Convenience Store Employee Packet by ihz40241

VIEWS: 0 PAGES: 43

Convenience Store Employee Packet document sample

More Info
									Internet / Intranet

    Fall 2000



     Class 5
Web Server Security
 Intro Javascript
                         Class 5 Agenda
Discuss Milestone 1
Discuss Homepages
Discuss Log File Homework

Web Security
Presentations
Intro JavaScript
Lab Work:
  JavaScript
Next Week:
  More Javascript
       DHTML, DOM
  Forms
  Brandeis University Internet/Intranet Spring 2000   2
             Practical Internet Security
Analogous to “Real-Life” Security (e.g. a Bank)
Like Software, Security Must Be Well-Designed
Implementing Security Requires Trade-Offs
  Ease of Use is Affected
  Business Processes are Affected
  Business Culture is Affected
  Affects Both Users and Employees
  Security is Expensive
       Time, Effort, Lost Productivity
       Enforcement
Physical Security is Only Half the Story
  Implementation/Enforcement is Just as Important

  Brandeis University Internet/Intranet Spring 2000   3
                Security Design Issues
Know the Threats You are Protecting Against
  What are the Probabilities?
  What is the Cost if it Happens?
       Dollars
       Customer/Employee Confidence
Know Your Environment
  What are the Customer/User Requirements?
  What are the Budget Constraints?
  What is the Culture/Attitude of Those Affected?
  What is the Probability That Policies Will Be Followed
  Enforced?



  Brandeis University Internet/Intranet Spring 2000   4
                        Security Sermon
Security is Often Mis-Used in Technology Environments
   Provides Peace of Mind
       Not Necessarily Real Security
   Often Avoids the Real Issues
       Appeases Management
Common Security Mistakes (Analogies)
   Using an Expensive/High Security Safe
       But Leaving the Key/Combination Where it Can Be Stolen
       Leaving the Safe Unlocked
       Little Professional Enforcement/Review of Procedures
   Storing a Dime in a Safe
       Cost of Security Exceeds Risk of Stolen Dime
   High-Tech Solution Instead of Low-Tech Common Sense
       E.g. Convenience Store Having a Safe vs. Nightly Bank Deposits
   Security Has Consequences on Human Perceptions
       E.g. Installing a Metal Detector May Make Employees Feel Less
       Secure

  Brandeis University Internet/Intranet Spring 2000                     5
                            Security Tips
Thieves/Hackers Follow Easiest Path
  One That Gives Them Most Value
  One They Know About
The Environment is Key!
  A Mercedes in a Lot Full of Chevys is Likely to Be Stolen First
  The Same Mercedes in a Lot Full of Rolls Royces is Likely to Be Stolen
  Last
  Same Mercedes in an Unsecure Garage is Safer Because Fewer
  Thieves Know About It
Therefore:
  Know Other Likely Targets and Be Less Attractive
  Than They Are
  Make Your Site More Difficult to Hack Than its Worth
  Don’t Publicize What Doesn’t Need to Be Public

  Brandeis University Internet/Intranet Spring 2000                   6
                        Security Tips (2)
Does Not Guarantee No Hacking
  But Reduces the Probability Significantly
Most Security Problems Come From Human Error,
Not From Intentional Hacking
  Focus on Minimizing Chance of Human Error
Identify Each Risk Separately
  Solutions May Vary Widely
Security is Only as Good as Your Expertise
  Professional Security Requires Professional System
  Administrator

Use Common Sense / Be Realistic
  Brandeis University Internet/Intranet Spring 2000    7
                         Internet Risks
Destruction of Data
     Random
     Targeted
Modification of Data
     Random
     Targeted
     Worms/Viruses
Publication of Private/Sensitive Data
     Sensitve/Embarassing Information
     Confidential Information
         Competitive Information
         Customer Information
     Keys
         Information That Furthers Other Risks
              E.g. Credit Card Information, Museum Floor Plan
Network Disruption
Machine Crashes / Inoperable Serving Software

