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    <h1>SSH Proxy Command -- connect.c</h1>\r
    <!-- Page published by Emacs Wiki begins here -->\r
<p>\r
<strong>connect.c</strong> is the simple relaying command to make network\r
connection via SOCKS and https proxy. It is mainly intended to\r
be used as <strong>proxy command</strong> of OpenSSH.  You can make SSH session\r
beyond the firewall with this command,\r
\r
</p>\r
\r
<p>\r
Features of <strong>connect.c</strong> are:\r
\r
</p>\r
\r
<ul>\r
<li>Supports SOCKS (version 4/4a/5) and https CONNECT method.\r
</li>\r
<li>Supports NO-AUTH and USERPASS authentication of SOCKS\r
</li>\r
<li>Partially supports telnet proxy (experimental).\r
</li>\r
<li>You can input password from tty, ssh-askpass or\r
     environment variable.\r
</li>\r
<li>Run on UNIX or Windows platform.\r
</li>\r
<li>You can compile with various C compiler (cc, gcc, Visual C, Borland C. etc.)\r
</li>\r
<li>Simple and general program independent from OpenSSH.\r
</li>\r
<li>You can also relay local socket stream instead of standard I/O.\r
</li>\r
</ul>\r
\r
<p>\r
Download source code from:\r
<a href="http://www.taiyo.co.jp/~gotoh/ssh/connect.c">http://www.taiyo.co.jp/~gotoh/ssh/connect.c</a>\r
<br/>\r
For windows user, pre-compiled binary is also available:\r
<a href="http://www.taiyo.co.jp/~gotoh/ssh/connect.exe">http://www.taiyo.co.jp/~gotoh/ssh/connect.exe</a> (compiled with MSVC)\r
\r
</p>\r
\r
<h2>Contents</h2>\r
<dl class="contents">\r
<dt class="contents">\r
<a href="#sec1">News</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec2">What is 'proxy command'</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec3">How to Use</a>\r
</dt>\r
<dd>\r
<dl class="contents">\r
<dt class="contents">\r
<a href="#sec4">Get Source</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec5">Compile and Install</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec6">Modify your ~/.ssh/config</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec7">Use SSH</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec8">Have trouble?</a>\r
</dt>\r
</dl>\r
</dd>\r
<dt class="contents">\r
<a href="#sec9">More Detail</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec10">Specifying user name via environment variables</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec11">Specifying password via environment variables</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec12">Limitations</a>\r
</dt>\r
<dd>\r
<dl class="contents">\r
<dt class="contents">\r
<a href="#sec13">SOCKS5 authentication</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec14">HTTP authentication</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec15">Switching proxy server</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec16">Telnet Proxy</a>\r
</dt>\r
</dl>\r
</dd>\r
<dt class="contents">\r
<a href="#sec17">Tips</a>\r
</dt>\r
<dd>\r
<dl class="contents">\r
<dt class="contents">\r
<a href="#sec18">Proxying socket connection</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec19">Use with ssh-askpass command</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec20">Use for Network Stream of Emacs</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec21">Remote resolver</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec22">Hopping Connection via SSH</a>\r
</dt>\r
</dl>\r
</dd>\r
<dt class="contents">\r
<a href="#sec23">Break The More Restricted Wall</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec24">F.Y.I.</a>\r
</dt>\r
<dd>\r
<dl class="contents">\r
<dt class="contents">\r
<a href="#sec25">Difference between SOCKS versions.</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec26">Configuration to use HTTPS</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec27">SOCKS5 Servers</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec28">Specifications</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec29">Related Links</a>\r
</dt>\r
<dt class="contents">\r
<a href="#sec30">Similars</a>\r
</dt>\r
</dl>\r
</dd>\r
<dt class="contents">\r
<a href="#sec31">hisotry</a>\r
</dt>\r
</dl>\r
\r
\r
<h2><a name="sec1" id="sec1"></a>News</h2>\r
<dl>\r
<dt>2005-07-08</dt>\r
<dd>\r
Rev. 1.95. Buf fix for previous change. The bug causes the fail of\r
  basic authentication. And also fixed bug of parameter file handling.\r
  Thanks reporting, Johannes Schindelin <Johannes.Schindelin at gmx.de>.\r
