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UNIVERSITY POLITEHNICA of BUCHAREST DEPARTMENT OF COMPUTER SCIENCE. Transmisia datelor multimedia in retele de calculatoare Steganografia. Milas Iulian Constantin < iulian_milas@yahoo.com >. Introducere. Scopul steganorafiei ; Diferenta intre criptografie si steganografie ;

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Transmisia datelor multimedia in retele de calculatoare Steganografia

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UNIVERSITY POLITEHNICA of BUCHAREST

DEPARTMENT OF COMPUTER SCIENCE

Transmisiadatelor multimedia in retele de calculatoareSteganografia

MilasIulianConstantin

<iulian_milas@yahoo.com>


Introducere

  • Scopulsteganorafiei;

  • Diferentaintrecriptografiesisteganografie;

  • steganography_medium = hidden_message + carrier + steganography_key


ClasificareaThenicilor de Steganografie


Null Ciphers

  • Pe Internet spam-urilesuntpotentialepurtatoare de mesaje:

    Dear Friend , This letter was specially selected to be sent to you ! We will comply with all removal requests ! This mail is being sent in compliance with Senate bill 1621 ; Title 5 ; Section 303 ! Do NOT confuse us with Internet scam artists . Why work for somebody else when you can become rich within 38 days ! Have you ever noticed the baby boomers are more demanding than their parents & more people than ever are surfing the web ! etc.

  • Meet at Main and Willard at 8:30


Metodefolosite in purtatoriidigitali:The Embedding Process


Metodefolosite in purtatoriidigitali: Fingerprinting si Watermarking

  • Ceestefingerprinting?

  • CeesteWatermarking?


Metodefolosite in purtatoriidigitali: Least Significant Bit Insertion #1


Metodefolosite in purtatoriidigitali: Least Significant Bit Insertion #2

  • Sa ascundemlitera “G” care are codul ASCII binar 01000111

  • Fie secventa de octetidintr-o imagine :

  • Codarealui “G” peLSB:


Metodefolosite in purtatoriidigitali: Public Key Steganography

  • Presupunem ca measajulestecodat cu o cheieprivata;

  • Dar unuldintreceidoi nu are decatcheiapublica;

  • Ce face primul?

  • Dar al doilea?


Metodefolosite in purtatoriidigitali: Transform Domain Based Steganography

  • Algoritmii de extractie se impart in douagrupuri:

    - domeniuspatiu/timp;

    - domeniutransformare;

  • AlgoritmulPatchwork ;


Metodefolosite in purtatoriidigitali:Diverse #1

  • Spread-spectrum steganography – se bazeazapeportiunile de “energie” ridicata;

  • Ascundere a mesajelor in portiunileneutilizate ale headerelorfisierelor;

  • Folosireapartitiilor secrete de pe hard;

  • Micimodificari ale sunetului: siftarefaza, cadentavorbirii;


Metodefolosite in purtatoriidigitali:Diverse #2

  • Fisierele audio suntfoartebunepentruascunsmesajedeoarecesuntmari, iarinformatiaascunsa se vagasiigreu;

  • Steganografia nu estelimitatadoar la imaginisifisiere audio:

    - executabilele – Ex: redundantainstructiunilori386 ==> se pastreazasidimensiuneaoriginala a fisierului;


DetectiaSteganografiei #1

  • Steganaliza :

    - detecteazasauestimeazainformatiaascunsapebazaobservariiunortransferuri de date, farasafacavreopresupunereasupraalgoritmului de steganografie;

  • O prima metodaesteurmarirea “purtatorului”;

  • O altametodaesteurmarireamodificarilorstructurale ale “purtatorului”;

  • Tehnicilesteganograficealtereaza de obiceistatisticiledespre un “purtator”;


DetectiaSteganografiei #2

  • Steganalizaeste in general signature-based;

  • SteganalizaAnomaly-based – (blind steganalysis);


Exemple de Steganografie

  • Vomascunde un GIF de 11,067 bytes intr-un GIF, JPEG si WAV;

    Fig 1:


Imagine ascunsaintr-un GIF #1

  • Fig urmeste o imagine a Washington DC ce confine Fig1. Imagineainitialaeste632,778 bytes sifoloseste 249 culoriunice; la final 677,733 bytes si 256 culoriunice; marimeaestemai mare din cauzafolosiriiextensiei de culori.


Imagine ascunsaintr-un GIF #2

  • Paleta de culori de la img Washington (purtatorul) inainte (stanga) sidupa (dreapta) ceFig1 a fostascunsa:


Imagine ascunsaintr-un JPEG

  • Initial 207,244 bytes si 224,274 culoriunice;

  • Dupasteganografiere: 207,275 bytes si 227,870 culoriunice;

  • Nu putemvedeavreopaleta de culorideoarece JPEG folosestecodarea 24 bit-color siDCT;


Imagine ascunsaintr-un WAV

  • Initial 178,544 bytes, iar WAV-ulsteganografiat 178,298 bytes :


Concluzii

  • Teroristiisi eBay;

  • Dupa11 Septembrie 2001 s-au efectuatmultestudiipecontinutulInternetului:

    - s-au verificatmilioane de JPEG-uripe eBay ==> 1-2% din imaginieraususpecte – niciunmesajgasit;

    - alt studiu a examinatcatveasute de mii de imagini de pe diverse pagini Web alese random ==> rezultatesimilare;

  • Decinimicconcludent – doar JPEG-uri s-au verificat; numarscazut de site-uri; unelerapoarte pot fitinute secrete;


Q&A


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