DSI - IP Telecom Security

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(No Transcript)
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IP Cyber Security Unit 4 Access Control
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UNIT 4
Content

• Access and Authentication Technology

• Authentication methods PPP, PAP, CHAP, EAP

• AAA, RADIUS, TACACS, TACACS, Kerberos

• Authentication Header (AH)

• Encapsulating Security Payload (ESP)

• Virtual Private Networks (VPN) VPN Architectures

• Authentication On Wireless LANs

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Access Control Processes
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Access Control (AC)

• Access control is the heart of security
• Definitions
• The ability to allow only authorized users,
  programs or processes system or resource access
• The granting or denying, according to a
  particular security model, of certain permissions
  to access a resource
• An entire set of procedures performed by
  hardware, software and administrators, to monitor
  access, identify users requesting access, record
  access attempts, and grant or deny access based
  on preestablished rules.

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Access Control

• Access Control
• Access control is the policy-driven limitation of
  access to systems, data, and dialogs
• Prevent attackers from gaining access, stopping
  them if they do

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Access Control

• What Access Permissions (Authorizations) Should
  They Have?
• Access permissions (authorizations) define
  whether a role or individual should have any
  access at all
• If so, exactly what the role or individual should
  be allowed to do to the resource.
• Usually given as a list of permissions for users
  to be able to do things (read, change, execute
  program, etc.) for each resource

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Access Control

• How Should Access Control Be Implemented?
• For each resource, need an access protection plan
  for how to implement protection in keeping with
  the selected control policy
• For a file on a server, for instance, limit
  authorizations to a small group, harden the
  server against attack, use a firewall to thwart
  external attackers, etc.

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Access Control

• Policy-Based Access Control and Protection
• Have a specific access control policy and an
  access protection policy for each resource
• Focuses attention on each resource
• Guides the selection and configuration of
  firewalls and other protections
• Guides the periodic auditing and testing of
  protection plans

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Access control lists (ACL)

• A file used by the access control system to
  determine who may access what programs and files,
  in what method and at what time
• Different operating systems have different ACL
  terms
• Types of access (locks)
• Read/Write/Create/Execute/Modify/Delete/Rename

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AC is implemented for all IS components including

• Hardware
• Software
• Application
• Protocol (Kerberos, IPSec)
• Physical
• Logical (policies)

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AC protect all IS components including

• Data Unauthorized viewing, modification or
  copying
• System Unauthorized use, modification or denial
  of service
• It should be noted that nearly every network
  operating system (NT, Unix, Vines, NetWare) is
  based on a secure physical infrastructure

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Access Control

• First Steps
• Enumeration of Resources
• Sensitivity of Each Resource
• Next, who Should Have Access?
• Can be made individual by individual
• More efficient to define by roles (logged-in
  users, system administrators, project team
  members, etc.)

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Access Control

• What Access Permissions (Authorizations) Should
  They Have (Keys)?
• Access permissions (authorizations) define
  whether a role or individual should have any
  access at all
• If so, exactly what the role or individual should
  be allowed to do to the resource.
• Usually given as a list of permissions for users
  to be able to do things (read, change, execute
  program, etc.) for each resource

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Access Control

• How Should Access Control Be Implemented?
• For each resource, need an access protection plan
  for how to implement protection in keeping with
  the selected control policy
• For a file on a server, for instance, limit
  authorizations to a small group, harden the
  server against attack, use a firewall to thwart
  external attackers, etc.

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Access Control

• Policy-Based Access Control and Protection
• Have a specific access control policy and an
  access protection policy for each resource
• Focuses attention on each resource
• Guides the selection and configuration of
  firewalls and other protections
• Guides the periodic auditing and testing of
  protection plans

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Access Control

• Is the ability to limit and control the access
  to
• the systems and application.

• Tools

• Physical access control

• Finger Prints.
• Eyes Recognition.

• Voice Identification.
• Smart Card.

• Logical access control

• Password.

• Firewalls.

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Access Control

• Smart Cards

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Access Control

• Password

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Personnel Identification and Authentication tools
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Access Control

• Finger Prints.

• Token Ring

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Password Hashing (or Encryption)
2. Hash My4Bad 11110000
1. User Aly Password My4Bad
3. Hashes Match
Client PC User Ali
Hashed Password File Ahmed 11001100 Ali 11110000 M
ohmd 00110011 Samir 11100010
4. Hashes Match, So User is Authenticated
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One way Hash Function
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Authentication

• Steps
• The user sends a request to the server seeking
  for permission to enter the secured website
• The server asks for his username and password to
  check if that person is who he is declared to be
• The user then signs in and sends the request back
  to the server
• Server will verify his identity and check if he
  is an authorized user .
• After confirming his identity, the server would
  send back an approval or a denial of access to
  the website..

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Authentication Forms
1. What a client knows 2. What a client
has 3. Who a client is 4. What a client
produces
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AUTHENTICATION METHODS

• What a client knows This form of authentication
  deals with what the client knows. For example
  passwords and user IDs.
• What a client has The second form of
  authentication deals with something that the
  client possesses. Such things include tokens and
  smart cards. Smart cards are cards that contain a
  computer chip to verify the user's identity.
  Tokens, on the other hand, are cards equipped
  with a computer chip and a liquid crystal display
  showing a computer-generated number sequence for
  remote login authentication
• What a client is The third form of
  authentication is related to the characteristics
  of the supplicant. Such characteristics are
  fingerprint, iris pattern, hand geometry and
  retinal print. Because these characteristics are
  unique to every individual supplicant, it can be
  used by systems to authenticate its users
• What a client produces The final form of
  authentication that we are covering addresses
  what the client produces. Such examples are
  technologies on signature or voice recognition,
  e.g. credit card payment system.

