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<-cipher cipherlist>] 46[B<-serverpref>] 47[B<-starttls protocol>] 48[B<-engine id>] 49[B<-tlsextdebug>] 50[B<-no_ticket>] 51[B<-sess_out filename>] 52[B<-sess_in filename>] 53[B<-rand file(s)>] 54[B<-serverinfo types>] 55[B<-status>] 56[B<-nextprotoneg protocols>] 57 58=head1 DESCRIPTION 59 60The B<s_client> command implements a generic SSL/TLS client which connects 61to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for 62SSL servers. 63 64=head1 OPTIONS 65 66=over 4 67 68=item B<-connect host:port> 69 70This specifies the host and optional port to connect to. If not specified 71then an attempt is made to connect to the local host on port 4433. 72 73=item B<-servername name> 74 75Set the TLS SNI (Server Name Indication) extension in the ClientHello message. 76 77=item B<-cert certname> 78 79The certificate to use, if one is requested by the server. The default is 80not to use a certificate. 81 82=item B<-certform format> 83 84The certificate format to use: DER or PEM. PEM is the default. 85 86=item B<-key keyfile> 87 88The private key to use. If not specified then the certificate file will 89be used. 90 91=item B<-keyform format> 92 93The private format to use: DER or PEM. PEM is the default. 94 95=item B<-pass arg> 96 97the private key password source. For more information about the format of B<arg> 98see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>. 99 100=item B<-verify depth> 101 102The verify depth to use. This specifies the maximum length of the 103server certificate chain and turns on server certificate verification. 104Currently the verify operation continues after errors so all the problems 105with a certificate chain can be seen. As a side effect the connection 106will never fail due to a server certificate verify failure. 107 108=item B<-verify_return_error> 109 110Return verification errors instead of continuing. This will typically 111abort the handshake with a fatal error. 112 113=item B<-CApath directory> 114 115The directory to use for server certificate verification. This directory 116must be in "hash format", see B<verify> for more information. These are 117also used when building the client certificate chain. 118 119=item B<-CAfile file> 120 121A file containing trusted certificates to use during server authentication 122and to use when attempting to build the client certificate chain. 123 124=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> 125 126Set various certificate chain valiadition option. See the 127L<B<verify>|verify(1)> manual page for details. 128 129=item B<-reconnect> 130 131reconnects to the same server 5 times using the same session ID, this can 132be used as a test that session caching is working. 133 134=item B<-pause> 135 136pauses 1 second between each read and write call. 137 138=item B<-showcerts> 139 140display the whole server certificate chain: normally only the server 141certificate itself is displayed. 142 143=item B<-prexit> 144 145print session information when the program exits. This will always attempt 146to print out information even if the connection fails. Normally information 147will only be printed out once if the connection succeeds. This option is useful 148because the cipher in use may be renegotiated or the connection may fail 149because a client certificate is required or is requested only after an 150attempt is made to access a certain URL. Note: the output produced by this 151option is not always accurate because a connection might never have been 152established. 153 154=item B<-state> 155 156prints out the SSL session states. 157 158=item B<-debug> 159 160print extensive debugging information including a hex dump of all traffic. 161 162=item B<-msg> 163 164show all protocol messages with hex dump. 165 166=item B<-nbio_test> 167 168tests non-blocking I/O 169 170=item B<-nbio> 171 172turns on non-blocking I/O 173 174=item B<-crlf> 175 176this option translated a line feed from the terminal into CR+LF as required 177by some servers. 178 179=item B<-ign_eof> 180 181inhibit shutting down the connection when end of file is reached in the 182input. 183 184=item B<-quiet> 185 186inhibit printing of session and certificate information. This implicitly 187turns on B<-ign_eof> as well. 188 189=item B<-no_ign_eof> 190 191shut down the connection when end of file is reached in the input. 192Can be used to override the implicit B<-ign_eof> after B<-quiet>. 193 194=item B<-psk_identity identity> 195 196Use the PSK identity B<identity> when using a PSK cipher suite. 197 198=item B<-psk key> 199 200Use the PSK key B<key> when using a PSK cipher suite. The key is 201given as a hexadecimal number without leading 0x, for example -psk 2021a2b3c4d. 203 204=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> 205 206These options require or disable the use of the specified SSL or TLS protocols. 207By default the initial handshake uses a I<version-flexible> method which will 208negotiate the highest mutually supported protocol version. 209 210=item B<-fallback_scsv> 211 212Send TLS_FALLBACK_SCSV in the ClientHello. 213 214=item B<-bugs> 215 216there are several known bug in SSL and TLS implementations. Adding this 217option enables various workarounds. 218 219=item B<-cipher cipherlist> 220 221this allows the cipher list sent by the client to be modified. Although 222the server determines which cipher suite is used it should take the first 223supported cipher in the list sent by the client. See the B<ciphers> 224command for more information. 225 226=item B<-serverpref> 227 228use the server's cipher preferences; only used for SSLV2. 