


Skip section 32.1 (IPSec and Virtual Private
Network-VPN) – They require information on
IP that I’ve not yet covered.
Possible paper topic
Will cover after TCP/IP, if time, but probably
won’t have it.
X.509 certificate (end of chapter 31)





identifies a server site and verifies it is who it says it is.
It’s like an ID card stored electronically.
Used for Internet transactions as part of a security
protocol
Issued by a trusted Certification Authority (CA)
Examples: thawte, verisign, entrust, godaddy.



EV (Extended validation) certificates
http://en.wikipedia.org/wiki/Extended_Validation_C
ertificate
I will not distinguish X.509 and EV but could be a
paper topic that gets into more detail than I will
CA’s responsibilities

Verify the entity is who they say they are.


This is an investigative procedure into the entity
requesting the certificate.
Create a certificate (and issue to the entity) to
contain the following information:
Certificate

Contains:








Owner's public key (and algorithm)
Owner's name
Expiration date of the public key
Name of the issuer (the CA that issued the Digital
Certificate)
Serial number of the Digital Certificate
Certificate thumbprint calculated with the CA’s private
key. This establishes the authenticity of the certificate and
guarantees the certificate cannot be tampered with
Version #
more
SSL/TLS – 32.2







TCP establishes a connection between two sites.
SSL-Secure Sockets Layer
End-to-end security protocols
Authenticate server and client to each other
Message integrity
Originally designed by Netscape
Used by virtually every Internet commerce site




TLS-Transport Layer Security
TLS is the IETF version of SSL
Openssl. For those of you with Linux accounts –
man openssl or man x509.
Won’t distinguish here but plenty of room for a
paper topic.
Figure 32.14 Location of SSL and TLS in the Internet model
32.8
Possible sequence of steps for SSL is.

Client sends info to server





SSL or TLS version #
list of compression/encryption techniques
key exchange algorithms supported
session ID
random data.

Server sends info to client




what it supports and wants to use
random data
certificate
Both sides now know what the other can do.
Authenticate the server

Client verifies certificate it received from the server




Check certificate expiration date
Check certificate authority (is it in a list of trusted CAs
maintained by the client)
use CA’s public key and apply it to the digital signature
(fingerprint, thumbprint) to get the digest value and
authenticate – is this a valid certificate?
compare domain name in certificate w/ domain name of
server (to prevent man-in-the-middle attack)




Client creates pre-master secret key and encrypts using
server’s public key (obtained from the certificate); sends to
server. Server gets it and decrypts using its private key.
Server may authenticate client.
Client and server feed random data from both sides and
premaster secret into a hash algorithm to generate a session
key.
Exchange information securely
Figure 32.15 Creation of cryptographic secrets in SSL
32.13
Some other references



[http://support.microsoft.com/kb/257591]
[http://msdn2.microsoft.com/en-us/library/aa380513.aspx]
[http://www.cisco.com/en/US/tech/tk583/tk618/tsd_technolog
y_support_protocol_home.html]
You can see certificates





connect to an https site (e.g. www.bankmutual.com
and select customer login)
Note the lock icon at the top next to the URL).
click on the icon and select view certificates and
select various tabs and options.
DO NOT ASSUME sites are secure
Look for the lock icon or https as opposed to http in
the URL.

To see trusted CAs:





Tools  Internet Options and select Content tab
Select Certificates button followed by one of the tabs.
Select a CA and click the View button.
Explore various tabs.
Book has a little more on SSL and TLS and could be
used as part of a paper topic.
What if the certificate does not check out?
PGP (Pretty good Privacy)






In the early 1990s, encryption algorithms were in the
same category as weapons and were declared as a
munitions – making them subject to strict export
laws.
PGP was developed by Phillip Zimmerman
Putting it on the Internet was akin to exporting it,
according to the State dept.
Subject of a 3-year criminal investigation
Since then, export laws governing encryption have
been relaxed.
Another reference at www.pgpi.org (trial versions
used to be available but are hard to find now-at least
Figure 32.19 Position of PGP in the TCP/IP protocol suite
32.19
Table 32.4 PGP Algorithms
32.20
Example use of PGP (run on an older
environment)
When the message is open the receiver sees:
---BEGIN PGP SIGNED MESSAGE--Hash: SHA1
this is a test message
---BEGIN PGP SIGNATURE--Version: PGPfreeware 6.5.8 for non-commercial use <http://www.pgp.com>
iQA/AwUBPVHAkz012x9/xPKqEQL7UQCg65yJ8I4c5o7s37iMvLcqqRtokhAAn
3E2
EzQd3vhFE41QGj3O8zvDSawR
=knKs
---END PGP SIGNATURE---
With the message open the user can select
decrypt/verify from the PGP dropdown menu
*** PGP Signature Status: good
*** Signer: William Shay ,[email protected].
*** Signed: 8/7/02 7:51:31 PM
*** Verified: 8/7/02 8:50:46 PM
*** BEGIN PGP VERIFIED MESSAGE ***
this is a test message
*** END PGP VERIFIED MESSAGE ***

Textbook covers a bit more and gets into key
rings and such. I will skip that but this a
possible paper topic.
Firewalls. - 32.4


Allows or disallows data to pass through.
How does it decide?
Packet filtering

IP packet format

May accept or reject a packet based on its IP address
and/or port number

For example, the client/server project works, in theory, if one
machine is on campus and the other is off.
It is, however, subject to firewall rules.