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Biometric Authentication
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Biometric Authentication

• Biometric Authentication
• Authentication based on body measurements and
  motions
• Because you always bring your body with you
• Biometric Systems
• Enrollment
• Later access attempts
• Acceptance or rejection

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Biometric Authentication System
1. Initial Enrollment
User Lee Scanning
User Lee Template (01101001)
Processing (Key Feature Extraction) A01, B101,
C001
Template Database Brown 10010010 Lee
01101001 Chun 00111011 Hirota 1101110

3. Match Index Decision Criterion (Close Enough?)
2. Subsequent Access
Applicant Scanning
User Access Data (01111001)
Processing (Key Feature Extraction) A01, B111,
C001
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Biometric Authentication

• Verification Versus Identification
• Verification Are applicants who they claim to
  be? (compare with single template)
• Identification Who is the applicant? (compare
  with all templates)
• More difficult than verification because must
  compare to many templates
• Watch list is this person a member of a specific
  group (e.g., known terrorists)
• Intermediate in difficulty

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Biometric Authentication

• Verification Versus Identification
• Verification is good for replacing passwords in
  logins
• Identification is good for door access and other
  situations where entering a name would be
  difficult

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Biometric Authentication

• Precision
• False acceptance rates (FARs) Percentage of
  unauthorized people allowed in
• Person falsely accepted as member of a group
• Person allowed through a door who should be
  allowed through it
• Very bad for security

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Biometric Authentication

• Precision
• False rejection rates (FRRs) Percentage of
  authorized people not recognized as being members
  of the group
• Valid person denied door access or server login
  because not recognized
• Can be reduced by allowing multiple access
  attempts
• High FRRs will harm user acceptance because users
  are angered by being falsely forbidden

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Biometric Authentication

• Precision
• Vendor claims for FARs and FRRs tend to be
  exaggerated because they often perform tests
  under ideal circumstances
• For instance, having only small numbers of users
  in the database
• For instance, by using perfect lighting,
  extremely clean readers, and other conditions
  rarely seen in the real world

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Biometric Authentication

• User Acceptance is Crucial
• Strong user resistance can kill a system
• Fingerprint recognition may have a criminal
  connotation
• Some methods are difficult to use, such as iris
  recognition, which requires the eye to be lined
  up carefully.
• These require a disciplined group

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Biometric Authentication

• Biometric Methods
• Fingerprint recognition
• Dominates the biometric market today
• Based on a fingers distinctive pattern of
  whorls, arches, and loops
• Simple, inexpensive, well-proven
• Weak security can be defeated fairly easily with
  copies
• Useful in modest-security areas

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Biometric Authentication

• Biometric Methods
• Iris recognition
• Pattern in colored part of eye
• Very low FARs
• High FRR if eye is not lined up correctly can
  harm acceptance
• Reader is a cameradoes not send light into the
  eye!

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Biometric Authentication

• Biometric Methods
• Face recognition
• Can be put in public places for surreptitious
  identification (identification without citizen
  or employee knowledge). More later.
• Hand geometry shape of hand
• Voice recognition
• High error rates
• Easy to fool with recordings

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Biometric Authentication

• Biometric Methods
• Keystroke recognition
• Rhythm of typing
• Normally restricted to passwords
• Ongoing during session could allow continuous
  authentication
• Signature recognition
• Pattern and writing dynamics

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Biometric Authentication

• Biometric Standards
• Almost no standardization
• Worst for user data (fingerprint feature
  databases)
• Get locked into single vendors

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Biometric Authentication

• Can Biometrics be Fooled?
• Airport face recognition
• Identification of people passing in front of a
  camera
• False rejection rate rate of not identifying
  person as being in the database
• Fail to recognize a criminal, terrorist, etc.
• FRRs are bad

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Biometric Authentication

• Can Biometrics be Fooled?
• Airport face recognition
• 4-week trial of face recognition at Palm Beach
  International Airport
• Only 250 volunteers in the user database
  (unrealistically small)
• Volunteers were scanned 958 times during the
  trial
• Only recognized 455 times! (47)
• 53 FRR

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Biometric Authentication

• Can Biometrics be Fooled?
• Airport face recognition
• Recognition rate fell if wore glasses (especially
  tinted), looked away
• Would be worse with larger database
• Would be worse if photographs were not good

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Biometric Authentication

• Can Biometrics be Fooled?
• DOD Tests indicate poor acceptance rates when
  subjects were not attempting to evade
• 270-person test
• Face recognition recognized person only 51
  percent of time
• Even iris recognition only recognized the person
  94 percent of the time!

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Biometrics Authentication

• Can Biometrics be Fooled?
• Other research has shown that evasion is often
  successful for some methods
• German ct magazine fooled most face and
  fingerprint recognition systems
• Prof. Matsumoto fooled fingerprint scanners 80
  percent of the time with a gelatin finger created
  from a latent (invisible to the naked eye) print
  on a drinking glass

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Password-Based Access Control
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Server Password Cracking

• Reusable Passwords
• A password you use repeatedly to get access to a
  resource on multiple occasions
• Bad because attacker will have time to learn it
  then can use it
• Difficulty of Cracking Passwords by Guessing
  Remotely
• Usually cut off after a few attempts
• However, if can steal the password file, can
  crack passwords at leisure

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Server Password Cracking

• Hacking Root
• Super accounts (can take any action in any
  directory)
• Hacking root in UNIX
• Super accounts in Windows (administrator) and
  NetWare (supervisor)
• Hacking root is rare usually can only hack an
  ordinary user account
• May be able to elevate the privileges of the user
  account to take root action

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Server Password Cracking

• Physical Access Password Cracking
• l0phtcrack
• Lower-case L, zero, phtcrack
• Password cracking program
• Run on a server (need physical access)
• Or copy password file and run l0phtcrack on
  another machine.