Brandeis University Internet/Intranet Spring 2000               8
                          Protecting Data
Machine Level
   Physical Isolation
        Physically Isolate Machines From Users
        Protect From Theft / Natural Disasters
   Users
        System Administration Permissions
        Remote Access
   Single-Purpose vs. Multi-Purpose Server
        Shared Hosting
        Test vs. Production
Application Level
   Server Configuration
   Server’s Ability to Access Files / System Resources
   Restrict Applications Running on Machine
        Don’t Load Applications/Protocols You Don’t Need

   Brandeis University Internet/Intranet Spring 2000       9
                     Protecting Data (2)
Script Level
   Who Can Modify Scripts?
        Remote Access
   Script’s Ability to Access Files / System Resources
   Scripts Identified by File Extension or Directory?
File Level
   Who Can Download Files?
   Who Can Upload Files?
   Exposed Directories
Communication Level
   IP Address Restrictions
   Password Requirements
   Encryption
Metaphysical Level
   Morals
   The Law
   Brandeis University Internet/Intranet Spring 2000     10
            Access Control Techniques
“Passive” Techniques
  Don’t Publish URL’s
  Always Have Default Pages – Avoid Directory
  Browsing
  Complex Page/Directory Names
Active Techniques
  Change Page/Directory Names Often
  Server Filters on IP Address, Domain Name
  Requiring a Name / Password
  Use Non-Standard Ports
Secure (Encrypted) Transmissions
Firewalls (Proxy Servers)
  Isolate LAN From General Internet

  Brandeis University Internet/Intranet Spring 2000   11
 All Techniques Have Some Negatives
Passive Techniques, Non-Standard Ports
   If User Guesses Correctly, They Have Full System Access
   Requires Publishers to Voluntarily Follow Standards
   Best for Non-Critical Security
        Security Breach Does Not Disable System
        Site Unlikely to Attract Hackers
IP Address / Domain Name Filters
   Requires Significant Effort to Administer
   Users Can’t Move Around Easily
   Serious Hackers Can Defeat via Spoofing
   Best For Local Intranet
        Site Unlikely to Attract Serious Hackers
Encryption
   Significant Overhead
Firewalls
   Limits Internet Access of Those Within the Firewall

   Brandeis University Internet/Intranet Spring 2000         12
            Name / Password Security
Requires All Parties to Maintain Secure Passwords
  Inconveniences Users
  Difficult to Enforce
  One Violation Can Compromise Entire Plan
Passed in Plain Text as Part of the URL
       Serious Hackers Can Intercept It
           Analogous to to credit card receipts in the trash
Web Servers Allow Unlimited Tries (Stateless)

Best Solution is a Combination of Techniques



  Brandeis University Internet/Intranet Spring 2000            13
                          Firewall Details
Proxy Server
   Gatekeeper Between a LAN and the Internet
   Acts as a Local DNS
   User Requests a URL
        Proxy Server Finds the Equivalent File on the LAN
Firewall
   Packet-Level-Filter
        Restrict Data at the Packet Level e.g. Don’t Allow FTP
   Circuit Filters
        Also Takes Into Account the Source and Destination of a Packet
        Maintains Some History Information
   Application-Level Filters
        Intercepts Transmissions and Analyzes Them to See if They Make
        Sense
             Requires Knowledge of the Application to be Effective

