Security

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Title: Security

1
Security
2
Reported Security Incidents 1995 2003 Source
http//www.cert.org/present/cert-overview-trends/m
odule-1.pdf
3
Imperative Need for Secure CommunicationCost of
downtime
4
Secure Communication

Characteristics of a secure communication
Confidentiality
Authentication
Message Integrity and non-repudiation
Availability and Access Control

5
Confidentiality

The communicator wants the following to be
confidential
The fact that the communication is occurring
Timing of communication
Frequency of communication
Confidentiality often relies on cryptographic
techniques for encrypting/ decrypting data using
one or more keys to encrypt/decrypt data

6
Authentication

Both sender and receiver should be able to
confirm identity of other party involved in
communication
Confirm that the other party is indeed who/what
they claim to be
Authentication relies on authentication
techniques, several of which rely on
cryptographic techniques

7
Message Integrity and Non-Repudiation

Message integrity
Content of communication is not altered
maliciously or by accident
Relies on cryptographic techniques
Non-repudiation
Not denying what was communicated

8
Availability

Can communication occur in first place?
Hackers preventing infrastructure from being used
by legitimate users e.g., viruses, DoS attacks
Detect breaches and respond to attacks

9
Access Control

Entities allowed to gain access to resources only
if they have the appropriate access rights (e.g.,
login ID, passwords, biometric devices)
Facilitated by firewalls, which provide access
control based on a per-packet basis, and on a
per-service basis.
Provide a degree of isolation and protection from
those outside of ones network

10
Cryptography

Symmetric Key Cryptography
Public Key Cryptography

11
Symmetric Key Cryptography

Symmetric Key Cryptography
Caesar Cipher
Monoalphabetic Cipher
Polyalphabetic Cipher
Data Encryption Standard (DES)
Triple DES (3DES)
Advanced Encryption Standard (AES)
Trusted Intermediaries for symmetric key
distribution
Key Distribution Center (KDC)
Kerberos

12
Basic Terminology

Plain Text
Original data not disguised
Cipher (Encrypted) Text
Disguised data looks unintelligible to intruder
Data disguised using encryption algorithm
Key
A string of s or characters used as input to
encryption algorithm to disguise plain text
Symmetric Key Both parties use same key to
encrypt and decrypt text

13
Symmetric Key Cryptography

Caesar Cipher
Each letter in plaintext is substituted with
letter that is K letters later
Wrap around is allowed (i.e., z followed by
letter a)
If K 3, a in plaintext becomes d in cipher text
b in plaintext becomes e in cipher text
Example Decrypt the following using a Caesar
Cipher of K 3 Assume wrap around is allowed.
L JP J JHHN

14
Symmetric Key Cryptography

Data Encryption Standard (DES)
Published in 1977, and updated in 1993
For commercial and non-classified U.S. Govt. use
Encodes plaintext using 56-bit key
Objective Scramble data and key so that every
bit of the cipher text depends on every bit of
the data and every bit of the key
Algorithm Complex (beyond the scope of the
course) Decryption works by reversing the
algorithms operations.

15
How well does DES work?

DES challenge contest
Launched in 1997 by RSA Data Security Inc. -- A
network security company
Encrypted strong cryptography makes the world a
safer place using a 56-bit DES.
Winning team took 4 months to decode.
Used volunteers throughout the Internet to
systematically explore key space.
Claimed 10K cash prize after testing only a
quarter of the key space (about 18 quadrillion
keys)

16
How well does DES work?

In 1999, RSA launched another DES challenge.
Message was decrypted in little over 22 hours by
a network of volunteers and a special purpose
computer called Deep Crack.
Claimed 250 K cash prize.

17
Symmetric Key Cryptography

Triple DES (3 DES)
If 56-bit DES is considered to be insecure, one
can simply run the algorithm multiple times,
using a different key each time
DES run three times (with a different 56-bit key
each time DES is run).

18
Symmetric Key Cryptography

Advanced Encryption Standard (AES)
NIST in Nov 2001 announced successor to DES.
AES is also a symmetric key algorithm that
processes data in 128-bit blocks
AES can operate with 128-bit keys, 192-bit keys,
and 256-bit keys

19
Trusted Intermediaries

Disadvantage of Symmetric Key Cryptography
2 communicating parties have to agree upon their
secret key ahead of time in a secure manner.
Since sender and receiver do not meet face to
face in the networking world , they need a
trusted intermediary
Trusted Intermediaries
Key Distribution Center
Kerberos

20
Key Distribution Center (KDC)

A server that shares a different secret
symmetric key with each registered user.
KDC knows the secret key of each user, and each
user can communicate securely with KDC using this
key.

21
Example Using KDC

Assume Sender (S) and Recipient (R) use KDC for
their communication.
Assume Ss secret key known to S and KDC is
KS-KDC
Assume Rs secret key known to R and KDC is
KR-KDC.

