S_CLIENT 1 2008-05-09 0.9.9-dev OpenSSL

NAME

s_client - SSL/TLS client program

LIBRARY

libcrypto, -lcrypto

SYNOPSIS

ooppeennssssll ss__cclliieenntt [--ccoonnnneecctt hhoosstt::ppoorrtt] [--vveerriiffyy ddeepptthh] [--cceerrtt ffiilleennaammee] [--cceerrttffoorrmm DDEERR||PPEEMM] [--kkeeyy ffiilleennaammee] [--kkeeyyffoorrmm DDEERR||PPEEMM] [--ppaassss aarrgg] [--CCAAppaatthh ddiirreeccttoorryy] [--CCAAffiillee ffiilleennaammee] [--rreeccoonnnneecctt] [--ppaauussee] [--sshhoowwcceerrttss] [--ddeebbuugg] [--mmssgg] [--nnbbiioo__tteesstt] [--ssttaattee] [--nnbbiioo] [--ccrrllff] [--iiggnn__eeooff] [--qquuiieett] [--ssssll22] [--ssssll33] [--ttllss11] [--nnoo__ssssll22] [--nnoo__ssssll33] [--nnoo__ttllss11] [--bbuuggss] [--cciipphheerr cciipphheerrlliisstt] [--ssttaarrttttllss pprroottooccooll] [--eennggiinnee iidd] [--ttllsseexxttddeebbuugg] [--nnoo__ttiicckkeett] [--sseessss__oouutt ffiilleennaammee] [--sseessss__iinn ffiilleennaammee] [--rraanndd ffiillee((ss))]

DESCRIPTION

The ss__cclliieenntt command implements a generic SSL/TLS client which connects to a remote host using SSL/TLS. It is a _v_e_r_y useful diagnostic tool for SSL servers.

OPTIONS

--ccoonnnneecctt hhoosstt::ppoorrtt This specifies the host and optional port to connect to. If not specified
then an attempt is made to connect to the local host on port 4433.
--cceerrtt cceerrttnnaammee The certificate to use, if one is requested by the server. The default is
not to use a certificate.
--cceerrttffoorrmm ffoorrmmaatt The certificate format to use: DER or PEM. PEM is the default.
--kkeeyy kkeeyyffiillee The private key to use. If not specified then the certificate file will
be used.
--kkeeyyffoorrmm ffoorrmmaatt The private format to use: DER or PEM. PEM is the default.
--ppaassss aarrgg the private key password source. For more information about the format of aarrgg
see the PPAASSSS PPHHRRAASSEE AARRGGUUMMEENNTTSS section in _o_p_e_n_s_s_l(1).
--vveerriiffyy ddeepptthh The verify depth to use. This specifies the maximum length of the
server certificate chain and turns on server certificate verification. Currently the verify operation continues after errors so all the problems with a certificate chain can be seen. As a side effect the connection will never fail due to a server certificate verify failure.
--CCAAppaatthh ddiirreeccttoorryy The directory to use for server certificate verification. This directory
must be in "hash format", see vveerriiffyy for more information. These are also used when building the client certificate chain.
--CCAAffiillee ffiillee A file containing trusted certificates to use during server authentication
and to use when attempting to build the client certificate chain.
--rreeccoonnnneecctt reconnects to the same server 5 times using the same session ID, this can
be used as a test that session caching is working.
--ppaauussee pauses 1 second between each read and write call.
--sshhoowwcceerrttss display the whole server certificate chain: normally only the server
certificate itself is displayed.
--pprreexxiitt print session information when the program exits. This will always attempt
to print out information even if the connection fails. Normally information will only be printed out once if the connection succeeds. This option is useful because the cipher in use may be renegotiated or the connection may fail because a client certificate is required or is requested only after an attempt is made to access a certain URL. Note: the output produced by this option is not always accurate because a connection might never have been established.
--ssttaattee prints out the SSL session states.
--ddeebbuugg print extensive debugging information including a hex dump of all traffic.
--mmssgg show all protocol messages with hex dump.
--nnbbiioo__tteesstt tests non-blocking I/O
--nnbbiioo turns on non-blocking I/O
--ccrrllff this option translated a line feed from the terminal into CR+LF as required
by some servers.
--iiggnn__eeooff inhibit shutting down the connection when end of file is reached in the
input.
--qquuiieett inhibit printing of session and certificate information. This implicitly
turns on --iiggnn__eeooff as well.
--ppsskk__iiddeennttiittyy iiddeennttiittyy Use the PSK identity iiddeennttiittyy when using a PSK cipher suite.
--ppsskk kkeeyy Use the PSK key kkeeyy when using a PSK cipher suite. The key is
given as a hexadecimal number without leading 0x, for example -psk 1a2b3c4d.
--ssssll22, --ssssll33, --ttllss11, --nnoo__ssssll22, --nnoo__ssssll33, --nnoo__ttllss11 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.