   Brandeis University Internet/Intranet Spring 2000                 14
                                Encryption
Basic Encryption – Privacy / Confidentiality
   “Scramble” a Document So Third Party Can’t Read It
        What Level of Scrambling is Required?
           Not Easily Reable By Human Eye
                Simple Replacement Algorithm
                Base64
           Extremely Difficult, But Possible to Crack
                E.g. passwords, “zip” encryption
           “Impossible” to Crack
Authentication (Signature)
   Can Be Assured That Document is From Recipient
   Can Be Assured That Document Was Not Tampered With
Non-Repudiation (Contract)
   Can Also Be Assured That Document Was Received Intact
   Neither Can Tamper With Document
Data Integrity
   Assurance That Document Was Not Corrupted
   Brandeis University Internet/Intranet Spring 2000       15
              Encryption Technologies
Symmetric Key Encryption
  Same Key Used For Encrypting / Decrypting
  Both Parties Use Same Key
  Analogy: Standard Door
Asymmetric Key Encryption (Public Key)
  Each Party Has a Different Private Key
  Third Key (Public Key) Required for
  Encryption/Decryption
       Key Held By Trusted Third-Party
  Analogy: Safe Deposit Box
Message Digest Algorithms
  Encrypted “Hash” Functions Used For Digital
  Signatures

  Brandeis University Internet/Intranet Spring 2000   16
    Methods of Defeating Encryption
Brute Force
  Trying All Possibilities
“Psychic” (For Human Generated Keys Only)
  Person Has to Be Able to Memorize Key
       Brute Force: Prioritized by Easily Memorized Keys
Cipher Attack
  View The Encrypted Data and Work Back
       Analogy: Cryptogram Puzzles
Cryptanalysis
  Science of Breaking Algorithms
       Exploit Mathematical Weaknesses in the Algorithm



  Brandeis University Internet/Intranet Spring 2000        17
                How Encryption Works
Develop a mathematical function such that:
       f (a,b) = c
       f’ (a,c) = b
       BUT f’’(b,c) = a Does Not Exist
Symmetric
   f( message,key) = encrypted_message
   f’ (encrypted_message, key) = message
Asymmetric
   f (my_message, your_public_key) = encrypted_message
   f’ (encrypted message, your_private_key) = my_message

Signature
   f (signature, my_private_key) =encrypted_signature
   f’ (signature, my_public_key) = signature


  Brandeis University Internet/Intranet Spring 2000        18
          Internet Encryption Protocols
Public Key Encryption Requires Trusted Third Party
   Certificate Authority
RSA – Rivest, Shamir, Adelman
   MIT Professors – Invented Algorithms
   Some are Patented
Size of Key is Important
   Longer Keys are Harder to Break
   Government Limits to Size of Keys
        Controls on Exports
PGP – Pretty Good Privacy
   Freeware Encryption
DES
   56-bit Symmetric Key
   Triple DES
   RC2, RC4 – Uses Shorter Keys – Can Be Used For Export


   Brandeis University Internet/Intranet Spring 2000       19
      Internet Encryption Protocols (2)
SET
  Protocol For Passing Credit Card Information
       Uses DES for Data, RSA for Keys and Credit Card Number
       Includes Protocols for Authorization and Validation of Credit Card
Encrypted HTTP
  S-HTTP (Secure HTTP) Commercenet
  SSL – (Secure Sockets Layer) Netscape
PPP
  TCP/IP Itself Cannot Be Encrypted
  Login Passwords Are in Clear
       PAP – (Password Authentication Protocol) Passwords Sent in Clear
       CHAP (Challenge Handshake Authentication Protocol)
           Password Used to Create a Response That is Passed to Server
Key Management
  Keys Must Be Kept Private or Security is Lost
       Keys are Too Long For Memorization
  Kerberos (MIT), (ISAKMP – Internet Security Association)
  Brandeis University Internet/Intranet Spring 2000                    20
                       IP Level Security
Virtual Private Networks (VPNs)
   Tunneling (Encapsulation)
       Encrypts Data at a Point Low in the ISO Stack
           Encapsulates it in Another Protocol
PPTP – Point-To-Point Tunneling Protocol
   Works Over Public Networks
       Only Client and Server Need to Be PPTP Aware
       IP Information is encrypted and carried within another IP packet
L2F – Layer 2 Forwarding
   Requires All Routers/Servers Between Client and Server to
   Support L2F
L2TP – Combination of PPTP and L2F
TACACS, RADIUS
   For Dial-Up Access


