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Digital Water Marking Seminar Documentation


Digital Water Marking Seminar Documentation

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  • pg 1
       This project will consist of one deliverable. A ten-minute PowerPoint
presentation will be developed and distributed for those that prefer to have an
interactive approach to learning about digital watermarking. The following
introductory sections describe the problem statement and goal, relevance and
significance, barriers and issues, approach, and a timeline of the milestones.

Common Watermarking

Digital Watermarked Image

Problem Statement and Goal

           The desire for the availability of information and quick distribution has
been a major factor in the development of new technology in the last decade (Zhao,
Koch, & Luo, 1998). There is the increased use of multimedia across the Internet.
Multimedia distribution has become an important way to deliver services to people

around the world (Arn, Gatlin, & Kordsmeier, 1998). It is commonly applied in
Internet marketing campaigns and electronic commerce web sites.
           Due to the growing usage of multimedia content on the Internet, serious
issues have emerged. Counterfeiting, forgery, fraud, and pirating of this content are
rising (Lan & Tewfik, 1999). Virtually anyone with a sound card, scanner, video
frame grabbers, or multimedia authoring systems allow them to incorporate
copyrighted material into presentations, web designs, and Internet marketing
campaigns. Consequently, copyright abuse is rampant among multimedia users who
are rarely caught (Gatlin, Arn, & Kordsmeier, 1999).
        This copyright abuse is the motivating factor in developing new encryption
technologies (Zhao et al., 1998). One such technology is digital watermarking. The
focus of this proposed PowerPoint presentation will detail digital watermarking for
multimedia applications. Areas that will be covered are definition of digital
watermarking, purpose, techniques, and types of watermarking attacks. Lastly, the
current laws in place for digital copyright and the future of digital watermarking
technology will be briefly detailed. This PowerPoint presentation could be used to
further one’s understanding of one type of multimedia encryption techniques.
Relevance and Significance

       Multimedia usage has developed from the need in satisfying human desires in
societies. It is this desire that relies on communication, personal interaction, and
entertainment (Lan & Tewfik, 1999). Thus, the emphasis has mostly been placed on
making information available and on transmitting and manipulating that information.
Protecting information and content has not received the attention that it
deserves (Zhao et al., 1998).
       It has only been recently that copyright laws regarding multimedia usage have
been established. Any extensive research in this area is non-existent (Arn et al., 1998,
December). However, even the current copyright laws are inadequate for dealing with
all this digital data (Memon & Wong, 1998). Digital watermarking seems to be the
only potential encryption technology to provide protection even after data is
decrypted (Zhao et al., 1998).

Barriers and Issues

         Several barriers prevent digital watermarking from being effective and
widespread. First, there is not a foolproof protection scheme while making the
watermarks imperceptible. Thus, absolute robustness is impossible (Zhao et al.,
         Second, it is difficult to offer an “off-the-shelf” solution to the mass market.
Although, there is significant interest in this technology from OEMs and system
integrators, there is no infrastructure or protocols. Besides, the legal status of
watermarks used as evidence in lawsuits involving intellectual property has not been
tested (Zhao et al., 1998).
         Lastly, out of fear of piracy, many professional photographers, artists, and
other content creators still do not put their work out in digital format. Thus, the
market for this new encryption technology is not widespread. Usually a new
technology goes through a dormancy period before widespread adoption (Zhao et al.,

         The goal of this project will enhance an individual’s understanding of digital
watermarking for multimedia applications. Areas that will be covered are definition of
digital watermarking, purpose, techniques, and types of watermarking attacks. Lastly,
the current laws in place for digital copyright and the future of digital watermarking
technology will be briefly detailed.
         The first step in accomplishing this will be to perform a thorough search into
digital watermarking. Next, the preliminary proposal will be written. It will include
the following three chapters. Chapter one will describe the deliverable, problem
statement, relevance, barriers and issues, and milestones. The review of literature of
digital watermarking will be chapter two. Chapter three will consist of the product
criteria, marketing plan, and expectations.
         To complete the project, the full development process of the PowerPoint
presentation will be detailed. During the development of the PowerPoint presentation,
two individuals will be asked for their input. Comments and observations will be
incorporated into the final PowerPoint presentation. These same individuals will be
asked for their comments on the final design. The development process and results

from these evaluations will be presented in chapter four. Chapter five will conclude
with recommendations for further enhancements.