</dd>\r
<dt>2005-07-07</dt>\r
<dd>\r
Rev. 1.94. Changed to use snprintf()/vsnprintf() for security issue\r
  that gcc complained them on OpenBSD 3.7/x86. The features are not\r
  changed.\r
</dd>\r
<dt>2005-03-04</dt>\r
<dd>\r
Updated compile option for Mac OS X.\r
</dd>\r
<dt>2005-02-21</dt>\r
<dd>\r
Rev.1.92. Removed assertions which has no mean and worse for windows\r
  suggested by OZAWA Takahiro.\r
</dd>\r
<dt>2005-01-12</dt>\r
<dd>\r
Rev.1.90. Fixed not to cause seg-fault on accessing to non HTTP\r
  port. This problem is reported by Jason Armstrong <ja at riverdrums.com>.\r
</dd>\r
<dt>2004-10-30</dt>\r
<dd>\r
Rev.1.89. Partial support for telnet proxy.\r
  Thanks to Gregory Shimansky &lt;gshimansky at mail dot ru&gt;. \r
  (Note: This is ad-hoc implementation, so it is not enough for\r
  various type of telnet proxies.\r
  And password interaction is not supported.)\r
</dd>\r
</dl>\r
\r
<h2><a name="sec2" id="sec2"></a>What is 'proxy command'</h2>\r
\r
<p>\r
OpenSSH development team decides to stop supporting SOCKS and any\r
other tunneling mechanism. It was aimed to separate complexity to\r
support various mechanism of proxying from core code.  And they\r
recommends more flexible mechanism: <strong>ProxyCommand</strong> option\r
instead.\r
\r
</p>\r
\r
<p>\r
Proxy command mechanism is delegation of network stream\r
communication.  If <strong>ProxyCommand</strong> options is specified, SSH\r
invoke specified external command and talk with standard I/O of thid\r
command.  Invoked command undertakes network communication with\r
relaying to/from standard input/output including iniitial\r
communication or negotiation for proxying.  Thus, ssh can split out\r
proxying code into external command.\r
\r
</p>\r
\r
<p>\r
The <strong>connect.c</strong> program was made for this purpose.\r
\r
</p>\r
\r
<h2><a name="sec3" id="sec3"></a>How to Use</h2>\r
\r
<h3><a name="sec4" id="sec4"></a>Get Source</h3>\r
\r
<p>\r
Download source code from <a href="http://www.taiyo.co.jp/~gotoh/ssh/connect.c">here</a>.\r
<br/>\r
If you are MS Windows user, you can get pre-compiled binary from\r
<a href="http://www.taiyo.co.jp/~gotoh/ssh/connect.exe">here</a>.\r
\r
</p>\r
\r
<h3><a name="sec5" id="sec5"></a>Compile and Install</h3>\r
\r
<p>\r
In most environment, you can compile <strong>connect.c</strong> simply.\r
On UNIX environment, you can use cc or gcc.\r
On Windows environment, you can use Microsoft Visual C, Borland C or Cygwin gcc.\r
\r
</p>\r
\r
<table border="2" cellpadding="5">\r
<thead>\r
<tr>\r
<th>Compiler</th><th>command line to compile</th>\r
</tr>\r
</thead>\r
<tbody>\r
<tr>\r
<td>UNIX cc</td><td>cc connect.c -o connect</td>\r
</tr>\r
<tr>\r
<td>UNIX gcc</td><td>gcc connect.c -o connect</td>\r
</tr>\r
<tr>\r
<td>Solaris</td><td>gcc connect.c -o connect -lnsl -lsocket -lresolv</td>\r
</tr>\r
<tr>\r
<td>Microsoft Visual C/C++</td><td>cl connect.c wsock32.lib advapi32.lib</td>\r
</tr>\r
<tr>\r
<td>Borland C</td><td>bcc32 connect.c wsock32.lib advapi32.lib</td>\r
</tr>\r
<tr>\r
<td>Cygwin gcc</td><td>gcc connect.c -o connect</td>\r
</tr>\r
<tr>\r
<td>Mac OS X</td><td>gcc connect.c -o connect -lresolv<br/>or<br/>gcc connect.c -o connect -DBIND_8_COMPAT=1</td>\r
</tr>\r
</tbody>\r
</table>\r
\r
<p>\r
To install <strong>connect</strong> command, simply copy compiled binary to directory\r
in your PATH (ex. /usr/local/bin).  Like this:\r
\r
</p>\r
\r
<pre class="example">\r
$ cp connect /usr/local/bin\r
</pre>\r
\r
<h3><a name="sec6" id="sec6"></a>Modify your ~/.ssh/config</h3>\r
\r
<p>\r
Modify your <code>~/.ssh/config</code> file to use <strong>connect</strong> command as\r
<strong>proxy command</strong>.  For the case of SOCKS server is running on\r
firewall host <code>socks.local.net</code> with port 1080, you can add\r
<strong>ProxyCommand</strong> option in <code>~/.ssh/config</code>, like this:\r
\r
</p>\r
\r
<pre class="example">\r
Host remote.outside.net\r
  ProxyCommand connect -S socks.local.net %h %p\r
</pre>\r
\r
<p>\r
<code>%h</code> and <code>%p</code> will be replaced on invoking proxy command with\r
target hostname and port specified to SSH command.\r
\r
</p>\r
\r
<p>\r
If you hate writing many entries of remote hosts, following example\r
may help you.\r
\r
</p>\r
\r
<pre class="example">\r
## Inside of the firewall, use connect command with direct connection.\r
Host *.local.net\r