22
Example Using KDC

Using key, S sends a message to KDC saying that S
wants to communicate with R. We denote this
message as MS-KDC(S, R).
KDC decrypts MS-KDC(S, R)
KDC generates a random number key KSR, which is
to be used as symmetric key by S and R during
their communication.

23
Example Using KDC contd

KDC sends S the key KSR, and a pair of values X
and KSR encrypted using Rs key. We denote this
message sent back to S by KDC as
MKDC-S(KSR, MKDC-R(X, KSR)).
S decrypts message and extracts symmetric key
KSR. S extracts and forwards MKDC-R(X, KSR) to R
Note that S cannot decrypt MKDC-R(X, KSR)
R decrypts MKDC-R(X, KSR) and uses KSR as
symmetric key to converse with S
R and S communicate using symmetric key KSR

24
Kerberos

Developed by MIT
Very similar to KDC
Has additional functions such as
Time stamp for validity of nonce KSR.
Has information about which users have access
privileges to which services on which network
servers.

25
Public Key CryptographyOverview

Define concept of Public and Private keys
Demonstrate RSA Algorithm
Review Authentication Protocols (ap)
Exchanging Public Keys
Person in the middle-attack

26
Introduction - Public Key Cryptography

Use public key cryptography so that two parties
can communicate using encryption/decryption
without using a shared secret key.
Key maintenance is difficult
Public key cryptography
A radically different and marvelously elegant
approach towards encryption/decryption
Also used for authentication and digital
signatures

27
Basic Idea of Public Key Cryptography

Each participant has a private key (known only to
the participant) and a public key.
Public key is made available to others
Could be posted even on a website which is
accessible by the rest of the world.
Public key of recipient is used by sender to
encrypt message.
Recipient decrypts message using recipients
private key.

28
Public Key Cryptography

Example
Sender (S) wishes to send a message to Recipient
(R)
S fetches Rs public key.
S uses Rs public key to encrypt message
S sends encrypted message to R.
R decrypts cipher text with Rs private key.

29
RSA Algorithm

Named after its founders, Ron Rivest, Adi Shamir,
and Leonard Adleman
Has become almost synonymous with public key
cryptography

30
Using the RSA Algorithm

Rs public key is denoted as KR and the private
key is denoted as KR-.
These keys are chosen such that
KR- (KR (m)) KR (KR- (m)) m
S will encrypt a plain text message, m, using
public key KR and send it to R

31
Using the RSA Algorithm

To encrypt the message, S uses Rs public key and
determines the cipher text, c as
c me mod n
To decrypt the message, R uses Rs private key
and determines the plain text, m as
m cd mod n

32
Using the RSA AlgorithmCreate Rs Keys

Choose two large prime numbers, p and q.
The larger the values, the more difficult it is
to break RSA, and the longer it takes to
encode/decode.
It is recommended that the product of p and q be
on the order of 1024 bits for corporate use and
768 bits for use with less valuable
information.
For a discussion on how to find large prime
numbers, see http//www.utm.edu/research/primes/pr
ove/).
For example, choose p 5 and q 7

33
Using the RSA AlgorithmCreate Rs Keys

Compute n pq 35
Compute z (p-1)(q-1) (4)(6) 24
Choose a number, e, less than n, which has no
common factors (other than 1) with z.
R chooses e 5
Find a number, d, such that ed-1 is exactly
divisible (that is, with no remainder) by z.
d 29
Note (ed-1) (5x29 -1) (145-1) 144
144 is exactly divisible by z 24

34
Using the RSA AlgorithmCreate Rs Keys

Recap p 5, q 7, n 35, z 24, e 5, d
29
Rs public key is given by
KR (n, e) (35, 5)
Rs private key is given by
KR- (n, d) (35, 29)
Example
Interpret each letter in the English alphabet as
a number between 1 and 26. That is, a 1, b
2, , z 26.
S will send message love to R

35
Using the RSA AlgorithmEncrypt Message using KR
(n, e) (35, 5)
Plaintext letter m (numeric representation) m e c me mod n
l 12 248832 17
o 15 759375 15
v 22 5153632 22
e 5 3125 10

S will send 17152210 to R

36
Using the RSA AlgorithmEncrypt Message using KR-
(n, d) (35, 29)
Cipher text cd m cd mod n msg
17 481968572106750915091411825223071697 12 l
15 12783403948858939111232757568359375 15 o
22 851643319086537701956194499721106030592 22 v
10 100000000000000000000000000000 5 e

37
RSA and DES/AES

RSA is a complex algorithm and uses concepts from
number theory.
DES is at least 100 times faster than RSA.
In practice, RSA is often used in combination
with DES or AES.
Message is encrypted using DES key
S encrypts DES key with Rs public key
R decrypts and obtains DES key with Rs private
key.
Message is decrypted using DES key

38
Authentication

ap 4.0 (symmetric)
S announces to R, I am S
R sends a plaintext nonce ( n) to S.
Note nonce is a one time value that is specific
to that communication session
S resends same nonce back to R but this time
nonce is encrypted with symmetric key used by S
and R.
R decrypts nonce using symmetric key. If
decrypted nonce equals the nonce sent to S
earlier (i.e. decrypted nonce n) , then S is
authenticated.
However, this implies that S and R must have
decided upon and exchanged their symmetric key.

