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Transmisia datelor multimedia in retele de calculatoare Steganografia

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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  1. UNIVERSITY POLITEHNICA of BUCHAREST DEPARTMENT OF COMPUTER SCIENCE Transmisiadatelor multimedia in retele de calculatoareSteganografia MilasIulianConstantin <iulian_milas@yahoo.com>

  2. Introducere • Scopulsteganorafiei; • Diferentaintrecriptografiesisteganografie; • steganography_medium = hidden_message + carrier + steganography_key

  3. ClasificareaThenicilor de Steganografie

  4. 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

  5. Metodefolosite in purtatoriidigitali:The Embedding Process

  6. Metodefolosite in purtatoriidigitali: Fingerprinting si Watermarking • Ceestefingerprinting? • CeesteWatermarking?

  7. Metodefolosite in purtatoriidigitali: Least Significant Bit Insertion #1

  8. 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:

  9. Metodefolosite in purtatoriidigitali: Public Key Steganography • Presupunem ca measajulestecodat cu o cheieprivata; • Dar unuldintreceidoi nu are decatcheiapublica; • Ce face primul? • Dar al doilea?

  10. Metodefolosite in purtatoriidigitali: Transform Domain Based Steganography • Algoritmii de extractie se impart in douagrupuri: - domeniuspatiu/timp; - domeniutransformare; • AlgoritmulPatchwork ;

  11. 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;

  12. Metodefolosite in purtatoriidigitali:Diverse #2 • Fisierele audio suntfoartebunepentruascunsmesajedeoarecesuntmari, iarinformatiaascunsa se vagasiigreu; • Steganografia nu estelimitatadoar la imaginisifisiere audio: - executabilele – Ex: redundantainstructiunilori386 ==> se pastreazasidimensiuneaoriginala a fisierului;

  13. DetectiaSteganografiei #1 • Steganaliza : - detecteazasauestimeazainformatiaascunsapebazaobservariiunortransferuri de date, farasafacavreopresupunereasupraalgoritmului de steganografie; • O prima metodaesteurmarirea “purtatorului”; • O altametodaesteurmarireamodificarilorstructurale ale “purtatorului”; • Tehnicilesteganograficealtereaza de obiceistatisticiledespre un “purtator”;

  14. DetectiaSteganografiei #2 • Steganalizaeste in general signature-based; • SteganalizaAnomaly-based – (blind steganalysis);

  15. Exemple de Steganografie • Vomascunde un GIF de 11,067 bytes intr-un GIF, JPEG si WAV; Fig 1:

  16. 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.

  17. Imagine ascunsaintr-un GIF #2 • Paleta de culori de la img Washington (purtatorul) inainte (stanga) sidupa (dreapta) ceFig1 a fostascunsa:

  18. 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;

  19. Imagine ascunsaintr-un WAV • Initial 178,544 bytes, iar WAV-ulsteganografiat 178,298 bytes :

  20. 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;

  21. Q&A

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