  ProxyCommand connect %h %p\r
\r
## Outside of the firewall, use connect command with SOCKS conenction.\r
Host *\r
  ProxyCommand connect -S socks.local.net %h %p\r
</pre>\r
\r
<p>\r
If you want to use http proxy, use <strong>-H</strong> option instead of <strong>-S</strong>\r
option in examle above, like this:\r
\r
</p>\r
\r
<pre class="example">\r
## Inside of the firewall, direct\r
Host *.local.net\r
  ProxyCommand connect %h %p\r
\r
## Outside of the firewall, with HTTP proxy\r
Host *\r
  ProxyCommand connect -H proxy.local.net:8080 %h %p\r
</pre>\r
\r
<h3><a name="sec7" id="sec7"></a>Use SSH</h3>\r
\r
<p>\r
After editing your <code>~/.ssh/config</code> file, you are ready to use ssh.\r
You can execute ssh without any special options as if remote host is\r
IP reachable host.  Following is an example to execute <code>hostname</code>\r
command on host <code>remote.outside.net</code>.\r
\r
</p>\r
\r
<pre class="example">\r
$ ssh remote.outside.net hostname\r
remote.outside.net\r
$\r
</pre>\r
\r
<h3><a name="sec8" id="sec8"></a>Have trouble?</h3>\r
\r
<p>\r
If you have trouble, execute <strong>connect</strong> command from command line\r
with <code>-d</code> option to see what is happened. Some debug message may\r
appear and reports progress. This information may tell you what is\r
wrong. In this example, error has occurred on authentication stage of\r
SOCKS5 protocol.\r
\r
</p>\r
\r
<pre class="example">\r
$ connect -d -S socks.local.net unknown.remote.outside.net 110\r
DEBUG: relay_method = SOCKS (2)\r
DEBUG: relay_host=socks.local.net\r
DEBUG: relay_port=1080\r
DEBUG: relay_user=gotoh\r
DEBUG: socks_version=5\r
DEBUG: socks_resolve=REMOTE (2)\r
DEBUG: local_type=stdio\r
DEBUG: dest_host=unknown.remote.outside.net\r
DEBUG: dest_port=110\r
DEBUG: Program is $Revision$\r
DEBUG: connecting to xxx.xxx.xxx.xxx:1080\r
DEBUG: begin_socks_relay()\r
DEBUG: atomic_out()  [4 bytes]\r
DEBUG: &gt;&gt;&gt; 05 02 00 02\r
DEBUG: atomic_in() [2 bytes]\r
DEBUG: &lt;&lt;&lt; 05 02\r
DEBUG: auth method: USERPASS\r
DEBUG: atomic_out()  [some bytes]\r
DEBUG: &gt;&gt;&gt; xx xx xx xx ...\r
DEBUG: atomic_in() [2 bytes]\r
DEBUG: &lt;&lt;&lt; 01 01\r
ERROR: Authentication faield.\r
FATAL: failed to begin relaying via SOCKS.\r
</pre>\r
\r
<h2><a name="sec9" id="sec9"></a>More Detail</h2>\r
\r
<p>\r
Command line usage is here:\r
\r
</p>\r
\r
<pre class="example">\r
usage:  connect [-dnhst45] [-R resolve] [-p local-port] [-w sec]\r
		[-H [user@]proxy-server[:port]]\r
		[-S [user@]socks-server[:port]]\r
		[-T socks-server:[port]]\r
                [-c telnet-proxy-command]\r
		host port\r
</pre>\r
\r
<p>\r
<strong><em>host</em></strong> and <strong><em>port</em></strong> is target hostname and port-number to connect.\r
\r
</p>\r
\r
<p>\r
<strong>-H</strong> option specify hostname and port number of http proxy server to\r
relay. If port is omitted, 80 is used. You can specify this value by\r
environment variable <code>HTTP_PROXY</code> and give <strong>-h</strong> option to use it.\r
\r
</p>\r
\r
<p>\r
<strong>-S</strong> option specify hostname and port number of SOCKS server to\r
relay.  Like <strong>-H</strong> option, port number can be omit and default is 1080. \r
You can also specify this value pair by environment variable\r
<code>SOCKS5_SERVER</code> and give <strong>-s</strong> option to use it.\r
\r
</p>\r
\r
<p>\r
<strong>-T</strong> option specify hostname and port number of telnet proxy to\r
relay. The port number can be omit and default is 23.\r
You can also specify this value pair by environment variable\r
<code>TELNET_PROXY</code> and give <strong>-t</strong> option to use it.\r
\r
</p>\r
\r
<p>\r
<strong>-4</strong> and <strong>-5</strong> is for specifying SOCKS protocol version. It is\r
valid only using with <strong>-s</strong> or <strong>-S</strong>. Default is <strong>-5</strong>\r
(protocol version 5)\r
\r
</p>\r
\r
<p>\r
<strong>-R</strong> is for specifying method to resolve hostname. 3 keywords\r
(<code>local</code>, <code>remote</code>, <code>both</code>) or dot-notation IP address is\r
allowed.  Keyword <code>both</code> means; "Try local first, then\r
remote". If dot-notation IP address is specified, use this host as\r
nameserver (UNIX only). Default is <code>remote</code> for SOCKS5 or <code>local</code>\r
for others. On SOCKS4 protocol, remote resolving method (<code>remote</code>\r
