Data hiding - Steganography

Data hiding - Steganography

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  Data Hiding Mohamed Talaat 1
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  Agenda • Introduction toData Hiding • Steganography and Cryptography • Steganography and Watermarking • Types of Digital Steganography • Network Steganography • Steganalysis • Advantages • Applications 2
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  3 Data Hiding -Introduction • Data hiding or steganography: embedding information within a medium in an imperceptible way. • The art of hiding data in a file so that only the sender and intended recipient suspect the presence of hidden data • Steganography means ”covered/secret writing”. • Information can be hidden in all types of digital media.
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  4 Data Hiding -Introduction • The human visual and auditory systems are not perfect. • Inability to distinguish slight color/audio tone alterations. • Information embedding by altering data values imperceptibly: – Image color at certain positions. – Audio intensity at certain time instants.
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  5 Data Hiding -Motivation Motivation: – An opponent cannot control your message, if he cannot find it. – If you hide communications, you can protect your thoughts from censorship or discovery.
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  6 Data Hiding -History • Information hiding dates back to ancient Egypt and Greece. • First techniques included invisible ink, secret writing using chemicals, templates laid over text messages, microdots, changing letter/word/line/paragraph spacing, changing fonts. • Images, video, and audio files provide sufficient redundancy for effective data hiding.
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  7 Steganography and Cryptography •Steganography and Cryptography are closely related. • The difference is in their goals... – Cryptography: although encypted and unreadable, the existence of data is not hidden – Steganography: no knowledge of the existence of the data • Steganography and Cryptography can be used together to produce better protection.
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  8 Steganography and Watermarking •Digital watermarking hides data in a file, and the act of hiding data makes it a form or steganography. • The key difference is their goals... – Steganography: hiding information – Watermarking: extending the file with extra information • Steganographic information must never be apparent to a viewer unaware of its presence.
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  9 Types of DigitalSteganography • Hiding a Message inside Text • Hiding a Message inside Images – Most popular technique • Hiding a Message inside Audio and Video Files
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  10 Hiding a Messageinside Text • First-letter algorithm • Every n-th character • Altering the amount of whitespace
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  11 Hiding a Messageinside Images • The most popular medium! • Least-significant bit (LSB) modifications – 24-bit vs. 8-bit images – Tools to implement LSB: EzStego and S-Tools • Masking and Filtering • Algorithms and Transformations
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  12 Least-Significant Bit (LSB)Method • Most common form of digital steganography. • In a RGB image, Information is hidden in the LSB[s] of the RGB values of each pixel. o In a 24-bit bitmap, each pixel represented by 3 bytes. o Effectively have 3-4 bits of data to hide information in for every pixel: - 8 required for ASCII character
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  13 Color Perception • Changingthe LSB of the Red value by 1 (in 24-bit color depth) is undetectable by the human eye.
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  14 Network Steganography • Modifyingnetwork packet’s header or payload o In TCP/IP networks, unused bits in the IP and TCP header may be used • Packet based length steganography o Manipulation of the MTU (Maximum Transmission Unit) • VoIP - Lost Audio Packets Steganographic Method (LACK) o Transmitter intentionally delays packets by an “excessive” amount of time. o Payload of these lost packets contains the secret information
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  15 Steganalysis • Detecting anddecoding the hidden data within a given medium. • Many algorithms perform a statistical analysis to detect anomalies in the cover object o E.g. repetitive patterns could indicate use of a steganography tool or hidden message • Investigating pixel “neighborhoods” to find inconsistencies with ways files are compressed.
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  16 Problems with Detecting Steganography •Impractical to actively scan all internet content for steganography. • Data is likely encrypted. • Data can be hidden in certain parts of image or scattered based on a random seed. • Messages can be hidden in chains of files: o Can be hidden in several files using different techniques for each. • Time consuming.
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  17 Advantages • Very easyto accomplish • Harder to detect and decrypt • Many mediums: – BMP, JPG, TXT, HTML/XML, PDF, PNG, GIF, AU, WAV, MP3, AVI, TIF, TGA, DLL, EXE
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  18 Applications • Military andintelligence agencies • Health care industry: hiding patients data to the medical images so that only authorized persons can decode this data. • All watermarking applications: – Automatic monitoring – Tamper proofing – Piracy tracking
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  Thanks  19