s_client.pod revision 325335
1 2=pod 3 4=head1 NAME 5 6s_client - SSL/TLS client program 7 8=head1 SYNOPSIS 9 10B<openssl> B<s_client> 11[B<-connect host:port>] 12[B<-servername name>] 13[B<-verify depth>] 14[B<-verify_return_error>] 15[B<-cert filename>] 16[B<-certform DER|PEM>] 17[B<-key filename>] 18[B<-keyform DER|PEM>] 19[B<-pass arg>] 20[B<-CApath directory>] 21[B<-CAfile filename>] 22[B<-no_alt_chains>] 23[B<-reconnect>] 24[B<-pause>] 25[B<-showcerts>] 26[B<-debug>] 27[B<-msg>] 28[B<-nbio_test>] 29[B<-state>] 30[B<-nbio>] 31[B<-crlf>] 32[B<-ign_eof>] 33[B<-no_ign_eof>] 34[B<-quiet>] 35[B<-ssl2>] 36[B<-ssl3>] 37[B<-tls1>] 38[B<-no_ssl2>] 39[B<-no_ssl3>] 40[B<-no_tls1>] 41[B<-no_tls1_1>] 42[B<-no_tls1_2>] 43[B<-fallback_scsv>] 44[B<-bugs>] 45[B<-sigalgs sigalglist>] 46[B<-curves curvelist>] 47[B<-cipher cipherlist>] 48[B<-serverpref>] 49[B<-starttls protocol>] 50[B<-engine id>] 51[B<-tlsextdebug>] 52[B<-no_ticket>] 53[B<-sess_out filename>] 54[B<-sess_in filename>] 55[B<-rand file(s)>] 56[B<-serverinfo types>] 57[B<-status>] 58[B<-alpn protocols>] 59[B<-nextprotoneg protocols>] 60 61=head1 DESCRIPTION 62 63The B<s_client> command implements a generic SSL/TLS client which connects 64to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for 65SSL servers. 66 67=head1 OPTIONS 68 69=over 4 70 71=item B<-connect host:port> 72 73This specifies the host and optional port to connect to. If not specified 74then an attempt is made to connect to the local host on port 4433. 75 76=item B<-servername name> 77 78Set the TLS SNI (Server Name Indication) extension in the ClientHello message. 79 80=item B<-cert certname> 81 82The certificate to use, if one is requested by the server. The default is 83not to use a certificate. 84 85=item B<-certform format> 86 87The certificate format to use: DER or PEM. PEM is the default. 88 89=item B<-key keyfile> 90 91The private key to use. If not specified then the certificate file will 92be used. 93 94=item B<-keyform format> 95 96The private format to use: DER or PEM. PEM is the default. 97 98=item B<-pass arg> 99 100the private key password source. For more information about the format of B<arg> 101see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>. 102 103=item B<-verify depth> 104 105The verify depth to use. This specifies the maximum length of the 106server certificate chain and turns on server certificate verification. 107Currently the verify operation continues after errors so all the problems 108with a certificate chain can be seen. As a side effect the connection 109will never fail due to a server certificate verify failure. 110 111=item B<-verify_return_error> 112 113Return verification errors instead of continuing. This will typically 114abort the handshake with a fatal error. 115 116=item B<-CApath directory> 117 118The directory to use for server certificate verification. This directory 119must be in "hash format", see B<verify> for more information. These are 120also used when building the client certificate chain. 121 122=item B<-CAfile file> 123 124A file containing trusted certificates to use during server authentication 125and to use when attempting to build the client certificate chain. 126 127=item B<-purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all, -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig -no_alt_chains> 128 129Set various certificate chain valiadition option. See the 130L<B<verify>|verify(1)> manual page for details. 131 132=item B<-reconnect> 133 134reconnects to the same server 5 times using the same session ID, this can 135be used as a test that session caching is working. 136 137=item B<-pause> 138 139pauses 1 second between each read and write call. 140 141=item B<-showcerts> 142 143display the whole server certificate chain: normally only the server 144certificate itself is displayed. 145 146=item B<-prexit> 147 148print session information when the program exits. This will always attempt 149to print out information even if the connection fails. Normally information 150will only be printed out once if the connection succeeds. This option is useful 151because the cipher in use may be renegotiated or the connection may fail 152because a client certificate is required or is requested only after an 153attempt is made to access a certain URL. Note: the output produced by this 154option is not always accurate because a connection might never have been 155established. 