s_client.pod revision 325337
1 2=pod 3 4=head1 NAME 5 6openssl-s_client, 7s_client - SSL/TLS client program 8 9=head1 SYNOPSIS 10 11B<openssl> B<s_client> 12[B<-connect host:port>] 13[B<-servername name>] 14[B<-verify depth>] 15[B<-verify_return_error>] 16[B<-cert filename>] 17[B<-certform DER|PEM>] 18[B<-key filename>] 19[B<-keyform DER|PEM>] 20[B<-pass arg>] 21[B<-CApath directory>] 22[B<-CAfile filename>] 23[B<-no_alt_chains>] 24[B<-reconnect>] 25[B<-pause>] 26[B<-showcerts>] 27[B<-debug>] 28[B<-msg>] 29[B<-nbio_test>] 30[B<-state>] 31[B<-nbio>] 32[B<-crlf>] 33[B<-ign_eof>] 34[B<-no_ign_eof>] 35[B<-quiet>] 36[B<-ssl2>] 37[B<-ssl3>] 38[B<-tls1>] 39[B<-no_ssl2>] 40[B<-no_ssl3>] 41[B<-no_tls1>] 42[B<-no_tls1_1>] 43[B<-no_tls1_2>] 44[B<-fallback_scsv>] 45[B<-bugs>] 46[B<-sigalgs sigalglist>] 47[B<-curves curvelist>] 48[B<-cipher cipherlist>] 49[B<-serverpref>] 50[B<-starttls protocol>] 51[B<-engine id>] 52[B<-tlsextdebug>] 53[B<-no_ticket>] 54[B<-sess_out filename>] 55[B<-sess_in filename>] 56[B<-rand file(s)>] 57[B<-serverinfo types>] 58[B<-status>] 59[B<-alpn protocols>] 60[B<-nextprotoneg protocols>] 61 62=head1 DESCRIPTION 63 64The B<s_client> command implements a generic SSL/TLS client which connects 65to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for 66SSL servers. 67 68=head1 OPTIONS 69 70=over 4 71 72=item B<-connect host:port> 73 74This specifies the host and optional port to connect to. If not specified 75then an attempt is made to connect to the local host on port 4433. 76 77=item B<-servername name> 78 79Set the TLS SNI (Server Name Indication) extension in the ClientHello message. 80 81=item B<-cert certname> 82 83The certificate to use, if one is requested by the server. The default is 84not to use a certificate. 85 86=item B<-certform format> 87 88The certificate format to use: DER or PEM. PEM is the default. 89 90=item B<-key keyfile> 91 92The private key to use. If not specified then the certificate file will 93be used. 94 95=item B<-keyform format> 96 97The private format to use: DER or PEM. PEM is the default. 98 99=item B<-pass arg> 100 101the private key password source. For more information about the format of B<arg> 102see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>. 103 104=item B<-verify depth> 105 106The verify depth to use. This specifies the maximum length of the 107server certificate chain and turns on server certificate verification. 108Currently the verify operation continues after errors so all the problems 109with a certificate chain can be seen. As a side effect the connection 110will never fail due to a server certificate verify failure. 111 112=item B<-verify_return_error> 113 114Return verification errors instead of continuing. This will typically 115abort the handshake with a fatal error. 116 117=item B<-CApath directory> 118 119The directory to use for server certificate verification. This directory 120must be in "hash format", see B<verify> for more information. These are 121also used when building the client certificate chain. 122 123=item B<-CAfile file> 124 125A file containing trusted certificates to use during server authentication 126and to use when attempting to build the client certificate chain. 127 128=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> 129 130Set various certificate chain valiadition option. See the 131L<B<verify>|verify(1)> manual page for details. 132 133=item B<-reconnect> 134 135reconnects to the same server 5 times using the same session ID, this can 136be used as a test that session caching is working. 137 138=item B<-pause> 139 140pauses 1 second between each read and write call. 141 142=item B<-showcerts> 143 144display the whole server certificate chain: normally only the server 145certificate itself is displayed. 146 147=item B<-prexit> 148 149print session information when the program exits. This will always attempt 150to print out information even if the connection fails. Normally information 151will only be printed out once if the connection succeeds. This option is useful 152because the cipher in use may be renegotiated or the connection may fail 153because a client certificate is required or is requested only after an 154attempt is made to access a certain URL. Note: the output produced by this 155option is not always accurate because a connection might never have been 156established. 