s_client.pod revision 296341
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<-bugs>] 42[B<-cipher cipherlist>] 43[B<-serverpref>] 44[B<-starttls protocol>] 45[B<-engine id>] 46[B<-tlsextdebug>] 47[B<-no_ticket>] 48[B<-sess_out filename>] 49[B<-sess_in filename>] 50[B<-rand file(s)>] 51[B<-status>] 52[B<-nextprotoneg protocols>] 53 54=head1 DESCRIPTION 55 56The B<s_client> command implements a generic SSL/TLS client which connects 57to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for 58SSL servers. 59 60=head1 OPTIONS 61 62=over 4 63 64=item B<-connect host:port> 65 66This specifies the host and optional port to connect to. If not specified 67then an attempt is made to connect to the local host on port 4433. 68 69=item B<-servername name> 70 71Set the TLS SNI (Server Name Indication) extension in the ClientHello message. 72 73=item B<-cert certname> 74 75The certificate to use, if one is requested by the server. The default is 76not to use a certificate. 77 78=item B<-certform format> 79 80The certificate format to use: DER or PEM. PEM is the default. 81 82=item B<-key keyfile> 83 84The private key to use. If not specified then the certificate file will 85be used. 86 87=item B<-keyform format> 88 89The private format to use: DER or PEM. PEM is the default. 90 91=item B<-pass arg> 92 93the private key password source. For more information about the format of B<arg> 94see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>. 95 96=item B<-verify depth> 97 98The verify depth to use. This specifies the maximum length of the 99server certificate chain and turns on server certificate verification. 100Currently the verify operation continues after errors so all the problems 101with a certificate chain can be seen. As a side effect the connection 102will never fail due to a server certificate verify failure. 103 104=item B<-verify_return_error> 105 106Return verification errors instead of continuing. This will typically 107abort the handshake with a fatal error. 108 109=item B<-CApath directory> 110 111The directory to use for server certificate verification. This directory 112must be in "hash format", see B<verify> for more information. These are 113also used when building the client certificate chain. 114 115=item B<-CAfile file> 116 117A file containing trusted certificates to use during server authentication 118and to use when attempting to build the client certificate chain. 119 120=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> 121 122Set various certificate chain valiadition option. See the 123L<B<verify>|verify(1)> manual page for details. 124 125=item B<-reconnect> 126 127reconnects to the same server 5 times using the same session ID, this can 128be used as a test that session caching is working. 129 130=item B<-pause> 131 132pauses 1 second between each read and write call. 133 134=item B<-showcerts> 135 136display the whole server certificate chain: normally only the server 137certificate itself is displayed. 138 139=item B<-prexit> 140 141print session information when the program exits. This will always attempt 142to print out information even if the connection fails. Normally information 143will only be printed out once if the connection succeeds. This option is useful 144because the cipher in use may be renegotiated or the connection may fail 145because a client certificate is required or is requested only after an 146attempt is made to access a certain URL. Note: the output produced by this 147option is not always accurate because a connection might never have been 148established. 149 150=item B<-state> 151 152prints out the SSL session states. 153 154=item B<-debug> 155 156print extensive debugging information including a hex dump of all traffic. 157 158=item B<-msg> 159 160show all protocol messages with hex dump. 161 162=item B<-nbio_test> 163 164tests non-blocking I/O 165 166=item B<-nbio> 167 168turns on non-blocking I/O 169 170=item B<-crlf> 171 172this option translated a line feed from the terminal into CR+LF as required 173by some servers. 174 175=item B<-ign_eof> 176 177inhibit shutting down the connection when end of file is reached in the 178input. 179 180=item B<-quiet> 181 182inhibit printing of session and certificate information. This implicitly 183turns on B<-ign_eof> as well. 184 185=item B<-no_ign_eof> 186 187shut down the connection when end of file is reached in the input. 188Can be used to override the implicit B<-ign_eof> after B<-quiet>. 189 190=item B<-psk_identity identity> 191 192Use the PSK identity B<identity> when using a PSK cipher suite. 193 194=item B<-psk key> 195 196Use the PSK key B<key> when using a PSK cipher suite. The key is 197given as a hexadecimal number without leading 0x, for example -psk 1981a2b3c4d. 199 200=item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> 201 202these options disable the use of certain SSL or TLS protocols. By default 203the initial handshake uses a method which should be compatible with all 204servers and permit them to use SSL v3, SSL v2 or TLS as appropriate. 205 206Unfortunately there are a lot of ancient and broken servers in use which 207cannot handle this technique and will fail to connect. Some servers only 208work if TLS is turned off with the B<-no_tls> option others will only 209support SSL v2 and may need the B<-ssl2> option. 210 211=item B<-bugs> 212 213there are several known bug in SSL and TLS implementations. Adding this 214option enables various workarounds. 215 216=item B<-cipher cipherlist> 217 218this allows the cipher list sent by the client to be modified. Although 219the server determines which cipher suite is used it should take the first 220supported cipher in the list sent by the client. See the B<ciphers> 221command for more information. 