Steganography - · PDF fileDecember 03 Seminar #1 in HTI 3 The Basic Types of Steganography Substitutional Steganography • Some elements of the redundant covering medium are substituted

October 2003Seminar #1 in HTI 1

SteganographySteganographythat isthat is

Hiding informationHiding informationinto pictures and other mediainto pictures and other media

ProfProf..Dr. Mihály TóthDr. Mihály Tóth

��ت��ت..دد[email protected]@szgti.bmf.hu

December 03December 03 Seminar #1 in HTISeminar #1 in HTI 22

Phenomena of SteganographyPhenomena of Steganography�� Carrying (or Covering) mediaCarrying (or Covering) media

•• Which may be picture, video, sound file,Which may be picture, video, sound file,radio communication, even theradio communication, even thestructure of a File system.structure of a File system.

•• The carry medium ought to lookThe carry medium ought to lookinnocent.innocent.

�� The hidden information (or theThe hidden information (or theinformation to hideinformation to hide)) called Stegocalled Stegomediummedium oror StegoStego messagemessage..•• Which may be open message, but mayWhich may be open message, but may

be encrypted one as well.be encrypted one as well.


The Basic Types of SteganographyThe Basic Types of Steganography

�� SubstitutionalSubstitutional SteganographySteganography•• Some elements of the redundant coveringSome elements of the redundant covering

medium are substituted bymedium are substituted by ththee elements ofelements ofthe stego medium.the stego medium.

�� Selecting SteganographySelecting Steganography•• Some elements of the covering medium areSome elements of the covering medium are

selected to carry the hidden information.selected to carry the hidden information.•• The relevant information is hidden in aThe relevant information is hidden in a

narrownarrow--band region of a wide band noise.band region of a wide band noise.The hiding (narrow) band is changed byThe hiding (narrow) band is changed bytime to time. (Radio Communication.)time to time. (Radio Communication.)


The Basic Types of SteganographyThe Basic Types of Steganography((contcont))

�� Constructional SteganographyConstructional Steganography•• The Stego message is made similarThe Stego message is made similar

to the structure of the coveringto the structure of the coveringmedium.medium.


Some characteristics (1)Some characteristics (1)�� The most simple hiding methods (likeThe most simple hiding methods (like

the substitution) cannot tolerate thethe substitution) cannot tolerate theedition of the covering mediumedition of the covering medium

•• Compression, picture edition,Compression, picture edition,resizing, printing, copying, etc..resizing, printing, copying, etc..

�� On the other hand it should be a basicOn the other hand it should be a basicrequirement, that the hiddenrequirement, that the hiddeninformation ought toinformation ought to survivesurvive suchsuchchanges of the covering mediumchanges of the covering medium


Some characteristics (2)Some characteristics (2)

�� The applied method strongly dependsThe applied method strongly dependsonon•• The characteristic of the coveringThe characteristic of the covering

mediummedium andand•• The goal of the hidingThe goal of the hiding

�� There exist cases when we do notThere exist cases when we do notwant the message being completelywant the message being completelyhiddenhidden (watermark).(watermark).


Some characteristics (Some characteristics (33))�� There are some cases when hidingThere are some cases when hiding

has one common feature withhas one common feature withencryption, for recovering hiddenencryption, for recovering hiddeninformation one needs a KEY.information one needs a KEY.

�� Nowadays Steganography is appliedNowadays Steganography is appliedmostly to put copy right informationmostly to put copy right informationto the media sold (This is known asto the media sold (This is known aselectronic watermarking.)electronic watermarking.)


Ancient methods for hiding (1)Ancient methods for hiding (1)AineasAineas TaktikoszTaktikosz ::PoliokretikaPoliokretika

(360(360 AA..DD. ). )– Every nth letter of a plaintext had to be

read, or nth letters of the words.– Passing through a thread on holes of a

pottery disc whose holes are meantdifferent letters agreed in advance.

– Letters on a certain page of a booksigned by hardly visible dots. It isapplicable for newspapers or letters aswell.