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Server Password Cracking

• Physical Access Password Cracking
• Brute-force password guessing
• Try all possible character combinations
• Longer passwords take longer to crack
• Using more characters also takes longer
• Alphabetic, no case (26 possibilities)
• Alphabetic, case (52)
• Alphanumeric (letters and numbers) (62)
• All keyboard characters (80)

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Password Length
Password Length In Characters
Alphanumeric Letters Digits (N62)
All Keyboard Characters (N80)
Alphabetic, Case (N52)
Alphabetic, No Case (N26)
1
62
80
52
26
2 (N2)
3,844
6,400
2,704
676
4 (N4)
14,776,336
40,960,000
7,311,616
456,976
6
56,800,235,584
2.62144E11
19,770,609,664
308,915,776
8
2.1834E14
1.67772E15
5.34597E13
2.08827E11
10
8.39299E17
1.07374E19
1.44555E17
1.41167E14
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Server Password Cracking

• Physical Access Password Cracking
• Brute Force Attacks
• Try all possible character combinations
• Slow with long passwords length
• Dictionary attacks
• Try common words (password, ouch, etc.)
• There are only a few thousand of these
• Cracked very rapidly
• Hybrid attacks
• Common word with single digit at end, etc.

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Server Password Cracking

• Password Policies
• Good passwords
• At least 6 characters long
• Change of case not at beginning
• Digit (0 through 9) not at end
• Other keyboard character not at end
• Example triV6ial

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Server Password Cracking

• Password Policies
• Testing and enforcing password policies
• Run password cracking program against own servers
• Caution requires approval! SysAdmins have been
  fired for doing this without permissionand
  should be
• Password duration policies How often passwords
  must be changed

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Server Password Cracking

• Password Policies
• Password sharing policies Generally, forbid
  shared passwords
• Removes ability to learn who took actions loses
  accountability
• Usually is not changed often or at all because of
  need to inform all sharers

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Server Password Cracking

• Password Policies
• Disabling passwords that are no longer valid
• As soon as an employee leaves the firm, etc.
• As soon as contractors, consultants leave
• In many firms, a large percentage of all accounts
  are for people no longer with the firm

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Server Password Cracking

• Password Policies
• Lost passwords
• Password resets Help desk gives new password for
  the account
• Opportunities for social engineering attacks
• Leave changed password on answering machine
• Biometrics voice print identification for
  requestor (but considerable false rejection rate)

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Server Password Cracking

• Password Policies
• Lost passwords
• Automated password resets
• Employee goes to website
• Must answer a question, such as In what city
  were you born?
• Problem of easily-guessed questions that can be
  answered with research

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Server Password Cracking

• Password Policies
• Encrypted (hashed) password files
• Passwords not stored in readable form
• Encrypted with DES or hashed with MD5
• In UNIX, etc/passwd puts x in place of password
• Encrypted or hashed passwords are stored in a
  different (shadow) file to which only high-level
  accounts have access

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Server Password Cracking

• Password Policies
• Windows passwords
• Obsolete LAN manager passwords (7 characters
  maximum) should not be used
• Windows NTLM passwords are better
• Option (not default) to enforce strong passwords

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Server Password Cracking

• Shoulder Surfing
• Watch someone as they type their password
• Keystroke Capture Software
• Professional versions of windows protect RAM
  during password typing
• Consumer versions do not
• Trojan horse throws up a login screen later,
  reports its finding to attackers

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Server Password Cracking

• Windows Client PC Software
• Consumer version login screen is not for security
• Windows professional and server versions provide
  good security with the login password
• BIOS passwords allow boot-up security
• Can be disabled by removing the PCs battery
• But during a battery removal, the attacker will
  be very visible
• Screen savers with passwords allow away-from-desk
  security after boot-up

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UNIT 4
Content

• Access and Authentication Technology

• Authentication methods PPP, PAP, CHAP, EAP

• AAA, RADIUS, TACACS, TACACS, Kerberos

• Authentication Header (AH)

• Encapsulating Security Payload (ESP)

• Virtual Private Networks (VPN) VPN Architectures

• Authentication On Wireless LANs

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AUTHENTICATION METHODS

• Authentication and authorization technologies
  (e.g., userID and password with PAP Password
  Authentication Protocol and CHAP Challenge
  Handshake Authentication Protocol, Kerberos,
  etc.)
• Token cards
• PPP Extensible Authentication Protocol (EAP)
• Microsoft Point-to-Point Encryption (MPPE)
• Key-management protocols, e.g., Internet Security
  Association and Key Management Protocol (ISAKMP),
  Internet Key Exchange (IKE), etc.
• Digital certificates
• Digital signatures
• Message authentication codes (MACs)
• Wireless Encryption Technologies (e.g., WEP,
  802.11i)

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AUTHENTICATION METHODS

• A number of other userID and password
  authentication technologies with improved
  security have also been designed, primarily to be
  employed during a user log-in process.
• A good example is Password Challenge Handshake
  Authentication Protocol (CHAP). In a network
  environment, because the log-in process first
  authenticates the user and then establishes a
  session (a logical connection) for the user if
  the user is indeed authorized

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PPP Authentication
No Authentication Is an Option
Server
Client

• To establish communications over a point-to-point
  link, each end of the PPP link must first send
  link configuration packets to configure the data
  link during the Link Establishment Phase.
• After the link has been established, PPP provides
  for an optional Authentication Phase before
  proceeding to the Network-Layer Protocol Phase.
• The authentication protocols are intended for use
  by hosts and routers that connect to a PPP
  network server via switched circuits, dial-up
  lines, or dedicated links.