        The following is a summary of the milestones for this project. The idea for the
Digital Watermarking PowerPoint presentation was decided in July 2000.
Refinements to chapter one was done on Sunday, October 8, 2000. Chapters two and
three were completed on Sunday, October 15, 2000. The preliminary proposal was
submitted before Friday, October 20, 2000.
        The development of the PowerPoint presentation will start in November 2000
with the initial design being complete on November 23, 2000. Evaluations of the
initial design will be done during the Thanksgiving holiday. Throughout December
2000, these evaluations will be incorporated into the final Digital Watermarking
PowerPoint presentation. The final product will be available at the end of January

                                                                        Chapter 1

                                                         Review of Literature

       The idea of watermarking can be dated back to the late Middle Ages. The
earliest use has been to record the manufacture’s trademark on the product so that
authenticity could be easily established. The Government uses it for currencies,
postage stamps, revenue stamps, etc (Berghel, 1998). Now due to the information and
computer age, digital watermarking is being expanded.
Definition of Digital Watermarking

       Digital watermarking is a process of embedding unobtrusive marks or labels
into digital content. These embedded marks are typically imperceptible (invisible) that
can later be detected or extracted (Yeung, Yeo, & Holliman, 1998). The concept of
digital watermarking is associated with steganography.
       Steganography is defined as covered writing. It has a long history of being
associated with methods of secret communication. Steganography does not
immediately arise the suspicion of something secret or valuable. Instead, it hides an
important message in an unimportant one. Therefore, digital watermarking is a way to
hide a secret or personal message to protect a product’s copyright or to demonstrate
data integrity (Voyatzis & Pitas, 1999).
Purpose of Digital Watermarking

       Watermarks added to digital content serve a variety of purposes. The
following list details six purposes of digital watermarking (Memon & Wong, 1998).
              Ownership Assertion – to establish ownership of the content (i.e.
              Fingerprinting – to avoid unauthorized duplication and distribution of
               publicly available multimedia content
              Authentication and integrity verification – the authenticator is
               inseparably bound to the content whereby the author has a unique key
               associated with the content and can verify integrity of that content by
               extracting the watermark

              Content labeling – bits embedded into the data that gives further
               information about the content such as a graphic image with time and
               place information
              Usage control – added to limit the number of copies created whereas
               the watermarks are modified by the hardware and at some point would
               not create any more copies (i.e. DVD)
              Content protection – content stamped with a visible watermark that is
               very difficult to remove so that it can be publicly and freely distributed
Unfortunately, there is not an universal watermarking technique to satisfy all of these
purposes (Memon & Wong, 1998). The content in the environment that it will be used
determines the digital watermarking technique. The following section describes some
digital watermarking techniques.
Digital Watermarking Techniques

       The most important properties of any digital watermarking techniques are
robustness, security, imperceptibility, complexity, and verification. Robustness is
defined as if the watermark can be detected after media (normal) operations such as
filtering, lossy compression, color correction, or geometric modifications. Security
means the embedded watermark cannot be removed beyond reliable detection by
targeted attacks. Imperceptibility means the watermark is not seen by the human
visual system. Complexity is described as the effort and time required for watermark
embedding and retrieval. Lastly, verification is a procedure where by there is a private
key or public key function (Dittmann, Mukherjee, & Steinebach, 2000).
       Each of these properties must be taken into consideration when applying a
certain digital watermarking technique. The following sections describe a few of the
most common digital watermarking techniques.
Spatial and Frequency Domain

       Spatial and frequency domain watermarking are applied to graphic images and
text. Spatial domain watermarking slightly modifies the pixels of one or two
randomly selected subsets of an image. Modifications might include flipping the low-
order bit of each pixel. However, this technique is not reliable when subjected to
normal media operations such as filtering or lossy compression (Berghel, 1998).