and <code>both</code>) use protocol version 4a.\r
\r
</p>\r
\r
<p>\r
The <strong>-p</strong> option specifys to wait a local TCP port and make relaying\r
with it instead of standard input and output.\r
\r
</p>\r
\r
<p>\r
The <strong>-w</strong> option specifys timeout seconds on making connection with\r
target host.\r
\r
</p>\r
\r
<p>\r
The <strong>-c</strong> option specifys request string against telnet\r
proxy server. The special word '%h' and '%p' in this string are replaced\r
as hostname and port number before sending. \r
For telnet proxy by <a class="nonexistent" href="mailto:gotoh@taiyo.co.jp">DeleGate</a>, both "telnet %h %p" and "%h:%p"\r
are acceptable.\r
Default is "telnet %h %p".\r
\r
</p>\r
\r
<p>\r
The <strong>-a</strong> option specifiys user intended authentication methods\r
separated by comma.  Currently <code>userpass</code> and <code>none</code> are\r
supported. Default is <code>userpass</code>. You can also specifying this\r
parameter by the environment variable <code>SOCKS5_AUTH</code>.\r
\r
</p>\r
\r
<p>\r
The <strong>-d</strong> option is used for debug. If you fail to connect, use this\r
and check request to and response from server.\r
\r
</p>\r
\r
<p>\r
You can omit <strong><em>port</em></strong> argument when program name is special format\r
containing port number itself. For example, \r
\r
</p>\r
\r
<pre class="example">\r
$ ln -s connect connect-25\r
$ ./connect-25 smtphost.outside.net\r
220 smtphost.outside.net ESMTP Sendmail\r
QUIT\r
221 2.0.0 smtphost.remote.net closing connection\r
$\r
</pre>\r
\r
<p>\r
This example means that the command name "<code>connect-25</code>" contains port number\r
25 so you can omit 2nd argument (and used if specified explicitly).\r
\r
</p>\r
\r
<h2><a name="sec10" id="sec10"></a>Specifying user name via environment variables</h2>\r
\r
<p>\r
There are 5 environemnt variables to specify\r
user name without command line option. This mechanism is usefull\r
for the user who using another user name different from system account.\r
\r
</p>\r
\r
<dl>\r
<dt>SOCKS5_USER</dt>\r
<dd>\r
Used for SOCKS v5 access.\r
</dd>\r
<dt>SOCKS4_USER</dt>\r
<dd>\r
Used for SOCKS v4 access.\r
</dd>\r
<dt>SOCKS_USER</dt>\r
<dd>\r
Used for SOCKS v5 or v4 access and varaibles above are not defined.\r
</dd>\r
<dt>HTTP_PROXY_USER</dt>\r
<dd>\r
Used for HTTP proxy access.\r
</dd>\r
<dt>CONNECT_USER</dt>\r
<dd>\r
Used for all type of access if all above are not defined.\r
</dd>\r
</dl>\r
\r
<p>\r
Following table describes how user name is determined.\r
Left most number is order to check. If variable is not defined,\r
check next variable, and so on.\r
\r
</p>\r
\r
<table border=1>\r
<tr align=center><th></th><th>SOCKS v5</th><th>SOCKS v4</th><th>HTTP proxy</th></tr>\r
<tr align=center><td>1</td><td>SOCKS5_USER</td><td>SOCKS4_USER</td><td rowspan=2>HTTP_PROXY_USER</td></tr>\r
<tr align=center><td>2</td><td colspan=2>SOCKS_USER</td></tr>\r
<tr align=center><td>3</td><td colspan=3>CONNECT_USER</td></tr>\r
<tr align=center><td>4</td><td colspan=3><i>(query user name to system)</i></td></tr>\r
</table>\r
\r
<h2><a name="sec11" id="sec11"></a>Specifying password via environment variables</h2>\r
\r
<p>\r
There are 5 environemnt variables to specify\r
password. If you use this feature, please note that it is\r
not secure way.\r
\r
</p>\r
\r
<dl>\r
<dt>SOCKS5_PASSWD</dt>\r
<dd>\r
Used for SOCKS v5 access. This variables is compatible\r
  with NEC SOCKS implementation.\r
</dd>\r
<dt>SOCKS5_PASSWORD</dt>\r
<dd>\r
Used for SOCKS v5 access if SOCKS5_PASSWD is not defined.\r
</dd>\r
<dt>SOCKS_PASSWORD</dt>\r
<dd>\r
Used for SOCKS v5 (or v4) access all above is not defined.\r
</dd>\r
<dt>HTTP_PROXY_PASSWORD</dt>\r
<dd>\r
Used for HTTP proxy access.\r
</dd>\r
<dt>CONNECT_PASSWORD</dt>\r
<dd>\r
Used for all type of access if all above are not defined.\r
</dd>\r
</dl>\r
\r
<p>\r
Following table describes how password is determined.\r
Left most number is order to check. If variable is not defined,\r
check next variable, and so on. Finally ask to user interactively\r
using external program or tty input.\r
\r
</p>\r
\r
<table border=1>\r
<tr align=center><th></th><th>SOCKS v5</th><th>HTTP proxy</th></tr>\r
<tr align=center><td>1</td><td>SOCKS5_PASSWD</td><td rowspan=2>HTTP_PROXY_PASSWORD</td></tr>\r
<tr align=center><td>2</td><td>SOCKS_PASSWORD</td></tr>\r
