web technology and commerce unit-5 by arun pratap singh

8/12/2019 Web Technology and Commerce Unit-5 by Arun Pratap Singh

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UNIT : V

PREPARED BY ARUN PRATAP SINGH

WEB TECHNOLOGY AND COMMERCE (MCSE 201)


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PREPARED BY ARUN PRATAP SINGH 1

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ADVANCED TECHNOLOGIES FOR E-COMMERCE:

INTRODUCTION TO MOBILE AGENTS:

UNIT : V


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Mobile agents are defined as active objects (or clusters of objects) that have

behavior, state and location.

Mobility: Agentsthat can travel in network

Autonomy: Agent itself decides when and where to migrate next

A Mobile Agent, namely, is a type of software agent, with the feature of autonomy, social

ability, learning, and most significantly, mobility.

More specifically, a mobile agentis aprocess that can transport its state from one environment

to another, with its data intact, and be capable of performing appropriately in the new environment.

Mobile agents decide when and where to move. Movement is often evolved from RPC methods.

Just as a user directs an Internet browser to "visit" a website (the browser merely downloads a

copy of the site or one version of it in the case of dynamic web sites), similarly, a mobile agent

accomplishes a move through data duplication. When a mobile agent decides to move, itsaves

its own state,transports this saved state to the new host, and resumes execution from the saved

state.

A mobile agent is a specific form ofmobile code,within the field ofcode mobility.However, in

contrast to theRemote evaluation andCode on demand programming paradigms, mobile agents

are active in that they can choose to migrate between computers at any time during their

execution. This makes them a powerful tool for implementing distributed applications in

acomputer network.
http://en.wikipedia.org/wiki/Software_agenthttp://en.wikipedia.org/wiki/Process_(computing)http://en.wikipedia.org/wiki/Remote_procedure_callhttp://en.wikipedia.org/wiki/Serializationhttp://en.wikipedia.org/wiki/Serializationhttp://en.wikipedia.org/wiki/Mobile_codehttp://en.wikipedia.org/wiki/Code_mobilityhttp://en.wikipedia.org/wiki/Remote_evaluationhttp://en.wikipedia.org/wiki/Code_on_demandhttp://en.wikipedia.org/wiki/Distributed_systemhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Distributed_systemhttp://en.wikipedia.org/wiki/Code_on_demandhttp://en.wikipedia.org/wiki/Remote_evaluationhttp://en.wikipedia.org/wiki/Code_mobilityhttp://en.wikipedia.org/wiki/Mobile_codehttp://en.wikipedia.org/wiki/Serializationhttp://en.wikipedia.org/wiki/Serializationhttp://en.wikipedia.org/wiki/Remote_procedure_callhttp://en.wikipedia.org/wiki/Process_(computing)http://en.wikipedia.org/wiki/Software_agent


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An open multi-agent systems (MAS) is a system in which agents, that are owned by a variety of

stakeholders, continuously enter and leave the system.


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Comparison of 3 Network computing paradigm

A mobile agent contains the following 3 components:

Code- the program (in a suitable language) that defines the agent's behavior.

State- the agent's internal variables etc., which enable it to resume its activities

after moving to another host.

Attributes - information describing the agent, its origin and owner, its movement

history, resource requirements, authentication keys etc. Part of this may be

accessible to the agent itself, but the agent must not be able to modify the attributes

MA System Arichitecture :

The main components include

mobile agents (defined before)

places

supports the execution of particular procedures and provides access to

local resources.

agent systems

Places inside an agent system may share resources, code, or security

mechanisms and, in general, have a privileged relationship with each other

and less expensive mobility.


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Mobility Support,

Unique Identification of Agents Support,

Transaction Support, and

Communication Support.


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Mobile Agent vs. Remote Procedure Call(RPC) :

RPC:

using Synchronous protocol-High Efficiency and low latency

Scaling -- Multiple servers

Mobile Agent:

Messaging(Asynchronous) :Robustness, especially in wide area network

Every node is a server

Application Areas for Mobile Agents :

Data collection from many places

Searching and filtering

Monitoring

Negotiating

Bartering

Parallel processing

Entertainment

Targeted information dissemination


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WIRELESS APPLICATION PROTOCOL (WAP) :

Wireless Application Protocol(WAP) is atechnical standard for accessing information over a

mobile wireless network.A WAP browser is aweb browser formobile devices such asmobile

phones that uses the protocol.

Before the introduction of WAP, mobile service providers had limited opportunities to offer

interactive data services, but needed interactivity to supportInternet andWebapplications such

as:

Email by mobile phone

Tracking of stock-market prices

Sports results

News headlines

Music downloads

What is WAP?

WAP stands for Wireless Application Protocol

WAP is an application communication protocol

WAP is used to access services and information

WAP is inherited from Internet standards

WAP is for handheld devices such as mobile phones

WAP is a protocol designed for micro browsers

WAP enables the creating of web applications for mobile devices.

WAP uses the mark-up language WML (not HTML)

WML is defined as an XML 1.0 application

The Wireless Application Protocol

The WAP is the leading standard for information services on wireless terminals like digital

mobile phones.

The WAP standard is based on Internet standards (HTML, XML and TCP/IP).

History of WAP

WAP is published by the WAP Forum, founded in 1997 by Ericsson, Motorola, Nokia, and

Unwired Planet.

Forum members now represent over 90% of the global handset market, as well as leading

infrastructure providers, software developers and other organizations.
http://en.wikipedia.org/wiki/Technical_standardhttp://en.wikipedia.org/wiki/Wireless_networkhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Mobile_devicehttp://en.wikipedia.org/wiki/Mobile_phoneshttp://en.wikipedia.org/wiki/Mobile_phoneshttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/WWWhttp://en.wikipedia.org/wiki/Emailhttp://en.wikipedia.org/wiki/Emailhttp://en.wikipedia.org/wiki/WWWhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Mobile_phoneshttp://en.wikipedia.org/wiki/Mobile_phoneshttp://en.wikipedia.org/wiki/Mobile_devicehttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Wireless_networkhttp://en.wikipedia.org/wiki/Technical_standard


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WAP Architecture :

WAP Application Server :


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How WAP Model Works?

When it comes to actual use, WAP works like this:


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WAP I

protocol stack :


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WAP is designed in a layered fashion so that it can be extensible, flexible, and scalable.

As a result, the WAP protocol stack is divided into five layers.

Application Layer

Wireless Application Environment (WAE). This layer is of most interest to content

developers because it contains, among other things, device specifications and thecontent development programming languages, WML and WMLScript.

