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Network Programming-Project 4 Solved
1 Introduction
In this project, you are going to implement the SOCKS 4/4A protocol in the application layer of the OSI model.
SOCKS is similar to a proxy (i.e., intermediary-program) that acts as both server and client for the purpose of making requests on behalf of other clients. Because the SOCKS protocol is independent of application protocols, it can be used for many different services: telnet, ftp, WWW, etc.
There are two types of the SOCKS operations, namely CONNECT and BIND. You have to implement both of them in this project. We will use Boost.Asio library to accomplish this project.
2 SOCKS 4 Implementation
After the SOCKS server starts listening, if a SOCKS client connects, use fork() to tackle with it. Each child process will do:
1. Receive SOCKS4 REQUEST from the SOCKS client
2. Get the destination IP and port from SOCKS4 REQUEST
3. Check the firewall (socks.conf), and send SOCKS4 REPLY to the SOCKS client if rejected
4. Check CD value and choose one of the operations
(a) CONNECT (CD=1)
i. Connect to the destination
ii. Send SOCKS4 REPLY to the SOCKS client
iii. Start relaying traffic on both directions
(b) BIND (CD=2)
i. Bind and listen a port
ii. Send SOCKS4 REPLY to SOCKS client to tell which port to connect
iii. (SOCKS client tells destination to connect to SOCKS server) iv. Accept connection from destination and send another SOCKS4 REPLY to SOCKS client
v. Start relaying traffic on both directions
If the SOCKS server decides to reject a request from a SOCKS client, the connection will be closed immediately.
SOCKS4_REQUEST packet (VN=4, CD=1 or 2) Type 1: CONNECT
+----+----+----+----+----+----+----+----+----+----+....+----+
| VN | CD | DSTPORT | DSTIP | USERID |NULL|
+----+----+----+----+----+----+----+----+----+----+....+----+
bytes: 1 1 2 4 variable 1
Type 2: BIND (SOCKS 4A)
+----+----+----+----+----+----+----+----+----+----+....+----+----+----+....+----+
| VN | CD | DSTPORT | DSTIP(0.0.0.x) | USERID |NULL| DOMAIN NAME |NULL|
+----+----+----+----+----+----+----+----+----+----+....+----+----+----+....+----+
bytes: 1 1 2 4 variable 1 variable 1 e.g. DSTIP=140.113.1.2
DSPPORT=1234 (hint: 1234 = 4*256 + 210 = DSTPORT[0]*256 + DSTPORT[1])
USERID=MOZ
+----+----+----+----+----+----+----+----+----+----+----+----+
| 4 | 1 | 4 |210 |140 |113 | 1 | 2 | M | O | Z | |
+----+----+----+----+----+----+----+----+----+----+----+----+
bytes: 1 | 1 | 2 | 4 | variable | 1
SOCKS4_REPLY packet (VN=0, CD=90(accepted) or 91(rejected or failed))
+----+----+----+----+----+----+----+----+
| VN | CD | DSTPORT | DSTIP |
+----+----+----+----+----+----+----+----+ bytes: 1 1 2 4
Please refer to these webpages for more detailed SOCKS 4 specification.
• SOCKS 4
• SOCKS 4A
We suggest you to reject SOCKS 5 request.
3 Requirements
• Part I: SOCKS 4 Server Connect Operation
– Turn on and set your SOCKS server, then
∗ Be able to connect any webpages on Google Search.
∗ We will only test this section on Firefox.
∗ Your SOCKS server need to show messages below:
· Do NOT print other contents (e.g., debug messages) in the SOCKS server
<S_IP>: source ip
<S_PORT>: source port
<D_IP>: destination ip
<D_PORT>: destination port <Command>: CONNECT or BIND
<Reply>: Accept or Reject
• Part II: SOCKS 4 Server Bind Operation
– Connect to FTP server with SOCKS
∗ Set config with your SOCKS server
∗ Connection type is FTP (cannot be SFTP)
∗ Data connection mode is Active Mode (PORT)
· You can use FlashFXP as the FTP client
– Download files larger than 1GB completely. E.g., Ubuntu 20.04 ISO image (download link)
∗ The SOCKS server’s output message should show that BIND operation is used
• Part III: CGI Proxy
– Modify console.cgi in Project 3 to implement SOCKS client mode
∗ Accept SocksIP and SocksPort parameters in QUERY STRING as sh and sp, respectively ∗ Use SocksIP and SocksPort to connect to your SOCKS server (by CONNECT operation) ∗ Rename console.cgi into hw4.cgi in Makefile – Use the HTTP server hosted on the NP Server
∗ Place files in ∼/public html
∗ Visit http://[NP_server_host]/~[your_user_name]/[your_cgi_name].cgi
– Clear browser’s proxy setting
Open your http server, connect to panel socks.cgi
Key in IP, port, filename, SocksIP, SocksPort
Connect to 5 ras/rwg servers through SOCKS server and check the output Test Case (same as
Project 3, no hidden test case) t1.txt-t5.txt
• Firewall
– You only need to implement a simple firewall. List permitted destination IPs into socks.conf (deny all traffic by default)
e.g.,
permit c 140.113.*.*
# permit NYCU IP for Connect operation
permit b *.*.*.*
# permit all IP for Bind operation
– Be able to change firewall rules without restarting the SOCKS server.
• Specification
– Port number of SOCKS server is specified by the first argument: ./socks server [port]
– The rules in socks.conf default to
permit c *.*.*.* permit b *.*.*.*
– You can only use C/C++ to implement this project. Except for Boost, other third-party libraries are NOT allowed.
– Every function that touches network operations (e.g., DNS query, connect, accept, send, receive)MUST be implemented using the library Boost.Asio.
– Both synchronous and asynchronous functions can be used. Notice that some situations onlywork with non-blocking operations. Be thoughtful when using the synchronous ones.
2. Bitbucket:
(a) Create a private repository: ${your student ID} np project4 inside the nycu np 2022 team, under np project4.
Set the ownership to nycu np 2022
e.g., 310551000_np_project4
(b) You need to commit on Bitbucket for at least 5 times.
(c) You can push anything you need onto bitbucket as long as the size of the file is reasonable.
5 Notes
1. We take plagiarism seriously. You will get zero points on this project for plagiarism.
2. You will lose points for violating any of the rules mentioned in this spec.
3. Any abuse of NP server will be recorded.