  Brandeis University Internet/Intranet Spring 2000                   21
               Non-Encrypted Security
Change Passwords Regularly
  Security Breaches are “Temporary”
       Increases Effort Necessary to Break In
       Analogy: Changing Locks
DHCP – IP Addresses are Temporary
  Similar to Changing Passwords at IP Level
  IP Addresses Dynamically Assigned
Private Network
  Traffic Between Customers of ISP Does Not Pass
  Through “Public” Internet
       ISP Keeps Routers Secure
       AT&T Strategy


  Brandeis University Internet/Intranet Spring 2000   22
                     Security Key Points
Use Common Sense Above All
Security is Useless if it is Not Enforceable
  Once Adopted Must Be Policed / Tested / Enforced
  Policing Software is Important
       Automate Mundane Tasks
Security Policies Will Usually Impact Productivity
  Use Them Wisely
Two Major Aspects to Security:
  Keys and Key Maintenance (e.g. Passwords)
  Encryption



  Brandeis University Internet/Intranet Spring 2000   23
    The Need For Client Side Scripting
Performance
   Move More Processing to Client
        Especially Items Requiring Faster Response
            E.g. Field Validation
Usability
   Make HTML More “Windows-Like”
        HTML Extensions (e.g. Tab Order)
           CSS Extensions (e.g. style=“cursor:hand”)
        Dynamic Event Handling (e.g. onMouseOver)
Requires Scripting Language
   ECMA Script – (European Computer Manufactuers Association)
   Netscape – Created Own Version: JavaScript (No Relation to
   Java)
        Marketing Ploy: to Capitalize on Java Popularity
   Microsoft – VBScript
             Windows/IIS Only
        Also Support JavaScript – (Called it JScript)
   Brandeis University Internet/Intranet Spring 2000       24
                               JavaScript
De-Facto Standard Client-Side Scripting Language
   However, Other Scripting Languages are Supported by Servers.
   Add-Ons for Others.
Interpreted Language
Object-Oriented
“Full” Scripting Language
   Core JavaScript – Standalone Scripting Language
       No File I/O
   Client-Side JavaScript – For Use in HTML Pages
       Primary Use of JavaScript
   Server-Side JavaScript – Perl/Java Alternative
Similar to Other Languages
   C-Like Syntactic Structure
   Untyped
   Associative Arrays


  Brandeis University Internet/Intranet Spring 2000         25
                            JavaScript (2)
Usability
   Fairly Complex Language
   Web Orientation
   Easiest to Look at and Modify Existing Code
   Full, Complex Language
        Many Ways to Achieve the Same Function
Versions
   1.0 – Base Version
        Netscape Navigator 2.0, IE 3.0
   1.1 – Improved Array Support, Other Features
        Netscape Navigator 3.0
   1.2 – (Current) Regular Expressions, Other Features
        Netscape Navigator 4.0
   ECMA-262 : Standardized Version of Javascript 1.2
        IE 4.0

   Brandeis University Internet/Intranet Spring 2000     26
                  Client-Side JavaScript
Core JavaScript Language
HTML Events
Document Object Model (DOM)
  Ability to Refer to the Elements of an HTML
  Document
Significant Differences Between Microsoft and
Netscape Implementations
  Especially in DOM Implementation

So, as With CSS, HTML, etc.
  Know Your Target Audience / Platform
       What Level of Support Will You Provide For Those Not
       Using Your Target Platform?