39
Authentication

ap 5.0 (public/private)
S announces to R, I am S
R sends a plaintext nonce ( n) to S
S resends same nonce back to R but this time
nonce is encrypted with Ss private key.
R decrypts nonce using Ss public key. If
decrypted nonce equals the nonce sent to S
earlier (i.e. decrypted nonce n) , then S is
authenticated.

40
Exchanging Public Keys

Why should public key be publicly available?
Wouldnt it be better for S and R to exchange
their respective public keys via e-mail, after
authenticating each other?
Possibility of person in the middle attack.

41
Person in the Middle Attack

S transmits, I am S
T eavesdrops.
R sends a nonce n.
T intercepts nonce, and sends R encrypted nonce
(encrypted using Ts private key).
R sends a message to S asking for Ss public key.
T intercepts message, and sends Ts public key to
R.
R decrypts nonce with Ts public key (thinking
that he is using Ss public key), and
inadvertently authenticates T.

While R is encrypting new data using Ts public
key, T is busy posing as R to S. In
particular
T transmits Rs nonce to S
S transmits encrypted nonce (encrypted using Ss
private key).
T intercepts encrypted nonce, and asks S for her
public key.
S sends her public key

42
Person in the Middle Attack contd

R sends encrypted data (encrypted using Ts
public key)
T decrypts using her private key, and finds out
Rs plain text.
T encrypts Rs plain text using Ss public key.
T transmits encrypted text to S.
S decrypts using her private key, and finds out
Rs plain text.
S and R presume that they have had a secure
communication. They are ignorant of the fact
that T has intercepted and decrypted all messages.

43
Availability and Access Control

Examples of common attacks
Firewalls

44
Examples of some attacks

Denial of Service attacks
Hacker attempts to disrupt the network by
flooding the network with messages so that the
network cannot process messages from legitimate
users
Examples
Ping attacks
Smurf attack
SYN flood attack
Distributed Denial of Service attacks

45
Ping Packets

Packets that ask a computer to respond with an
acknowledgement
Used to see if a computer is still operational in
a network
Ping by computer name
Ping bus.orst.edu
Ping by IP address
Ping 128.193.76.73

46
(No Transcript)
47
TCP header Packet s (Sequence s)

Assume a file has 500,000 bytes
Assume TCP breaks this file into packets, where
each packet size is 1000 bytes
Each packet is given a packet
The packet for a packet is the number of the
first byte in that packet.
The packet of first packet would be 1
The packet of next packet would be 1001
The packet of third packet would be 2002 and so
on

48
TCP Acknowledgement

Assume S transmits to R
R acknowledges receipt of Ss message, by
specifying an acknowledgment .
The ACK sent by R is the packet of the next
packet that R is expecting from S.
Example
After S sends first packet, R sends an
acknowledgment to S by specifying ACK 1001.
After S sends second packet, R acknowledges by
specifying ACK 2001.

49
SYN Flood Attack

Nature of attack
Attacker (client) sends a TCP SYN (Synchronize
Sequence/Packet Number) request to server.
The server responds by sending a TCP SYN/ACK
packet.
The attacker does not respond resulting in
half-open session using up server resources.
The attacker sends a flood of such TCP SYN
requests without responding.
Requests from other legitimate clients are unable
to reach the server due to multiple half-open
sessions

50
Distributed DoS (DDos) attack

In a DDoS attack, a hacker first gains control of
hundreds/thousands of computers (slaves).
Plants software referred to as DDoS agent on each
of the slaves
Hacker then uses software referred to as DDoS
handler (master) to control the agents (slaves)
Attacker launches attacks from all the slaves and
it is difficult to trace hacker

51
High Profile Victims of DDoS

Yahoo, eBay, Amazon, Microsoft and eTrade
websites have been rendered inaccessible to
legitimate visitors after being flooded with
traffic from hundreds of hijacked system
www.msn.com www.expedia.com www.carpoint.com
sites were flooded with DDoS attack for almost
one day
DDoS attack high-level DNS servers on the Internet

52
Firewalls

Firewalls are used to prevent intruders on the
Internet from making unauthorized access and
denial of service attacks to your network.
Examines packets flowing into and out of the
organizations network (usually via the Internet
or corporate Intranet), restricting access to
that network.
Two main types of firewalls are packet level
firewalls and application-level firewalls.