<tr align=center><td>3</td><td colspan=2>CONNECT_PASSWORD</td></tr>\r
<tr align=center><td>4</td><td colspan=2><i>(ask to user interactively)</i></td></tr>\r
</table>\r
\r
<h2><a name="sec12" id="sec12"></a>Limitations</h2>\r
\r
<h3><a name="sec13" id="sec13"></a>SOCKS5 authentication</h3>\r
\r
<p>\r
Only NO-AUTH and USER/PASSWORD authentications are supported.\r
GSSAPI authentication (RFC 1961) and other draft authentications (CHAP,\r
EAP, MAF, etc.) is not supported.\r
\r
</p>\r
\r
<h3><a name="sec14" id="sec14"></a>HTTP authentication</h3>\r
\r
<p>\r
BASIC authentication is supported but DIGEST authentication is not.\r
\r
</p>\r
\r
<h3><a name="sec15" id="sec15"></a>Switching proxy server</h3>\r
\r
<p>\r
There is no mechanism to switch proxy server regarding to PC environment.\r
This limitation might be bad news for mobile user.\r
Since I do not want to make this program complex, I do not want to\r
support although this feature is already requested.  Please advice me\r
if there is good idea of detecting environment to swich and simple way\r
to specify conditioned directive of servers.\r
\r
</p>\r
\r
<p>\r
One tricky workaround exists. It is replacing ~/.ssh/config file\r
by script on ppp up/down.\r
\r
</p>\r
\r
<p>\r
There's another example of wrapper script (contributed by Darren Tucker).\r
This script costs executing ifconfig and grep to detect\r
current environment, but it works. (NOTE: you should modify addresses\r
if you use it.)\r
\r
</p>\r
\r
<pre class="example">\r
#!/bin/sh\r
## ~/bin/myconnect --- Proxy server switching wrapper\r
\r
if ifconfig eth0 |grep &quot;inet addr:192\.168\.1&quot; &gt;/dev/null; then\r
	opts=&quot;-S 192.168.1.1:1080&quot;  \r
elif ifconfig eth0 |grep &quot;inet addr:10\.&quot; &gt;/dev/null; then\r
	opts=&quot;-H 10.1.1.1:80&quot;\r
else\r
	opts=&quot;-s&quot;\r
fi\r
exec /usr/local/bin/connect $opts $@\r
</pre>\r
\r
<h3><a name="sec16" id="sec16"></a>Telnet Proxy</h3>\r
\r
<p>\r
At first, note that the telnet proxy support is an partial feature.\r
In this implementation, <strong>connect</strong> single requestinting and proxy\r
returns some success/error detective in talked back lines including\r
greeting, prompt and connected messages.\r
\r
</p>\r
\r
<p>\r
The <strong>connect</strong> simply send request after connection to proxy is\r
established before any response reading, then repeat reading response\r
strings from proxy to decide remote connection request is succeeded or\r
not by checking pre-defined phrase in each lines. There are\r
pre-defined phrases which are good-phrase and bad-phrases.  First\r
good-phrase is checked and change state as relaying if exist.\r
<strong>connect</strong> treat this line as final response from proxy before\r
starting acutal communication with remote host.  Or if good-phrase is\r
not matched, bad-phrases will be checked.  If one of bad-phrase\r
matched, it cause connection error immediately.\r
\r
</p>\r
\r
<p>\r
The pre-defined phrases are currently fixed string so you cannot\r
change without modifying and compiling.  The good-phrase is:\r
"connected to".  The bad-phrases are: " failed", " refused", "\r
rejected", " closed".\r
\r
</p>\r
\r
<h2><a name="sec17" id="sec17"></a>Tips</h2>\r
\r
<h3><a name="sec18" id="sec18"></a>Proxying socket connection</h3>\r
\r
<p>\r
In usual, <strong>connect.c</strong> relays network connection to/from standard\r
input/output. By specifying <strong>-p</strong> option, however, <strong>connect.c</strong>\r
relays local network stream instead of standard input/output.\r
With this option, <strong>connect</strong> command waits connection\r
from other program, then start relaying between both network stream.\r
\r
</p>\r
\r
<p>\r
This feature may be useful for the program which is hard to SOCKSify.\r
\r
</p>\r
\r
<h3><a name="sec19" id="sec19"></a>Use with ssh-askpass command</h3>\r
\r
<p>\r
<strong>connect.c</strong> ask you password when authentication is required.  If\r
you are using on tty/pty terminal, connect can input from terminal\r
with prompt. But you can also use <code>ssh-askpass</code> program to input\r
password.  If you are graphical environment like X Window or MS\r
Windows, and program does not have tty/pty, and environment variable\r
SSH_ASKPASS is specified, then <strong>connect.c</strong> invoke command\r
specified by environment variable <code>SSH_ASKPASS</code> to input password.\r