Session Layer

Wireless Session Protocol (WSP). Unlike HTTP, WSP has been designed by the WAP

Forum to provide fast connection suspension and reconnection.

WSP-The WAP session protocol (WSP) layer provides a lightweight session layer to

allow efficient exchange of data between applications.

Transaction Layer

Wireless Transaction Protocol (WTP). The WTP runs on top of a datagram service such

as User Datagram Protocol (UDP) and is part of the standard suite of TCP/IP protocols

used to provide a simplified protocol suitable for low bandwidth wireless stations.

WTP -- The WAP transaction protocol (WTP) layer provides transaction support, adding

reliability to the datagram service provided by WDP.

WDP-- The WAP datagram protocol (WDP) is the transport layer that sends and

receives messages via any available bearer network, including SMS, USSD, CSD,

CDPD and GPRS.

Security Layer

Wireless Transport Layer Security (WTLS). WTLS incorporates security features that are based

upon the established Transport Layer Security (TLS) protocol standard. It includes data integritychecks, privacy, service denial, and authentication services.

WTLS -- Wireless transport layer security (WTLS), an optional security layer, has

encryption facilities that provide the secure transport service required by many

applications, such as e-commerce.

Transport layer

Wireless Datagram Protocol (WDP). The WDP allows WAP to be bearer-independent by

adapting the transport layer of the underlying bearer. The WDP presents a consistent data

format to the higher layers of the WAP protocol stack, thereby offering the advantage of bearer

independence to application developers. Each of these layers provides a well-defined interface to the layer. This means that

the internal workings of any layer are transparent or invisible to the layers. The layered

architecture allows other applications and services to utilize the features provided by the

WAP-stack as well. This makes it possible to use the WAP-stack for services and

applications that currently are not specified by WAP.


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What is the purpose of WAP?

To enable easy, fast delivery of relevant information and services to mobile users.

It consists of a WML language specification, a WMLScript specification, and a

Wireless Telephony Application Interface(WTAI) specification.

WAP-Environment :

The Wireless Application Environment (WAE) provides an environment that enables a

wide range of applications to be used on wireless devices.

"WAP - The wireless service enabler" the WAP WAE programming model was

introduced.

Goals

device and network independent application environment

for low-bandwidth, wireless devices

considerations of slow links, limited memory, low computing power, small display,

simple user interface (compared to desktops)

integrated Internet/WWW programming model

high interoperability

WAE Components :

Architecture

Application model, Microbrowser, Gateway, Server

User Agents

WML/WTA/Others

content formats: vCard, vCalendar, Wireless Bitmap, WML, ...

WML

XML-Syntax, based on card stacks, variables, ...

WMLScript

procedural, loops, conditions, ... (similar to JavaScript)

WTA

telephone services, such as call control, text messages, phone book, ...

(accessible from WML/WMLScript)

Proxy (Method/Push)


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WAE: Logical Model :

WML: Wireless Markup Language :

Tag-based browsing language:

Screen management (text, images)

Data input (text, selection lists, etc.)

Hyperlinks & navigation support

Takes into account limited display, navigation capabilities of devices

XML-based language

describes only intent of interaction in an abstract manner

presentation depends upon device capabilities

Cards and Decks

document consists of many cards

User interactions are split into cards

Explicit navigation between cards

cards are grouped to decks

deck is similar to HTML page, unit of content transmission

Events, variables and state mgmt


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WML Script

WMLScript is based on ECMA Script, the same scripting language that

JavaScript is based on.

It can be used for enhancing services written in WML in the way that it to some

extent adds intelligence to the services, for example procedural logic, loops,

conditional expressions, and computational functions.

Wireless Telephony Application (WTA)

A framework and programming interface for telephony services.

The Wireless Telephony Application (WTA) environment provides a means to create

telephony services using WAP.

Collection of telephony specific extensions

designed primarily for network operators


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Example

calling a number (WML)

wtai://wp/mc;07216086415

calling a number (WMLScript)

WTAPublic.makeCall("07216086415");

Implementation

Extension of basic WAE application model

Extensions added to standard WML/WMLScript browser

Exposes additional API (WTAI)

WTA Logical Architecture

WAP - KEY BENEFITS :

Subscribers:

It is crucial that the subscribers will benefit from using WAP based services, otherwise

there will be no incentive neither for WAP as a whole nor for any of the other groups

mentioned below. The key-benefits can be summarised as:

Portability


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Use standard tools like ASP or CGI to generate content dynamically

Utilise existing investments in databases etc that are the basis of existing Internet

services

Manufacturers:

Mobile devices supporting WAP will be available in many different form factors, e.g.

cellular phones, pagers, and handheld PCs. Hardware manufacturers will also need to

supply operators etc with equipment, such as WAP Gateway/Proxys and WTA servers.

Manufacturer benefits are for example:

WAP scales across a broad range of mobile networks, meaning that WAP

implementations can be used in devices supporting different types of networks.

The expected wide adoption of WAP implies that economies of scales can be achieved,

meaning that the huge mass-market can be addressed

The fact that WAP is designed to consume minimal amount of memory, and that the use

of proxy technology relieves the CPU, means that inexpensive components can be used

in the handsets

Reuse the deep knowledge about wireless network infrastructure to develop advanced

servers that seamlessly integrates mobile VAS with telephony

Seize the opportunity to introduce new innovative products

Tools Providers:

Today there is a large amount of tools available for creating applications for the web.Content developers have become used to the convenience that tools like FrontPage and

DreamWeaver provides. Tools providers will be able to:

Reuse and modify existing products to support WAP, or even integrate WAP support in

existing tools.

Address a new customer base in the wireless community.

WAP Push Services :

Web push

Scheduled pull by client (browser)

example: Active Channels

no real-time alerting/response


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example: stock quotes

Wireless push

accomplished by using the network itself

example: SMS

limited to simple text, cannot be used as starting point for service

example: if SMS contains news, user cannot request specific news item

WAP push

Network supported push of WML content

example: Alerts or service indications

Pre-caching of data (channels/resources)

WAP Push Framework


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WEB SECURITY :

Many sensitive tasks are done through web

Online banking, online shopping

Database access

System administration

Web applications and web users are targets of many attacks

Cross site scripting

SQL injection

Cross site request forgery

Information leakage

Session hijacking

Web security is a tree branch of computer security specifically related to the Internet, often

involvingbrowser security but alsonetwork security on a more general level as it applies to otherapplications oroperating systems on a whole. Its objective is to establish rules and measures to

use against attacks over the Internet. The Internet represents an insecure channel for exchanging

information leading to a high risk ofintrusion or fraud, such asphishing.[2]Different methods have

been used to protect the transfer of data, includingencryption.