       Frequency domain watermarking technique is also called transform domain.
Values of certain frequencies are altered from their original. Typically, these
frequency alterations are done in the lower frequency levels, since alternations at the
higher frequencies are lost during compression. The watermark is applied to the
whole image so as not to be removed during a cropping operation. However, there is a
tradeoff with the frequency domain technique. Verification can be difficult since this
watermark is applied indiscriminately across the whole image (Berghel, 1998).
The Zhao Koch Algorithm and the Fridrich Algorithm

       The Zhao Koch Algorithm and The Fridrich Algorithm watermark techniques
are applied to MPEG videos. The Zhao Koch Algorithm embeds a copyright label in
the frequency domain of the video. The algorithm randomly selects three coefficients
from the discrete cosine transform encoded block and manipulates them to store a
single bit of information using a secret key. This single bit information can be the
name or address of the owner. The watermark can be easily embedded into the video
with minimal operation. Thus, complexity is not an issue. However, the Zhao Koch
Algorithm watermark technique is not robust against normal media operations such as
scaling or rotation (Dittmann, Stabenau, & Steinmetz, 1998).
       The Fridrich Algorithm watermark technique is where a pattern is overlaid in
the low frequency domain. The pattern is created using a pseudo random number
generator and a cellular automation with voting rules. The pseudo random number
generator creates a white and black initial pattern that is the same size as the image. A
cellular automation with voting rules is then applied until there is a convergence to
fixed points. The voting rule randomly patches the pattern into these connected points.
Thus, the pattern is now overlaid into the image. This algorithm is resistant to normal
media operations. However, verification using this algorithm is not reliable. This is
because the watermark technique does not include detail information about the owner
when the pattern is created and overlaid (Dittmann et al., 1998).

       Digital watermarking does not have the same capability or level of security as
data encryption. It does not prevent the viewing or listening of content, nor does it
prevent accessing that content. Therefore, digital watermarking is not immune to

hacker attacks (Yeung et al., 1998). The following are some intentional attacks on
watermarks (Cox, Miller, & Bloom, 2000).
              Active Attacks – hacker tries to remove the watermark or make it
               undetectable. An example is to crop it out.
              Passive Attacks – hacker tries to determine whether there is a
               watermark and identify it. However, no damage or removal is done.
              Collusion Attacks – hacker uses several copies of one piece of media,
               each with a different watermark, to construct a copy with no
              Forgery Attacks – hacker tries to embed a valid watermark of their
               own rather than remove one.
              Distortive Attacks – hacker applies some distortive transformation
               uniformly over the object in order to degrade the watermark so that it
               becomes undetectable/unreadable (Collberg & Thomborson, 1999).
These intentional attacks are just one of the barriers of why authors do not put their
works into digital format. However, the government has stepped in to help these
authors by establishing new laws.
Current Laws

       There are three main laws concerning digital copyright. They are the Digital
Millennium Copyright Act (DMCA), the Collections of Information Antipiracy Act,
and changes to Article 2B of the Uniform Commercial Code. Each of these laws is
briefly described below.
Digital Millennium Copyright Act (DMCA)

       The Clinton Administration established this policy by making online service
providers (OSPs) responsible for guarding against copyright infringements. However,
major OSPs and telephone companies argued that it was technologically and
economically infeasible to monitor all user activities. Therefore, a compromise has
been established (Samuelson, 1999).
       Under the Digital Millennium Copyright Act, OSPs can qualify for exemption
of liability by taking the following steps. The following steps are termination of
service to repeat offenders, accommodating standard technological measures adopted
by copyright industries to protect works, and abide by removing material from their

system when notified of copyright infringement. This law was passed in September
1998 (Samuelson, 1999).
Collections of Information Antipiracy Act

       This bill would protect the intellectual property in databases. Currently
copyright does not protect all data compilations, but only those that exhibit sufficient
creativity in the selection and arrangement. For example, the white pages are not
copyright protected. However, many private companies feel that data complied should
be. However, due to strong opposition from the scientific and educational
communities in the United States, this law was never passed (Samuelson, 1999).
Article 2B of the Uniform Commercial Code

       Article 2B regulates all information as it relates to computer information
transactions. Thus, it would apply to multimedia products, software licensing, and
interactive services. However, there is much controversy over this proposed law. This
is why it is still not passed (Samuelson, 1999).
Future of Digital Watermarking

       Digital information can easily be disseminated and copied via global
networks. Due to this ease, challenges regarding digital information have created a
need for more copyright laws. However, laws cannot be the only entity required to
protect digital works. Digital watermarking and its technological advancements
should continue to be researched and developed. The future of digital watermarking
relies on setting standards and creating applications so that creators of digital content
can easily implement it.