222 223=item B<-serverpref> 224 225use the server's cipher preferences; only used for SSLV2. 226 227=item B<-starttls protocol> 228 229send the protocol-specific message(s) to switch to TLS for communication. 230B<protocol> is a keyword for the intended protocol. Currently, the only 231supported keywords are "smtp", "pop3", "imap", and "ftp". 232 233=item B<-tlsextdebug> 234 235print out a hex dump of any TLS extensions received from the server. 236 237=item B<-no_ticket> 238 239disable RFC4507bis session ticket support. 240 241=item B<-sess_out filename> 242 243output SSL session to B<filename> 244 245=item B<-sess_in sess.pem> 246 247load SSL session from B<filename>. The client will attempt to resume a 248connection from this session. 249 250=item B<-engine id> 251 252specifying an engine (by its unique B<id> string) will cause B<s_client> 253to attempt to obtain a functional reference to the specified engine, 254thus initialising it if needed. The engine will then be set as the default 255for all available algorithms. 256 257=item B<-rand file(s)> 258 259a file or files containing random data used to seed the random number 260generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>). 261Multiple files can be specified separated by a OS-dependent character. 262The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for 263all others. 264 265=item B<-status> 266 267sends a certificate status request to the server (OCSP stapling). The server 268response (if any) is printed out. 269 270=item B<-nextprotoneg protocols> 271 272enable Next Protocol Negotiation TLS extension and provide a list of 273comma-separated protocol names that the client should advertise 274support for. The list should contain most wanted protocols first. 275Protocol names are printable ASCII strings, for example "http/1.1" or 276"spdy/3". 277Empty list of protocols is treated specially and will cause the client to 278advertise support for the TLS extension but disconnect just after 279reciving ServerHello with a list of server supported protocols. 280 281=back 282 283=head1 CONNECTED COMMANDS 284 285If a connection is established with an SSL server then any data received 286from the server is displayed and any key presses will be sent to the 287server. When used interactively (which means neither B<-quiet> nor B<-ign_eof> 288have been given), the session will be renegotiated if the line begins with an 289B<R>, and if the line begins with a B<Q> or if end of file is reached, the 290connection will be closed down. 291 292=head1 NOTES 293 294B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP 295server the command: 296 297 openssl s_client -connect servername:443 298 299would typically be used (https uses port 443). If the connection succeeds 300then an HTTP command can be given such as "GET /" to retrieve a web page. 301 302If the handshake fails then there are several possible causes, if it is 303nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>, 304B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried 305in case it is a buggy server. In particular you should play with these 306options B<before> submitting a bug report to an OpenSSL mailing list. 307 308A frequent problem when attempting to get client certificates working 309is that a web client complains it has no certificates or gives an empty 310list to choose from. This is normally because the server is not sending 311the clients certificate authority in its "acceptable CA list" when it 312requests a certificate. By using B<s_client> the CA list can be viewed 313and checked. However some servers only request client authentication 314after a specific URL is requested. To obtain the list in this case it 315is necessary to use the B<-prexit> option and send an HTTP request 316for an appropriate page. 317 318If a certificate is specified on the command line using the B<-cert> 319option it will not be used unless the server specifically requests 320a client certificate. Therefor merely including a client certificate 321on the command line is no guarantee that the certificate works. 322 323If there are problems verifying a server certificate then the 324B<-showcerts> option can be used to show the whole chain. 325 326Since the SSLv23 client hello cannot include compression methods or extensions 327these will only be supported if its use is disabled, for example by using the 328B<-no_sslv2> option. 329 330The B<s_client> utility is a test tool and is designed to continue the 331handshake after any certificate verification errors. As a result it will 332accept any certificate chain (trusted or not) sent by the peer. None test 333applications should B<not> do this as it makes them vulnerable to a MITM 334attack. This behaviour can be changed by with the B<-verify_return_error> 335option: any verify errors are then returned aborting the handshake. 336 337=head1 BUGS 338 339Because this program has a lot of options and also because some of 340the techniques used are rather old, the C source of s_client is rather 341hard to read and not a model of how things should be done. A typical 342SSL client program would be much simpler. 343 344The B<-prexit> option is a bit of a hack. We should really report 345information whenever a session is renegotiated. 346 347=head1 SEE ALSO 348 349L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)> 350 351=head1 HISTORY 352 353The -no_alt_chains options was first added to OpenSSL 1.0.1n and 1.0.2b. 354 355=cut 356