156 157=item B<-state> 158 159prints out the SSL session states. 160 161=item B<-debug> 162 163print extensive debugging information including a hex dump of all traffic. 164 165=item B<-msg> 166 167show all protocol messages with hex dump. 168 169=item B<-nbio_test> 170 171tests non-blocking I/O 172 173=item B<-nbio> 174 175turns on non-blocking I/O 176 177=item B<-crlf> 178 179this option translated a line feed from the terminal into CR+LF as required 180by some servers. 181 182=item B<-ign_eof> 183 184inhibit shutting down the connection when end of file is reached in the 185input. 186 187=item B<-quiet> 188 189inhibit printing of session and certificate information. This implicitly 190turns on B<-ign_eof> as well. 191 192=item B<-no_ign_eof> 193 194shut down the connection when end of file is reached in the input. 195Can be used to override the implicit B<-ign_eof> after B<-quiet>. 196 197=item B<-psk_identity identity> 198 199Use the PSK identity B<identity> when using a PSK cipher suite. 200 201=item B<-psk key> 202 203Use the PSK key B<key> when using a PSK cipher suite. The key is 204given as a hexadecimal number without leading 0x, for example -psk 2051a2b3c4d. 206 207=item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-tls1_1>, B<-tls1_2>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2> 208 209These options require or disable the use of the specified SSL or TLS protocols. 210By default the initial handshake uses a I<version-flexible> method which will 211negotiate the highest mutually supported protocol version. 212 213=item B<-fallback_scsv> 214 215Send TLS_FALLBACK_SCSV in the ClientHello. 216 217=item B<-bugs> 218 219there are several known bug in SSL and TLS implementations. Adding this 220option enables various workarounds. 221 222=item B<-sigalgs sigalglist> 223 224Specifies the list of signature algorithms that are sent by the client. 225The server selects one entry in the list based on its preferences. 226For example strings, see L<SSL_CTX_set1_sigalgs(3)> 227 228=item B<-curves curvelist> 229 230Specifies the list of supported curves to be sent by the client. The curve is 231is ultimately selected by the server. For a list of all curves, use: 232 233 $ openssl ecparam -list_curves 234 235=item B<-cipher cipherlist> 236 237this allows the cipher list sent by the client to be modified. Although 238the server determines which cipher suite is used it should take the first 239supported cipher in the list sent by the client. See the B<ciphers> 240command for more information. 241 242=item B<-serverpref> 243 244use the server's cipher preferences; only used for SSLV2. 245 246=item B<-starttls protocol> 247 248send the protocol-specific message(s) to switch to TLS for communication. 249B<protocol> is a keyword for the intended protocol. Currently, the only 250supported keywords are "smtp", "pop3", "imap", and "ftp". 251 252=item B<-tlsextdebug> 253 254print out a hex dump of any TLS extensions received from the server. 255 256=item B<-no_ticket> 257 258disable RFC4507bis session ticket support. 259 260=item B<-sess_out filename> 261 262output SSL session to B<filename> 263 264=item B<-sess_in sess.pem> 265 266load SSL session from B<filename>. The client will attempt to resume a 267connection from this session. 268 269=item B<-engine id> 270 271specifying an engine (by its unique B<id> string) will cause B<s_client> 272to attempt to obtain a functional reference to the specified engine, 273thus initialising it if needed. The engine will then be set as the default 274for all available algorithms. 275 276=item B<-rand file(s)> 277 278a file or files containing random data used to seed the random number 279generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>). 280Multiple files can be specified separated by a OS-dependent character. 281The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for 282all others. 283 284=item B<-serverinfo types> 285 286a list of comma-separated TLS Extension Types (numbers between 0 and 28765535). Each type will be sent as an empty ClientHello TLS Extension. 