Digital Water Marking Life Cycle Process

        The information to be embedded in a signal is called a digital watermark,
although in some contexts the phrase digital watermark means the difference between
the watermarked signal and the cover signal. The signal where the watermark is to be
embedded is called the host signal. A watermarking system is usually divided into

three distinct steps, embedding, attack, and detection. In embedding, an algorithm
accepts the host and the data to be embedded, and produces a watermarked signal.

                                                          Then     the   watermarked
digital signal is transmitted or stored, usually transmitted to another person. If this
person makes a modification, this is called an attack. While the modification may not
be malicious, the term attack arises from copyright protection application,
where pirates attempt to remove the digital watermark through modification. There
are many possible modifications, for example, lossy compression of the data (in
which resolution is diminished), cropping an image or video, or intentionally adding

         Detection (often called extraction) is an algorithm which is applied to the
attacked signal to attempt to extract the watermark from it. If the signal was
unmodified during transmission, then the watermark still is present and it may be
extracted. In robust digital watermarking applications, the extraction algorithm should
be able to produce the watermark correctly, even if the modifications were strong.
In fragile digital watermarking, the extraction algorithm should fail if any change is
made to the signal.


         A digital watermark is called robust with respect to transformations if the
embedded information may be detected reliably from the marked signal, even if
degraded by any number of transformations. Typical image degradations are JPEG
compression, rotation, cropping, additive noise, and quantization. For video content,
temporal modifications and MPEG compression often are added to this list. A digital

watermark is called imperceptible if the watermarked content is perceptually
equivalent to the original, unwatermarked content. In general, it is easy to create
robust watermarks or imperceptible watermarks, but the creation of robust and
imperceptible watermarks has proven to be quite challenging. Robust imperceptible
watermarks have been proposed as tool for the protection of digital content, for
example as an embedded no copy allowed flag in professional video content.

Digital watermarking techniques may be classified in several ways.


A digital watermark is called fragile if it fails to be detectable after the slightest
modification. Fragile watermarks are commonly used for tamper detection (integrity
proof). Modifications to an original work that clearly are noticeable, commonly are
not referred to as watermarks, but as generalized barcodes.

A digital watermark is called semi-fragile if it resists benign transformations, but fails
detection after malignant transformations. Semi-fragile watermarks commonly are
used to detect malignant transformations.

A digital watermark is called robust if it resists a designated class of transformations.
Robust watermarks may be used in copy protection applications to carry copy and no
access control information.


A digital watermark is called imperceptible if the original cover signal and the marked
signal are (close to) perceptually indistinguishable.

A digital watermark is called perceptible if its presence in the marked signal is
noticeable, but non-intrusive.


The length of the embedded message determines two different main classes of digital
watermarking schemes:

       The message is conceptually zero-bit long and the system is designed in order
        to detect the presence or the absence of the watermark in the marked object.

       This kind of watermarking scheme is usually referred to as Italic zero-
       bit or Italic presence watermarking schemes. Sometimes, this type of
       watermarking scheme is called 1-bit watermark, because a 1 denotes the
       presence (and a 0 the absence) of a watermark.

      The message is a n-bit-long stream (                                  , with n =
       | m | ) or M = {0,1}n and is modulated in the watermark. These kinds of
       schemes usually are referred to as multiple-bit watermarking or non-zero-bit
       watermarking schemes.
Embedding method

A digital watermarking method is referred to as spread-spectrum if the marked signal
is obtained by an additive modification. Spread-spectrum watermarks are known to be
modestly robust, but also to have a low information capacity due to host interference.

A digital watermarking method is said to be of quantization type if the marked signal
is obtained by quantization. Quantization watermarks suffer from low robustness, but
have a high information capacity due to rejection of host interference.