– Cutting the hair of a slave and writingthe message to his bald head skin.(Herodotus about 450 A.D.)


Ancient methods for hiding (Ancient methods for hiding (22))

�� Naturally our ancestors appliedNaturally our ancestors appliedsecret writings as wsecret writings as weell. They usedll. They usedboth substitution and permutation ofboth substitution and permutation ofletters and other codes for lightletters and other codes for lightsignals.signals.

–Sewing into clothes, shues, collar of a dog,rein of a horse, or anything else.

–Writing it onto a blown bladder of a cow, thencompressing the bladder

–Writing between the rows of an innocent textby invisible ink.


Hiding methods in WW 2Hiding methods in WW 2

�� In WW2 the hardly visible dots still wereIn WW2 the hardly visible dots still wereused toused to denodenotete the selected letters in athe selected letters in anewspaper, for example.newspaper, for example.

�� Many soldiers tried to send home hiddenMany soldiers tried to send home hiddenmessages that way, but the method wasmessages that way, but the method waswell known by the censors.well known by the censors. (If they cannot(If they cannotdiscover the hiding method, they mixed the wordsdiscover the hiding method, they mixed the wordsat least or put the stamp in an other position,at least or put the stamp in an other position,etc.)etc.)

�� TheThe encryptonencrypton of messages, however,of messages, however,acquired more and more importance.acquired more and more importance.


History of securing informationHistory of securing information

�� In ancient times hiding was preferredIn ancient times hiding was preferredrather then encryption.rather then encryption.

�� Since the middle centuriesSince the middle centuriesencryption (vs. Decryptencryption (vs. Decryptiion) playon) playmore and more important role.more and more important role.

�� Nowadays cryptographic methodsNowadays cryptographic methodsare preferred more then hidingare preferred more then hiding(when securing messages).(when securing messages).


Goals of hiding nowadaysGoals of hiding nowadays

�� Hiding CopyHiding Copy--right into media.right into media.�� Identifying message in a hidden wayIdentifying message in a hidden way

•• Identifying the sender orIdentifying the sender or ownerowner•• Identifying the individual addresseeIdentifying the individual addressee•• Hiding commercial informationHiding commercial information

�� In common name:In common name:electronic watermarkingelectronic watermarking


Hiding message in textHiding message in text�� DenotatingDenotating some way the letters of thesome way the letters of the

carrier textcarrier text to hide a secret message into hide a secret message init.it. FoForr exampleexample• Hardly visible dots below or above the

selected letters or marking them byinvisible ink. (Applied from ancient timesup to WW. II.

• Hardly visible dislocation of the selectedletters.

• Very little modification of the shapes ofselected fonts.

• An example of dislocation of letters isshown in the next slide.



AdvantagesAdvantages//disadvantagesdisadvantages

�� Methods when the hidden information isMethods when the hidden information iscarried by the appearance of the text,carried by the appearance of the text,(not only the text file.)(not only the text file.)

�� Such a way the printed or copied text alsoSuch a way the printed or copied text alsocarries the hidden information. (E.g. acarries the hidden information. (E.g. aconfidential circular letter.)confidential circular letter.)

�� This makes difficult to select out theThis makes difficult to select out theappropriate letters by a computer.appropriate letters by a computer.

�� The printing/copying/scanning processesThe printing/copying/scanning processesbring additional problems to revoke thebring additional problems to revoke thehidden text.hidden text.


Marking the selected letters in aMarking the selected letters in acovering text by an other way.covering text by an other way.

�� Each font in the text occupies a standardEach font in the text occupies a standardarea.area.

�� That area iThat area iss not necessarily the same for eachnot necessarily the same for eachfont. For example the letterfont. For example the letter mm is generallyis generallywider then the letterwider then the letter ii. (Proportional vs. fix. (Proportional vs. fixfont size.)font size.)

�� Any letter could be moved or modified a bitAny letter could be moved or modified a bitwithin its standard font area. Such waywithin its standard font area. Such wayparticular letters of a carrier text could beparticular letters of a carrier text could bemarked.marked.

