EMTM 553: E-commerce Systems
Lecture 7: Implementing Security
Insup Lee
Department of Computer and Information Science
University of Pennsylvania
lee@cis.upenn.edu
www.cis.upenn.edu/~lee
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Objectives
• Security measures that can reduce or eliminate
intellectual property theft
• Securing client computers from attack by viruses
and by ill-intentioned programs and scripts
downloaded in Web pages
• Authenticate users to servers and authenticate
servers
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Objectives
• Available protection mechanisms to secure information sent
between a client and a server
• Message integrity security, preventing another program
from altering information as it travels across the Internet
• Safeguards that are available so commerce servers can
authenticate users
• Protecting intranets with firewalls and corporate servers
against being attacked through the Internet
• The role Secure Socket Layer, Secure HTTP and secure
electronic transaction protocols play in protecting ecommerce
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Protecting Electronic
Commerce Assets
• You cannot hope to produce secure commerce
systems unless there is a written security policy
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What assets are to be protected
What is needed to protect those assets
Analysis of the likelihood of threats
Rules to be enforced to protect those assets
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Protecting Electronic
Commerce Assets
• Both defense and commercial security guidelines
state that you must protect assets from
– Unauthorized disclosure
– Modification
– Destruction
• Typical security policy concerning confidential
company information
– Do not reveal company confidential information to anyone
outside the company
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Minimum Requirements for
Secure Electronic Commerce
Figure 6-1
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Protecting
Intellectual Property
• The dilemma for digital property is how to display
and make available intellectual property on the
Web while protecting those copyrighted works
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Companies Providing Intellectual
Property Protection Software
• ARIS Technologies (part of verance.com)
– Digital audio watermarking systems
o Embedded code in audio file uniquely identifying the
intellectual property
• Digimarc Corporation
– Watermarking for various file formats
– Controls software and playback devices
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Companies Providing Intellectual
Property Protection Software
• SoftLock Services
– Allows authors and publishers to lock files containing
digital information for sale on the Web
– Posts files to the Web that must be unlocked with a
purchased ‘key’ before viewing
• Digitalgoods.com
– infrastructure and integrated services necessary to
securely market and distribute multimedia digital content
to its maximum audience
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Protecting Client Computers
• Active content, delivered over the Internet in
dynamic Web pages, can be one of the most
serious threats to client computers
• Threats can hide in
– Web pages
– Downloaded graphics and plug-ins
– E-mail attachments
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Protecting Client Computers
• Cookies
– Small pieces of text stored on your computer and contain
sensitive information that is not encrypted
– Anyone can read and interpret cookie data
– Do not harm client machines directly, but potentially
could still cause damage
• Misplaced trust
– Web sites that aren’t really what they seem and trick
the user into revealing sensitive data
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Monitoring Active Content
• Netscape Navigator and Microsoft Internet
Explorer browsers are equipped to allow the user
to monitor active content before allowing it to
download
• Digital certificates provide assurance to clients
and servers that the participant is authenticated
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Digital Certificates
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Also known as a digital ID
An attachment to an e-mail message
Embedded in a Web page
Serves as proof that the holder is the person or
company identified by the certificate
• Encoded so that others cannot read or duplicate it
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VeriSign -- A Certification Authority
Figure 6-3
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VeriSign
• Oldest and best-known Certification Authority
(CA)
• Offers several classes of certificates
– Class 1 (lowest level)
o Bind e-mail address and associated public keys
– Class 4 (highest level)
o Apply to servers and their organizations
o Offers assurance of an individual’s identity and
relationship to a specified organization
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Structure of a VeriSign Certificate
Figure 6-4
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Microsoft Internet Explorer
• Provides client-side protection right inside the
browser
• Reacts to ActiveX and Java-based content
• Authenticode verifies the identity of downloaded
content
• The user decides to ‘trust’ code from individual
companies
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Security Warning and Certificate Validation
Figure 6-5
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Internet Explorer Zones and Security Levels
Figure 6-6
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Internet Explorer Security Zone Default Settings
Figure 6-7
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Netscape Navigator
• User can decide to allow Navigator to download
active content
• User can view the signature attached to Java and
JavaSript
• Security is set in the Preferences dialog box
• Cookie options are also set in the Preferences
dialog box
