server which listens for connections on a given port using

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.

-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.

-ssl2, -ssl3, -tls1, -tls1_1, -tls1_2, -no_ssl2, -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.

-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

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

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.

-nextprotoneg protocols

enable Next Protocol Negotiation

TLS

extension and provide 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 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 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

) only support cipher suites, so they cannot connect to servers which don't use a certificate carrying an key or a version of OpenSSL with disabled.

Although specifying an empty list of CAs when requesting a client certificate is strictly speaking a protocol violation, some

clients interpret this to mean any 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 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.