The document provides information on firewalls and IP security: - A firewall acts as a choke point, allowing only authorized traffic between networks. It implements access controls, auditing, and can enable VPNs and detect abnormal behavior. - IP security (IPSec) provides encryption, authentication, and access controls for IP packets. It uses security associations and algorithms like ESP and AH to validate traffic and ensure confidentiality. - The document discusses firewall types including packet filters, application gateways, and circuit gateways, and covers concepts like security associations, the IPSec architecture, and header formats.

1. Security Concept
Part-3
Mr.Gopal Sakarkar
Mr. Gopal Sakarkar

2. What is a Firewall?
a choke point of control and monitoring
interconnects networks with differing trust
imposes restrictions on network services
– only authorized traffic is allowed
auditing and controlling access
– can implement alarms for abnormal behavior
implement VPNs using IPSec
must be immune to penetration
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3. Firewall Design Principles
Centralized data processing system , with a central
mainframe supporting number of directly connected
terminals.
LAN’s interconnected PCs and terminals to each
other and the mainframe.
Premises network that consisting of a number of
LANs, interconnecting PCs , servers .
Enterprise –wide network consisting of multiple ,
geographical distributed premises network
interconnected by private WAN.
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4. Characteristics of Firewall
 All traffic from inside to outside and vice
versa must pass through the firewall.
Only authorize traffic as defined by the
local security policy will be allowed to pass.
Firewall itself is immune to penetration .
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5. Firewall Techniques for control
Access
 Service control : the firewall may filter traffic on the
basis of IP address. It determines the types of Internet
services that can be accessed inbound or outbound.
Direction Control: It determiner the direction in which
particular service request may be initiated and allowed to
flow through the firewall.
 User Control : Controls access to a service according
to which user is attempting to access it. It is typically
applied to local user only.
Behavior control : Controls how particular service are
used. The firewall may filter e-mail to eliminated spam or it
may enable external access to specific portion of the
infromation.
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6. Firewall Limitations
cannot protect from attacks bypassing it
cannot protect against internal threats
– eg unhappy or plan employees
cannot protect against transfer of all virus
infected programs or files
– because of huge range of O/S & file types
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7. Types of Firewalls
1.Packet filtering router
2.Application level gateways
3.Circuit- level gateways
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8. Firewalls – Packet Filters
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9. Firewalls – Packet Filters
simplest, fastest firewall component
It applies a set of rule to each incoming and outgoing IP packet
Examine each IP packet and permit or deny according to rules
Filtering rules are for
1. Source IP address : the IP address of the system that
originated the IP packet.
2. Destination IP address : the IP address of the systems that the
IP packet is trying to reach
Mr. Gopal Sakarkar

10. Firewalls – 2. Application Level
Gateway (or Proxy)
have application specific gateway also called a proxy server
has a full access to protocol
– user requests service from proxy
– proxy validates request as legal
– then actions request and returns result to user
– can log / audit traffic at application level
need separate proxies for each service
– some services naturally support proxying
Eg. Feedback Application, online examination
Application ,MIS etc
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11. Firewalls – 2. Application Level
Gateway (or Proxy)
Application level gateways tend to be more secure
than packet filters because it scrutinize a few
allowable applications.
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12. Firewalls – 3.Circuit Level
Gateway
This is for a stand-alone system.
Imposes security by limiting which such connections are allowed.
once created, usually relays traffic without examining contents.
Typically used by trust internal users for allowing general outbound
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connections

13. Firewalls – 3.Circuit Level
Gateway
It has two TCP connection , one between itself and a TCP user on an
inner host and one between itself and a TCP user on an outside host.
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14. Data Access Control
• Through the user access control procedure
(log on), a user can be identified to the system
• There can be a profile that specifies
permissible operations and file accesses
• The operating system can enforce rules based
on the user profile.
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15. Data Access Control
• General models of access control:
– Access matrix
– Access control list
– Capability list
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16. Data Access Control
Mr. Gopal Sakarkar
• Access Matrix

17. Data Access Control
• Access Matrix: Basic elements of the model
– Subject: An entity capable of accessing objects, the
concept of subject associate with that of process (e.g.
Application soft.)
– Object: Anything to which access is controlled (e.g. files,
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programs)
– Access right: The way in which an object is accessed by a
subject (e.g. read, write, execute)