Unfortunately there are a lot of ancient and broken servers in use which cannot handle this technique and will fail to connect. Some servers only work if TLS is turned off with the --nnoo__ttllss option others will only support SSL v2 and may need the --ssssll22 option.
--bbuuggss there are several known bug in SSL and TLS implementations. Adding this
option enables various workarounds.
--cciipphheerr cciipphheerrlliisstt this allows the cipher list sent by the client to be modified. Although
the server determines which cipher suite is used it should take the first supported cipher in the list sent by the client. See the cciipphheerrss command for more information.
--ssttaarrttttllss pprroottooccooll send the protocol-specific message(s) to switch to TLS for communication.
pprroottooccooll is a keyword for the intended protocol. Currently, the only supported keywords are "smtp", "pop3", "imap", and "ftp".
--ttllsseexxttddeebbuugg print out a hex dump of any TLS extensions received from the server.
--nnoo__ttiicckkeett disable RFC4507bis session ticket support.
--sseessss__oouutt ffiilleennaammee output SSL session to ffiilleennaammee
--sseessss__iinn sseessss..ppeemm load SSL session from ffiilleennaammee. The client will attempt to resume a
connection from this session.
--eennggiinnee iidd specifying an engine (by it's unique iidd string) will cause ss__cclliieenntt
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.
--rraanndd ffiillee((ss)) a file or files containing random data used to seed the random number
generator, or an EGD socket (see _R_A_N_D___e_g_d(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 is established with an SSL server then any data received from the server is displayed and any key presses will be sent to the server. When used interactively (which means neither --qquuiieett nor --iiggnn__eeooff have been given), the session will be renegotiated if the line begins with an RR, and if the line begins with a QQ or if end of file is reached, the connection will be closed down.

NOTES

ss__cclliieenntt can be used to debug SSL servers. To connect to an SSL HTTP server the command:


 openssl s_client -connect servername:443

would typically be used (https uses port 443). If the connection succeeds then an HTTP command can be given such as "GET /" to retrieve a web page.

If the handshake fails then there are several possible causes, if it is nothing obvious like no client certificate then the --bbuuggss, --ssssll22, --ssssll33, --ttllss11, --nnoo__ssssll22, --nnoo__ssssll33, --nnoo__ttllss11 options can be tried in case it is a buggy server. In particular you should play with these options bbeeffoorree submitting a bug report to an OpenSSL mailing list.

A frequent problem when attempting to get client certificates working is that a web client complains it has no certificates or gives an empty list to choose from. This is normally because the server is not sending the clients certificate authority in its "acceptable CA list" when it requests a certificate. By using ss__cclliieenntt the CA list can be viewed and checked. However some servers only request client authentication after a specific URL is requested. To obtain the list in this case it is necessary to use the --pprreexxiitt option and send an HTTP request for an appropriate page.

If a certificate is specified on the command line using the --cceerrtt option it will not be used unless the server specifically requests a client certificate. Therefor merely including a client certificate on the command line is no guarantee that the certificate works.

If there are problems verifying a server certificate then the --sshhoowwcceerrttss option can be used to show the whole chain.

Since the SSLv23 client hello cannot include compression methods or extensions these will only be supported if its use is disabled, for example by using the --nnoo__ssssllvv22 option.

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_client is rather hard to read and not a model of how things should be done. A typical SSL client program would be much simpler.

The --vveerriiffyy option should really exit if the server verification fails.

The --pprreexxiitt option is a bit of a hack. We should really report information whenever a session is renegotiated.

SEE ALSO

_o_p_e_n_s_s_l___s_e_s_s___i_d(1), _o_p_e_n_s_s_l___s___s_e_r_v_e_r(1), _o_p_e_n_s_s_l___c_i_p_h_e_r_s(1)