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PAP Password Authentication Protocol

• PAP is a simple proprietary userID and password
  authentication protocol.
• With PAP, the password is sent across the network
  to be compared against an encrypted password file
  on the access server. If the password matches the
  associated userID, the connection is established.
  
• Because the password can potentially be
  intercepted by a hacker, PAP is not considered to
  be secure.

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PPP Authentication
PAP Authentication
Authentication-Request Messages (Send Until
Response)
Authentication-Response Message
Server
Client
Poor Security Usernames and Passwords Are Sent
in the Clear
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Password Challenge Handshake Authentication
Protocol (CHAP)

• CHAP addresses the PAP deficiencies by having a
  server send a randomly generated challenge to
  the client along with the hostname.
• The hostname is used by the client to look up the
  appropriate password, which is then combined with
  the challenge and encrypted using a one-way
  hashing function to produce a result that is then
  sent to the server along with the client userID.
• The server performs the same computation using
  the password and compares the result with the
  result that has been sent back by the client.
• If there is a match, the connection will be
  established. Because the challenge is different
  in every session, a hacker cannot replay the
  sequence.
• The specific method to be used can be negotiated
  by a client when connecting to an RAS.
• CHAP allows different types of encryption
  algorithms to be used. Most commercial RASs
  support Data Encryption Standard (DES) and
  Message Digest 5 (MD5).

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(No Transcript)
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MS-CHAP Challenge-Response Authentication Protocol
Note Both the client and the server know the
clients password.
1. Verifier creates Challenge Message
Challenge
2. Verifier sends Challenge Message
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MS-CHAP Challenge-Response Authentication Protocol

• 3.
• Applicant (Supplicant)creates a Response
  Message
• Adds password toChallenge Message
• (b) Hashes the resultant bitstring (does not
  encrypt)
• (c) The hash is theResponse Message

Challenge
Password
Hashing (Not Encryption)
Response
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MS-CHAP Challenge-Response Authentication Protocol
4. Applicant sends Response Message without
encryption
Transmitted Response
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MS-CHAP Challenge-Response Authentication Protocol
5. Verifier adds password to theChallenge
Message it sent. Hashes the combination.This is
the expectedResponse Message.
Challenge
Password
Hashing
Expected Response
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MS-CHAP Challenge-Response Authentication Protocol
Expected Response
Transmitted Response
?
6. If the two Response Messages are equal,
the applicant knows the password and is
authenticated. Sever logs Client in.
7. Note that only hashing is involved. There is
no encryption.
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PPP Authentication
CHAP Authentication
Challenge Message
Response Message Hash (Challenge Message Secret)
Server
Client
Server computes hash of challenge message plus
secret If equals the response message,
authentication is successful
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PPP Authentication
MS-CHAP Authentication
Challenge Message
Response Message Hash (Challenge Message
Password)
Server
Client
CHAP, but with password as the secret. Widely
used because allows password authentication Standa
rd on Microsoft Windows client Only as secure as
password strength
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PPP Extensible Authentication Protocol (EAP)

• EAP is a general protocol for PPP authentication
  that supports multiple authentication mechanisms.
  EAP does not select a specific authentication
  mechanism at Link Control Phase, but rather
  postpones this until the Authentication Phase.
  This allows the authenticator to request more
  information before determining the specific
  authentication mechanism. This also permits the
  use of a back-end server that actually implements
  the various mechanisms, whereas the PPP
  authenticator merely passes through the
  authentication exchange.
• The following are the basic steps involved in the
  EAP authentication process
• After the Link Establishment phase is complete,
  the authenticator sends one or more Requests to
  authenticate the peer. The Request has a type
  field to indicate what is being requested.
  Examples of Request types include Identity,
  MD5-challenge, One-Time Passwords, Generic Token
  Card, etc. The MD5-challenge type corresponds
  closely to the CHAP authentication protocol.
  Typically, the authenticator will send an initial
  Identity Request followed by one or more Requests
  for authentication information. An initial
  Identity Request is not required, and may be
  bypassed in cases where the identity is presumed
  (leased lines, dedicated dial-ups, etc.).
• The peer sends a Response packet in reply to each
  Request. As with the Request packet, the Response
  packet contains a type field that corresponds to
  the type field of the Request.
• The authenticator ends the authentication phase
  with a Success or Failure packet.

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PPP Authentication
EAP Authentication
Authenticate
Defer authentication Will provide more
information
Server
Client
EAP defers authentication to a later process Such
as RADIUS authentication
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PPP Encryption
New PPP Header. Plaintext.
Original PPP Frame. Encrypted.
New PPP Trailer. Plaintext.
PPP with EAP Encryption
New PPP Header. Plaintext.
EAP header
New PPP Trailer. Plaintext.
Code
Identifier
Length
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PPP on Direct Links and Internets
PPP Frame
Connection over Direct Link
PPP Provides End-to-End Link
Applicant (Client)
Verifier (Server)
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PPP on Direct Links and Internets
PPP Frame in IP Packet
Connection over Internet
PPP Limited to First Data Link (Network)
Router
Router
Applicant (Client)
Verifier (Server)
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PPP on Direct Links and Internets

• Note
• Tunneling Places the PPP Frame in an IP Packet,
  Which Delivers the Frame.
• To the Receiver, Appears to be a Direct Link.
• Allows organization to continue using existing
  PPP-based security such as encryption and
  authentication

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Layer 2 Tunneling Protocol (L2TP)
DSL Access Multiplexer (DSLAM) with L2TP
Client Running PPP
Internal Server
L2TP RAS
DSL
L2TP Tunnel
Local Network
Carrier Network
Note L2TP does not provide security. It
provides only tunneling. L2TP recommends the use
of IPsec for security.
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UNIT 4
Content