18. Data Access Control
• Access Control List: Decomposition of the
matrix by columns.
• One process , many program. E.g. CD Writer is one process in which writing is one
program and data verification of write data is second program.
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19. Data Access Control
• Access Control List
– An access control list, lists users and their
permitted access right
– The list may contain a default or public entry
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20. Data Access Control
• Capability list: Decomposition of the
matrix by rows
A capability list specifies authorized objects and operations for a user.
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21. Trusted Systems
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• Trusted Systems
– Protection of data and resources on the basis of
levels of security (e.g. military)
– In military, information is categorize as
unclassified , confidential , secret , top secret .
– Users can be granted clearances to access certain
categories of data.

22. Trusted Systems
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• Multilevel security
– In which a subject at high level may not convey
information to a subject at low level
• A multilevel secure system must enforce:
– No read up: A subject can only read an object of less or
equal security level (Simple Security Property)
– No write down: A subject can only write into an object of
greater or equal security level (*-Property)

23. Trusted Systems
• Reference Monitor Concept: Multilevel
security for a data processing system
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24. The Concept of
Trusted Systems
• Reference Monitor
– Controlling element in the hardware and operating
system of a computer that regulates the access of
subjects to objects on basis of security parameters
– The Reference monitor has access to a file
(security kernel database)
– The monitor enforces the security rules (no read
up, no write down)
Mr. Gopal Sakarkar

25. Trusted Systems
• Properties of the Reference Monitor
– Complete mediation: Security rules are enforced
on every access
– Isolation: The reference monitor and database are
protected from unauthorized modification
– Verifiability: The reference monitor’s correctness
must be provable (mathematically)
– i.e. it is possible to demonstrate mathematically that the reference
monitor enforce the security rules and provides complete mediation and
isolation.
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26. Trusted Systems
• A system that can provide such verifications
(properties) is referred to as a trusted system
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27. Summary
 Data Access Control is use to control procedure
by which user can be identified to the system.
 Trusted Systems is a computer and operating system that can br verified to
implement a given security policy.
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28. Mr. Gopal Sakarkar

29. Outline
• IP Security Overview
• IP Security Architecture
• Authentication Header
• Encapsulating Security Payload
• Combinations of Security Associations
• Key Management
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30. IP Security Overview
IPSec is not a single protocol. Instead,
IPSec provides a set of security
algorithms plus a general framework
that allows a pair of communicating
entities to use whichever algorithms
provide security appropriate for the
communication.
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31. IP Security Overview
• Applications of IPSec
– Secure branch office connectivity over the
Internet
– Secure remote access over the Internet
– Establsihing extranet and intranet connectivity
with partners
– Enhancing electronic commerce security
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32. IP Security Scenario
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33. IP Security Overview
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• Benefits of IPSec
– When IP Sec is implemented in a firewall , it provide
strong security that can be applied to all traffic
crossing the perimeter.
– IPSec in a firewall is resistant to bypass, if all traffic
from the outside must use IP.
– IPSec can be transparent to end user. No need to
trian user on security mechanisms.
– IPSec can provide security for individual users if
needed.

34. IP Security Architecture
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35. IPSec Architecture Overview
• Architecture : Cover the general concept , security
requirements, definitions and mechanisms defining IPSec
technology.
• Encapsulating Security Payload (ESP) :Cover the packet
format and general issues related to the use of the ESP.
• Authentication Header (AH): Cover the packet format and
general issues related to the use of AH for packet
authentication.
• Key management : A set of documents that describe how
various authentication algorithms are used for AH.
• Domain of Interpretation (DOI): Contains values needed for
the document to relate to each other.
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36. IPSec Services
• Access Control
• Connectionless integrity
• Data origin authentication
• Rejection of replayed packets
• Confidentiality (encryption)
• Limited traffic flow confidentiallity
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37. Security Associations (SA)
• It is a one way relationsship between a
sender and a receiver that provide security
services to a traffic.
• Identified by three parameters:
– Security Parameter Index (SPI)
– Destination IP address
– Security Protocol Identifier :
– This indicate whether the association is an AH or ESP security
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association
(SPI) is an identification tag
added to the header while using
IPsec for tunnelling the IP traffic.
This tag helps the kernel discern
between two traffic streams
where different encryption rules
and algorithms may be in use