�� The marked letters can be selected out of theThe marked letters can be selected out of thetext by an appropriate program. (The texttext by an appropriate program. (The textcould be photocopied as well.)could be photocopied as well.)


Moving the font out of its standard areaMoving the font out of its standard area

Done by Mr. ÁrpádHorváth assistant


Moving the selected fontsMoving the selected fonts�� Text processors ofText processors of WysiwygWysiwyg ((wwhathat yyouou sseeee isis

wwhathat yyouou gget) generally cannot do that.et) generally cannot do that.(Word, WordPerfect, Desktop publishing(Word, WordPerfect, Desktop publishingsoftwaressoftwares, like Adobe’s PageMaker,, like Adobe’s PageMaker,FrameMakerFrameMaker))

�� „Programmable” text processors„Programmable” text processors(like(like LateXLateX) are able to do.) are able to do.

�� Such applicationSuch application neneeedsds a separate selectinga separate selectingprogram which is able to accept picture filesprogram which is able to accept picture filesas well. (E.g. scanned or copied texts). Thisas well. (E.g. scanned or copied texts). Thisis not a simple job and the addressee mustis not a simple job and the addressee musthave it in advance.have it in advance.

�� The characterThe character recogniserrecogniser software loose suchsoftware loose suchhidden information.hidden information.


Modifying fontsModifying fonts

�� Increasing theIncreasing the lenghtlenght of the vertical linesof the vertical linesin some characters (likein some characters (like b,d,h,k,l,p,qb,d,h,k,l,p,q) with) witha small amount is not prominent.a small amount is not prominent.

�� This also may carry information.This also may carry information.�� Arabic writing allows many decorativeArabic writing allows many decorative

variations of the letters in a textvariations of the letters in a text�� Which may be used to mark selectedWhich may be used to mark selected

letters.letters.Any proposition?Any proposition?


Methods for hiding codedMethods for hiding codedinformation into a textinformation into a text

�� At the ends of rows we may insertAt the ends of rows we may insert exraexraspaces. Each space at a rowspaces. Each space at a row--end mayend mayrepresent a single bit. (Max 3 spaces, forrepresent a single bit. (Max 3 spaces, formore then 3 could be conspicuous.)more then 3 could be conspicuous.)In an A4 page there are 50 rows andIn an A4 page there are 50 rows andaltogether 50x3 bit= 150 bits (less then 20altogether 50x3 bit= 150 bits (less then 20bytes) could be hidden such a way. Thisbytes) could be hidden such a way. Thismethod can resist compression.method can resist compression.

�� One has to read the first letters of wordsOne has to read the first letters of wordspreceded by double spaces.preceded by double spaces.

�� Modifying the font sizes oModifying the font sizes orr spaces.spaces.


Modifying the structure of the textModifying the structure of the text

�� SynonimsSynonims of some words can be usedof some words can be usedinstead of the original word, orinstead of the original word, or

�� changing the linguistic structure of thechanging the linguistic structure of thetext (applicable in most cases)text (applicable in most cases)

�� Both of the above can be used to hideBoth of the above can be used to hideinformation.information.

�� Revocation the hidden information theRevocation the hidden information theoriginal text (like a key) is needed.original text (like a key) is needed.Very small amount of information can beVery small amount of information can behidden that way. (Goal: identification)hidden that way. (Goal: identification)


Hiding information into picturesHiding information into pictures1.1. If the picture (graphics) wasIf the picture (graphics) was

made directly for that purposemade directly for that purposeSee the example in the nextSee the example in the nextslide.slide.

2.2. In so called cover pictures. (WeIn so called cover pictures. (Wewill come back to that.)will come back to that.)Using covering pictures is the mostUsing covering pictures is the mostfrequent method of hidingfrequent method of hidinginformation.information.



Hiding in covering pictures (1)Hiding in covering pictures (1)�� Applicability dependsApplicability depends

upon the way ofupon the way ofrepresenting colors.representing colors.