<code>ssh-askpass</code> program might be installed if you are using OpenSSH on\r
UNIX environment. On Windows environment, pre-compiled binary is\r
available from\r
<a href="http://www.taiyo.co.jp/~gotoh/ssh/ssh-askpass.exe">here</a>.\r
\r
</p>\r
\r
<p>\r
This feature is limited on window system environment.\r
\r
</p>\r
\r
<p>\r
And also useful on Emacs on MS Windows (NT Emacs or Meadow).  It is\r
hard to send passphrase to <strong>connect</strong> command (and also ssh)\r
because external command is invoked on hidden terminal and do I/O with\r
this terminal.  Using ssh-askpass avoids this problem.\r
\r
</p>\r
\r
<h3><a name="sec20" id="sec20"></a>Use for Network Stream of Emacs</h3>\r
\r
<p>\r
Although <strong>connect.c</strong> is made for OpenSSH, it is generic and\r
independent from OpenSSH. So we can use this for other purpose.  For\r
example, you can use this command in Emacs to open network connection\r
with remote host over the firewall via SOCKS or HTTP proxy without\r
SOCKSifying Emacs itself.\r
\r
</p>\r
\r
<p>\r
There is sample code: \r
<a href="http://www.taiyo.co.jp/~gotoh/lisp/relay.el">http://www.taiyo.co.jp/~gotoh/lisp/relay.el</a>\r
\r
</p>\r
\r
<p>\r
With this code, you can use <code>relay-open-network-stream</code> function\r
instead of <code>open-network-stream</code> to make network connection. See top\r
comments of source for more detail.\r
\r
</p>\r
\r
<h3><a name="sec21" id="sec21"></a>Remote resolver</h3>\r
\r
<p>\r
If you are SOCKS4 user on UNIX environment, you might want specify\r
nameserver to resolve remote hostname.  You can do it specifying\r
<strong>-R</strong> option followed by IP address of resolver.\r
\r
</p>\r
\r
<h3><a name="sec22" id="sec22"></a>Hopping Connection via SSH</h3>\r
\r
<p>\r
Conbination of ssh and <strong>connect</strong> command have more interesting usage.\r
Following command makes indirect connection to host2:port from your\r
current host via host1.\r
\r
</p>\r
\r
<pre class="example">\r
ssh host1 connect host2 port\r
</pre>\r
\r
<p>\r
This method is useful for the situations like:\r
\r
</p>\r
\r
<ul>\r
<li>You are outside of organizasion now, but you want to access an\r
    internal host barriered by firewall.\r
</li>\r
<li>You want to use some service which is allowed only from some\r
    limited hosts.\r
</li>\r
</ul>\r
\r
<p>\r
For example, I want to use local NetNews service in my office\r
from home.  I cannot make NNTP session directly because NNTP host is\r
barriered by firewall.  Fortunately, I have ssh account on internal\r
host and allowed using SOCKS5 on firewall from outside.  So I use\r
following command to connect to NNTP service.\r
\r
</p>\r
\r
<pre class="example">\r
$ ssh host1 connect news 119\r
200 news.my-office.com InterNetNews NNRP server INN 2.3.2 ready (posting ok).\r
quit\r
205 .\r
$\r
</pre>\r
\r
<p>\r
By combinating hopping connection and relay.el, I can read NetNews\r
using <a href="http://www.gohome.org/wl/">Wanderlust</a> on Emacs at home.\r
\r
</p>\r
\r
<pre class="example">\r
                        |\r
    External (internet) | Internal (office)\r
                        |\r
+------+           +----------+          +-------+           +-----------+\r
| HOME |           | firewall |          | host1 |           | NNTP host |\r
+------+           +----------+          +-------+           +-----------+\r
 emacs &lt;-------------- ssh ---------------&gt; sshd &lt;-- connect --&gt; nntpd\r
       &lt;-- connect --&gt; socksd &lt;-- SOCKS --&gt;\r
</pre>\r
\r
<p>\r
As an advanced example, you can use SSH hopping as fetchmail's plug-in\r
program to access via secure tunnel. This method requires that\r
<strong>connect</strong> program is insatalled on remote host.  There's example\r
of .fetchmailrc bellow. When fetchmail access to mail-server, you will\r
login to remote host using SSH then execute <strong>connect</strong> program on\r
remote host to relay conversation with pop server. Thus fetchmail can\r
retrieve mails in secure.\r
\r
</p>\r
\r
<pre class="example">\r
poll mail-server\r
  protocol pop3\r
  plugin &quot;ssh %h connect localhost %p&quot;\r
  username &quot;username&quot;\r
  password &quot;password&quot;\r
&lt;/exmaple&gt;\r
\r
* &lt;a name=&quot;sec23&quot; id=&quot;sec23&quot;&gt;&lt;/a&gt;Break The More Restricted Wall\r
\r
If firewall does not provide SOCKS nor HTTPS other than port 443, you\r