• Access and Authentication Technology

• Authentication methods PPP, PAP, CHAP, EAP

• AAA, RADIUS, TACACS, TACACS, Kerberos

• Authentication Header (AH)

• Encapsulating Security Payload (ESP)

• Virtual Private Networks (VPN) VPN Architectures

• Authentication On Wireless LANs

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Point-to-Point Tunneling Protocol (PPP)
RADIUS Server
IP Protocol 47 (GRE) Data Connection
Local ISP Access (Not Secure)
Internet
Remote Corporate PC
RADIUS Server
PPTP RAS
ISP PPTP Access Concentrator
TCP Port 1723 Supervisory Connection (Vulnerable)
Corporate Site A
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Point-to-Point Tunneling Protocol (PPP)
Direct connection between PC And RADIUS Server
IP Protocol 47 (GRE) Data Connection
Internet
Remote Corporate PC
RADIUS Server
PPTP RAS
TCP Port 1723 Supervisory Connection (Vulnerable)
Corporate Site A
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PPTP Encapsulation for Data Frames
Enhanced General Routing Encapsulation (GRE)
Header Information About Encapsulated Packet
New IP Header Protocol47 IP Destination Address
Is That of Remote Access Server
Encapsulated Original IP Packet
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RADIUS for Dial-Up Remote Access
Remote Corporate PC
1. Login Username And Password
2. OK?
Dial-Up Connection
RADIUS Server
RAS 1
Remote Corporate PC
Public Switched Telephone Network
Corporate Site A
Dial-Up Connection
RAS 2
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RADIUS for Dial-Up Remote Access
Remote Corporate PC
Dial-Up Connection
3. OK
4. Welcome
RADIUS Server
RAS 1
Remote Corporate PC
Public Switched Telephone Network
Corporate Site A
Dial-Up Connection
RAS 2
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Kerberos Authentication System
Kerberos Server Key Distribution Center (K)
Abbreviations A Applicant V Verifier K
Kerberos Server
Verifier (V)
Applicant (A)
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Kerberos Authentication System
Kerberos Server Key Distribution Center (K)
TGT (Ticket-Granting Ticket) is encrypted in
a way that only K can decrypt.
Contains information that K will read later.
1. Request for Ticket-Granting Ticket
Key nA (Network Login Key for A) is encrypted
with As Master Key (Key mA). In future
interactions with K, A will use nA to limit the
master keys exposure.
2. Response TGT, Key nA
Verifier (V)
Applicant (A)
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Kerberos Ticket-Granting Service Part 1
Authenticator is As IP address, user name, and
time stamp. This authenticator is encrypted with
Key nA to prove that A sent it.
Kerberos Server Key Distribution Center (K)
1. Request Ticket for V TGT Authenticator encr
ypted with Key nA
Key AV is a symmetric session key that A will
use with V.
2. Response Key AV encrypted with Key
nA Service Ticket
Verifier (V)
Applicant (A)
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Kerberos Ticket-Granting Service Part 2
Authenticator (Auth) encrypted with Key
AV. Service Ticket contains Key AV encrypted
with the Verifiers master key, Key mV.
Kerberos Server Key Distribution Center (K)
3. Request for Connection Auth Service Ticket
5. Ongoing Communication with Key AV
4. V decrypts Service Ticket Uses Key AV to test
Auth
95
KERBEROS AUTHENTICATION ALGORITHM

• Kerberos uses a conventional symmetric
  cryptography, meaning the encryption and
  decryption uses the same key for both processes.
• It makes use of a third trusted party, which
  stores a database of secret keys, and is called a
  Key Distribution Centre (KDC).
• It consists of an Authentication Server (AS) and
  a Ticket Granting Server (TGS), to verify the
  identity of the client.
• There are 3 basic steps that are done in order to
  authenticate using Kerberos

96

• Step 1
• The client sends a request to the authenticating
  server (Kerberos).
• The server then locates the client in the
  database and generates a session key (SK1) to
  start a session between the client and the
  ticket-granting server.
• Using the clients secret key, Kerberos will
  encrypt the SK1, after which it will use the
  secret key generated by the TGS to create a
  ticket- granting ticket (TGT) and send it back to
  the client.

97

• Step 2
• The client decrypts the message sent by the
  authentication server and receives the session
  key.
• It then uses it to create an authenticator which
  includes the users name, IP address and
  timestamp, which disallows others to steal the
  information from the ticket and the authenticator
  for later use, and sends it to the TGS together
  with the TGT it received.
• The TGS uses the SK1 inside the TGT to decrypt
  the authenticator and then verifies the
  information it contains, including the ticket. If
  all are correct, the request is granted.
• The TGS then creates a new session key (SK2) to
  start a session between the client and the target
  server. Using SK1, it encrypts this message, and
  sends it back to the client together with a new
  ticket containing the clients name, IP address,
  timestamp and an expiration time (all of which
  encrypted with the target servers secret key),
  as well as the name of the server.

98

• Step 3
• The client decrypts the message sent by the TGS
  and receives the second session key.
• It then creates a new authenticator encrypted
  with SK2 and sends it to the target server,
  together with the session key encrypted using the
  target servers secret key.
• The target server decrypts and checks all of the
  information received.
• Applications that require 2-way authentication
  are returned a message with time stamp plus 1,
  encrypted with SK2.