288The server's response (if any) will be encoded and displayed as a PEM 289file. 290 291=item B<-status> 292 293sends a certificate status request to the server (OCSP stapling). The server 294response (if any) is printed out. 295 296=item B<-alpn protocols>, B<-nextprotoneg protocols> 297 298these flags enable the 299Enable the Application-Layer Protocol Negotiation or Next Protocol 300Negotiation extension, respectively. ALPN is the IETF standard and 301replaces NPN. 302The B<protocols> list is a 303comma-separated protocol names that the client should advertise 304support for. The list should contain most wanted protocols first. 305Protocol names are printable ASCII strings, for example "http/1.1" or 306"spdy/3". 307Empty list of protocols is treated specially and will cause the client to 308advertise support for the TLS extension but disconnect just after 309reciving ServerHello with a list of server supported protocols. 310 311=back 312 313=head1 CONNECTED COMMANDS 314 315If a connection is established with an SSL server then any data received 316from the server is displayed and any key presses will be sent to the 317server. When used interactively (which means neither B<-quiet> nor B<-ign_eof> 318have been given), the session will be renegotiated if the line begins with an 319B<R>, and if the line begins with a B<Q> or if end of file is reached, the 320connection will be closed down. 321 322=head1 NOTES 323 324B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP 325server the command: 326 327 openssl s_client -connect servername:443 328 329would typically be used (https uses port 443). If the connection succeeds 330then an HTTP command can be given such as "GET /" to retrieve a web page. 331 332If the handshake fails then there are several possible causes, if it is 333nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>, 334B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried 335in case it is a buggy server. In particular you should play with these 336options B<before> submitting a bug report to an OpenSSL mailing list. 337 338A frequent problem when attempting to get client certificates working 339is that a web client complains it has no certificates or gives an empty 340list to choose from. This is normally because the server is not sending 341the clients certificate authority in its "acceptable CA list" when it 342requests a certificate. By using B<s_client> the CA list can be viewed 343and checked. However some servers only request client authentication 344after a specific URL is requested. To obtain the list in this case it 345is necessary to use the B<-prexit> option and send an HTTP request 346for an appropriate page. 347 348If a certificate is specified on the command line using the B<-cert> 349option it will not be used unless the server specifically requests 350a client certificate. Therefor merely including a client certificate 351on the command line is no guarantee that the certificate works. 352 353If there are problems verifying a server certificate then the 354B<-showcerts> option can be used to show the whole chain. 355 356Since the SSLv23 client hello cannot include compression methods or extensions 357these will only be supported if its use is disabled, for example by using the 358B<-no_sslv2> option. 359 360The B<s_client> utility is a test tool and is designed to continue the 361handshake after any certificate verification errors. As a result it will 362accept any certificate chain (trusted or not) sent by the peer. None test 363applications should B<not> do this as it makes them vulnerable to a MITM 364attack. This behaviour can be changed by with the B<-verify_return_error> 365option: any verify errors are then returned aborting the handshake. 366 367=head1 BUGS 368 369Because this program has a lot of options and also because some of 370the techniques used are rather old, the C source of s_client is rather 371hard to read and not a model of how things should be done. A typical 372SSL client program would be much simpler. 373 374The B<-prexit> option is a bit of a hack. We should really report 375information whenever a session is renegotiated. 376 377=head1 SEE ALSO 378 379L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)> 380 381=head1 HISTORY 382 383The -no_alt_chains options was first added to OpenSSL 1.0.2b. 384 385=cut 386