Web Security blocks web threats to reduce malware infections, decrease help desk

incidents and free up valuable IT resources.
http://en.wikipedia.org/wiki/Computer_securityhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Browser_securityhttp://en.wikipedia.org/wiki/Network_securityhttp://en.wikipedia.org/wiki/Operating_systemshttp://en.wikipedia.org/wiki/Hacker_(computer_security)http://en.wikipedia.org/wiki/Phishinghttp://en.wikipedia.org/wiki/Internet_security#cite_note-2http://en.wikipedia.org/wiki/Internet_security#cite_note-2http://en.wikipedia.org/wiki/Internet_security#cite_note-2http://en.wikipedia.org/wiki/Encryptionhttp://en.wikipedia.org/wiki/Encryptionhttp://en.wikipedia.org/wiki/Internet_security#cite_note-2http://en.wikipedia.org/wiki/Phishinghttp://en.wikipedia.org/wiki/Hacker_(computer_security)http://en.wikipedia.org/wiki/Operating_systemshttp://en.wikipedia.org/wiki/Network_securityhttp://en.wikipedia.org/wiki/Browser_securityhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Computer_security


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Web Security Issues :

Secure communications between client & server

HTTPS (HTTP over SSL)

User authentication & session management

Cookies & other methods

Active contents from different websites

Protecting resources maintained by browsers

Web application security

Web site authentication (e.g., anti-phishing)

Privacy concerns

HTTP: HyperText Transfer Protocol :

Browser sends HTTP requests to the server

Methods: GET, POST, HEAD,

GET: to retrieve a resource (html, image, script, css,)

POST: to submit a form (login, register, )

HEAD

Server replies with a HTTP response

Stateless request/response protocol

Each request is independent of previous requests

Statelessness has a significant impact on design and implementation of

applications

HTTP Authentication -

Protect web content from those who dont have a need to know

Require users to authenticate using a userid/password before they are allowed access to

certain URLs

HTTP/1.1 requires that when a user makes a request for a protected resource the server

responds with a authentication request header

WWW-Authenticate

contains enough pertinent information to carry out a challenge-response

session between the user and the server


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Secure Sockets Layer (SSL)

Invented by Netscape and made public domain for everyones use

An additional layer to the TCP/IP stack that sits between the Application and

Transport layers

ensures that all application data is encrypted but TCP/IP headers are not

usually run on port 443 (default HTTPS port)

Public Key Cryptography

owner of a private key sends a public key to all who want to communicate with

him (keys are both prime factors of a large (1024 bit) number). Owner keeps the

private key secret and uses it to decrypt information sent to him that has been

encrypted with the public-key

RSA algorithm is most notable public-key cipher algorithm

Digital Certificates

issued by a disinterested third party (ex. Verisign)

the Certificate contains the public-key for the specific Web Server and a digital

signature of the certifying authority

Cookies

A cookie is a name/value pair created by a website to store information on your

computer


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Cookies Fields

An example cookie

Name session-token

Content "s7yZiOvFm4YymG.

Domain .amazon.com

Path /

Send For Any type of connection

Expires Monday, September 08, 2031 7:19:41 PM

Stored by the browser

Used by the web applications

used for authenticating, tracking, and maintaining specific information about

users

e.g., site preferences, contents of shopping carts

data may be sensitive

may be used to gather information about specific users

Cookie ownership

Once a cookie is saved on your computer, only the website that created the

cookie can read it

Web Authentication via Cookies-

HTTP is stateless

How does the server recognize a user who has signed in?

Servers can use cookies to store state on client


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After client successfully authenticates, server computes an authenticator and

gives it to browser in a cookie

Client cannot forge authenticator on his own (session id)

With each request, browser presents the cookie

Server verifies the authenticator


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Security threats :

With the emergence of Web 2.0, increased information sharing through social networking and

increasing business adoption of theWeb as a means of doing business and delivering service,

websites are often attacked directly.Hackers either seek to compromise the corporate network

or the end-users accessing the website by subjecting them todrive-by downloading.

As a result, industry is paying increased attention to the security of the web

applications themselves in addition to the security of the underlying computer network and

operating systems.

The majority of web application attacks occur through cross-site scripting (XSS) and SQL

injection attackswhich typically result from flawed coding, and failure to sanitize input to and

output from the web application. These are ranked in the 2009 CWE/SANS Top 25 Most

Dangerous Programming Errors. According the security vendor Cenzic, the top vulnerabilities in

March 2012 include:

Cross Site Scripting,37%

SQL Injection,16%

Path Disclosure,5%

Denial of Service,5%

Code Execution,4%

Memory Corruption,4%

Cross Site Request Forgery,4%

Information Disclosure,3%

Arbitrary File,3%

Local File Include,2%

Remote File Include,1%

Buffer overflow,1%

Other (PHP Injection,Javascript Injection,etc.), 15%

Security technology

While security is fundamentally based on people and processes, there are a number of technical

solutions to consider when designing, building and testing secure web applications. At a high

level, these solutions include:

Black Box testing tools such as Web application security scanners, vulnerability

scanners andpenetration testing software

White Box testing tools such asstatic source code analyzers
http://en.wikipedia.org/wiki/Web_2.0http://en.wikipedia.org/wiki/Social_networkinghttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Hacker_(computer_security)http://en.wikipedia.org/wiki/Drive-by_downloadhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Cross-site_scriptinghttp://en.wikipedia.org/wiki/SQL_injectionhttp://en.wikipedia.org/wiki/SQL_injectionhttp://en.wikipedia.org/wiki/Mitre_Corporationhttp://en.wikipedia.org/wiki/SANS_Institutehttp://en.wikipedia.org/wiki/Cross_Site_Scriptinghttp://en.wikipedia.org/wiki/SQL_Injectionhttp://en.wikipedia.org/w/index.php?title=Path_Disclosure&action=edit&redlink=1http://en.wikipedia.org/wiki/Denial-of-service_attackhttp://en.wikipedia.org/wiki/Arbitrary_code_executionhttp://en.wikipedia.org/w/index.php?title=Memory_Corruption&action=edit&redlink=1http://en.wikipedia.org/wiki/Cross-site_request_forgeryhttp://en.wikipedia.org/wiki/Data_breachhttp://en.wikipedia.org/w/index.php?title=Arbitrary_File&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Local_File_Include&action=edit&redlink=1http://en.wikipedia.org/wiki/Remote_file_inclusionhttp://en.wikipedia.org/wiki/Buffer_overflowhttp://en.wikipedia.org/w/index.php?title=PHP_Injection&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Javascript_Injection&action=edit&redlink=1http://en.wikipedia.org/wiki/Application_security#Security_testing_for_applicationshttp://en.wikipedia.org/wiki/Web_application_security_scannerhttp://en.wikipedia.org/wiki/Vulnerability_scannerhttp://en.wikipedia.org/wiki/Vulnerability_scannerhttp://en.wikipedia.org/wiki/Penetration_testing#Web_application_penetration_testinghttp://en.wikipedia.org/wiki/Application_security#Security_testing_for_applicationshttp://en.wikipedia.org/wiki/Static_code_analysishttp://en.wikipedia.org/wiki/Static_code_analysishttp://en.wikipedia.org/wiki/Application_security#Security_testing_for_applicationshttp://en.wikipedia.org/wiki/Penetration_testing#Web_application_penetration_testinghttp://en.wikipedia.org/wiki/Vulnerability_scannerhttp://en.wikipedia.org/wiki/Vulnerability_scannerhttp://en.wikipedia.org/wiki/Web_application_security_scannerhttp://en.wikipedia.org/wiki/Application_security#Security_testing_for_applicationshttp://en.wikipedia.org/w/index.php?title=Javascript_Injection&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=PHP_Injection&action=edit&redlink=1http://en.wikipedia.org/wiki/Buffer_overflowhttp://en.wikipedia.org/wiki/Remote_file_inclusionhttp://en.wikipedia.org/w/index.php?title=Local_File_Include&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Arbitrary_File&action=edit&redlink=1http://en.wikipedia.org/wiki/Data_breachhttp://en.wikipedia.org/wiki/Cross-site_request_forgeryhttp://en.wikipedia.org/w/index.php?title=Memory_Corruption&action=edit&redlink=1http://en.wikipedia.org/wiki/Arbitrary_code_executionhttp://en.wikipedia.org/wiki/Denial-of-service_attackhttp://en.wikipedia.org/w/index.php?title=Path_Disclosure&action=edit&redlink=1http://en.wikipedia.org/wiki/SQL_Injectionhttp://en.wikipedia.org/wiki/Cross_Site_Scriptinghttp://en.wikipedia.org/wiki/SANS_Institutehttp://en.wikipedia.org/wiki/Mitre_Corporationhttp://en.wikipedia.org/wiki/SQL_injectionhttp://en.wikipedia.org/wiki/SQL_injectionhttp://en.wikipedia.org/wiki/Cross-site_scriptinghttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Drive-by_downloadhttp://en.wikipedia.org/wiki/Hacker_(computer_security)http://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Social_networkinghttp://en.wikipedia.org/wiki/Web_2.0


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Fuzzing Tools used for input testing

Web application firewalls (WAF) used to providefirewall-type protection at the web application

layer

Password cracking tools for testingpassword strength and implementation

ENCRYPTION SCHEMES :

The process of converting plain text into an unintelligible format (cipher text) is called Encryption.

Incryptography,encryptionis the process of encoding messages or information in such a way

that only authorized parties can read it. Encryption doesn't prevent hacking but it reduces the

likelihood that the hacker will be able to read the data that is encrypted. In an encryption scheme,

the message or information, referred to asplaintext,is encrypted using an encryption algorithm,

turning it into an unreadableciphertext.This is usually done with the use of anencryption key,

which specifies how the message is to be encoded. Any adversary that can see the ciphertext

should not be able to determine anything about the original message. An authorized party,

however, is able to decode the ciphertext using a decryption algorithm, that usually requires a

secret decryption key, that adversaries do not have access to. For technical reasons, an

encryption scheme usually needs a key-generation algorithm to randomly produce keys.
http://en.wikipedia.org/wiki/Fuzz_testinghttp://en.wikipedia.org/wiki/Web_application_firewallhttp://en.wikipedia.org/wiki/Firewall_(computing)http://en.wikipedia.org/wiki/Password_crackinghttp://en.wikipedia.org/wiki/Password_strengthhttp://en.wikipedia.org/wiki/Cryptographyhttp://en.wikipedia.org/wiki/Plaintexthttp://en.wikipedia.org/wiki/Ciphertexthttp://en.wikipedia.org/wiki/Key_(cryptography)http://en.wikipedia.org/wiki/Key_(cryptography)http://en.wikipedia.org/wiki/Ciphertexthttp://en.wikipedia.org/wiki/Plaintexthttp://en.wikipedia.org/wiki/Cryptographyhttp://en.wikipedia.org/wiki/Password_strengthhttp://en.wikipedia.org/wiki/Password_crackinghttp://en.wikipedia.org/wiki/Firewall_(computing)http://en.wikipedia.org/wiki/Web_application_firewallhttp://en.wikipedia.org/wiki/Fuzz_testing


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ENCRYPTION SCHEMES-

People use encryption to change readable text, called plaintext, into an unreadable secret format,

called cipher text. Encrypting data provides additional benefits besides protecting the

confidentiality of a message. These advantages include ensuring that messages have not been

altered during transit and verifying the identity of the sender. All of these benefits can be realized

by using any of these encryption methods.

Hashing Encryption

The first encryption method, called hashing, creates a unique, fixed-length signature for a

message or data set. Hashes are created with an algorithm, or hash function, and people

commonly use them to compare sets of data. Since a hash is unique to a specific message, even

minor changes to that message result in a dramatically different hash, thereby alerting a user to

potential tampering.

A key difference between hashing and the other two encryption methods is that once the data is

encrypted, the process cannot be reversed or deciphered. This means that even if a potential attackerwere able to obtain a hash, he or she would not be able to use a decryption method to discover the

contents of the original message. Some common hashing algorithms are Message Digest 5 (MD5)

and SecureHashing Algorithm (SHA).

Symmetric Methods

Symmetric cryptography, also called private-key cryptography, is one of the oldest and most

secure encryption methods. The term "private key" comes from the fact that the key used

toencrypt and decrypt data must remain secure because anyone with access to it can read the

coded messages. A sender encodes a message intociphertext using a key, and the receiver uses

the same key to decode it.People can use this encryption method as either a "stream"cipher or a "block" cipher, depending

on the amount of data being encrypted or decrypted at a time. A stream cipher encrypts data one

character at a time as it is sent or received, while ablock cipher processes fixed chunks of data.

Common symmetric encryption algorithms includeData Encryption Standard (DES), Advanced

Encryption Standard (AES), and International Data Encryption Algorithm (IDEA).