A digital watermarking method is referred to as amplitude modulation if the marked
signal is embedded by additive modification which is similar to spread spectrum
method, but is particularly embedded in the spatial domain.

Digimarc Watermarking

Digimarc Corp. has developed watermarking technology for digital and printed
images and for digital and analog video and audio. Specialized software embeds
these "imperceptible" messages by making subtle changes to the data of the original
digital content. These watermarks can then be "read" to validate original content
and/or deliver an action, such as delivering content to a mobile phone or providing
contact information about the owner of an image.

                                                                         Chapter 2
Product Criteria (Test Plan)

       The main purpose of the Digital Watermarking PowerPoint presentation is to
provide an interactive learning experience. This presentation should accomplish the
following items:
                Provide an enjoyable learning experience using multimedia content
                Make it easier to study in depth on digital watermarking by having all
                 resources in one central area
                Provide a more clear overview of digital watermarking versus having
                 the user read various sources
                Allow users to learn at their own speed about digital watermarking
These objectives are complied based on various readings regarding multimedia
learning. The processes that will be used to validate these objectives are the
                Quantitative measure - the number of errors that occurred during the
                 navigation of the PowerPoint presentation
                Two qualitative measures - think aloud (comments/observations) and
                 post-test questionnaire
       The target audience is a vast resource. Many potential users would be very
interested in the Digital Watermarking PowerPoint presentation. They include content
creators (i.e. artists, authors, and movie studios), content providers (i.e. libraries,
professional photographers), electronic commerce and graphic software vendors,
manufacturers of digital still images, video camera, and digital video discs
(DVDs) (Zhao et al., 1998). In essence, it is anyone who creates something and would
like it copyright protected.
       The hardware requirements for the Digital Watermarking PowerPoint
presentation include having a Pentium computer with at least 64 MB of RAM and a
CD-ROM drive. The software requirements include Microsoft Windows 98,
Microsoft PowerPoint 2000 and access to the Internet.
Marketing Plan

       In this digital age, information and/or created works can easily be found and
disseminated globally. The Internet has opened the door where it is easy to download
or use other individual’s works. Therefore, in order to protect the digital works of
these creators, a Digital Watermarking PowerPoint presentation is available to inform
these creators there are ways to protect their works from copyright abuse. Within the
next three months, a PowerPoint 2000 presentation will be available in two forms:
downloadable from the Internet from various websites including those companies who
specialize in digital watermarking and CD-ROM.

        The creation of the multimedia PowerPoint presentation is a legitimate
solution to helping targeted users understand digital watermarking. The trend towards
learning is one of asynchronous, just-in-time, and instruction delivered for which a
multimedia PowerPoint presentation is suited (Zemke, 1998). The PowerPoint
presentation will be structured and provide adequate guidance, therefore it should
provide an effective forum to learning about digital watermarking. However, there are
some potential disadvantages to using a PowerPoint presentation to learn about digital
       First, not all targeted users are familiar with computers or how to go about
using the Internet. Second, some targeted users prefer to learn by having a professor
teach or by experimenting with an actual application. Lastly, the PowerPoint
presentation may not address the target user needs, thus it could fall short of their
expectations (Zemke, 1998).

                                                                                     Chapter 3

                                                     Applications and Advantages

Digital watermarking is defined as the imperceptibly altering a work in order to
embed information about that work. In the recent years copyright protection of digital
content became a serious problem due to rapid development in technology.
Watermarking is one of the alternatives to copyright-protection problem.

Digital watermarking can be classified as visible and invisible. The visible
watermarks are viewable to the normal eye such as bills, company logos and
television channel logos etc. This type of watermarks is easily viewable without any
mathematical calculation but these embedded watermarks can be destroyed easily. In
the case of invisible watermarks, the locations in which the watermark is embedded
are secret, only the authorized persons extract the watermark. Some mathematical
calculations are required to retrieve the watermark. This kind of watermarks is not
viewable by an ordinary eye. Invisible watermarks are more secure and robust than
visible watermarks.