�� It cannot be applied inIt cannot be applied incase of color palette.case of color palette.

�� In case of the colorsIn case of the colorsrepresented by 3 colorrepresented by 3 colorbytes it is applicable,bytes it is applicable,but,but,

�� Very vulnerableVery vulnerable

Neighboring color coordinates maydenote very different colors.


Hiding in covering picturesHiding in covering pictures (2)(2)�� The color of each pixel) is defined by 3 bytes.The color of each pixel) is defined by 3 bytes.

(There are a couple of methods defining color.(There are a couple of methods defining color.This is just one of them.)This is just one of them.)

�� The different colors for a pixel can be as many asThe different colors for a pixel can be as many as2^(8*3)=16 777 216.2^(8*3)=16 777 216.

�� Though human eye is very sensitive,Though human eye is very sensitive, such an extremesuch an extremevariety of colors cannot be distinguishedvariety of colors cannot be distinguished.. The colorThe color--change of a pixel is not visiblechange of a pixel is not visible if theif the LSBsLSBs of the color bytesof the color bytesare changed. (In fact the average number of changes affectare changed. (In fact the average number of changes affecthalf of the color bytes only)half of the color bytes only)

�� The hidden information is carried by theThe hidden information is carried by the LSBsLSBs ofofthe color bytes.the color bytes.

A rejtett üzenet bitjei

Color information that belongs to each pixel of a picture


Changes of the three basic (additive)Changes of the three basic (additive)colors (Sat:240,colors (Sat:240, LumLum: 120/112): 120/112)

�� In the first row the LSB changed by 1 bitIn the first row the LSB changed by 1 bit�� In the second row the change is 1 bit at theIn the second row the change is 1 bit at the

16th positional value.16th positional value.


In an otherIn an other coordinatacoordinata system:system:�� Perhaps some veryPerhaps some very

little change oflittle change ofsome colors aresome colors arevisible in thevisible in thesecond row of thesecond row of theprevious slide. Itprevious slide. Ithappened on 256happened on 256grade scale of thegrade scale of thebasic colors.basic colors.

�� The luminescenceThe luminescenceis also changedis also changedfrom 120 to 112.from 120 to 112.

255239

0

255239

0

255239

0


Visual experiencesVisual experiences�� Changing theChanging the LSBsLSBs of the basic colorsof the basic colors

cannot be detected by a visual way, at leastcannot be detected by a visual way, at leastnot on a computer screen. Changing,not on a computer screen. Changing,however, the last four bits of a color bytehowever, the last four bits of a color bytecould be detected visually.could be detected visually.

�� The reason for that is in the physiologicalThe reason for that is in the physiologicalcharacteristic of the human eyes.characteristic of the human eyes.

�� The black and white and grayThe black and white and gray--scale sensingscale sensingabilities of the human eyes are much better,abilities of the human eyes are much better,but in spite of that the graybut in spite of that the gray--scale picturesscale picturesare more suitable for hiding information inare more suitable for hiding information inthem.them.

�� ChangingChanging LSBsLSBs the average byte change isthe average byte change ishalf of the total number of color bytes.half of the total number of color bytes.


How much information could beHow much information could behidden in a picture?hidden in a picture?

�� In a Kodak format CD picture the maximumIn a Kodak format CD picture the maximumnumber of pixels are 2048 x 3072 pixel. (number of pixels are 2048 x 3072 pixel. (≅≅19 MB)19 MB) A single digital photo is able to hideA single digital photo is able to hide2,3 MB (12 %) information such way that it2,3 MB (12 %) information such way that itdoes not cause any visible change of thedoes not cause any visible change of thepicture.picture.

�� I am going to demonstrate it by a programI am going to demonstrate it by a programdeveloped by a student of mine, Mr.developed by a student of mine, Mr. PéterPéterTelekiTeleki.. It has been developed exactly forIt has been developed exactly forexperimental and demonstration purposeexperimental and demonstration purposeand it operates very fast. Instead describingand it operates very fast. Instead describingthe program I am to show some of itsthe program I am to show some of itsresults.results.


