Assignment 2: simple standalone backdoor program

Assignment 2

Weight: 16% of your final grade.
In this assignment you are going to implement a simple standalone backdoor program. You can write your
program in C, C++ or Python. Your backdoor must be able to run on the Linux machines in the computer labs.
When your backdoor program starts, it will listen on some port for a client to connect. It should be possible to
specify the port number on the command line. When the client connects, it should perform a simple hand-shake
mechanism, e.g. by accepting a hard-coded password. After the handshake is successfully finished, the server
will start accepting commands from the client, execute them and return results. When a client disconnects, the
backdoor should resume waiting for a new connection. If the handshake is unsuccessful, i.e. the secret sent is
incorrect, the backdoor should drop the connection.
Your backdoor should be usable by connecting to it using netcat (nc). This means that you do not need to write
a client program for this assignment. Also, your backdoor program only needs to service one client at a time.
There is no need to support multiple simultaneous clients.
At minimum, your backdoor must support the following commands:
Command Description
pwd return the current working directory
cd <dir change the current working directory to <dir
ls list the contents of the current working directory
cp <file1 <file2 copy file1 to file2
mv <file1 <file2 rename file1 to file2
rm <file delete file
cat <file return contents of the file
snap take a snapshot of all the files in the current directory and save it in memory
the snapshot should only include the filenames and hashes of the files
the snapshot should survive client disconnecting and reconnecting later
diff compare the contents of the current directory to the saved snapshot, and report
differences (deleted files, new files and changed files)
this does not need to be recursive
help [cmd] print a list of commands, and if given an argument, print more detailed help for
the command
logout disconnect client (server closes the socket)
off terminate the backdoor program
On top of the required commands, you must implement at least two additional commands of your own choice.
You can be creative with these. Below are some suggestions:
Command Description
who list user[s] currently logged in
net show current networking configuration
ps show currently running processes
nmap <params run nmap with parameters <params
ext <program <params run program <program with parameters <params
Each command should give user at least a minimum feedback, eg. success or failure.
Starting the backdoor
Your backdoor should accept at least one command line argument – the port number on which the backdoor will
listen. If you want to pass additional command line arguments, fell free to do so. Also, it is OK for your
backdoor to print any debugging information to stdout or stderr while it’s running.
$ ./backdoor.py 9312
backdoor listening on port 9312
Sample netcat session:
Once your backdoor is running, you should be able to interact with it using netcat. Here is a sample session:
$ nc localhost 9312
Identify yourself!
pass p@ssw0rD
welcome boss
hello
sorry, I don’t understand this command
help
supported commands:
pwd, cd, cwd, ls, cp, rm, mv, cat, snap, diff, off, nmap, ext
help cp
cp <file1 <file2 - copies file1 to file2
cd /usr
OK
ls
drwxr-xr-x. 3 root root 4096 Apr 19 2016 abrt
-rw-r--r--. 1 root root 18 Aug 17 2015 adjtime
-rw-r--r--. 1 root root 1518 Feb 23 2015 aliases
-rw-r-----. 1 root smmsp 12288 Apr 19 2016 aliases.db
drwxr-xr-x. 2 root root 4096 Aug 17 2015 alsa
cat /etc/passwd
root:x:0:0:Mr. Rooter Fedora Workstation,,,:/root:/usr/bin/tcsh
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
diff
ERROR: no snapshot
snap
OK
mv passwd passwd.old
OK
mv aliases aliases.old
OK
mv passwd.old aliases
OK
diff
passwd – was deleted
aliases – was changed
aliases.old – was added
off
I am terminating myself. So long...
$
Additional notes
 You may call external commands from your implementation. For example, you can use system() or
popen() from C/C++, and subprocess.run() or subprocess.Popen() from Python.
 The “snap” command should calculate a cryptographic hash for every file in the current directory, and
then store these hashes together with the filenames in memory. You can use MD5, SHA1, SHA2 or
SHA3. You can compute the hashes using a library (openssl, or cryptography), or you can use an
external command for this (eg. openssl dgst -md5 -hex file).
 The “diff” command will compare the contents of the current directory to the saved snapshot. It should
be possible to call “snap” in one directory, then “cd” to a different directory, and call “diff” there. The
“diff” command should only report the differences observed (deleted/added/modified files).
Group work:
Although this is a fairly simple assignment, and it was designed to be easily completed by a single person, you
are allowed to work on it with another student (max. group size is 2). Just beware that during the demo you will
be asked to demonstrate your familiarity with all of the code. So if you do decide to group up, both of you
should understand the code 100%.
Demo
You are required to demo your assignments individually. During the demo you will be asked to run the
backdoor program on one computer, and access the backdoor from another computer. Then you will be asked to
demonstrate the functionality of your backdoor. You might be asked to adjust some functionality of the
backdoor program to illustrate you are familiar with the internals of the implementation. The time for your demo
will be arranged by your TAs.
Submissions
Submit your code via D2L. If you decide to work in a group, each group member needs to submit the
assignment. You also need to submit a document (text or pdf) that includes: your name, ID and tutorial section,
as well as the name of your partner (if applicable). The document should also include a brief description of the
functionality of your backdoor:
● how to run it;
● how to connect to it;
● handshake details; and
● supported commands.
Marking
Category Marks
Starting the server, being able to connect to it, disconnect from it, reconnect to it
- you will receive no marks for this assignment without this basic functionality
required
Basic authentication functioning 10
Basic commands: pwd, cd, ls, cat, cp, mv, rm, help, logout, off
- 5 mark penalty for any missing command
- 4 mark penalty for any incorrect behavior
- 3 mark penalty for missing / incorrect feedback
40
Snap / diff – report deleted files 10
Snap / diff – report new files 10
Snap / diff – report modified files 10
Snap / diff – working across different directories 5
Snap / diff – preserving snapshot through disconnect / reconnect 5
Extra command 1 5
Extra command 2 5
Style & documentation
- up to 15 mark penalty for ugly code
- up to 15 mark penalty for missing/inadequate documentation
Report TXT or PDF uploaded to D2L
- up to 20 mark penalty for missing information
Code uploaded to D2L required