  Brandeis University Internet/Intranet Spring 2000           27
            Dynamic HTML - Scripting
All Properties Can Be Set by Scripts
New Dynamic Properties: Useful for Scripting
  DISABLED / ENABLED Attribute (Form Fields)
  Display Property
  Visibility Property
Pop-Up Boxes
Creation of New Windows
  New Instance of Browser




  Brandeis University Internet/Intranet Spring 2000   28
                       Invoking a Script
Script Code Within HTML
Buttons
   Button Selection Invokes a Script
Events
   Focus Events
       onfocus, onblur
   Mouse Events
       onmouseover, onmouseout
       onmousedown, onmouseup
       onclick, ondblclick, onselect
   Keyboard Events
       Onkeydown, onkeyup, onkeypress
   Scroll Event
       Onscroll
   Help Event
       onhelp – (F1 key, not Browser Help Button)
   Timer Events
  Brandeis University Internet/Intranet Spring 2000   29
               Document Object Model
Defines Hierarchy of Objects
  Each Has its Own Event Handlers
  Event Bubbling
       Which Event Handler Gets Events?
  Name Space Definitions
       Each Object in HTML Form Can Be Addressed
          E.g. Clicking Button Can Be Used to Change Text Value
          in a Specific Field of Another Window
A Caveat
  Javascript is Still a Scripting Language
       Not Great For Large, Complex Programs
            e.g. Limited Debugging
       As With Perl, Powerful Features Can Also Make Bugs
       Difficult to Detect / Prevent


  Brandeis University Internet/Intranet Spring 2000          30
      Stepping Back: Basic JavaScript
    <SCRIPT Language=“JavaScript”>
    <!--
    Document.write (“Hello World”);
    -->
    </SCRIPT>
Older Browsers Ignore Script Tag if They Don’t Support
Script
   However, They Will Try to Display Text Within Tags
   Therefore, Enclose All Script Within Tags as HTML Comments
       Script Processor Will Ignore HTML Comment Tags
            Use // For JavaScript Comments
   Newer Browsers Will Ignore All Within Tags if They Don’t
   Recognize the Language. JavaScript is the Default.
       <NOSCRIPT> </NOSCRIPT> Tags Can Then Be Used to Specify
       Alternative. All in Between Ignored By Browser.
       Note That Specific Version of Language Can Be Specified (e.g.
       Javascript1.2>


  Brandeis University Internet/Intranet Spring 2000                31
                       Javascript Basics
  Similar to C/Java
  Case Sensitive
       Case Conventions Not Always Obvious
       In Most Cases Don’t Get Error Message,
           Just Unexpected Result
  == vs. = in if statement (Like C)
       E.g. if (a == 2) {
       Vs. if (a = 2 ) {
  Lines end in ;
In Line JavaScript: Executed Where Encountered
  document.write (“<H1>Hello World</H1> \n”);
  document.writeln (“Hello World”);
NOTE: Output is Interpreted as HTML
Dynamic Page                     Example

  Brandeis University Internet/Intranet Spring 2000   32
                 Objects and Properties
Objects
   Objects are Collections of Named Data
        Often Called Properties or Fields
Properties
   Untyped
        Can be Data, Arrays, Functions, Other Objects
            If Property is a Function it is Called a Method
   Referenced by object.property
        e.g. document.myform.button
   Properties Can be Dynamically Assigned to Objects
        var point = new Object();
        point.x = 7;
        point.y = 3;
Associative Arrays
   Properties Can Be Accessed via Associative Arrays
        E.g. point[“x”]
             document.myform[“button”]
   Brandeis University Internet/Intranet Spring 2000          33
                        Creating Objects
Variables Can Be Used Without Declaration
   e.g. myname=“evan”
However it is Preferable to Declare Them First
   var i, j, k;
   Can Be Initialized on Declaration:
       var i=0, j=0, k=0;
Objects and Arrays Must First Be Created
   var book = new Object();
   Then Can Assign Properties Without Declaration
       book.chapter1 = “How To”;
       Book.chapter1.length = “20 pages”;
All Objects / Variables Have Default Methods/Properties
   E.g.
       st=“abcdefg”;
       stlen = st.length;