Demonstrating how to hide informationDemonstrating how to hide informationin a bitmap format picturein a bitmap format picture

�� In the following slides I am to show tIn the following slides I am to show twwoopictures in each slide.pictures in each slide.

�� The left picture is the one inThe left picture is the one in whicwhichh there isthere isno hidden information while the right oneno hidden information while the right onecontains a text of 4862 bytes in thecontains a text of 4862 bytes in the LSBsLSBsof the pixels.of the pixels.

�� To hide that big amount of information weTo hide that big amount of information weused theused the LSBsLSBs of all three color bytes ofof all three color bytes ofthe three basic colors.the three basic colors.


LSBLSB hidinghiding inin 24 bit24 bit bmpbmp picturepictureThe right picture contains 4862 hidden letters


Sizes of picture files shownSizes of picture files shown

21 952 bytes21 952 bytes21 795 bytes21 795 bytesJPGJPG

308 614 bytes308 614 bytes308 614 bytes308 614 bytesBitmapBitmap

Kandó_2Kandó_2includesincludeshiddenhidden

informationinformation

Kandó_1Kandó_1without hiddenwithout hidden

informationinformation


Four bit hidingFour bit hiding

�� The following slides demonstrate theThe following slides demonstrate thecase when the second half (icase when the second half (i..e. foure. fourbits) of the color bytes are used forbits) of the color bytes are used forhiding. In thosehiding. In those cascasees the changings the changingof the picture can be sensed visuallyof the picture can be sensed visuallytoo.too.

�� Exceptionally on the bigger areas ofExceptionally on the bigger areas ofthe same or similarly colored parts ofthe same or similarly colored parts ofthe picture.the picture.


Steganography (cont.)Steganography (cont.)

Hiding by 1 bitHiding by 1 bit Hiding by 4 bits


SteganographySteganography (cont.)(cont.)

�� Though the hiding method shown isThough the hiding method shown isvery sensitive to the editing of thevery sensitive to the editing of thecovering picture, it has acovering picture, it has aconsiderable advantage too:considerable advantage too:It does not increase the size of theIt does not increase the size of thecovering filecovering filefor it utilizes its redundancyfor it utilizes its redundancy(As it was shown by bitmap images(As it was shown by bitmap imagesofof KandóKandó sculpture)sculpture)


Steganography (cont.)Steganography (cont.)�� Steganography covers even the existence of anySteganography covers even the existence of any

hidden messagehidden message..�� One disadvantage is thatOne disadvantage is that quite an amount ofquite an amount of

covering information is neededcovering information is needed to hide whateverto hide whateverwe want to. At least 8 to 10 times more if wewe want to. At least 8 to 10 times more if wereally want it to be non detectable.really want it to be non detectable.

�� Nevertheless if the fact of the hiding becomesNevertheless if the fact of the hiding becomesevidentevident then the entire business is virtuallythen the entire business is virtuallyuseless,useless, if we had not encrypted the information inif we had not encrypted the information inadvance.advance.

�� The really big disadvantage is thatThe really big disadvantage is that editing orediting orcompressing the picture do catastrophic damagecompressing the picture do catastrophic damageto the hidden informationto the hidden information..


The electronic watermarkingThe electronic watermarking

�� It has at least two meanings as followsIt has at least two meanings as follows�� There areThere are

•• visible andvisible and•• non visible enon visible e--watermarks.watermarks.

�� The problem is that visibility as such isThe problem is that visibility as such isvery subjective.very subjective.

�� We may talk aboutWe may talk about hardly visiblehardly visible andandvery much visiblevery much visible ee--watermarks as well.watermarks as well.


