S_CLIENT(1) OpenSSL S_CLIENT(1) NNAAMMEE s_client - SSL/TLS client program SSYYNNOOPPSSIISS ooppeennssssll ss__cclliieenntt [--ccoonnnneecctt hhoosstt::ppoorrtt] [--sseerrvveerrnnaammee nnaammee] [--vveerriiffyy ddeepptthh] [--vveerriiffyy__rreettuurrnn__eerrrroorr] [--cceerrtt ffiilleennaammee] [--cceerrttffoorrmm DDEERR||PPEEMM] [--kkeeyy ffiilleennaammee] [--kkeeyyffoorrmm DDEERR||PPEEMM] [--ppaassss aarrgg] [--CCAAppaatthh ddiirreeccttoorryy] [--CCAAffiillee ffiilleennaammee] [--nnoo__aalltt__cchhaaiinnss] [--rreeccoonnnneecctt] [--ppaauussee] [--sshhoowwcceerrttss] [--ddeebbuugg] [--mmssgg] [--nnbbiioo__tteesstt] [--ssttaattee] [--nnbbiioo] [--ccrrllff] [--iiggnn__eeooff] [--nnoo__iiggnn__eeooff] [--qquuiieett] [--ssssll22] [--ssssll33] [--ttllss11] [--nnoo__ssssll22] [--nnoo__ssssll33] [--nnoo__ttllss11] [--bbuuggss] [--cciipphheerr cciipphheerrlliisstt] [--sseerrvveerrpprreeff] [--ssttaarrttttllss pprroottoo-- ccooll] [--eennggiinnee iidd] [--ttllsseexxttddeebbuugg] [--nnoo__ttiicckkeett] [--sseessss__oouutt ffiilleennaammee] [--sseessss__iinn ffiilleennaammee] [--rraanndd ffiillee((ss))] [--ssttaattuuss] [--nneexxttpprroottoonneegg pprroottooccoollss] DDEESSCCRRIIPPTTIIOONN 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. OOPPTTIIOONNSS --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. --sseerrvveerrnnaammee nnaammee Set the TLS SNI (Server Name Indication) extension in the Clien- tHello message. --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 verifica- tion. 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. --vveerriiffyy__rreettuurrnn__eerrrroorr Return verification errors instead of continuing. This will typi- cally abort the handshake with a fatal error. --CCAAppaatthh ddiirreeccttoorryy The directory to use for server certificate verification. This directory must be in "hash format", see vveerriiffyy for more informa- tion. These are also used when building the client certificate chain. --CCAAffiillee ffiillee A file containing trusted certificates to use during server authen- tication and to use when attempting to build the client certificate chain. --ppuurrppoossee,, --iiggnnoorree__ccrriittiiccaall,, --iissssuueerr__cchheecckkss,, --ccrrll__cchheecckk,, --ccrrll__cchheecckk__aallll,, --ppoolliiccyy__cchheecckk,, --eexxtteennddeedd__ccrrll,, --xx550099__ssttrriicctt,, --ppoolliiccyy --cchheecckk__ssss__ssiigg --nnoo__aalltt__cchhaaiinnss Set various certificate chain valiadition option. See the vveerriiffyy manual page for details. --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. Nor- mally 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 certifi- cate 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. --nnoo__iiggnn__eeooff shut down the connection when end of file is reached in the input. Can be used to override the implicit --iiggnn__eeooff after --qquuiieett. --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, --ttllss11__11, --ttllss11__22, --nnoo__ssssll22, --nnoo__ssssll33, --nnoo__ttllss11, --nnoo__ttllss11__11, --nnoo__ttllss11__22 These options require or disable the use of the specified SSL or TLS protocols. By default the initial handshake uses a _v_e_r_s_i_o_n_- _f_l_e_x_i_b_l_e method which will negotiate the highest mutually supported protocol version. --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. --sseerrvveerrpprreeff use the server's cipher preferences; only used for SSLV2. --ssttaarrttttllss pprroottooccooll send the protocol-specific message(s) to switch to TLS for communi- cation. pprroottooccooll is a keyword for the intended protocol. Cur- rently, 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 its 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 num- ber 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 sepa- rator is ;; for MS-Windows, ,, for OpenVMS, and :: for all others. --ssttaattuuss sends a certificate status request to the server (OCSP stapling). The server response (if any) is printed out. --nneexxttpprroottoonneegg pprroottooccoollss enable Next Protocol Negotiation TLS extension and provide a list of comma-separated protocol names that the client should advertise support for. The list should contain most wanted protocols first. Protocol names are printable ASCII strings, for example "http/1.1" or "spdy/3". Empty list of protocols is treated specially and will cause the client to advertise support for the TLS extension but disconnect just after reciving ServerHello with a list of server supported protocols. CCOONNNNEECCTTEEDD CCOOMMMMAANNDDSS 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. NNOOTTEESS 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 suc- ceeds 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 nec- essary to use the --pprreexxiitt option and send an HTTP request for an appro- priate 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. The ss__cclliieenntt utility is a test tool and is designed to continue the handshake after any certificate verification errors. As a result it will accept any certificate chain (trusted or not) sent by the peer. None test applications should nnoott do this as it makes them vulnerable to a MITM attack. This behaviour can be changed by with the --vveerr-- iiffyy__rreettuurrnn__eerrrroorr option: any verify errors are then returned aborting the handshake. BBUUGGSS 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 --pprreexxiitt option is a bit of a hack. We should really report informa- tion whenever a session is renegotiated. SSEEEE AALLSSOO _s_e_s_s___i_d(1), _s___s_e_r_v_e_r(1), _c_i_p_h_e_r_s(1) HHIISSTTOORRYY The -no_alt_chains options was first added to OpenSSL 1.0.1n and 1.0.2b. 1.0.1u 2016-09-22 S_CLIENT(1)