157 158=item B<-state> 159 160prints out the SSL session states. 161 162=item B<-debug> 163 164print extensive debugging information including a hex dump of all traffic. 165 166=item B<-msg> 167 168show all protocol messages with hex dump. 169 170=item B<-nbio_test> 171 172tests non-blocking I/O 173 174=item B<-nbio> 175 176turns on non-blocking I/O 177 178=item B<-crlf> 179 180this option translated a line feed from the terminal into CR+LF as required 181by some servers. 182 183=item B<-ign_eof> 184 185inhibit shutting down the connection when end of file is reached in the 186input. 187 188=item B<-quiet> 189 190inhibit printing of session and certificate information. This implicitly 191turns on B<-ign_eof> as well. 192 193=item B<-no_ign_eof> 194 195shut down the connection when end of file is reached in the input. 196Can be used to override the implicit B<-ign_eof> after B<-quiet>. 197 198=item B<-psk_identity identity> 199 200Use the PSK identity B<identity> when using a PSK cipher suite. 201The default value is "Client_identity" (without the quotes). 202 203=item B<-psk key> 204 205Use the PSK key B<key> when using a PSK cipher suite. The key is 206given as a hexadecimal number without leading 0x, for example -psk 2071a2b3c4d. 208This option must be provided in order to use a PSK cipher. 209 210=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> 211 212These options require or disable the use of the specified SSL or TLS protocols. 213By default the initial handshake uses a I<version-flexible> method which will 214negotiate the highest mutually supported protocol version. 215 216=item B<-fallback_scsv> 217 218Send TLS_FALLBACK_SCSV in the ClientHello. 219 220=item B<-bugs> 221 222there are several known bug in SSL and TLS implementations. Adding this 223option enables various workarounds. 224 225=item B<-sigalgs sigalglist> 226 227Specifies the list of signature algorithms that are sent by the client. 228The server selects one entry in the list based on its preferences. 229For example strings, see L<SSL_CTX_set1_sigalgs(3)> 230 231=item B<-curves curvelist> 232 233Specifies the list of supported curves to be sent by the client. The curve is 234is ultimately selected by the server. For a list of all curves, use: 235 236 $ openssl ecparam -list_curves 237 238=item B<-cipher cipherlist> 239 240this allows the cipher list sent by the client to be modified. Although 241the server determines which cipher suite is used it should take the first 242supported cipher in the list sent by the client. See the B<ciphers> 243command for more information. 244 245=item B<-serverpref> 246 247use the server's cipher preferences; only used for SSLV2. 248 249=item B<-starttls protocol> 250 251send the protocol-specific message(s) to switch to TLS for communication. 252B<protocol> is a keyword for the intended protocol. Currently, the only 253supported keywords are "smtp", "pop3", "imap", and "ftp". 254 255=item B<-tlsextdebug> 256 257print out a hex dump of any TLS extensions received from the server. 258 259=item B<-no_ticket> 260 261disable RFC4507bis session ticket support. 262 263=item B<-sess_out filename> 264 265output SSL session to B<filename> 266 267=item B<-sess_in sess.pem> 268 269load SSL session from B<filename>. The client will attempt to resume a 270connection from this session. 271 272=item B<-engine id> 273 274specifying an engine (by its unique B<id> string) will cause B<s_client> 275to attempt to obtain a functional reference to the specified engine, 276thus initialising it if needed. The engine will then be set as the default 277for all available algorithms. 278 279=item B<-rand file(s)> 280 281a file or files containing random data used to seed the random number 282generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>). 283Multiple files can be specified separated by a OS-dependent character. 284The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for 285all others. 286 287=item B<-serverinfo types> 288 289a list of comma-separated TLS Extension Types (numbers between 0 and 29065535). Each type will be sent as an empty ClientHello TLS Extension. 