99
Finally, the clients identity has been verified
by the server, and now both are able to
communicate securely using a shared encryption
key.
100
Smart card authentication

• Cryptographic key is stored on the smart card,
  which is unlocked by the user using a special key
  pair.
• In order to authenticate the user, he places his
  smart card into a special card reader attached to
  the system he is trying to log in to.
• The key from the smart card is being read by the
  system.
• The system asks the user for his password to
  unlock the key.
• After the user key in the password, the system
  performs a cryptographic key exchange with the
  central server for verification of the key. The
  user is being authenticated when the key is
  verified.

101
Sender Policy Framework (SPF)

• The Sender Policy Framework (SPF) is an extension
  to the Simple Mail Transfer Protocol (SMTP).
• It is an e-mail authentication method that
  prevents the forgery of the sender address
  residing in the return-path of an e-mail.
  Malicious spammers tend to disguise their
  identity by making use of other e-mail addresses
  to send spam e-mails. In this way, these spammers
  could avoid being tracked down and get caught.
• Secondly, they could avoid having their own
  mailbox filled with undelivered bounce e-mails.
  SPF helps to reduce such incidences of email
  address and domain spoofing by ensuring that
  e-mail receivers only receive e-mails from
  senders that use a legitimate server of a
  particular domain.

102
UNIT 4
Content

• Access and Authentication Technology

• Authentication methods PPP, PAP, CHAP, EAP

• AAA, RADIUS, TACACS, TACACS, Kerberos

• Authentication Header (AH)

• Encapsulating Security Payload (ESP)

• Virtual Private Networks (VPN) VPN Architectures

• Authentication On Wireless LANs

103
Levels of Access Privilege

• General users in an enterprise should be grouped
  at a minimum into the following three privilege
  levels
• Employees as users with general access privileges
  for free access around the network to default
  network and systems resources
• Partners as users with lower access privileges
  for access to some limited, predetermined network
  and systems resources
• Outside users with authority to access very
  limited systems resources (probably only some
  pieces of data or applications) through some
  proxy servers.
• Additional special privilege levels are likely
  needed, e.g., for administrators as users with
  higher access privileges, which are required to
  gain access to and to administer network and
  systems components like servers, routers, etc.

104
IP-AUTHENTICATION MECHANISMS

• Because IP is by definition a connectionless
  transport technology utilizing datagram exchanges
  over the network, special facilities are needed
  to ensure user authentication for each of the IP
  packets transmitted and received.
• Two IP authentication mechanisms
• Authentication Header AH which provides
  integrity and authentication without
  confidentiality.
• Encapsulating Security Payload ESP which always
  provides confidentiality and optionally also
  provides integrity and authentication.
• Both AH and ESP use an authentication algorithm
  to generate authentication information known as
  the Integrity Check Value (ICV), which is placed
  in the authentication data field in the
  corresponding header.

105
Authentication Header AH

• AH defines an Authentication Header that contains
  the authentication information for the particular
  IP datagram and is used to provide connectionless
  data integrity and source identity authentication
  for IP datagrams and protection against replays.
• This latter, optional service may be selected by
  the receiver when a Security Association is
  established. (Although the default calls for the
  sender to increment the Sequence Number used for
  anti-replay, the service is effective only if the
  receiver checks the Sequence Number.)
• AH provides authentication for as much of the IP
  header as possible, as well as for upper-level
  protocol data.
• However, some IP header fields may change in
  transit, and the value of these fields, when the
  packet arrives at the receiver, may not be
  predictable by the sender.
• The values of such fields cannot be protected by
  AH.
• Thus, the protection provided to the IP header by
  AH is somewhat piecemeal.

106
Authentication Header AH

• AH may be applied alone, in combination with ESP,
  or in a nested fashion through the use of a
  tunnel mode.
• Security services can be provided between a pair
  of communicating hosts, between a pair of
  communicating security gateways, or between a
  security gateway and a host.
• ESP may be used to provide similar security
  services as AH, and it also provides an added
  confidentiality (encryption) service.
• The primary difference between the authentication
  capabilities provided by ESP and AH is the extent
  of the coverage offered by each. Specifically,
  ESP does not protect any IP header fields unless
  those with certain authenticating encryption
  algorithms. Adding the AH header to an IP
  datagram prior to encapsulating the datagram
  using ESP might be desirable for users wishing to
  have strong integrity, authentication, and
  confidentiality, and perhaps also for users who
  require strong non-repudiation.
• When the two mechanisms are combined, the
  placement of the IP AH makes clear which part of
  the data is being authenticated.

107
Authentication Header AH
AH Header Format The IP protocol header (IPv4,
IPv6, or Extension) immediately preceding AH will
contain the value 51 in its Protocol (IPv4) or
Next Header (IPv6, Extension) field, where
108
AUTHENTICATION METHODS
109
UNIT 4
Content

• Access and Authentication Technology

• Authentication methods PPP, PAP, CHAP, EAP

• AAA, RADIUS, TACACS, TACACS, Kerberos

• Authentication Header (AH)

• Encapsulating Security Payload (ESP)

