Update beginning of intercepting communication challenges

dojo.yml

@@ -24,14 +24,16 @@ modules:
   challenges:
   - id: level-1
     name: Connect
+  - id: level-1a
+    name: Send
+  - id: level-1b
+    name: Shutdown
   - id: level-2
     name: Listen
   - id: level-3
-    name: level3
-    description: Find and connect to a remote host
+    name: Scan
   - id: level-4
-    name: level4
-    description: Find and connect to a remote host on a large network
+    name: Scan 2
   - id: level-5
     name: level5
     description: Monitor traffic from a remote host

intercepting-communication/level-1/DESCRIPTION.md

@@ -1 +1,8 @@
 From your host at 10.0.0.1, connect to the remote host at 10.0.0.2 on port 31337.
+
+A great way to do this is to use the `nc` command (pronounced "netcat"), which allows you to open network connections from the command line.
+For example, to connect to the remote host at 10.0.0.42 on port 4242, you would run:
+
+```sh
+nc 10.0.0.42 4242
+```

intercepting-communication/level-1/run

@@ -20,7 +20,7 @@ class ServerHost(Host):
 
 user_host = Host("ip-10-0-0-1")
 server_host = ServerHost("ip-10-0-0-2")
-network = Network(hosts=[user_host, server_host])
+network = Network(hosts={user_host: "10.0.0.1", server_host: "10.0.0.2"}, subnet="10.0.0.0/24")
 network.run()
 
 user_host.interact()

intercepting-communication/level-1a/.init

@@ -0,0 +1 @@
+../.init

intercepting-communication/level-1a/DESCRIPTION.md

@@ -0,0 +1,11 @@
+From your host at 10.0.0.1, connect to the remote host at 10.0.0.2 on port 31337, and send the message "Hello, world!".
+
+As before, you'll want to use the `nc` command.
+
+You'll notice that `nc` will hang (e.g. you will not get a shell prompt back), waiting until the connection is closed.
+You can, as with most hanging processes, kill the process by pressing `Ctrl-C`.
+
+In this challenge though, you need to send a message to the remote host.
+If you type that message into the terminal, nothing will immediately happen.
+That is because your terminal, by default, buffers the input you type until you press `Enter`!
+Press `Enter` after typing your message, and a single packet containing the entire message will be sent to the remote host.

intercepting-communication/level-1a/run

@@ -0,0 +1,32 @@
+#!/usr/bin/exec-suid --real -- /usr/bin/python -I
+
+import socket
+from dojjail import Host, Network
+
+flag = open("/flag").read()
+
+class ServerHost(Host):
+    def entrypoint(self):
+        server_socket = socket.socket()
+        server_socket.bind(("0.0.0.0", 31337))
+        server_socket.listen()
+        while True:
+            try:
+                connection, _ = server_socket.accept()
+                while True:
+                    client_message = connection.recv(1024).decode().strip()
+                    if not client_message:
+                        break
+                    if client_message == "Hello, World!":
+                        connection.sendall(flag.encode())
+                        break
+                connection.close()
+            except ConnectionError:
+                continue
+
+user_host = Host("ip-10-0-0-1")
+server_host = ServerHost("ip-10-0-0-2")
+network = Network(hosts={user_host: "10.0.0.1", server_host: "10.0.0.2"}, subnet="10.0.0.0/24")
+network.run()
+
+user_host.interact()

intercepting-communication/level-1b/.init

@@ -0,0 +1 @@
+../.init

intercepting-communication/level-1b/DESCRIPTION.md

@@ -0,0 +1,20 @@
+From your host at 10.0.0.1, connect to the remote host at 10.0.0.2 on port 31337, and then shut down the connection.
+
+As before, you'll want to use the `nc` command.
+
+Sometimes the other side of a connection wants to wait for you to finish sending all of your data before it finishes sending data back to you.
+Imagine a protocol where the client might need to send lots of data, over a long duration, before the server can respond with some final result.
+In this case, it might not make sense to preestablish how much data will be sent in total as part of the protocol, because the client might not know at the beginning how much data it will need to send.
+How can we handle this situation?
+
+One option would be to have the client send a single packet at the end that just says "END".
+But network packets can be complicated, with no guarantees from the network that they won't be split apart or merged together.
+Or what if you want to be able to send "END" as part of the data?
+
+Fortunately, TCP provides a solution to this problem, with the TCP "FIN" flag.
+When a client sends a packet with the FIN flag set, it is saying "I'm done sending data, but I'm still listening for data from you."
+
+Netcat is ultimately a simple tool, that translates data from standard input to network packets and vice versa to standard output.
+So how do you send a packet with the FIN flag set?
+You do the equivalent file operation: you close standard input!
+In an interactive terminal session, you can do this by pressing `Ctrl-D`.