53
Packet-level Firewall

Examines the source and destination address of
packets that pass through it
Only allowing packets that have acceptable
addresses to pass.
Since each packet is examined separately, the
firewall cant understand what the senders goal
is.
Does not monitor the contents of the packets or
why they are being transmitted and typically does
not log the packets for later analysis.

54
Packet-level Firewall contd

In general, addresses are typically examined at
the transport layer (TCP Port ID) and network
layer (IP address)
Example 1 Dont allow Telnet (Dest. Port ID 23
not allowed)
Example 2 Dont allow packets from Internet on
an Intranet (Source IP has to be that of a device
in the intranet)
May be vulnerable to IP spoofing
Accomplished by changing the source address on
incoming packets from their real address to an
address inside the organizations network.
Packet-level firewalls have strengthened their
security since the first cases of IP spoofing
(Dec 1994).
Example Some firewalls automatically delete any
packets arriving from the Internet that have
internal source addresses

55
Application-Level Firewalls

Acts as an intermediate host computer, separating
a private network from the rest of the Internet,
but it works on specific applications, such as
Web site access.
Application gateway acts as an intermediary
between the outside client making the request and
the destination server responding to that
request, hiding individual computers on the
network behind the firewall.
Because of the increased complexity of what they
do, application level firewalls require more
processing power than packet filters which can
impact network performance.

56
Network Address Translation (NAT)

Used to shield a private network from outside
interference.
An NAT proxy server uses an address table,
translating network addresses inside the
organization into aliases for use on the
Internet. So, internal IP addresses remain
hidden.
Many organizations combine NAT proxy servers,
packet filters and application gateways,
maintaining their online resources in a DMZ
network

57
Typical network design using firewalls.
58
Security in many layers

5 layer model
Application Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
Each layer can have its own security protocols.

59
Security at Application Layer

Secure E-mail
PGP (Pretty Good Privacy)
e-mail encryption scheme that has become a de
facto standard.
Uses MD5 or SHA for message digest/fingerprints.
Uses CAST, 3DES, IDEA for symmetric key
cryptography
Uses RSA for public key cryptography
S/MIME (Secure Multipurpose Internet Mail
Extensions)
PEM (Privacy Enhanced Mail)
Secure-HTTP or S-HTTP

60
Secure E-mail using PGP

When PGP is installed, software creates a private
key and public key for user.
Public key is posted on the website.
Private key is protected using a password.
Password has to be entered every time user
accesses private key.

61
Security at Application Layer

SET (Secure Electronic Transactions)
Developed by MasterCard and VISA in 1997
Developed to provide protection from electronic
payment fraud.
SET uses DES for Symmetric Key Cryptography and
RSA for key exchange.

62
Security at Transport LayerSSL Secure Socket
Layer

Developed to provide data encryption and
authentication between a Web client and a Web
server.
Client and server perform handshake and negotiate
cryptographic technique to be used.
Client and server authenticate each other
Encrypted session progresses after handshake is
completed.
SSL is typically applied at the transport layer
Implies that SSL is not limited to one
application
Can be applied to Web, e-mail, HTTP applications
etc.

63
SSL (Continued)

SSL was not developed for payment transactions.
Assume Bob makes a purchase from ABC Incorporated
over SSL
ABCs certificate issued by CA does not indicate
whether ABC Incorporated is authorized to accept
payment card purchases nor if the company is a
reliable merchant.
Similarly, ABC Incorporated has no assurance that
Bob is authorized to make a payment card purchase
May result in stolen credit card transactions,
customer repudiation of purchased goods.

64
Network Layer SecurityIPSecurity IPSec

IPSec is a suite of protocols that provide
security at the network layer.
Complex suite of protocols
IPSec would encrypt all parts of the packet
including user data at application layer, TCP
header and IP header.
Implies that all data sent by hosts e-mail, Web
pages etc., would be hidden from Intruder.

65
IPSec (Continued)

2 key protocols in the IPSec suite are
Authentication Header (AH) protocol
provides source authentication and data integrity
but not confidentiality
Encapsulation Security Payload (ESP) protocol
provides authentication, data integrity and
confidentiality.

66
IPSec (Continued)

Before sending secure packets, source and
destination handshake and create a one-way
(simplex) network-layer logical connection
known as Security Association (SA).
SA is uniquely identified by
Security protocol (AH or ESP) identifier
Source IP address for simplex connection
A 32-bit connection identifier called the
Security Parameter Index (SPI)

67
SA and Key Management

IKE (Internet Key Exchange) algorithm is the
default key management protocol for IPsec.
ISKMP (Internet Security Association and Key
Management Protocol) defines procedures for
establishing and tearing down SAs.

68
Security in IEEE 802.11Wireless Network