Examples




Disallow incoming packets with port # 23 (disables
telnet).
Disallow outgoing packets with specified destination
addresses. Could be used to restrict employees from
access certain external sites (competitors or game
playing sites) during work hours.
Example: Some businesses disallow employees to
access youtube, facebook, or similar sites.
Disallow outgoing with specified source addresses
(to prevent address spoofing – a form of attack
discussed later)


Initial firewall setup.
Can allow all by default then specify which to reject


Runs the risk of missing something that should be rejected
Can reject all by default and then specify which to
allow

Runs the risk of people getting PO’d if you miss an
application that should pass

Possible policies: firewall setting (from Kurose &
Ross)



No outside web access: Drop all outgoing packets to an IP
address, port 80 (HTTP).
No incoming TCP connections, except those for
organization's public Web server (130.207.244.203): Drop
all incoming TCP SYN packets to any IP except
130.207.244.203, port 80.
Prevent web-radios from eating up the available
bandwidth: Drop all incoming UDP packets – except
DNS packets.


Prevent network from being used for a smurf DoS attack:
drop all ICMP ping packets going to a broadcast address.
Prevent your network from being tracerouted: drop all
outgoing ICMP TTL expired traffic.
Application level gateway (proxy server)


Packet filtering uses layer 3/4 information
Book example:



Only those Internet users who have previously established
business relations with the company can have access to
certain web pages.
Packet filtering won’t work
Cannot distinguish the above cases




Runs a program for each type of application
Intercepts all requests at a high layer and forwards (or rejects)
them as needed.
More overhead than packet filtering (firewall must run
duplicate apps)
Increased flexibility based on intent of applications
Stateful inspection (not in text)

Packets examined based on contents AND context
(i.e. what has happened previously).



Admin defines a rule base that determines course of
action.
Example: a ping packet sends an echo-request packet
Example: type ping url in a dos window – or in Linux

Could reject an echo-response packet if there was no previous
echo-request packet in the other direction.

Deny an incoming acknowledgment to a request
that never happened.


Client established a ftp connection and server attempts
to initiate a file transfer before the client has requested
it. Denied.
Maybe client tries to sneak a packet with a different
port # through the existing connection. Denied.



Refs:
[http://en.wikipedia.org/wiki/Stateful_firewall]
[http://www.webopedia.com/TERM/S/stateful_inspection.ht
ml]





Can purchase different levels of firewall protection.
Can install on your machine.
Can specify which apps can access the Internet or which
sources from the Internet can access your computer.
Administrator defines a rule base defining actions.
Firewalls can also restrict # packets per second (prevent
student from setting up game servers on campus)
Attacks (not in text) – I will provide an overview
only – a possible paper topic

Smurf (DoS) attack:





send a ping packet but falsify the source and use a
broadcast address for the destination.
All nodes in the broadcast group reply to the “source”
inundating it with traffic.
Presumably the attacker creates an infinite loop sending
such packets.
[http://www.cert.org/advisories/CA-1998-01.html]
[http://en.wikipedia.org/wiki/Denial-of-service_attack]

SYN flood




send connection requests (with a false source) to a site.
Site waits for a confirmation and times out if it does not
arrive.
If requests are sent faster than timeouts occur, problems
occur.
[http://www.cert.org/advisories/CA-1996-21.html]

Slowloris attack






Utilizes legitimate HTTP traffic
Sends partial http requests
Sends additional information periodically to keep
socket connections open
Ties up connections making them unavailable to
legitimate use
Like SYN flood but over http
http://www.funtoo.org/en/security/slowloris/ and
http://en.wikipedia.org/wiki/Slowloris
There are bad things are out there


Malware – a generic term covering a wide variety of
bad things.
Virus – program attached to another that does
unintended things



May be destructive
May not be (technically)
All are disruptive and cause loss or work or trust

Worm: a program that can invade a computer but is
NOT attached to another program.




Trojan Horse: hidden part of other useful program


Might be running something that’s prone to accepting a
worm from the internet and run it.
Might access your outlook contacts and send a copy of
itself to everyone there.
Blaster worm: allow others to control your computer.
Typically doesn’t replicate like worms and viruses
Summary

Packet sniffer:



Spyware:



records copies of packets that it sees
A good reason to secure wireless connections
watch what you do and perhaps report it to someone else.
You may be completely unaware
Botnet:

collection of computers working together for a purpose
Clipper Chip (of historical interest):


[http://en.wikipedia.org/wiki/Clipper_chip]
[http://www.epic.org/crypto/clipper/]

For wiretapping (provided by a court order), each
clipper chip has




encryption algorithm in a chip
inserted into a phone.
Press button & security devices exchange encryption
keys.
Designed by engineers at NSA w/ no input from private
industry in response to private sectors developing their
own to combat business and industrial espionage.




K = 80-bit session key to encrypt – needed for wiretap
F = 80-bit family key (all chips in a group have the same one)
N = 30-bit serial # (unique to a chip)
S = 80-bit secret key – unique to each chip, used by law
enforcement


V = voice message – Ek(V) is the transmitted voice message
Clipper chip also generates EF(ES(K)+N) (+ is concatenate
here)



Suppose a wiretap is approved;
Apply DF to above to get ES(K)+N. Easy since F is not secret
S IS secret so cannot apply DS easily. Need to use N to get S
but first need to know how S is formed and stored.



Two parties – each generates one 80-bit string. Call them S1
and S2.
Calculate S= S1  S2
Each of S1 and S2 are maintained by separate key escrow
agencies along with chip serial number. Who the agencies are
and who they report to is an issue.


Officials get N and, with a court order, get S1 and S2 from
each agency.
Apply DS to get K and then apply DK to get V