Digital watermarking may be used for a wide range of applications, such as:

       Copyright protection
       Source tracking (different recipients get differently watermarked content)
       Broadcast monitoring (television news often contains watermarked video from international

       Covert communication


Robustness: The watermark should be able to withstand after normal signal
processing operations such as image cropping, transformation, compression etc.
Imperceptibility: The watermarked image should look like same as the original image
to the normal eye. The viewer cannot detect that watermark is embedded in it.
Security: An unauthorized person cannot detect, retrieve or modify the embedded

Depending on the ability of the watermark to withstand normal signal processing
operations, digital watermarking can be categorized as robust, fragile and semi-fragile
watermarking. Robust watermarks are detectable even after some image processing
operations has been performed on the watermarked image such as image scaling,
bending and cropping, and so on. Robust watermarks are mainly used for copyright
protection. Fragile watermarks became invalid even if a slight modification is done to
the watermarked image. Fragile watermarks are mainly used for authentication
purpose. Semi-fragile watermarks allow some acceptable distortion to the
watermarked image. Beyond this acceptance level if any modification is done to the
watermarked image, the watermark will not be detected.

                                                                           Chapter 4


Steganography is the art and science of writing hidden messages in such a way that
no one, apart from the sender and intended recipient, suspects the existence of the
message, a form of security through obscurity. The word steganography is
of Greek origin     and     means      "concealed      writing"     from    the   Greek
words steganos (στεγανός) meaning "covered or protected", and graphein (γράφειν)
meaning "to write". The first recorded use of the term was in 1499 by Johannes
Trithemius in his Steganographia, a treatise on cryptography and steganography
disguised as a book on magic. Generally, messages will appear to be something else:
images, articles, shopping lists, or some other covertext and, classically, the hidden
message may be in invisible ink between the visible lines of a private letter.

The advantage of steganography, over cryptography alone, is that messages do not
attract attention to themselves. Plainly visible encrypted messages—no matter how
unbreakable—will arouse suspicion, and may in themselves be incriminating in
countries where encryption is illegal. Therefore, whereas cryptography protects the
contents of a message, steganography can be said to protect both messages and
communicating parties.

Steganography includes the concealment of information within computer files. In
digital steganography, electronic communications may include steganographic coding
inside of a transport layer, such as a document file, image file, program or protocol.
Media files are ideal for steganographic transmission because of their large size. As a
simple example, a sender might start with an innocuous image file and adjust the
color of every 100th pixel to correspond to a letter in the alphabet, a change so subtle
that someone not specifically looking for it is unlikely to notice it.

Digital Steganography

Modern Steganography entered the world in 1985 with the advent of the personal
computer being applied to classical Steganography problems. Development following
that was slow, but has since taken off, going by the number of "stego" programs
available: Over 800 digital Steganography applications have been identified by the
Steganography Analysis and Research Center. Digital Steganography techniques

       Concealing messages within the lowest bits of noisy images or sound files.
       Concealing data within encrypted data or within random data. The data to be
    concealed is first encrypted before being used to overwrite part of a much larger
    block of encrypted data or a block of random data (an unbreakable cipher like
    the one-time pad generates cipher texts that look perfectly random if you don't
    have the private key).
       Chaffing and winnowing.
       Mimic functions convert one file to have the statistical profile of another. This
    can thwart statistical methods that help brute-force attacks identify the right
    solution in a cipher text-only attack.
       Concealed messages in tampered executable files, exploiting redundancy in
    the targeted instruction set.
       Pictures embedded in video material (optionally played at slower or faster
       Injecting imperceptible delays to packets sent over the network from the
    keyboard. Delays in key presses in some applications (telnet or remote desktop
    software) can mean a delay in packets, and the delays in the packets can be used
    to encode data.
       Changing the order of elements in a set.
       Content-Aware Steganography hides information in the semantics a human
    user assigns to a datagram. These systems offer security against a non-human
       Blog Steganographia. Messages are fractionalized and the (encrypted) pieces
    are added as comments of orphaned web-logs (or pin boards on social network

platforms). In this case the selection of blogs is the symmetric key that sender and
recipient are using; the carrier of the hidden message is the whole blogosphere.