Asymmetric Forms

Asymmetric, or public key, cryptography is, potentially, more secure than symmetric methods of

encryption. This type of cryptography uses two keys, a "private" key and a "public key," to perform

encryption and decryption. The use of two keys overcomes a major weakness in symmetric keycryptography, since a single key does not need to be securely managed among multiple users.

In asymmetric cryptography, a public key is freely available to everyone and used to encrypt

messages before sending them. A different, private key remains with the receiver of ciphertext

messages, who uses it to decrypt them. Algorithms that use public key encryption methods

include RSA and Diffie-Hellman.
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Data encryption has become a sad necessity for responsible data managers. However

cryptography is jargon-heavy even by the discouraging standards of the IT world symmetric

and asymmetric cryptosystems, public versus private keys, digital signatures, hash algorithms,

RSA, DES, Rijndael, PGP, MD5, SHA-1, https, secure sockets, Camellia, IDEA; what does it all

mean? What are the differences? Relative advantages and disadvantages? Hopefully this

article will clear some of the fog.

Substitution ciphers

Although we tend to use the words code and cipher interchangeably, technically they're two

entirely different things. When you substitute each letter in a message for a different symbol

that's a cipher. A code on the other hand means assigning a secret meaning to a word or

phrase.

For example, if "The birds are flying south" means "Flee! The police are on to us!" that's a code.

But the simple schoolboy code, 1 = 'A', 2 = 'B' etc. (invented, legend has it, by Julius Caesar),

is a cipher, a substitution cipher in fact. So the ASCII code is actually a kind of cipher for

example.

Substitution ciphers were good enough for nearly two thousand years but they eventually failed

in the face of improving technology. The Enigma cipher used by the German military during

World War II is a substitution cipher and it was broken long before the days of computers, both

by the Poles and more famously the British. Dont, however, dismiss substitution ciphers. If you

just want to deter prying eyes a substitution cipher using multiple substitutions and several

different substitutions schemes offers a reasonable level of encryption for virtually no

computational effort. (This is the way Enigma works and after all, it did take Alan Turing to break

it).

Random substitution

There is a form of substitution cipher that does offer excellent security. By making randomsubstitutions, the patterns that make other substitution ciphers vulnerable are eliminated. The

simplest form of random substitution is to break a message into blocks of 4 bytes (4 ASCII

characters) and add a pseudo-random number to each block. To recover the plaintext (the input

message) subtract the same series of pseudo-random numbers from the ciphertext (the

encrypted message). The key is simply the seed value for the pseudo-random number

generator.

This form of encryption is widely used (the file encryption options offered by word processors

often use this method) as its simple, highly reliable and will defeat all but the most determined

and skillful attackers.

Symmetric cryptosystems: DES and AESIf, however, you need higher levels of security there are plenty of alternatives. Block ciphers

break the message into fixed-length blocks, then each block of plaintext is converted into a

block of ciphertext using a sequence of arithmetic operations and/or substitutions. The best

known of these is DES (the Data Encryption Standard), developed by the National Institute of

Standards and Technology in the US.

DES uses 64-bit blocks with a 64-bit key (although only 56 bits are significant; the other 8 are

parity bits). The bits within a block are shuffled and XORed with the key in a sequence of 16


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reversed to recover the original message? Nonetheless, thats exactly how it is. Given a pa ir of

keys, a message encrypted with one can only be decrypted with the other and vice-versa.

There are a number of asymmetric key systems but the best known and most widely used is

RSA, named for its (three) co-inventors. Originally patented, the patent expired in September

2000 and the algorithm is now in the public domain. The Secure Sockets Layer used for securecommunications on the Internet uses RSA (the https protocol is simply http over SSL).

Unfortunately, nothing in life is free, and so it is with asymmetric cryptosystems. Since d can be

computed from e given p and q, and p and q are the factors of N, they must be chosen so large

that N cannot be factorised in any reasonable time. As computer power has grown so too has

the ability to compute the factors of very large numbers. Current hardware means key lengths

should be 1024 bits for complete security.

Raising such very large numbers to very large exponents is computationally much more

demanding than the bit shifting and XOR'ing of symmetric cryptosystems such as DES, so

asymmetric encryption is really only practical for short messages. A common workaround when

encrypting long messages is to use RSA to encrypt a short preamble containing a DES or AES

key selected at random, then send the main body of the message encrypted with that key. A

recipient with the corresponding private key can decrypt the preamble and use the key it

contains to decipher the rest of the message. Modern web browsers use exactly this method to

conduct secure communications.

Digital signatures

An increasingly important use for asymmetric encryption is digital signing. A digital signature is

the reverse of public key encryption. Just like an ordinary signature it is used to prove the

identity of the sender of a message. This can happen in several ways. The simplest is to send a

random message as both plaintext and ciphertext. The recipient deciphers the ciphertextversion using the published public key and if the two versions match it proves the sender was in

possession of the private key.

One drawback of this form of signature is that it only verifies itself, not any message to which it

is attached. An alternative form uses a redundancy or hash function to create a message digest

from a message in order to verify the source and reliability of the message. Suppose A and B

(the Alice and Bob so beloved of cryptographers) want to exchange messages. A encrypts a

message using Bs public key and appends the hashed value of the message encrypted with

her own private key. On receiving the message B deciphers it using his private key, and also

deciphers the accompanying message digest using As public key. If it matches the hash value

he computes from the message he received, he can conclude that:

(a) The message originated from A (the only person who could have encrypted the digest

correctly) and

(b) The message has not been altered in transit.

The RSA algorithm has become the standard for digital signature applications and the company

founded by the co-inventors of RSA, RSA Data Security Inc, has developed (and published) a


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number of improvements on this basic scheme. Digital signatures on the Web are based on

RSA, as is the popular PGPPretty Good Privacypackage.

In detail :

SYMMETRIC KEY ENCRYPTION:

Symmetric-key cryptography is sometimes called secret-key cryptography. The most popular

symmetric-key system is the Data Encryption Standard (DES).

In the simpler types of cryptography, the same key is used to encrypt and decrypt information.

This key is sometimes called a symmetric key.

Everybody who is supposed to be able to read the information must have the key. The problem

with this sort of code is that the key has to be given to them over a secure line. If you're able to

give a key securely, why not send the whole message securely?

Thinking of the key as the key to a room may help explain this better. Everybody who should haveaccess to the room is given a copy of the key. Anybody who has that key can go in, put new

information in, take old information out, and lock the room again when they leave. Without the

key, you can't enter the room. Furthermore, if you send somebody a copy of the key by way of

the Post Office, somebody working at the Post Office could intercept this key, make a copy of it,

and then send it along. This would allow them to access this same locked room, and do the same

things with it. Now, think of sending the key over the Internet. That key could be intercepted by

anybody between you and the other machine, letting them read everything you locked up with

that key, even letting them modify it.