38. Authentication Header
• Provides support for data integrity and authentication
(MAC code) of IP packets.
• Guards against replay attacks.
Mr. Gopal Sakarkar
Conti…

39. What are replay attacks?
• Replay attacks are the network attacks in which an attacker spies
the conversation between the sender and receiver and takes the
authenticated information e.g. sharing key and then contact to the
receiver with that key. In Replay attack the attacker gives the proof
of his identity and authenticity.
Example:
Suppose in the communication of two parties A and B; A is sharing
his key to B to prove his identity but in the meanwhile Attacker C
eavesdrop the conversation between them and keeps the
information which are needed to prove his identity to B. Later C
contacts to B and prove its authenticity.
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40. Authentication Header
• Next header (8bits):
identifies the type of header immediately following this header.
• Payload length (8bits):
it is a length of Authentication Header in 32 bits words minus 2.
• Reserved (16bits) :
For future use.
• Security parameter index(SPI) (32 bits):
Identifies a security association.
• Sequence Number(32bits):
It is used to increase counter value.
• Authentication data (Variable) : A variable length field that contain the Integrity
Check Value. Mr. Gopal Sakarkar

41. End-to-end VS End-to-Intermediate
Authentication
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42. Encapsulating Security Payload
• ESP provides confidentiality services
• ESP provides confidentiality of message contens
• ESP provide limited traffic flow confidentiality
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43. Encapsulating Security Payload
• Designed to provide both confidentiality
and integrity protection
• Everything after the IP header is encrypted
• The ESP header is inserted after the IP
header
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44. Encryption and Authentication
Algorithms
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• Encryption:
– Three-key triple DES
– RC5
– IDEA
– Three-key triple IDEA
– CAST
– Blowfish
• Authentication:
– HMAC-MD5-96
– HMAC-SHA-1-96

45. TCP/IP Example
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46. Basics: OSI 7-Layer RM

47. Congratulation for selecting papers
in
National Conference, Pune
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48. IPv4 Header
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49. IPv4 Header
• Internet Protocol version 4 (IPv4) is the fourth version in the development of the
Internet Protocol (IP) and the first version of the protocol to be widely deployed.
• It is one of the core protocols of standards-based internetworking methods of the
Internet, and routes most traffic in the Internet.
• IPv4 is a connectionless protocol for use on packet-switched networks.
• A connectionless protocol describes the communication between two network end
points where a message is sent from one end point to another without a prior
arrangement.
• At one end, the device transmits data to the other before ensuring that the device on
the other end is ready to use.
Mr. Gopal Sakarkar

50. 60
IPv4 Header Fields
• Version: IP Version
– 4 for IPv4
– 6 for IPv6
• HLen: Header Length
– 32-bit words
• TOS: Type of Service
– Priority information
0 4 8 12 16 19 24 28 31
version HLen TOS Length
Identifier Flags Offset
TTL Protocol Checksum
Source Address
Destination Address
Options (if any)
Data
• Length: Packet Length
– Bytes (including header)
• Header format can change with versions
– First byte identifies version
– IPv6 header are very different – will see later
• Length field limits packets to 65,535 bytes
– In practice, break into much smaller packets for network performance
considerations

51. 61
IPv4 Header Fields
• Identifier, flags, fragment
offset  used primarily for
fragmentation
• Time to live
– Must be decremented
at each router
– Packets with TTL=0
are thrown away
– Ensure packets exit
the network
• Protocol
– Demultiplexing to higher layer protocols
– TCP = 6, ICMP = 1, UDP = 17…
• Header checksum
– Ensures some degree of header integrity
– Relatively weak – only 16 bits
• Options
– E.g. Source routing, record route, etc.
– Performance issues at routers
• Poorly supported or not at all
0 4 8 12 16 19 24 28 31
version HLen TOS Length
Identifier Flags Offset
TTL Protocol Checksum
Source Address
Destination Address
Options (if any)
Data

52. 62
IPv4 Header Fields
• Source Address
– 32-bit IP address of
sender
• Destination Address
– 32-bit IP address of
destination
0 4 8 12 16 19 24 28 31
version HLen TOS Length
Identifier Flags Offset
TTL Protocol Checksum
Source Address
Destination Address
Options (if any)
Data

53. Why IPv6?
• Deficiency of IPv4
• Address space exhaustion
• New types of service  Integration
– Multicast
– Quality of Service
– Security
– Mobility (MIPv6)
• Header and format limitations

