mirror of
https://gitlab.torproject.org/tpo/core/tor.git
synced 2024-11-24 12:23:32 +01:00
61 lines
2.3 KiB
Plaintext
61 lines
2.3 KiB
Plaintext
$Id$
|
|
Tor's extensions to the SOCKS protocol
|
|
|
|
1. Overview
|
|
|
|
The SOCKS protocol provides a generic interface for TCP proxies. Client
|
|
software connects to a SOCKS server via TCP, and requests a TCP connection
|
|
to another address and port. The SOCKS server establishes the connection,
|
|
and reports success or failure to the client. After the connection has
|
|
been established, the client application uses the TCP stream as usual.
|
|
|
|
Tor supports SOCKS4 as defined in [1], SOCKS4A as defined in [2], and
|
|
SOCKS5 as defined in [3].
|
|
|
|
The stickiest issue for Tor in supporting clients, in practice, is forcing
|
|
DNS lookups to occur at the OR side: if clients do their own DNS lookup,
|
|
the DNS server can learn which addresses the client wants to reach.
|
|
SOCKS4 supports addressing by IPv4 address; SOCKS4A is a kludge on top of
|
|
SOCKS4 to allow addressing by hostname; SOCKS5 supports IPv4, IPv6, and
|
|
hostnames.
|
|
|
|
1.1. Extent of support
|
|
|
|
Tor supports the SOCKS4, SOCKS4A, and SOCKS5 standards, except as follows:
|
|
|
|
BOTH:
|
|
- The BIND command is not supported.
|
|
|
|
SOCKS4,4A:
|
|
- SOCKS4 usernames are ignored.
|
|
|
|
SOCKS5:
|
|
- The (SOCKS5) "UDP ASSOCIATE" command is not supported.
|
|
- IPv6 is not supported in CONNECT commands.
|
|
- Only the "NO AUTHENTICATION" (SOCKS5) authentication method [00] is
|
|
supported.
|
|
|
|
2. Name lookup
|
|
|
|
As an extension to SOCKS4A and SOCKS5, Tor implements a new command value,
|
|
"RESOLVE" [F0]. When Tor receives a "RESOLVE" SOCKS command, it initiates
|
|
a remote lookup of the hostname provided as the target address in the SOCKS
|
|
request. The reply is either an error (if the address couldn't be
|
|
resolved) or a success response. In the case of success, the address is
|
|
stored in the portion of the SOCKS response reserved for remote IP address.
|
|
|
|
(We support RESOLVE in SOCKS4 too, even though it is unnecessary.)
|
|
|
|
3. HTTP-resistance
|
|
|
|
Tor checks the first byte of each socks request to see whether it looks
|
|
more like an HTTP request (that is, it starts with a "G", "H", or "P"). If
|
|
so, Tor returns a small webpage, telling the user that his/her browser is
|
|
misconfigured. This is helpful for the many users who mistakenly try to
|
|
use Tor as an HTTP proxy instead of a SOCKS proxy.
|
|
|
|
References:
|
|
[1] http://archive.socks.permeo.com/protocol/socks4.protocol
|
|
[2] http://archive.socks.permeo.com/protocol/socks4a.protocol
|
|
[3] SOCKS5: RFC1928
|