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Or we can say that Public-key cryptography, also known as asymmetric cryptography, is a

class of cryptographic algorithms which require two separate keys, one of which

is secret(orprivate) and one of which ispublic. Although different, the two parts of this key pair

are mathematically linked. The public key is used to encrypt plaintext or to verify a digital

signature;whereas the private key is used to decryptciphertext or to create a digital signature.The term "asymmetric" stems from the use of different keys to perform these opposite functions,

each the inverse of the otheras contrasted with conventional ("symmetric") cryptography which

relies on the same key to perform both.

Public-key algorithms are based on mathematical problems which currently admit no efficient

solution that are inherent in certain integer factorization, discrete logarithm, and elliptic

curve relationships. It is computationally easy for a user to generate their own public and private

key-pair and to use them for encryption and decryption. The strength lies in the fact that it is

"impossible" (computationally unfeasible) for a properly generated private key to be determined

from its corresponding public key. Thus the public key may be published without compromisingsecurity, whereas the private key must not be revealed to anyone not authorized to read

messages or perform digital signatures. Public key algorithms, unlikesymmetric key algorithms,

do notrequire asecure initialexchange of one (or more)secret keys between the parties.

Message authentication involves processing a message with a private key to produce a digital

signature.Thereafter anyone can verify this signature by processing the signature value with the

signer's corresponding public key and comparing that result with the message. Success confirms

the message is unmodified since it was signed, and presuming the signer's private key has

remained secret to the signer that the signer, and no one else, intentionally performed the

signature operation. In practice, typically only a hash or digest of the message, and not themessage itself, is encrypted as the signature.

Public-key algorithms are fundamental security ingredients in cryptosystems, applications and

protocols. They underpin such Internet standards as Transport Layer Security (TLS), PGP,

andGPG.Some public key algorithms providekey distribution and secrecy (e.g.,DiffieHellman

key exchange), some provide digital signatures (e.g., Digital Signature Algorithm), and some

provide both (e.g.,RSA).

Public-key cryptography finds application in, amongst others, the IT security disciplineinformation

security.Information security (IS) is concerned with all aspects of protecting electronic information

assets against security threats.[1]Public-key cryptography is used as a method of assuring the

confidentiality, authenticity andnon-repudiability of electronic communications and data storage.
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In an asymmetric key encryption scheme, anyone can encrypt messages using the public key, but only the holder of

the paired private key can decrypt. Security depends on the secrecy of the private key.

In theDiffieHellman key exchangescheme, each party generates a public/private key pair and distributes the public

key. After obtaining an authentic copy of each other's public keys,Alice and Bobcan compute a shared secret offline.

The shared secret can be used, for instance, as the key for asymmetric cipher.
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Asymmetric key crypto graphy u ses two separate keys: one private and on e public.

General idea of asymmetric-key crypto system :


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Public-key cryptography is often used to secure electronic communication over an opennetworked environment such as the internet. Open networked environments are susceptible to a

variety of communication security problems such asman-in-the-middle attacks and other security

threats. Sending a secure communication means that the communication being sent must not be

readable during transit (preserving confidentiality), the communication must not be modified

during transit (preserving the integrity of the communication) and to enforcenon-repudiation or

non-denial of the sending of the communication. Combining public-key cryptography with an

Enveloped Public Key Encryption (EPKE) method, allows for the secure sending of a

communication over an open networked environment.

The distinguishing technique used in public-key cryptography is the use of asymmetric keyalgorithms, where thekey used toencrypt a message is not the same as the key used todecrypt it.

Each user has a pair ofcryptographic keysa public encryption keyand a private decryption

key. Similarly, a key pair used for digital signatures consists of a private signing key and

a public verification key. The public key is widely distributed, while the private key is known only

to its proprietor. The keys are related mathematically, but the parameters are chosen so that

calculating the private key from the public key is either impossible or prohibitively expensive.

In contrast,symmetric-key algorithmsvariations of which have been used for thousands of years

use a singlesecret key, which must be shared and kept private by both the sender and the

receiver, for both encryption and decryption. To use a symmetric encryption scheme, the sender

and receiver must securely share a key in advance.

Because symmetric key algorithms are nearly always much less computationally intensive than

asymmetric ones, it is common to exchange a key using akey-exchange algorithm,then transmit

data using that key and a symmetric key algorithm.PGP and theSSL/TLS family of schemes use

this procedure, and are thus calledhybrid cryptosystems.
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There are two main uses for public-key cryptography:

Public-key encryption, in which a message is encrypted with a recipient's public key. The

message cannot be decrypted by anyone who does not possess the matching private key,

who is thus presumed to be the owner of that key and the person associated with the public

key. This is used in an attempt to ensureconfidentiality.

Digital signatures, in which a message is signed with the sender's private key and can be

verified by anyone who has access to the sender's public key. This verification proves that

the sender had access to the private key, and therefore is likely to be the person associated

with the public key. This also ensures that the message has not been tampered, as any

manipulation of the message will result in changes to the encodedmessage digest,which

otherwise remains unchanged between the sender and receiver.

An analogy to public-key encryption is that of a lockedmail box with a mail slot. The mail slot is

exposed and accessible to the publicits location (the street address) is, in essence, the public

key. Anyone knowing the street address can go to the door and drop a written message through

the slot. However, only the person who possesses the key can open the mailbox and read the

message.

An analogy for digital signatures is the sealing of an envelope with a personal wax seal. The

message can be opened by anyone, but the presence of the unique seal authenticates the sender.

A central problem with the use of public-key cryptography is confidence/proof that a particular

public key is authentic, in that it is correct and belongs to the person or entity claimed, and has

not been tampered with or replaced by a malicious third party. The usual approach to this problemis to use apublic-key infrastructure (PKI), in which one or more third partiesknown ascertificate

authorities certify ownership of key pairs. PGP, in addition to being a certificate authority

structure, has used a scheme generally called the "web of trust", which decentralizes such

authentication of public keys by a central mechanism, and substitutes individual endorsements of

the link between user and public key. To date, no fully satisfactory solution to the "public key

authentication problem" has been found.

Forward Public Key Encryption

The goal of Forward Public Key Encryption (FPKE) encryption is to ensure that the communication

being sent is kept confidential during transit.

