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)