54. Advantages of IPv6 over IPv4
• Larger address space
• Better header format
• New options
• Allowance for extension
• Support for resource allocation
• Support for more security
• Support for mobility

55. IPv6 Header
Avoid Checksum Redundancy
Fragmentation at end-to-end
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56. The following list describes the function of each header field.
• Version – 4-bit Version number of Internet Protocol = 6.
• Traffic Class – 8-bit traffic class field.
• Flow Label – 20-bit field.
• Payload Length – 16-bit unsigned integer, which is the rest of the packet
that follows the IPv6 header, in octets.
• Next Header – 8-bit selector. Identifies the type of header that immediately
follows the IPv6 header. Uses the same values as the IPv4 protocol field.
• Hop Limit – 8-bit unsigned integer. Decremented by one by each node that
forwards the packet. The packet is discarded if Hop Limit is decremented to
zero.
• Source Address – 128 bits. The address of the initial sender of the packet.
• Destination Address – 128 bits. The address of the intended recipient of
the packet. The intended recipient is not necessarily the recipient if an
optional Routing Header is present.
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Video OSI-7 Layer

57. Video Lectures
• Complete working of Internet
• OSI Model with packets, IPs, Firewalls
ect.
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58. WEB Security
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59. Outline
• Web Security Considerations
• Secure Socket Layer (SSL) and Transport
Layer Security (TLS)
• Secure Electronic Transaction (SET)
• Recommended Reading and WEB Sites
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60. Web Security Considerations
• The WEB is very visible.
• Complex software hide many security
flaws.
• Web servers are easy to configure and
manage.
• Users are not aware of the risks.
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61. Security facilities in the TCP/IP
protocol stack
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62. SSL and TLS
• SSL was originated by Netscape
• TLS working group was formed within
IETF
• First version of TLS can be viewed as an
SSLv3.1
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63. SSL Architecture
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64. SSL Record Protocol Operation
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65. SSL Record Format
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66. SSL Record Protocol Payload
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67. Handshake Protocol
• The most complex part of SSL.
• Allows the server and client to
authenticate each other.
• Negotiate encryption, MAC algorithm and
cryptographic keys.
• Used before any application data are
transmitted.
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68. Handshake Protocol Action
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69. Transport Layer Security
• The same record format as the SSL record format.
• Defined in RFC 2246.
• Similar to SSLv3.
• Differences in the:
– version number
– message authentication code
– pseudorandom function
– alert codes
– cipher suites
– client certificate types
– certificate_verify and finished message
– cryptographic computations
– padding
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70. Secure Electronic Transactions
• An open encryption and security specification.
• Protect credit card transaction on the Internet.
• Companies involved:
– MasterCard, Visa, IBM, Microsoft, Netscape, RSA,
Terisa and Verisign
• Not a payment system.
• Set of security protocols and formats.
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71. SET Services
• Provides a secure communication channel
in a transaction.
• Provides trust by the use of X.509v3 digital
certificates.
• Ensures privacy.
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72. SET Overview
• Key Features of SET:
– Confidentiality of information
– Integrity of data
– Cardholder account authentication
– Merchant authentication
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73. SET Participants
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74. Sequence of events for
transactions
1. The customer opens an account.
2. The customer receives a certificate.
3. Merchants have their own certificates.
4. The customer places an order.
5. The merchant is verified.
6. The order and payment are sent.
7. The merchant request payment authorization.
8. The merchant confirm the order.
9. The merchant provides the goods or service.
10. The merchant requests payments.
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75. Dual Signature
DS E [H(H(PI ) || H(OI))]
KRc 
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76. Payment processing
Cardholder sends Purchase Request
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77. Payment processing
Merchant Verifies Customer Purchase Request
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78. Payment processing
• Payment Authorization:
– Authorization Request
– Authorization Response
• Payment Capture:
– Capture Request
– Capture Response
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79. Recommended Reading and
WEB sites
• Drew, G. Using SET for Secure Electronic
Commerce. Prentice Hall, 1999
• Garfinkel, S., and Spafford, G. Web Security &
Commerce. O’Reilly and Associates, 1997
• MasterCard SET site
• Visa Electronic Commerce Site
• SETCo (documents and glossary of terms)
Mr. Gopal Sakarkar