To send a message using FPKE, the sender of the message uses the public key of the receiver

to encrypt the contents of the message. The encrypted message is then transmitted electronically

to the receiver and the receiver can then use their own matching private key to decrypt the

message.
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The encryption process of using the receivers public key is useful for preserving the confidentiality

of the message as only the receiver has the matching private key to decrypt the message.

Therefore, the sender of the message cannot decrypt the message once it has been encrypted

using the receivers public key. However, FKPE does not address the problem of non-repudiation,

as the message could have been sent by anyone that has access to the receivers public key.

Inverse Public Key Encryption

The goal of Inverse Public Key Encryption (IPKE) is to ensure that the sender of the

communication that is being sent is known to the receiver and that the sender of the message

cannot refute that the message that they have sent was not sent by them. Therefore, the purpose

of IPKE is to ensure thenon-repudiation of the message being sent. This is useful in a practical

setting where a sender wishes to make an electronic purchase of shares and the receiver wants

to confirm that it was indeed the actual sender requesting the purchase and not someone else.

IPKE is also known as adigital signature.

To send a message using IPKE, the message is encrypted using the senders private key which

serves as the senders digital signature. The digitally "signed" and encrypted message is then sent

to the receiver who can then use the senders public key to decrypt the message and reveal the

original contents.

IPKE is useful for applying ones digital signature to a message thus enforcing non-repudiation

however, when the message is transmitted it is possible for the message to be intercepted by an

unauthorized person and the unauthorized person could then use the senders public key to

decrypt the contents of the message thus not enforcing the confidentiality of the message being

sent.Certification Authority

In order for Enveloped Public Key Encryption to be as secure as possible, there needs to be a

"gatekeeper" of public and private keys, or else anyone could publish their public key and

masquerade as the intended sender of a communication. This digital key "gatekeeper" is known

as acertification authority.A certification authority is a trusted third party that can issue public and

private keys thus certifying public keys.

Advantages

- Convenience:It solves the problem of distributing the key for encryption. Everyone publishes

their public keys and private keys are kept secret.
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- Provides for message authentication: Public key encryption allows the use of digital

signatures which enables the recipient of a message to verify that the message is truly from a

particular sender.

- Detection of tampering: The use of digital signatures in public key encryption allows the

receiver to detect if the message was altered in transit. A digitally signed message cannot be

modified without invalidating the signature.

- Provide for non-repudiation: Digitally signing a message is akin to physically signing a

document. It is an acknowledgement of the message and thus, the sender cannot deny it.

Disadvantages

- Public keys should/must be authenticated:No one can be absolutely sure that a public key

belongs to the person it specifies and so everyone must verify that their public keys belong tothem.

- Slow:Public key encryption is slow compared to symmetric encryption. Not feasible for use in

decrypting bulk messages.

- Uses up more computer resources: It requires a lot more computer supplies compared to

single-key encryption.

- Widespread security compromise is possible:If an attacker determines a person's private

key, his or her entire messages can be read.

- Loss of private key may be irreparable:The loss of a private key means that all received

messages cannot be decrypted.


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DATA ENCRYPTION STANDARD (DES) :


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The overall Feistel structure of DES


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RSA ALGORITHM :

RSA is one of the first practicablepublic-key cryptosystems and is widely used for secure data

transmission. In such acryptosystem,theencryption key is public and differs from thedecryption

key which is kept secret. In RSA, this asymmetry is based on the practical difficulty offactoring the

product of two large prime numbers, the factoring problem. RSA stands for Ron Rivest,Adi

Shamir andLeonard Adleman,who first publicly described the algorithm in 1977.Clifford Cocks,

an English mathematician, had developed an equivalent system in 1973, but it

wasn'tdeclassified until 1997.

A user of RSA creates and then publishes theproduct of two largeprime numbers,along with an

auxiliary value, as their public key. The prime factors must be kept secret. Anyone can use the

public key to encrypt a message, but with currently published methods, if the public key is large

enough, only someone with knowledge of the prime factors can feasibly decode the
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message.[2] Breaking RSA encryption is known as the RSA problem. It is an open question

whether it is as hard as the factoring problem.

Comp lexity of operations in RSA

Encrypt ion , decrypt ion, and key generat ion in RSA
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Example :

Here is an example of RSA encryption and decryption. The parameters used here are artificially

small, but one can alsouse OpenSSL to generate and examine a real keypair.

1. Choose two distinct prime numbers, such as

and

2. Compute n=pqgiving

3. Compute thetotient of the product as (n) = (p1)(q1) giving

4. Choose any number 1 < e< 3120 that is coprime to 3120. Choosing a prime number

for eleaves us only to check that eis not a divisor of 3120.

Let5. Compute d, themodular multiplicative inverse of e(mod (n)) yielding

The public keyis (n= 3233, e= 17). For a paddedplaintext message m, the encryption function

is

The private keyis (n= 3233, d= 2753). For an encryptedciphertext c, the decryption function is

For instance, in order to encrypt m= 65, we calculate

To decrypt c= 2790, we calculate

Both of these calculations can be computed efficiently using the square-and-multiply

algorithm formodular exponentiation.In real-life situations the primes selected would be much

larger; in our example it would be trivial to factor n, 3233 (obtained from the freely available public

key) back to the primespand q. Given e, also from the public key, we could then compute dandso acquire the private key.

Practical implementations use theChinese remainder theorem to speed up the calculation using

modulus of factors (modpqusing modpand mod q).

The values dp, dqand qinv, which are part of the private key are computed as follows:
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Here is how dp, dqand qinvare used for efficient decryption. (Encryption is efficient by choice of

public exponent e)


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SECURE WEB DOCUMENTS :


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Most of the data transfer in the current WWW is insecure. Clients simply connect to Web servers

and request the documents stored there. This approach is clearly vulnerable to man-in-the-middle

attacks, not to mention malicious caches. In such an attack scenario, an active attacker intercepts

the clients request, and answers with his own document. Although such attacks are infrequent,

that is probably as much due to the lack of determination on the part of the attackers as to the

inherent security of the underlying network architecture. Furthermore, due to the possibility of

such attacks, the security of an HTTP request is downgraded to the security of the weakest

network link/router on the request path. In the current WWW, the most common protection against

such attacks is through TLS (Transport Layer Security). TLS uses public-key cryptography to

authenticate servers and establish secure channels between servers and clients.

The main problem with TLS is that it requires servers to be trusted. The secure channel between

the client and server does not help at all if a malicious server sends bogus data over it. For this

reason, TLS allows documents to be replicated only on trusted servers, which greatly restricts the

set of acceptable hosts.