229 230=item B<-starttls protocol> 231 232send the protocol-specific message(s) to switch to TLS for communication. 233B<protocol> is a keyword for the intended protocol. Currently, the only 234supported keywords are "smtp", "pop3", "imap", and "ftp". 235 236=item B<-tlsextdebug> 237 238print out a hex dump of any TLS extensions received from the server. 239 240=item B<-no_ticket> 241 242disable RFC4507bis session ticket support. 243 244=item B<-sess_out filename> 245 246output SSL session to B<filename> 247 248=item B<-sess_in sess.pem> 249 250load SSL session from B<filename>. The client will attempt to resume a 251connection from this session. 252 253=item B<-engine id> 254 255specifying an engine (by its unique B<id> string) will cause B<s_client> 256to attempt to obtain a functional reference to the specified engine, 257thus initialising it if needed. The engine will then be set as the default 258for all available algorithms. 259 260=item B<-rand file(s)> 261 262a file or files containing random data used to seed the random number 263generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>). 264Multiple files can be specified separated by a OS-dependent character. 265The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for 266all others. 267 268=item B<-serverinfo types> 269 270a list of comma-separated TLS Extension Types (numbers between 0 and 27165535). Each type will be sent as an empty ClientHello TLS Extension. 272The server's response (if any) will be encoded and displayed as a PEM 273file. 274 275=item B<-status> 276 277sends a certificate status request to the server (OCSP stapling). The server 278response (if any) is printed out. 279 280=item B<-nextprotoneg protocols> 281 282enable Next Protocol Negotiation TLS extension and provide a list of 283comma-separated protocol names that the client should advertise 284support for. The list should contain most wanted protocols first. 285Protocol names are printable ASCII strings, for example "http/1.1" or 286"spdy/3". 287Empty list of protocols is treated specially and will cause the client to 288advertise support for the TLS extension but disconnect just after 289reciving ServerHello with a list of server supported protocols. 290 291=back 292 293=head1 CONNECTED COMMANDS 294 295If a connection is established with an SSL server then any data received 296from the server is displayed and any key presses will be sent to the 297server. When used interactively (which means neither B<-quiet> nor B<-ign_eof> 298have been given), the session will be renegotiated if the line begins with an 299B<R>, and if the line begins with a B<Q> or if end of file is reached, the 300connection will be closed down. 301 302=head1 NOTES 303 304B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP 305server the command: 306 307 openssl s_client -connect servername:443 308 309would typically be used (https uses port 443). If the connection succeeds 310then an HTTP command can be given such as "GET /" to retrieve a web page. 311 312If the handshake fails then there are several possible causes, if it is 313nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>, 314B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried 315in case it is a buggy server. In particular you should play with these 316options B<before> submitting a bug report to an OpenSSL mailing list. 317 318A frequent problem when attempting to get client certificates working 319is that a web client complains it has no certificates or gives an empty 320list to choose from. This is normally because the server is not sending 321the clients certificate authority in its "acceptable CA list" when it 322requests a certificate. By using B<s_client> the CA list can be viewed 323and checked. However some servers only request client authentication 324after a specific URL is requested. To obtain the list in this case it 325is necessary to use the B<-prexit> option and send an HTTP request 326for an appropriate page. 327 328If a certificate is specified on the command line using the B<-cert> 329option it will not be used unless the server specifically requests 330a client certificate. Therefor merely including a client certificate 331on the command line is no guarantee that the certificate works. 332 333If there are problems verifying a server certificate then the 334B<-showcerts> option can be used to show the whole chain. 335 336Since the SSLv23 client hello cannot include compression methods or extensions 337these will only be supported if its use is disabled, for example by using the 338B<-no_sslv2> option. 339 340The B<s_client> utility is a test tool and is designed to continue the 341handshake after any certificate verification errors. As a result it will 342accept any certificate chain (trusted or not) sent by the peer. None test 343applications should B<not> do this as it makes them vulnerable to a MITM 344attack. This behaviour can be changed by with the B<-verify_return_error> 345option: any verify errors are then returned aborting the handshake. 346 347=head1 BUGS 348 349Because this program has a lot of options and also because some of 350the techniques used are rather old, the C source of s_client is rather 351hard to read and not a model of how things should be done. A typical 352SSL client program would be much simpler. 353 354The B<-prexit> option is a bit of a hack. We should really report 355information whenever a session is renegotiated. 356 357=head1 SEE ALSO 358 359L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)> 360 361=head1 HISTORY 362 363The -no_alt_chains options was first added to OpenSSL 1.0.2b. 364 365=cut 366