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Setting Netscape Navigator Preferences
Figure 6-8
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A Typical Netscape Navigator
Java Security Alert
Figure 6-9
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Viewing a Content Provider’s Certificate
Figure 6-10
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Dealing with Cookies
• Can be set to expire within 10, 20, or 30 days
• Retrievable only by the site that created them
• Collect information so that the user doesn’t have
to continually enter usernames and passwords to
access Web sites
• Earlier browsers simply stored cookies without
comment
• Today’s browsers allow the user to
– Store cookies without permission or warning
– Receive a warning that a cookie is about to be stored
– Unconditionally disallow cookies altogether
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Protecting Electronic Commerce
Channels
• Protecting assets while they are in transit
between client computers and remote servers
• Providing channel security includes
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Channel secrecy
Guaranteeing message integrity
Ensuring channel availability
Authentication
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Providing Transaction Privacy
• Encryption
– The coding of information by using a mathematically
based program and secret key to produce unintelligible
characters
– Steganography
o Makes text invisible to the naked eye
– Cryptography
o Converts text to strings that appear to have no
meaning
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Encryption
• 40-bit keys are considered minimal,128-bit keys
provide much more secure encryption
• Encryption can be subdivided into three functions
– Hash Coding
o Calculates a number from any length string
– Asymmetric (Public-key) Encryption
o Encodes by using two mathematically related keys
– Symmetric (Private-key) Encryption
o Encodes by using one key, both sender and receiver
must know
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Hash Coding, Private-key, and Public-key Encryption
Figure 6-11
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Significant Encryption Algorithms and Standards
Figure 6-12
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Secure Sockets
Layer (SSL) Protocol
• Secures connections between two computers
• Provides a security handshake in which the client
and server computers exchange the level of
security to be used, certificates, among other
things
• Secures many different types of communications
between computers
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Secure Sockets
Layer (SSL) Protocol
• Provides either 40-bit or 128-bit encryption
• Session keys are used to create the cipher text
from plain text during the session
• The longer the key, the more resistant to attack
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SSL Handshake
The SSL handshake consists of nine steps that authenticate
the two parties and create aEMTM
shared
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SSL Web Server Information
Figure 6-14
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Secure HTTP (S-HTTP) Protocol
• Developed by CommerceNet Consortium
• Extension to HTTP that provides numerous security
features
– Client and server authentication
– Spontaneous encryption
– Request/response nonrepudiation
• Provides symmetric and public-key encryption, and message
digests (summaries of messages as integers)
• Whereas SSL is designed to establish a secure connection
between two computers, S-HTTP is designed to send
individual messages securely.
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Ensuring Transaction Integrity
Figure 6-15
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Guaranteeing
Transaction Delivery
• Neither encryption nor digital signatures protect
packets from theft or slowdown
• Transmission Control Protocol (TCP) is responsible
for end-to-end control of packets
• TCP requests that the client computer resend
data when packets appear to be missing
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Protecting the
Commerce Server
• Access control and authentication
– Controlling who and what has access to the server
– Requests that the client send a certificate as part of
authentication
– Server checks the timestamp on the certificate to
ensure that it hasn’t expired
– Can use a callback system in which the client computer
address and name are checked against a list
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Protecting the
Commerce Server
• Usernames and passwords are the most common
method of providing protection for the server
• Usernames are stored in clear text, while
passwords are encrypted
• The password entered by the user is encrypted
and compared to the one on file
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Logging On With A Username And Password
Figure 6-16
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Operating System Controls
• Most operating systems employ username and
password authentication
• A common defense is a firewall
– All traffic from inside to outside and outside to inside
must pass through it
– Only authorized traffic is allowed
– The firewall itself must be immune to penetration
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Firewalls
• Should be stripped of any unnecessary software
• Categories of firewalls include
– Packet filters
o Examine all packets flowing through the firewall
– Gateway servers
o Filter traffic based on the requested application
– Proxy servers
o Communicate on behalf of the private network
o Serve as a huge cache for Web pages
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Traffic Cop
Firewalls
Internet
Site 1
Site 2
OSI
Application
Presentation
Session
Transport
Network
Data Link
Physical
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Check Point Software’s Firewall-1 Web Page
Figure 6-17
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