  Brandeis University Internet/Intranet Spring 2000       34
                                  Scoping
Objects Declared Outside of a Function are Global
Objects Declared With var Statement in a Function
are Local
  Objects Not Declared are Treated as Globals
  This is the Reason All Variable Should be Declared
Local – Only Defined Within the Local Function
Global – Defined Within All
NOTE: A Local Variable Can Have Same Name as
Global
  The Local Variable Takes Precedence



  Brandeis University Internet/Intranet Spring 2000    35
                                    Arrays
Some Useful Array Functions
   array.concat (array1, array2, …)
       Concatenates Arrays
   array.join (separator)
       Returns a String of All Elements of Array Separated by Separator
   array.length – Returns the Number of Elements in the Array
   array.pop – Remove and Return the Last Element of an Array
   array.push – Append an Element to an Array
   array.reverse – Reverses the Elements of An Array
   array.shift – Removes and Returns the First Element of An
   Array
   array.unshift – Insert an Element at the Beginning of an Array
   array.slice (start,end) – Return a Portion of the Array.
   array.sort – Sorts an Array
   array.splice – Inserts or Deletes Elements of an Array

  Brandeis University Internet/Intranet Spring 2000                  36
                            Miscellaneous
Concatenate Strings Using +
Variables are Untyped
   Automatically Converted
   May Cause Unexpected Results
       e.g. v1 = 1 + 2 + “ classes”
         v1 contains “3 classes”
       But: v1 = “I took “ + 1 +2+ “classes”
         v1 contains “I took 12 classes”
Arrays Identified With Brackets
   E.g. point[0]
         Not { as with Perl
null
   Special Value
         Different Than 0
this
   Identifies Current Object

   Brandeis University Internet/Intranet Spring 2000   37
                                Functions
Use return Statement to Return a Value from a
Function
       E.g. return (3);
arguments is a Special Object Available in a
Function
  arguments[] Holds the Argument Values Passed In
  Arguments.length – The Number of Arguments
  Passed




  Brandeis University Internet/Intranet Spring 2000   38
                        More JavaScript
Comments are // or /* */
Strings concatenated with +
Functions Should be Declared Before Being Used
  Typically Defined in <HEAD> Section
alert – Creates a Pop-Up Message Box
prompt – Prompts User for Input
Buttons - <Input Type = “Button” Value=“Click
Here” onclick = “functionname()”
window.open – Opens a New Instance of Browser

                              Example


  Brandeis University Internet/Intranet Spring 2000   39
                         More Examples
  Events                                              Example
       onLoad
       onUnload
Environment Information                               Example
  HTTP Header Information
  Cookies




  Brandeis University Internet/Intranet Spring 2000             40
                         In-Class Exercise
  Create a JavaScript version of your test page
  <SCRIPT LANGUAGE = “JavaScript”>
  myname = “Evan”;
  Document.writeln(“<H1>Welcome to “ + myname
  + “’s Homepage”</H1>”)
</SCRIPT>

  Add a BUTTON to your Homepage to show this
  page in a new Browser Window
  Advanced: Choose the Name at Random. Set this
  in a function.

    Brandeis University Internet/Intranet Spring 2000   41
                     FOR NEXT CLASS




Brandeis University Internet/Intranet Spring 2000   42
            HTML Extensions for Forms
“Tool Tips”
   TITLE Attribute on Form Tags
Label Associated With Form Entry
   User Can Click On Label to Select Entry Field
        <LABEL FOR=“TextID”>Enter Name: </LABEL>
        <INPUT TYPE=“Text” ID=“TextID” Name=“Tname”>
Shortcuts
   Alt-Character selects Entry Field
   ACCESSKEY=“X”
Tab Order
   TABINDEX=3
   Negative Number Excludes Field From Tab Order
FieldSet
   Groups Controls Together (Outline Box)
   <Legend> Adds Text To Outline Box
                                                       Example

   Brandeis University Internet/Intranet Spring 2000             43

								
To top