cannot break the wall in usual way.  But if you have you own host\r
which is accessible from internet, you can make ssh connection to your\r
own host by configuring sshd as waiting at port 443 instead of\r
standard 22. By this, you can login to your own host via port 443.\r
Once you have logged-in to extenal home machine, you can execute\r
**connect** as second hop to make connection from your own host to\r
final target host, like this:\r
\r
&lt;example&gt;\r
$ cat ~/.ssh/config\r
Host home\r
  ProxyCommand connect -H firewall:8080 %h 443\r
\r
Host server\r
  ProxyCommand ssh home connect %h %p\r
...\r
internal$ ssh home\r
You are logged in to home!\r
home# exit\r
internal$ ssh server\r
You are logged in to server!\r
server# exit\r
internal$\r
</pre>\r
\r
<p>\r
This way is similar to "Hopping connection via SSH" except configuring\r
outer sshd as waiting at port 443 (https).  This means that you have a\r
capability to break the strongly restricted wall if you have own host\r
out side of the wall.\r
\r
</p>\r
\r
<pre class="example">\r
                        |\r
      Internal (office) | External (internet)\r
                        |\r
+--------+         +----------+                 +------+          +--------+\r
| office |         | firewall |                 | home |          | server |\r
+--------+         +----------+                 +------+          +--------+\r
   &lt;------------------ ssh ---------------------&gt;sshd:443\r
    &lt;-- connect --&gt; http-proxy &lt;-- https:443 --&gt;                      any\r
                                                 connect &lt;-- tcp --&gt;  port\r
</pre>\r
\r
<p>\r
NOTE: If you wanna use this, you should give up hosting https service\r
at port 443 on you external host 'home'.\r
\r
</p>\r
\r
<h2><a name="sec24" id="sec24"></a>F.Y.I.</h2>\r
\r
<h3><a name="sec25" id="sec25"></a>Difference between SOCKS versions.</h3>\r
\r
<p>\r
SOCKS version 4 is first popular implementation which is documented\r
<a href="http://www.socks.nec.com/protocol/socks4.protocol">here</a>. Since\r
this protocol provide IP address based requesting, client program\r
should resolve name of outer host by itself. Version 4a (documented\r
<a href="http://www.socks.nec.com/protocol/socks4a.protocol">here</a>) is\r
enhanced to allow request by hostname instead of IP address.\r
\r
</p>\r
\r
<p>\r
SOCKS version 5 is re-designed protocol stands on experience of\r
version 4 and 4a.  There is no compativility with previous\r
versions. Instead, there's some improvement: IPv6 support, request by\r
hostname, UDP proxying, etc.\r
\r
</p>\r
\r
<h3><a name="sec26" id="sec26"></a>Configuration to use HTTPS</h3>\r
\r
<p>\r
Many http proxy servers implementation supports https <code>CONNECT</code> method\r
(SLL).  You might add configuration to allow using https.  For the\r
example of <a href="http://www.delegate.org/delegate/">DeleGate</a> (\r
DeleGate is a multi-purpose application level gateway, or a proxy\r
server) , you should add <code>https</code> to <code>REMITTABLE</code> parameter to\r
allow HTTP-Proxy like this:\r
\r
</p>\r
\r
<pre class="example">\r
delegated -Pxxxx ...... REMITTABLE='+,https' ...\r
</pre>\r
\r
<p>\r
For the case of Squid, you should allow target ports via https by ACL,\r
and so on.\r
\r
</p>\r
\r
<h3><a name="sec27" id="sec27"></a>SOCKS5 Servers</h3>\r
\r
<dl>\r
<dt><a href="http://www.socks.nec.com/refsoftware.html">NEC SOCKS Reference Implementation</a></dt>\r
<dd>\r
Reference implementation of SOKCS server and library.\r
</dd>\r
<dt><a href="http://www.inet.no/dante/index.html">Dante</a></dt>\r
<dd>\r
Dante is free implementation of SOKCS server and library.\r
  Many enhancements and modulalized.\r
</dd>\r
<dt><a href="http://www.delegate.org/delegate/">DeleGate</a></dt>\r
<dd>\r
DeleGate is multi function proxy service provider.\r
  DeleGate 5.x.x or earlier can be SOCKS4 server,\r
  and 6.x.x can be SOCKS5 and SOCKS4 server.\r
  and 7.7.0 or later can be SOCKS5 and SOCKS4a server.\r
</dd>\r
</dl>\r
\r
<h3><a name="sec28" id="sec28"></a>Specifications</h3>\r
\r
<dl>\r
<dt><a href="http://www.socks.nec.com/protocol/socks4.protocol">socks4.protocol.txt</a></dt>\r
<dd>\r
SOCKS: A protocol for TCP proxy across firewalls\r
</dd>\r
<dt><a href="http://www.socks.nec.com/protocol/socks4a.protocol">socks4a.protocol.txt</a></dt>\r
<dd>\r