MaskingMasking�� This is a hiding technology which isThis is a hiding technology which is

suitable to produce bothsuitable to produce both•• NonNon--detectable edetectable e--watermarks andwatermarks and•• ee--watermarks of different grade ofwatermarks of different grade of

visibilityvisibility�� The carrier medium is modified aThe carrier medium is modified a

suitable way by the information to besuitable way by the information to bethe watermark and the colors of thethe watermark and the colors of thepixels below the mask are modified.pixels below the mask are modified.

�� The visibility depends upon the amountThe visibility depends upon the amountof modification.of modification.


Demonstrating masking (1)Demonstrating masking (1)

Theoriginalpicture(18 957bytes)


Demonstrating masking (2)Demonstrating masking (2)

MaskingAppliedTo thePicture.VisibleWater-Mark(19 296bytes =+ 1,8%

watermark


Applying maskingApplying masking

�� The location of masked stegoThe location of masked stegoinformation within the picture’s areainformation within the picture’s areais NOT indifferent.is NOT indifferent.

�� Essentially the same technology isEssentially the same technology isapplied in case of video tapes orapplied in case of video tapes orDVDs, butDVDs, but•• the watermark is put different locationsthe watermark is put different locations

on the subsequent slideson the subsequent slides•• there is no watermark in EVERY slides ofthere is no watermark in EVERY slides of

the movie.the movie.


DCT: Discrete Cosine TransformationDCT: Discrete Cosine Transformation

�� The JPEG technologyThe JPEG technologydivides the picturedivides the pictureinto 8x8 pixelinto 8x8 pixelss matmat--ricesrices, then it performs, then it performsa diagonal scanninga diagonal scanningand quantize theand quantize thepixels’ difference topixels’ difference tothe average pixelthe average pixelcolor of the 8 by 8color of the 8 by 8matrix. Whenmatrix. When quantiquanti--zing it applies azing it applies a modimodi--fiedfied version of FFT.version of FFT.

Scanning the 8 by 8 pixels matrix


DCT: Discrete Cosine TransformationDCT: Discrete Cosine Transformation

�� The floating point results got fromThe floating point results got fromthe scanning and quantizing can bethe scanning and quantizing can betruncated either to downward ortruncated either to downward orupward correlating the bit values toupward correlating the bit values tobe hidden.be hidden.

�� This technology is applied mostly toThis technology is applied mostly toJPEG compressions.JPEG compressions.


The DCT can be a tool as wellThe DCT can be a tool as wellto reveal hidingto reveal hiding

�� For the close relation between DFT andFor the close relation between DFT andDCT the last one could be considered as aDCT the last one could be considered as akind of discrete frequency spectrum.kind of discrete frequency spectrum.

�� ThThatat spectrum is the one that changesspectrum is the one that changessignificantly if there is any hiddensignificantly if there is any hiddeninformation in a given picture.information in a given picture.

�� In fact, the size of the picture file is alsoIn fact, the size of the picture file is alsoincreases when it contains hiddenincreases when it contains hiddeninformation.information.

�� It does not recover the hidden informationIt does not recover the hidden informationjust detects its existence.just detects its existence. ((We’llWe’lldemonstratedemonstrate itit laterlater.).)


The Spread SpectrumThe Spread SpectrumCommunicationCommunication

�� Its principle was invented at the end of theIts principle was invented at the end of theSecond WWSecond WW alongalong withwith the RADARthe RADARtechnology.technology.

�� Such a communication applies a very wideSuch a communication applies a very wideband spectrum, butband spectrum, but

�� At a time a narrow band of that spectrumAt a time a narrow band of that spectrumcarries valuable information only, while in allcarries valuable information only, while in allthe other part of the spectrum noise isthe other part of the spectrum noise istransmitted.transmitted.

�� In addition the relevant narrow band isIn addition the relevant narrow band ischanged by time to time following a patternchanged by time to time following a patternthat has been agreed upon between thethat has been agreed upon between thecommunicating partners.communicating partners.