• Virtual Private Networks (VPN) VPN Architectures

• Authentication On Wireless LANs

110
IPsec ESP and AH Protection
Encapsulating Security Payload
IP Header
ESP Header
Protected
ESP Trailer
Protocol 50
Protocol 51
IP Header
Authentication Header
Protected
Authentication Header
111
Modes and Protections
112
Digital Signature for Message-by-Message
Authentication
To Create the Digital Signature 1. Hash the
plaintext to create a brief message digest this
is NOT the Digital Signature. 2. Sign (encrypt)
the message digest with the senders private key
to create the digital signature. 3. Transmit the
plaintext digital signature, encrypted
with symmetric key encryption.
Plaintext
Hash
MD
Sign (Encrypt) with Senders Private Key
DS
113
Digital Signature for Message-by-Message
Authentication
4. Encrypted with Session Key
Sender
Receiver
114
Digital Signature for Message-by-Message
Authentication
To Test the Digital Signature 5. Hash the
received plaintext with the same hashing
algorithm the sender used. This gives the message
digest. 6. Decrypt the digital signature with
the senders public key. This also should give
the message digest. 7. If the two match,
the message is authenticated.
5.
6.
Received Plaintext
DS
Decrypt with True Partys Public Key
Hash
MD
MD
7. Are they equal?
115
Public Key Deception
Impostor I am the True Person. Here is TPs
public key. (Sends Impostors public key) Here
is authentication based on TPs private
key. (Really Impostors private key) Decryption
of message from Verifier encrypted with
Imposters public key, so Impostor can decrypt it
Verifier Must authenticate True
Person. Believes now has TPs public
key Believes True Person is authenticated based
on Impostors public key True Person, here is a
message encrypted with your public key.
Critical Deception
116
Important X.509 Digital Certificate Fields
Field
Description
Version Number
Version number of the X.509. Most certificates
follow Version 3. Different versions have
different fields. This figure reflects the
Version 3 standard.
Issuer
Name of the Certificate Authority (CA).
Serial Number
Unique serial number for the certificate, set by
the CA.
117
Important X.509 Digital Certificate Fields
Field
Description
Subject
The name of the person, organization, computer,
or program to which the certificate has been
issued. This is the true party.
Public Key
The public key of the subjectthe public key of
the true party.
Public Key Algorithm
The algorithm the subject uses to sign messages
with digital signatures.
118
Important X.509 Digital Certificate Fields
Field
Description
Valid Period
The period before which and after which the
certificate should not be used. Note Certificate
may be revoked before the end of this period.
Digital Signature
The digital signature of the certificate, signed
by the CA with the CAs own private
key. Provides authentication and certificate
integrity. User must know the CAs public key
independently.
119
Important X.509 Digital Certificate Fields
Field
Description
Signature Algorithm Identifier
The digital signature algorithm the CA uses to
sign its certificates.
120
Digital Signature and Digital Certificate in
Authentication
Digital Certificate
Digital Signature
Public Key of True Party
Signature to Be Tested with Public Key of True
Party
Authentication
121
Public Key Infrastructure (PKI) with a
Certificate Authority
Certificate Authority PKI Server
Verifier (Cheng)
6. Request Certificate Revocation List (CRL)
3. Request Certificate for Lee
7. Copy of CRL
5. Certificate for Lee
4. Certificate for Lee

• Create
• Distribute
• Private Key
• and
• (2) Digital Certificate

Applicant (Lee)
Verifier (Brown)
122
Public Key Infrastructure (PKI)

• Goals of PKI
• Authenticate the user/system at the sending end
  of a transaction
• Authenticate the user/system at the receiving end
  of a transaction
• Non-repudiation
• PKI components
• Certification Authority (CA)
• Registration Authority (RA)
• Certificate Repository
• Certificate Archive

123
Certification Authority (CA) The CA acts like a
trusted third-party which is made up of hardware,
software and the people operating it. It is in
charge of issuing, managing, authenticating,
signing and revoking of digital certificates.
Digital certificates are like evidence that shows
the binding between an entity and its public key.
Every CA is identified by its name and public
key. Therefore, certificates are signed by the CA
using its name and encrypted with its private key
to prove their authenticity. Verification of the
certificates is done by decrypting with the CAs
public key therefore, the CA must adequately
protect its private key. Registration Authority
(RA) Not everyone is entitled to possess a
digital certificate. The RA is set up to assist
the CA in verifying an entitys identity and
determines if it is eligible to have a public key
certificate issued.
124
Certificate Repository This is a database that
stores all the active digital certificates
managed by the CA. The repository is publicly
readable, but the CA is the only authorized
entity that can modify or update it. The
certificate repository also consists of a
Certificate Revocation List (CRL) which is
issued, time-stamped and signed by the CA. A CRL
contains unique information about revoked
certificates to enable relying entities to
determine a particular certificates
validity. Certificate Archive It contains old
certificates that were issued by the CA and valid
at that point in time. Therefore, if there are
any verification disputes on signatures of old
documents, archived certificates can be retrieved
to prove the authenticity of these documents.
125
Authentication using Public Key Infrastructure
(PKI) In order for authentication to take
place, there must be some sort of cryptography
system to be put in place. PKI supports the
authentication of users and systems by making use
of public key cryptography, which is the
cryptography system that PKI is based on.
126
Implementation of PKI
127
Cross Certification of PKIs
128
Digital Signature for Message-by-Message
Authentication
To Create the Digital Signature 1. Hash the
plaintext to create a brief message digest this
is NOT the Digital Signature. 2. Sign (encrypt)
the message digest with the senders private key
to create the digital signature. 3. Transmit the
plaintext digital signature, encrypted
with symmetric key encryption.
Plaintext
Hash
MD
Sign (Encrypt) with Senders Private Key
DS
129
Digital Signature for Message-by-Message
Authentication
4. Encrypted with Session Key
Sender
Receiver
130
Digital Signature for Message-by-Message
Authentication
To Test the Digital Signature 5. Hash the
received plaintext with the same hashing
algorithm the sender used. This gives the message
digest. 6. Decrypt the digital signature with
the senders public key. This also should give
the message digest. 7. If the two match,
the message is authenticated.
5.
6.
Received Plaintext
DS
Decrypt with True Partys Public Key
Hash
MD
MD
7. Are they equal?
131
Public Key Deception
Impostor I am the True Person. Here is TPs
public key. (Sends Impostors public key) Here
is authentication based on TPs private
key. (Really Impostors private key) Decryption
of message from Verifier encrypted with
Imposters public key, so Impostor can decrypt it
Verifier Must authenticate True
Person. Believes now has TPs public
key Believes True Person is authenticated based
on Impostors public key True Person, here is a
message encrypted with your public key.
Critical Deception
132
Important X.509 Digital Certificate Fields
Field
Description
Version Number
Version number of the X.509. Most certificates
follow Version 3. Different versions have
different fields. This figure reflects the
Version 3 standard.
Issuer
Name of the Certificate Authority (CA).
Serial Number
Unique serial number for the certificate, set by
the CA.
133
Important X.509 Digital Certificate Fields
Field
Description
Subject
The name of the person, organization, computer,
or program to which the certificate has been
issued. This is the true party.
Public Key
The public key of the subjectthe public key of
the true party.
Public Key Algorithm
The algorithm the subject uses to sign messages
with digital signatures.
134
Important X.509 Digital Certificate Fields
Field
Description
Valid Period
The period before which and after which the
certificate should not be used. Note Certificate
may be revoked before the end of this period.
Digital Signature
The digital signature of the certificate, signed
by the CA with the CAs own private
key. Provides authentication and certificate
integrity. User must know the CAs public key
independently.
135
Important X.509 Digital Certificate Fields
Field
Description
Signature Algorithm Identifier
The digital signature algorithm the CA uses to
sign its certificates.
136
Digital Signature and Digital Certificate in
Authentication
Digital Certificate
Digital Signature
Public Key of True Party
Signature to Be Tested with Public Key of True
Party
Authentication
137
Public Key Infrastructure (PKI) with a
Certificate Authority
Certificate Authority PKI Server
Verifier (Cheng)
6. Request Certificate Revocation List (CRL)
3. Request Certificate for Lee
7. Copy of CRL
5. Certificate for Lee
4. Certificate for Lee

