EVOLUTION-MANAGER

Edit File: socks-extensions.txt

$Id: socks-extensions.txt,v 1.1 2008-06-18 21:17:02 hoganrobert Exp $ 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.) For SOCKS5 only, we support reverse resolution with a new command value, "RESOLVE_PTR" [F1]. In response to a "RESOLVE_PTR" SOCKS5 command with an IPv4 address as its target, Tor attempts to find the canonical hostname for that IPv4 record, and returns it in the "server bound address" portion of the reply. (This command was not supported before Tor 0.1.2.2-alpha.) 3. Other command extensions. Tor 0.1.2.4-alpha added a new command value: "CONNECT_DIR" [F2]. In this case, Tor will open an encrypted direct TCP connection to the directory port of the Tor server specified by address:port (the port specified should be the ORPort of the server). It uses a one-hop tunnel and a "BEGIN_DIR" relay cell to accomplish this secure connection. The F2 command value was removed in Tor 0.2.0.10-alpha in favor of a new use_begindir flag in edge_connection_t. 4. 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