Hiding information intoHiding information intosound tracks (1)sound tracks (1)

�� The carrier is a digitized audio information.The carrier is a digitized audio information.�� In case of digital sound CDs the samplingIn case of digital sound CDs the sampling

frequency standard is 44 kHz andfrequency standard is 44 kHz and�� the quantizing resolution is at least 12 bits.the quantizing resolution is at least 12 bits.�� That yields an amplitude scale of 4096 levels, inThat yields an amplitude scale of 4096 levels, in

which changing the LSB means a 0.025 % relativewhich changing the LSB means a 0.025 % relativemodification which is essentially a distortion.modification which is essentially a distortion.

�� Such an extremely little distortion cannot beSuch an extremely little distortion cannot beperceived by human ear.perceived by human ear.

�� In case of silent parts of a sound track it still mayIn case of silent parts of a sound track it still maybe overheard.be overheard.


Hiding information intoHiding information intosound tracks(2)sound tracks(2)

�� Both the hiding and the recoveringBoth the hiding and the recoveringtechnology is essentially the same astechnology is essentially the same asit was shown in case of coveringit was shown in case of coveringpictures.pictures.

�� Naturally it needs computer andNaturally it needs computer andappropriate program.appropriate program.

�� Some commercial studio software areSome commercial studio software areprepared in advance to insertprepared in advance to insertee--watermarks.watermarks.


Summary (1)Summary (1)�� The meaning of Steganography isThe meaning of Steganography is

hiding information and the relatedhiding information and the relatedtechnologies.technologies.

�� There is a principal difference betweenThere is a principal difference betweenSteganography and Encryption,Steganography and Encryption,however they can meet at some pointshowever they can meet at some pointstoo.too.

�� They can be applied together, i.e.They can be applied together, i.e.eencryptedncrypted information can be hidden ininformation can be hidden inaddition.addition. (As it will be demonstrated soon.)(As it will be demonstrated soon.)


Summary (2)Summary (2)

�� To hide something a coveringTo hide something a coveringmedium is always needed. (Picture,medium is always needed. (Picture,sound track, text or even thesound track, text or even thestructure of a file systemstructure of a file system,, etcetc.).)

�� The covering medium must beThe covering medium must beredundant, otherwise the hiddenredundant, otherwise the hiddeninformation could be detected easily.information could be detected easily.(This is the conception of hiding into noise.)(This is the conception of hiding into noise.)



�� The technology of hiding shouldThe technology of hiding shouldmatch the nature of the medium.match the nature of the medium.

�� The hidden information should not beThe hidden information should not belost, if the carrying medium islost, if the carrying medium isedited, modified, formatted, reedited, modified, formatted, re--sized,sized,compressed or printed.compressed or printed.

�� That’s a difficult task to realize.That’s a difficult task to realize.



�� It’s an expectation as well, that theIt’s an expectation as well, that thefact of hidden informationfact of hidden information shouldshould bebeimpossible to detect by other thenimpossible to detect by other thenthe addressee.the addressee.

�� On the other hand securityOn the other hand security servicesservicesshould have methods to detect suchshould have methods to detect suchinformation. At least its existence.information. At least its existence.

�� Realizing a good tradeRealizing a good trade--off there areoff there aredifferent technologies.different technologies.



�� Nowadays the most popular applicationNowadays the most popular applicationof Steganography is hidingof Steganography is hiding copy rightscopy rightsand otherand other commercial informationcommercial information..

�� Such kind of hidden information isSuch kind of hidden information isknown asknown as ee--watermarkwatermark..

�� TheThe ee--watermark is not alwayswatermark is not alwaysinvisibleinvisible. There are cases when it is. There are cases when it ismade deliberately strikingly visible. E.g.made deliberately strikingly visible. E.g.in case of trial versions of software.in case of trial versions of software.

October 2003Seminar #1 in HTI 53

Now a demonstration of aNow a demonstration of acommercial stego softwarecommercial stego software

willwill commencecommence!!

http://www.invisiblesecrets.com

Steganography - · PDF fileDecember 03 Seminar #1 in HTI 3 The Basic Types of Steganography Substitutional Steganography • Some elements of the redundant covering medium are substituted

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