SYNOPSIS
openssl s_client
[
DESCRIPTION
The s_client command implements a generic SSL/TLS client which connects to a remote host using SSL/TLS. It is a very useful diagnostic tool for SSL servers.
Options
-connect host:port-
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.
-cert certname-
specifies the certificate to use, if one is requested by the server. The default is not to use a certificate.
-key keyfile-
specifies the private key to use. If not specified then the certificate file will be used.
-verify depth-
specifies the verify depth to use. This specifies the maximum length of the server certificate chain and turns on server certificate verification. 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.
-CApath directory-
specifies the directory to use for server certificate verification. This directory must be in "hash format", see verify for more information. These are also used when building the client certificate chain.
-CAfile file-
specifies a file containing trusted certificates to use during server authentication and to use when attempting to build the client certificate chain.
-reconnect -
reconnects to the same server 5 times using the same session ID, this can be used as a test that session caching is working.
-pause -
pauses 1 second between each read and write call.
-showcerts -
displays the whole server certificate chain: normally only the server certificate itself is displayed.
-prexit -
prints session information when the program exits. This will always attempt to print out information even if the connection fails. Normally 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 certificate 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.
-state -
prints out the SSL session states.
-debug -
prints extensive debugging information including a hex dump of all traffic.
-nbio_test -
tests non-blocking I/O.
-nbio -
turns on non-blocking I/O.
-crlf -
translates a line feed from the terminal into CR+LF as required by some servers.
-ign_eof -
inhibits shutting down the connection when end of file is reached in the input.
-quiet -
inhibits printing of session and certificate information. This implicitely turns on
-ign_eof as well. -ssl2 -ssl3 -tls1 -no_ssl2 -no_ssl3 -no_tls1 -
these options disable the use of certain SSL or TLS protocols. By default the initial handshake uses a method which should be compatible with all servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
Unfortunately there are a lot of ancient and broken servers in use which cannot handle this technique and will fail to connect. Some servers only work if TLS is turned off with the
-no_tls option others will only support SSL v2 and may need the-ssl2 option. -bugs -
enables various workarounds to several known bug in SSL and TLS implementations.
-cipher cipherlist-
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 ciphers command for more information.
-rand file(s)-
specifies a file or files containing random data used to seed the random number generator, or an EGD socket. Multiple files can be specified separated by a OS-dependent character. The separator is ; for MS-Windows, , for OpenVMS, and : for all others.
CONNECTED COMMANDS
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
NOTES
s_client 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 succeeds 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
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 s_client 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
necessary to use the
If a certificate is specified on the command line using the
If there are problems verifying a server certificate then the
BUGS
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
The
AVAILABILITY
MKS Toolkit for System Administrators
MKS Toolkit for Developers
MKS Toolkit for Interoperability
MKS Toolkit for Professional Developers
MKS Toolkit for Enterprise Developers
MKS Toolkit for Enterprise Developers 64-Bit Edition
MKS AlertCentre
SEE ALSO
- Commands:
- openssl ciphers, openssl s_server, openssl sess_id