• Create
• Distribute
• Private Key
• and
• (2) Digital Certificate

Applicant (Lee)
Verifier (Brown)
138
Public Key Infrastructure (PKI)

• Goals of PKI
• Authenticate the user/system at the sending end
  of a transaction
• Authenticate the user/system at the receiving end
  of a transaction
• Non-repudiation
• PKI components
• Certification Authority (CA)
• Registration Authority (RA)
• Certificate Repository
• Certificate Archive

139
Certification Authority (CA) The CA acts like a
trusted third-party which is made up of hardware,
software and the people operating it. It is in
charge of issuing, managing, authenticating,
signing and revoking of digital certificates.
Digital certificates are like evidence that shows
the binding between an entity and its public key.
Every CA is identified by its name and public
key. Therefore, certificates are signed by the CA
using its name and encrypted with its private key
to prove their authenticity. Verification of the
certificates is done by decrypting with the CAs
public key therefore, the CA must adequately
protect its private key. Registration Authority
(RA) Not everyone is entitled to possess a
digital certificate. The RA is set up to assist
the CA in verifying an entitys identity and
determines if it is eligible to have a public key
certificate issued.
140
Certificate Repository This is a database that
stores all the active digital certificates
managed by the CA. The repository is publicly
readable, but the CA is the only authorized
entity that can modify or update it. The
certificate repository also consists of a
Certificate Revocation List (CRL) which is
issued, time-stamped and signed by the CA. A CRL
contains unique information about revoked
certificates to enable relying entities to
determine a particular certificates
validity. Certificate Archive It contains old
certificates that were issued by the CA and valid
at that point in time. Therefore, if there are
any verification disputes on signatures of old
documents, archived certificates can be retrieved
to prove the authenticity of these documents.
141
Authentication using Public Key Infrastructure
(PKI) In order for authentication to take
place, there must be some sort of cryptography
system to be put in place. PKI supports the
authentication of users and systems by making use
of public key cryptography, which is the
cryptography system that PKI is based on.
142
Implementation of PKI
143
Cross Certification of PKIs
144
UNIT 4
Content

• Access and Authentication Technology

• Authentication methods PPP, PAP, CHAP, EAP

• AAA, RADIUS, TACACS, TACACS, Kerberos

• Authentication Header (AH)

• Encapsulating Security Payload (ESP)

• Virtual Private Networks (VPN) VPN Architectures

• Authentication On Wireless LANs

145
VPN

• VPN is used to provide secure network links
  across networks
• VPN is constructed on top of existing network
  media and protocols
• On protocol level IPsec is the first choice
• Other protocols are PPTP, L2TP

146
VPN
147
VPN? Whats that?
A VPN is a service that simulates a PRIVATE link
over a PUBLIC network (usually a SP).
Ideally
Private Line (leased)
148
VPN? Whats that?
149
Access VPN Client Initiated
Internet
Encrypted IP
CorporateNetwork

• Encrypted tunnel from the remote clientto the
  corporate network
• Independent of broadband access technology
• Standards compliant
• IPSec encapsulated tunnel
• IKE key management

150
VPN Types Intranet VPN
Remote Office
Main Office
POP
Internet/ IP VPNs
POP
Remote Office
POP
Service Provider

• Extends the connectionlessIP model across a
  shared WAN
• Reduces application development time
• Reduces support costs
• Reduces line costs

151
VPN Types Extranet VPN
Remote Office
Business Partner
POP
Internet/ IP VPNs
POP
Remote Office
Main Office
POP
Service Provider
Supplier
Customer

• Extend connectivity to suppliers, customers, and
  business partners
• Over a shared infrastructure
• Using dedicated connections
• While ensuring proper level of authorized access

152
Requirements for a VPN
3.Data should not be altered (any
change should be detectable) (DATA INTEGRITY)
1.Identify and authenticate the other
party (AUTHENTICATION) 2.Un-authorized person
should not be able to intercept, record or
e