291The server's response (if any) will be encoded and displayed as a PEM 292file. 293 294=item B<-status> 295 296sends a certificate status request to the server (OCSP stapling). The server 297response (if any) is printed out. 298 299=item B<-alpn protocols>, B<-nextprotoneg protocols> 300 301these flags enable the 302Enable the Application-Layer Protocol Negotiation or Next Protocol 303Negotiation extension, respectively. ALPN is the IETF standard and 304replaces NPN. 305The B<protocols> list is a 306comma-separated protocol names that the client should advertise 307support for. The list should contain most wanted protocols first. 308Protocol names are printable ASCII strings, for example "http/1.1" or 309"spdy/3". 310Empty list of protocols is treated specially and will cause the client to 311advertise support for the TLS extension but disconnect just after 312reciving ServerHello with a list of server supported protocols. 313 314=back 315 316=head1 CONNECTED COMMANDS 317 318If a connection is established with an SSL server then any data received 319from the server is displayed and any key presses will be sent to the 320server. When used interactively (which means neither B<-quiet> nor B<-ign_eof> 321have been given), the session will be renegotiated if the line begins with an 322B<R>, and if the line begins with a B<Q> or if end of file is reached, the 323connection will be closed down. 324 325=head1 NOTES 326 327B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP 328server the command: 329 330 openssl s_client -connect servername:443 331 332would typically be used (https uses port 443). If the connection succeeds 333then an HTTP command can be given such as "GET /" to retrieve a web page. 334 335If the handshake fails then there are several possible causes, if it is 336nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>, 337B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried 338in case it is a buggy server. In particular you should play with these 339options B<before> submitting a bug report to an OpenSSL mailing list. 340 341A frequent problem when attempting to get client certificates working 342is that a web client complains it has no certificates or gives an empty 343list to choose from. This is normally because the server is not sending 344the clients certificate authority in its "acceptable CA list" when it 345requests a certificate. By using B<s_client> the CA list can be viewed 346and checked. However some servers only request client authentication 347after a specific URL is requested. To obtain the list in this case it 348is necessary to use the B<-prexit> option and send an HTTP request 349for an appropriate page. 350 351If a certificate is specified on the command line using the B<-cert> 352option it will not be used unless the server specifically requests 353a client certificate. Therefor merely including a client certificate 354on the command line is no guarantee that the certificate works. 355 356If there are problems verifying a server certificate then the 357B<-showcerts> option can be used to show the whole chain. 358 359Since the SSLv23 client hello cannot include compression methods or extensions 360these will only be supported if its use is disabled, for example by using the 361B<-no_sslv2> option. 362 363The B<s_client> utility is a test tool and is designed to continue the 364handshake after any certificate verification errors. As a result it will 365accept any certificate chain (trusted or not) sent by the peer. None test 366applications should B<not> do this as it makes them vulnerable to a MITM 367attack. This behaviour can be changed by with the B<-verify_return_error> 368option: any verify errors are then returned aborting the handshake. 369 370=head1 BUGS 371 372Because this program has a lot of options and also because some of 373the techniques used are rather old, the C source of s_client is rather 374hard to read and not a model of how things should be done. A typical 375SSL client program would be much simpler. 376 377The B<-prexit> option is a bit of a hack. We should really report 378information whenever a session is renegotiated. 379 380=head1 SEE ALSO 381 382L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)> 383 384=head1 HISTORY 385 386The -no_alt_chains options was first added to OpenSSL 1.0.2b. 387 388=cut 389