Turning back to our GlobeDoc objects, we can see that a mechanism like TLS is clearly not suited

for ensuring data integrity. As mentioned in Section 2, GlobeDoc objects dynamically place their

replicas on (possibly) untrusted object servers close to where their client requests are coming

from. Our assumption is that most of these servers are honest, but we need to consider the

possibility that some of them may try to replace the documents they host with fake data. Therefore,

we need a security mechanism that enforces the following three properties on the replicated state

of a GlobeDoc:

Authenticity - the document the client receives from a server has indeed been created by the

objects owner. No attacker or malicious server should be able to pass off one of their own

documents as being part of the object.

Freshness - the client is guaranteed to receive the most recent version of a document part of a

object. No attacker or malicious server should be able to pass off genuine but old versions of a

document and convince the client they are fresh.

Consistency - the client is guaranteed to receive a document, part of the object, that is consistent

to what she has requested. No attacker or malicious server should be able to replace the

requested document with another fresh document part of the same object.

DIGITAL SIGNATURE :

A digital signature is a mathematical scheme for demonstrating the authenticity of a digital

message or document. A valid digital signature gives a recipient reason to believe that themessage was created by a known sender, such that the sender cannot deny having sent the

message (authentication and non-repudiation)and that the message was not altered in transit

(integrity). Digital signatures are commonly used for software distribution, financial transactions,

and in other cases where it is important to detect forgery or tampering.
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OR

A digital signature scheme typically consists of three algorithms:

A key generation algorithm that selects a private key uniformly at random from a set of

possible private keys. The algorithm outputs the private key and a correspondingpublic key.

A signingalgorithm that, given a message and a private key, produces a signature.

A signature verifying algorithm that, given a message, public key and a signature, either

accepts or rejects the message's claim to authenticity.

Two main properties are required. First, the authenticity of a signature generated from a fixedmessage and fixed private key can be verified by using the corresponding public key. Secondly,

it should be computationally infeasible to generate a valid signature for a party without knowing

that party's private key.
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A diagram showing how a digital signature is applied and then verified.

Why Digital Signatures?

To provide Authenticity, Integrity and Non-repudiation to electronic documents

To use the Internet as the safe and secure medium for e-Commerce and e-Governance


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Digital signatures are often used to implementelectronic signatures,a broader term that refers to

any electronic data that carries the intent of a signature, but not all electronic signatures use digital

signatures. In some countries, including the United States, India, Brazil, and members of

theEuropean Union,electronic signatures have legal significance.

Digital signatures employ a type ofasymmetric cryptography.For messages sent through a non

secure channel, a properly implemented digital signature gives the receiver reason to believe the

message was sent by the claimed sender. Digital signatures are equivalent to traditional

handwritten signatures in many respects, but properly implemented digital signatures are more

difficult to forge than the handwritten type. Digital signature schemes, in the sense used here, are

cryptographically based, and must be implemented properly to be effective. Digital signatures can

also providenon-repudiation,meaning that the signer cannot successfully claim they did not sign

a message, while also claiming theirprivate key remains secret; further, some non-repudiation

schemes offer a time stamp for the digital signature, so that even if the private key is exposed,

the signature is valid. Digitally signed messages may be anything representable as abit string:examples includeelectronic mail, contracts, or a message sent via some other cryptographic

protocol.

How they work :

To create RSA signature keys, generate an RSA key pair containing a modulus N that is the

product of two large primes, along with integers eand dsuch that e d1 (mod (N)), where is

theEuler phi-function.The signer's public key consists of Nand e, and the signer's secret key

contains d.

To sign a message m, the signer computes md(mod N). To verify, the receiver checks that

em(mod N).

As noted earlier, this basic scheme is not very secure. To prevent attacks, one can first apply

a cryptographic hash function to the message mand then apply the RSA algorithm described

above to the result. This approach can be proven secure in the so-calledrandom oracle model.

Most early signature schemes were of a similar type: they involve the use of a trapdoorpermutation,such as the RSA function, or in the case of the Rabin signature scheme, computing

square modulo composite n.A trapdoor permutation family is a family ofpermutations,specified

by a parameter, that is easy to compute in the forward direction, but is difficult to compute in the

reverse direction without already knowing the private key. However, for every parameter there is

a "trapdoor" (private key) which when known, easily decrypts the message. Trapdoor

permutations can be viewed as public-key encryption systems, where the parameter is the public
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key and the trapdoor is the secret key, and where encrypting corresponds to computing the

forward direction of the permutation, while decrypting corresponds to the reverse direction.

Trapdoor permutations can also be viewed as digital signature schemes, where computing the

reverse direction with the secret key is thought of as signing, and computing the forward direction

is done to verify signatures. Because of this correspondence, digital signatures are oftendescribed as based on public-key cryptosystems, where signing is equivalent to decryption and

verification is equivalent to encryption, but this is not the only way digital signatures are computed.

Used directly, this type of signature scheme is vulnerable to a key-only existential forgery attack.

To create a forgery, the attacker picks a random signature and uses the verification procedure

to determine the message mcorresponding to that signature. In practice, however, this type of

signature is not used directly, but rather, the message to be signed is first hashed to produce a

short digest that is then signed. This forgery attack, then, only produces the hash function output

that corresponds to , but not a message that leads to that value, which does not lead to an

attack. In the random oracle model, this hash-then-sign form of signature is existentiallyunforgeable, even against achosen-plaintext attack.

There are several reasons to sign such a hash (or message digest) instead of the whole

document.

For efficiency: The signature will be much shorter and thus save time since hashing is

generally much faster than signing in practice.

For compatibility:Messages are typically bit strings, but some signature schemes operate

on other domains (such as, in the case of RSA, numbers modulo a composite number N). A

hash function can be used to convert an arbitrary input into the proper format. For integrity: Without the hash function, the text "to be signed" may have to be split

(separated) in blocks small enough for the signature scheme to act on them directly. However,

the receiver of the signed blocks is not able to recognize if all the blocks are present and in

the appropriate order.

Applications of digital signatures

As organizations move away from paper documents with ink signatures or authenticity stamps,

digital signatures can provide added assurances of the evidence to provenance, identity, and

status of an electronic document as well as acknowledging informed consent and approval by a

signatory. The United States Government Printing Office (GPO) publishes electronic versions of

the budget, public and private laws, and congressional bills with digital signatures. Universities

including Penn State, University of Chicago, and Stanford are publishing electronic student

transcripts with digital signatures.

Below are some common reasons for applying a digital signature to communications:
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web technology and commerce unit-5 by arun pratap singh

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