intercepting-communication/level-1b/run

@@ -0,0 +1,30 @@
+#!/usr/bin/exec-suid --real -- /usr/bin/python -I
+
+import socket
+from dojjail import Host, Network
+
+flag = open("/flag").read()
+
+class ServerHost(Host):
+    def entrypoint(self):
+        server_socket = socket.socket()
+        server_socket.bind(("0.0.0.0", 31337))
+        server_socket.listen()
+        while True:
+            try:
+                connection, _ = server_socket.accept()
+                while True:
+                    client_message = connection.recv(1024).decode().strip()
+                    if not client_message:
+                        connection.sendall(flag.encode())
+                        break
+                connection.close()
+            except ConnectionError:
+                continue
+
+user_host = Host("ip-10-0-0-1")
+server_host = ServerHost("ip-10-0-0-2")
+network = Network(hosts={user_host: "10.0.0.1", server_host: "10.0.0.2"}, subnet="10.0.0.0/24")
+network.run()
+
+user_host.interact()

intercepting-communication/level-2/run

@@ -20,7 +20,7 @@ class ClientHost(Host):
 
 user_host = Host("ip-10-0-0-1")
 server_host = ClientHost("ip-10-0-0-2")
-network = Network(hosts=[user_host, server_host])
+network = Network(hosts={user_host: "10.0.0.1", server_host: "10.0.0.2"}, subnet="10.0.0.0/24")
 network.run()
 
 user_host.interact()

intercepting-communication/level-3/.init

@@ -0,0 +1 @@
+../.init

intercepting-communication/level-3/DESCRIPTION.md

@@ -0,0 +1,3 @@
+From your host at 10.0.0.1, connect to some unknown remote host on the 10.0.0.0/24 subnet, on port 31337.
+Fortunately, there are only 256 possible hosts on this subnet, so you can just try them all!
+

intercepting-communication/level-3/run

@@ -0,0 +1,29 @@
+#!/usr/bin/exec-suid --real -- /usr/bin/python -I
+
+import random
+import socket
+from dojjail import Host, Network
+
+flag = open("/flag").read()
+
+class ServerHost(Host):
+    def entrypoint(self):
+        server_socket = socket.socket()
+        server_socket.bind(("0.0.0.0", 31337))
+        server_socket.listen()
+        while True:
+            try:
+                connection, _ = server_socket.accept()
+                connection.sendall(flag.encode())
+                connection.close()
+            except ConnectionError:
+                continue
+
+unknown_ip = f"10.0.0.{random.randint(10, 255)}"
+
+user_host = Host("ip-10-0-0-1")
+server_host = ServerHost("ip-10-0-0-?")
+network = Network(hosts={user_host: "10.0.0.1", server_host: unknown_ip}, subnet="10.0.0.0/24")
+network.run()
+
+user_host.interact()

intercepting-communication/level-4/.init

@@ -0,0 +1 @@
+../.init

intercepting-communication/level-4/DESCRIPTION.md

@@ -0,0 +1 @@
+From your host at 10.0.0.1, connect to some unknown remote host on the 10.0.0.0/16 subnet, on port 31337.

intercepting-communication/level-4/run

@@ -0,0 +1,29 @@
+#!/usr/bin/exec-suid --real -- /usr/bin/python -I
+
+import random
+import socket
+from dojjail import Host, Network
+
+flag = open("/flag").read()
+
+class ServerHost(Host):
+    def entrypoint(self):
+        server_socket = socket.socket()
+        server_socket.bind(("0.0.0.0", 31337))
+        server_socket.listen()
+        while True:
+            try:
+                connection, _ = server_socket.accept()
+                connection.sendall(flag.encode())
+                connection.close()
+            except ConnectionError:
+                continue
+
+unknown_ip = f"10.0.{random.randint(1, 255)}.{random.randint(10, 255)}"
+
+user_host = Host("ip-10-0-0-1")
+server_host = ServerHost("ip-10-0-?-?")
+network = Network(hosts={user_host: "10.0.0.1", server_host: unknown_ip}, subnet="10.0.0.0/16")
+network.run()
+
+user_host.interact()