Transcript Computer Security: Principles and Practice, 1/e

Computer Security:
Principles and Practice
Chapter 21 – Internet Security
Protocols and Standards
First Edition
by William Stallings and Lawrie Brown
Lecture slides by Lawrie Brown
Objectives
The student should be able to
 Define VPN, intranet VPN, extranet VPN, tunnel.
 Describe the advantages of link versus end-to-end encryption.
 Define the protection provided by SSL, TLS, IPsec.
 Show where the following protocols exist in the protocol stack, and describe
which applications they can be used with: SSL, TLS, IPSec, S-MIME.
 Show a diagram of what happens to a packet during Tunnel versus
Transport mode concerning the packet format.
 Describe the difference between IPSec’s Authentication Header and
.
Encapsulated Security Payload protocols
Internet Security Protocols
and Standards
 Secure
Sockets Layer (SSL) / Transport
Layer Security (TLS)
 IPv4 and IPv6 Security
 S/MIME (Secure/Multipurpose Internet
Mail Extension)
VPNs
Virtual Private Network (VPN): A means of carrying private traffic
over a public network
 Uses link encryption to give users sense that they are operating on a
private network when they are actually transmitting over a public
network
 Communications pass through an encrypted tunnel
Intranet VPN: Connects two or more private networks within the same
company
Extranet VPN: Connects two or more private networks between
different companies
 E.g., B2B or business-to-business communication.
Remote Access VPN: A roaming user has access to a private network
via wireless, hotel room, etc.
Encryption Types
Source
Destination
Router
End-to-End Encryption
Link Encryption
Importance of
Encryption Location: MAC
A P L I C
A P L I C
TCP
TCP
IP
IP
IP
LLC
MAC
LLC
MAC
LLC
MAC
LLC
MAC
Physical
Physical
Physical
Physical
Wireless
MAC
LLC IP
Wired
TCP
App - Data
CRC
Importance of
Encryption Location: IP
A P L I C
A P L I C
TCP
VPN Router/Firewall
may unencrypt
IPSEC/
IP
LLC
MAC
IPSEC/
IP
LLC
LLC
MAC
MAC
Physical
MAC
Physical
LLC IP
TCP
Physical
App - Data
TCP
IP
LLC
MAC
Physical
CRC
Importance of
Encryption Location: App.
HTTPS
HTTPS
HTTP
HTTP
A P L I C
A P L I C
TCP
TCP
IP
IP
IP
LLC
MAC
LLC
MAC
LLC
MAC
LLC
MAC
Physical
Physical
Physical
Physical
MAC
LLC IP
TCP
App - Data
CRC
Link versus End-to-End
Encryption
Use when LINK is vulnerable: Packet
sniffers & eavesdroppers
Use when Intermediate nodes may be
compromised
Link-Specific: All packets transmitted on
the single link are encrypted
Connection-Specific: A connection is
encrypted across all its links
Encrypted for all protocol layers (at or
above encryption layer)
Encrypted for upper layer protocols only
Intermediate nodes decrypt
Intermediate nodes cannot decrypt
Provides node authentication
Provides user authentication
Transparent to user: One key per link
Not user-transparent: One key per
connection
One algorithm for all users
User selects encryption algorithm
Encryption done in hardware
Encryption done in hardware or software
Virtual Private Network (VPN)
IP Security (IPsec)
Secure Shell (SSH)
Secure Socket Layer (SSL)
Encryption Protocols
HTTP
FTP
SMTP
TCP or UDP
HTTP
HTTP
SSL or TLS
TCP
IPSec
IP
IP
VPN
HTTPS
Secure Sockets Layer (SSL)

transport layer security service






originally developed by Netscape
version 3 designed with public input
subsequently became Internet
standard RFC2246: Transport
Layer Security (TLS)
use TCP to provide a reliable endto-end service
may be provided in underlying
protocol suite
or embedded in specific packages

SSL + HTTP used together = HTTPS
HTTP
SSL or TLS
TCP
IP
SSL Protocol Stack

Record: Fragmentation, compression, MAC, encryption
 Handshake: Setup: Negotiation of security
 Alert: Notifications of warnings or serious problems
 Change Cipher Spec: Change state to active
SSL Record Protocol
Services
 message


integrity
using a MAC with shared secret key
similar to HMAC but with different padding
 confidentiality



using symmetric encryption with a shared
secret key defined by Handshake Protocol
AES, IDEA, RC2-40, DES-40, DES, 3DES,
Fortezza, RC4-40, RC4-128
message is compressed before encryption
SSL Record Protocol
Operation
SSL Change Cipher Spec
Protocol
 one
of 3 SSL specific protocols which use
the SSL Record protocol
 a single message
 causes pending state to become current
 hence updating the cipher suite in use
SSL Alert Protocol

conveys SSL-related alerts to peer entity
 severity
• warning or fatal

specific alert
• fatal: unexpected message, bad record mac,
decompression failure, handshake failure, illegal
parameter
• warning: close notify, no certificate, bad certificate,
unsupported certificate, certificate revoked,
certificate expired, certificate unknown

compressed & encrypted like all SSL data
SSL Handshake Protocol
allows server & client to:




authenticate each other
to negotiate encryption & MAC algorithms
to negotiate cryptographic keys to be used
comprises a series of messages in phases