SOCKS 4A: A  Simple Extension to SOCKS 4 Protocol\r
</dd>\r
<dt><a href="http://www.socks.nec.com/rfc/rfc1928.txt">RFC 1928</a></dt>\r
<dd>\r
SOCKS Protocol Version 5\r
</dd>\r
<dt><a href="http://www.socks.nec.com/rfc/rfc1929.txt">RFC 1929</a></dt>\r
<dd>\r
Username/Password Authentication for SOCKS V5\r
</dd>\r
<dt><a href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a></dt>\r
<dd>\r
Hypertext Transfer Protocol -- HTTP/1.1\r
</dd>\r
<dt><a href="http://www.ietf.org/rfc/rfc2617.txt">RFC 2617</a></dt>\r
<dd>\r
HTTP Authentication: Basic and Digest Access Authentication\r
</dd>\r
</dl>\r
\r
<h3><a name="sec29" id="sec29"></a>Related Links</h3>\r
\r
<ul>\r
<li><a href="http://www.openssh.org">OpenSSH Home</a>\r
</li>\r
<li><a href="http://www.ssh.com/">Proprietary SSH</a>\r
</li>\r
<li><a href="http://www.taiyo.co.jp/~gotoh/ssh/openssh-socks.html">Using OpenSSH through a SOCKS compatible PROXY on your LAN</a> (J. Grant)\r
</li>\r
</ul>\r
\r
<h3><a name="sec30" id="sec30"></a>Similars</h3>\r
\r
<ul>\r
<li><a href="http://proxytunnel.sourceforge.net/">Proxy Tunnel</a> -- Proxying command using https CONNECT.\r
</li>\r
<li><a href="http://www.snurgle.org/~griffon/ssh-https-tunnel">stunnel</a> -- Proxy through an https tunnel (Perl script)\r
</li>\r
</ul>\r
\r
<h2><a name="sec31" id="sec31"></a>hisotry</h2>\r
\r
<dl>\r
<dt>2004-07-21</dt>\r
<dd>\r
Rev.1.84. Fixed some typo.\r
</dd>\r
<dt>2004-05-18</dt>\r
<dd>\r
Rev.1.83. Fixed problem not work on Solaris.\r
</dd>\r
<dt>2004-04-27</dt>\r
<dd>\r
Rev.1.82. Bug fix of memory clear on http proxying.\r
</dd>\r
<dt>2004-04-22</dt>\r
<dd>\r
Rev. 1.81. Fixed memory violation and memory leak bug. New environment\r
  variable SOCKS5_PASSWD for sharing value with NEC SOCKS implementation.\r
  And document (this page) is updated.\r
</dd>\r
<dt>2004-03-30</dt>\r
<dd>\r
Rev. 1.76. Fixed to accept multiple 'Proxy-Authorization' response.\r
</dd>\r
<dt>2003-01-07</dt>\r
<dd>\r
Rev. 1.68. Fixed a trouble around timeout support.\r
</dd>\r
<dt>2002-11-21</dt>\r
<dd>\r
Rev. 1.64 supports reading parameters from file /etc/connectrc or\r
  ~/.connectrc instead of specifying via environment variables. For\r
  examle, you can use this feature to switch setting by replacing file\r
  when network environment is changed. And added SOCKS_DIRECT,\r
  SOCKS5_DIRECT, SOCKS4_DIRECT, HTTP_DIRECT, SOCKS5_AUTH, environment\r
  parameters. (Thanks Masatoshi TSUCHIYA)\r
</dd>\r
<dt>2002-11-20</dt>\r
<dd>\r
Rev. 1.63 supports some old proxies which make response 401 with\r
  WWW-Authenticate: header. And fixed to use username specified in\r
  proxy host by -H option correctly. (contributed from Des Herriott, thanks)\r
</dd>\r
<dt>2002-10-14</dt>\r
<dd>\r
Rev. 1.61 with New option -w for specifying connection timeout.\r
  Currently, it works on UNIX only. (contributed from Darren Tucker, thanks)\r
</dd>\r
<dt>2002-09-29</dt>\r
<dd>\r
Add sample script for switching proxy server\r
  advised from Darren Tucker, thanks.\r
</dd>\r
<dt>2002-08-27</dt>\r
<dd>\r
connect.c is updataed to rev. 1.60.\r
</dd>\r
<dt>2002-04-08</dt>\r
<dd>\r
Updated <a href="http://www.taiyo.co.jp/~gotoh/ssh/openssh-socks.html">"Using OpenSSH through a SOCKS compatible PROXY on your LAN"</a> written by  J. Grant. (version 0.8)\r
</dd>\r
<dt>2002-02-20</dt>\r
<dd>\r
Add link of new document "Using OpenSSH through a SOCKS compatible PROXY on your LAN"\r
  written by J. Grant.\r
</dd>\r
<dt>2002-01-31</dt>\r
<dd>\r
Rev. 1.53 -- On Win32 and with MSVC, handle password\r
  input from console correctly.\r
</dd>\r
<dt>2002-01-30</dt>\r
<dd>\r
Rev. 1.50 -- [Security Fix] Do not print secure info in debug mode.\r
</dd>\r
<dt>2002-01-09</dt>\r
<dd>\r
Web page was made.\r
  connect.c is rev. 1.48.\r
</dd>\r
</dl>\r
<br>\r
\r
    <!-- Page published by Emacs Wiki ends here -->\r
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      <hr/>\r
      <table width="100%" border="0" summary="Footer navigation">\r
       <tbody><tr>\r
	  <td width="50%" align="left">\r
	    <span class="footdate">Last Updated: 2005-07-18</span><br/>\r
	  </td>\r
	  <td width="50%" align="right">\r
            This page is authored by <a href="mailto:gotoh@taiyo.co.jp">Shun-ichi GOTO</a>\r
	    using <a href="http://repose.cx/emacs/wiki">emacs-wiki.el</a><br/>\r
	  </td>\r
	</tr></tbody>\r
      </table>\r
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