                                                                            Chapter 5


In cryptography, encryption is the process of transforming information (referred to
as plaintext) using an algorithm (called cipher) to make it unreadable to anyone
except those possessing special knowledge, usually referred to as a key. The result of
the process is encrypted information (in cryptography, referred to as cipher text). In
many contexts, the word encryption also implicitly refers to the reverse
process, decryption (e.g. “software for encryption” can typically also perform
decryption), to make the encrypted information readable again (i.e. to make it

Encryption has long been used by militaries and governments to facilitate secret
communication. Encryption is now commonly used in protecting information within
many kinds of civilian systems. For example, the Computer Security Institute reported
that in 2007, 71% of companies surveyed utilized encryption for some of their data in
transit, and 53% utilized encryption for some of their data in storage. Encryption can
be used to protect data "at rest", such as files on computers and storage devices
(e.g. USB flash drives). In recent years there have been numerous reports of
confidential data such as customers' personal records being exposed through loss or
theft of laptops or backup drives. Encrypting such files at rest helps protect them
should physical security measures fail. Digital rights management systems which
prevent unauthorized use or reproduction of copyrighted material and protect software
against reverse engineering (see also copy protection) are another somewhat different
example of using encryption on data at rest.

Encryption is also used to protect data in transit, for example data being transferred
via networks (e.g.        the Internet, e-commerce), mobile           telephones, wireless
microphones, wireless intercom systems, Bluetooth devices and bank automatic teller
machines. There have been numerous reports of data in transit being intercepted in
recent years. Encrypting data in transit also helps to secure it as it is often difficult to
physically secure all access to networks.

Encryption, by itself, can protect the confidentiality of messages, but other techniques
are still needed to protect the integrity and authenticity of a message; for example,
verification of a message authentication code (MAC) or a digital signature. Standards
and cryptographic software and hardware to perform encryption are widely available,
but successfully using encryption to ensure security may be a challenging problem. A
single slip-up in system design or execution can allow successful attacks. Sometimes
an adversary can obtain unencrypted information without directly undoing the
encryption. See, e.g., traffic analysis, TEMPEST, or Trojan horse.

One of the earliest public key encryption applications was called Pretty Good
Privacy (PGP). It was written in 1991 by Phil Zimmermann and was purchased
by Network Associates (now PGP Corporation) in 1997.

There are a number of reasons why an encryption product may not be suitable in all
cases. First, e-mail must be digitally signed at the point it was created to provide non-
repudiation for some legal purposes, otherwise the sender could argue that it was
tampered with after it left their computer but before it was encrypted at a gateway. An
encryption product may also not be practical when mobile users need to send e-mail
from outside the corporate network.


Legitimate businesses and webmasters have nothing to fear from copyright law or the
new wave of on-line enforcement technology found in digital watermarks and
tracking services. By using audio files and images only when they have obtained
permission of the copyright owner or the appropriate licensing agency, webmasters
should be free to continue making their sites audio visually appealing.

Scrupulous webmasters, however, should not be lulled into a false sense of security in
the age of digital watermarks. While a webmaster would be wise to examine images
and sound files for watermarks before incorporating them on any web site, the
absence of a watermark does not necessarily mean that a file is unprotected by
copyright and is therefore available for use without liability. Not only might a digital
watermark have disappeared through editing or been stripped before it arrives on a
webmaster's desktop, but the technology is too new to apply to a significant number
of pre-existing images and audio files. Just as an author is not required to affix a
copyright notice on the hard copies of his work in order to gain protection from the
copyright laws, use of a digital watermark surely is a voluntary act -- and those who
do not use it will not forfeit their intellectual property rights.

In addition, webmasters should remain aware that a significant portion of content on
the World Wide Web -- plain old text -- may be protected by copyright even though it
cannot be imbedded with a digital watermark. Copying magazine articles without
permission of the copyright owner can be just as significant a copyright violation as
copying photographs from the same magazine.

If anything, law-abiding webmasters should welcome digital watermarks and
tracking. While Internet scofflaws have been stealing copyrighted works by scanning
images, right-clicking on icons and lifting music from commercial CDs, webmasters
who did not want to risk their businesses always have ensured that they used royalty-
free or works in the public domain or obtained permission of the copyright owner. If
nothing else, digital watermarks will deter illegal copying, leveling the playing field
for all webmasters.


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