1.
2.
3.
4.
Establish Security Capabilities
Server Authentication and Key Exchange
Client Authentication and Key Exchange
Finish
SSL
Handshake
Protocol
First 3 phases:
Handshake Protocol
Phase 4: Change
Cipher Spec
Public Key Infrastructure
(PKI)
7. Tom confirms
Sue’s DS
5. Tom requests Sue’s DC 
6. CA sends Sue’s DC 
Tom
4. Sue sends
Tom message
signed with
Digital Signature
Digital
Certificate
User: Sue
Public Key:
2456
Certificate Authority
(CA)
3. Send approved
Digital Certificates
1. Sue registers with
CA through RA
Sue
Register(Owner, Public Key)
2. Registration Authority
(RA) verifies owners
IP Security
 various
application security mechanisms
exist

eg. S/MIME, PGP, Kerberos, SSL/HTTPS
 security
concerns cross protocol layers
 hence would like security implemented by
the network for all applications
 authentication & encryption security
features included in next-generation IPv6
 also usable in existing IPv4
IPSec
 general
IP Security mechanisms
 provides



authentication
confidentiality
key management
 applicable
to use over LANs, across public
& private WANs, & for the Internet
IPSec Uses
Tunnel vs. Transport Mode
Encrypted:
Transport Mode: End-to-End Encryption
Host D
Host A
IP=D | ESP | Data
Internet
Gtwy
B
Gtwy
C
IP=D | ESP | Data
IP=D | ESP | Data
Host D
Host A
IP=D | Data
Internet
Gtwy
B
Gtwy
C
IP=D | Data
IP=C | ESP | IP=D | Data
Tunnel Mode: Encryption between two gateways: Virtual Private Network
(A form of link encryption)
Benefits of IPSec
 in
a firewall/router provides strong security
to all traffic crossing the perimeter
 in a firewall/router is resistant to bypass
 is below transport layer, hence transparent
to applications
 can be transparent to end users
 can provide security for individual users
 secures routing architecture
IP Security Architecture
 mandatory
in IPv6, optional in IPv4
 have two security header extensions:



Authentication Header (AH)
Encapsulating Security Payload (ESP)
Key Exchange function
 VPNs

want both authentication/encryption
hence usually use ESP
 specification

is quite complex
numerous RFC’s 2401/2402/2406/2408
Two Modes
(From Network Security Essentials 2nd Ed., W. Stallings, Prentice Hall)
Authentication
Header
(AH)
Encapsulated Security
Payload
(ESP encryption &
authentication)
Access control
X
X
Connectionless integrity
X
X (AH opt.)
Data Origin
Authentication
X
X (AH opt.)
Rejection of Replayed
Packets
X
X
Confidentiality
X
Limited Traffic Flow
Confidentiality
X
Security Associations
a
one-way relationship between sender &
receiver that affords security for traffic flow
 defined by 3 parameters:



Security Parameters Index (SPI): SA
IP Destination Address: Unicast
Security Protocol Identifier: AH or EH
 has

a number of other parameters
seq no, AH & EH info, lifetime etc
 have

a database of Security Associations
Holds data for each SA
Authentication Header (AH)
 provides
support for data integrity &
authentication of IP packets


end system/router can authenticate user/app
prevents address spoofing attacks by tracking
sequence numbers
 based

on use of a MAC
HMAC-MD5-96 or HMAC-SHA-1-96
 parties
must share a secret key
Authentication Header
SPI = Security Association #
Authentication Data = Message Authentication Code
Encapsulating Security
Payload (ESP)
Key Management
 handles
key generation & distribution
 typically need 2 pairs of keys

2 per direction for AH & ESP
 manual

key management
sysadmin manually configures every system
 automated


key management
automated system for on demand creation of
keys for SA’s in large systems
has Oakley & ISAKMP elements
S/MIME (Secure/Multipurpose
Internet Mail Extensions)
 security




original Internet RFC822 email was text only
MIME provided support for varying content
types and multi-part messages
with encoding of binary data to textual form
S/MIME added security enhancements
 have

enhancement to MIME email
S/MIME support in many mail agents
eg MS Outlook, Mozilla, Mac Mail etc
S/MIME Process
S/MIME Cryptographic
Algorithms
 digital
signatures: DSS & RSA
 hash functions: SHA-1 & MD5
 session key encryption: ElGamal & RSA
 message encryption: AES, 3DES, etc
 MAC: HMAC with SHA-1
 must map binary values to printable ASCII

use radix-64 or base64 mapping
S/MIME Public Key Certificates
 S/MIME
has effective encryption and
signature services
 but also need to manage public-keys
 S/MIME uses X.509 v3 certificates
 each client has a list of trusted CA’s certs
 and own public/private key pairs & certs
 certificates must be signed by trusted CA’s
Summary
 Secure
Sockets Layer (SSL) / Transport
Layer Security (TLS)
 IPsec: IPv4 and IPv6 Security
 S/MIME (Secure/Multipurpose Internet
Mail Extension)