1. DNS

is a distributed database that is used by TCP/IP applications to map between hostnames and IP addresses
no single site knows all the information
DNS name space is hierarchical
diagram shows how the IP address 199.232.41.7 is mapped onto prep.ai.mit.edu
note that DNS dictates that a FQDN must not exceed 255 octets and a machine name must not exceed 63 octets
note that the DNS map is broken into zones
- com, org, mil
- requests for names into IP addresses are resolved by hierarchy
note the clever technique of reverse name lookup
- 199.232.41.7
use the same algorithm for name lookup but with numbers
- look up the domain 7 , then 41 , then 232 and 199

2. Internet Cafés

may consist of wireless networks which uses a gateway
- which may rewrite HTML pages to include a house style frame
which may result in including advertising around the edge of your browser screen

3. Tunnelling IP over DNS

IP can be run over any piece of digital string
Internet café users became increasingly annoyed with the force fed advertising
devised a mechanism whereby this could be by-passed

4. Architecture of IP over DNS

protocol stack now looks like:
notice that the Internet café no longer sees any of the computers
- IP, TCP, UDP or HTTP traffic
- as it is all encapsulated within the DNS packets
users machine has to run a DNS over IP protocol stack
which takes in IP packets and issues requests which take the form:
- xyz123.personal.name.com
- any 63 ASCII characters in range a to z and 0 to 9 added to .personal.name.com

5. Tunnelling IP over DNS

Internet café DNS sees requests made on weird hostnames at .personal.name.com and forwards these values to users remote machine at .personal.name.com
- which also runs the same DNS over IP protocol and which translates these weird 63 byte names into an IP datagram
  - and transmits the datagram on behalf of the Internet Café user
  - it returns the result
Internet café gets the DNS reply and returns the reply to the user
ultimately the DNS over IP will be much slower than using normal TCP/IP over 802.11g
- but it does work and is an ingenious idea
it has huge implications in security of networks as it renders all firewalls useless (at the time of writing)
- why?

6. SSH

Secure SHell is a popular software approach to network security
- operates at the application layer
offers transparent encryption, authentication and integrity of data
provides command line commands:
- ssh
- sftp
- scp
- slogin

7. SSH architecture

8. SSH Protocol

provides Authentication
- reliably determines someones identity using public/private key
provides encryption
- scrambles data as it passes across the network
provides integrity
- guarentees data travels across the network unaltered

9. SSH Port Forwarding

the ssh tools: ssh , slogin , scp and sftp are useful enough to warrent investment in time with ssh
however the port forwarding capability ensures that ssh enters non command line networking!
any port can be forwarded across ssh
certain protocols transmit usernames/passwords in plaintext or using weak passwords
- imap, pop3 and vnc, X windows
ssh can be used to harden these very useful protocols

10. SSH examples

connecting to a remote machine

ssh moppsy.comp.glam.ac.uk
Password:

Linux moppsy i686 GNU/Linux
Last login: Tue Feb  8 10:47:44

fred@moppsy:~/$ exit

using a command line ftp equivalent

sftp moppsy.comp.glam.ac.uk
Password:
sftp> dir
sftp> get foo.ps
sftp> quit

11. X Windows Port forwarding

GNU/Linux allows graphical applications to be run remotely
- remote desktop per application
  - as well as per desktop (using vnc)

ssh -X moppsy.comp.glam.ac.uk
Password:

Linux moppsy i686 GNU/Linux
Last login: Tue Feb  8 10:47:44


fred@moppsy:~/$ xterm
fred@moppsy:~/$ exit

ssh is forwarding all X traffic across port 22

12. Browsing the web through an ssh connection

suppose we want read the web pages of floppsie.comp.glam.ac.uk securely

ssh -g -A -X -N -T -L2001:localhost:80 floppsie.comp.glam.ac.uk

which means create a secure link between port 2001 on localhost and port 80 on floppsie.comp.glam.ac.uk
```
telnet localhost 2001
get index.html
```
or http://localhost:2001/index.html

13. SSH through an untrusted proxy ssh server

on your local machine you type:

ssh -g -A -X -N -T -L2001:trusted.com:22 untrusted.proxy.com

which says open a secure connection starting at port 2001 on our local machine
- which provides a connection between untrusted.proxy.com and trusted.com on port 22
- the flags turn all port forwarding capability
and in another terminal window type:
```
ssh -v -g -A -X -p 2001 localhost
```
which now opens up a connection between your keyboard and localhost:2001
- effectively giving you a secure encrypted connection to trusted.com:22

14. Laboratory work

try out all the examples presented in todays lecture

15. Python and SSH

type in the following code and analyse what it does!

#!/usr/bin/python

#  secure shell pipe module

import os
import sys
from socket import *

localPortNo=8000
maxTries=10

#  createTCPSocketSSH - creates a secure TCP socket between
#                       localhost:localPort and
#                       remoteHostname:remotePort


def createTCPSocketSSH (remoteHostname, remotePort=22,
                        localPort=-1):

    global localPortNo
    if localPort == -1:
        localPort = localPortNo
        localPortNo = localPortNo+1
    tryNo = 1
    while 1:
        command = "ssh -f -g -A -X -N -T -L%d:localhost:%d %s\n" %
                  (localPort, remotePort, remoteHostname)
        print command
        result = os.system(command)
        if result == 0:
            break
        localPortNo = localPortNo+1
        tryNo = tryNo + 1
        if tryNo == maxTries:
            os.exit(1)

    # create a TCP socket which connects to our ssh pipe
    s = socket(AF_INET, SOCK_STREAM)
    s.connect(("localhost", localPort))
    return s



s = createTCPSocketSSH("floppsie.comp.glam.ac.uk", 80)
s.send(’get index.html0)
print s.recv(1024)

16. Tutorial

firstly reaquaint yourself with ssh by logging into mcgreg.comp.glam.ac.uk
- then exit from this server
now sftp a file from your desktop to mcgreg.comp.glam.ac.uk to your $HOME directory
now ssh to mcgreg.comp.glam.ac.uk with X forwarding enabled
- and run firefox on mcgreg.comp.glam.ac.uk to confirm that this works
now create a secure link between localhost:8080 and mcgreg.comp.glam.ac.uk:80
- you will need to use the following options on the ssh command line -g -A -X -N -T as well as the port and hostname parameters
do not kill the previous ssh command and now, using a browser on your local machine open up a URL which matches http://localhost:8080
- can you read the web page on mcgreg?
- draw a diagram clearly showing the various hostname:port network connections and clearly highlight which components are encrypted

Index

1. DNS
2. Internet Cafés
3. Tunnelling IP over DNS
4. Architecture of IP over DNS
5. Tunnelling IP over DNS
6. SSH
7. SSH architecture
8. SSH Protocol
9. SSH Port Forwarding
10. SSH examples
11. X Windows Port forwarding
12. Browsing the web through an ssh connection
13. SSH through an untrusted proxy ssh server
14. Laboratory work
15. Python and SSH
16. Tutorial
Index

This document was produced using groff-1.19.