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Secure Multimedia Communication. Curtsey of Professor Min Wu Electrical & Computer Engineering Univ. of Maryland, College Park. Evolving Multimedia and Comm. Technologies. Well-developed multimedia standards @ Source compression has matured: MPEG-1 Layer 3, JPEG-2000, MPEG-4

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Secure multimedia communication l.jpg

Secure Multimedia Communication

Curtsey of Professor Min Wu Electrical & Computer EngineeringUniv. of Maryland, College Park


Evolving multimedia and comm technologies l.jpg
Evolving Multimedia and Comm. Technologies

  • Well-developed multimedia standards @

    • Source compression has matured: MPEG-1 Layer 3, JPEG-2000, MPEG-4

    • Mature standards have created many devices and applications: MP3, DVD, Streaming video

  • Rapid development of communication technologies

    • Broadband: DSL, Cable Modems, Satellite

    • HDTV will convey data and media

    • Wireless for any-where any-time connections: 3G, 802.11A/B

  • Advances in networking technologies

    • Promise of ubiquitous, heterogeneous networks.

Min Wu @ U. Maryland 2002


Compression l.jpg

@

Compression

  • Color image of 600x800 pixels

    • 600*800 * 24 bits/pixel = 1.44M bytes

    • After JPEG compression (popularly used on web)

      • only 89K bytes

      • compression ratio ~ 16:1

  • Movie

    • 720x480 per frame, 30 frames/sec, 24 bits/pixel ~ 243M bits/sec

    • DVD ~ about 5M bits/sec

      • Compression ratio ~ 48:1

  • Audio

    • 44.1KHz * 16bit * 2 ch. = 1.4 Mbps

    • MP3 ~ about 64K – 128 Kbps

“Library of Congress” by M.Wu (600x800)

Min Wu @ U. Maryland 2002


Mm data comm effective mm comm l.jpg
MM + Data Comm. = Effective MM Comm.?

  • Multimedia vs. Generic Data

    • Perceptual no-difference vs. Bit-by-bit accuracy

    • Unequal importance within multimedia data

    • High data volume and real-time requirements

  • Need consider the interplay between source coding and transmission and make use of MM specific properties

  • E.g. wireless video need “good” compression algo. to:

    • Support scalable video compression rate ( from 10 to several hundred kbps)

    • Be robust to the transmission errors and channel impairments

    • Minimize end-to-end delay

    • Handle missing frames intelligently

Min Wu @ U. Maryland 2002


Example error concealment l.jpg

(a) original lenna image

(b) corrupted lenna image

(c) concealed lenna image

25% blocks in a checkerboard pattern are corrupted

corrupted blocks are concealed via edge-directed interpolation

Example: Error Concealment

  • Multimedia-specific ways of error recovery

Examples were generated using the source codes provided by W.Zeng.

Min Wu @ U. Maryland 2002


Error resilient coding with localized synch marker l.jpg

H.263 encoder

H.263 decoder

Output sequence

Input

sequence

Error concealment

MB detection

LRM

Random noise

H.263 with FRM

H.263 with LRM

Error-Resilient Coding with Localized Synch Marker

  • Reduce error propagation

(From D. Lun @ HK PolyUniv. Short Course 6/01)

Min Wu @ U. Maryland 2002


Demands on info security and protection l.jpg
Demands on Info. Security and Protection

  • Intellectual property management for digital media

    • Promising electronic marketplace for digital music and movies

    • Napster controversy

  • Conventional encryption alone still leaves many problems unsolved

    • Directly apply conventional encryption to compressed MM bitstream?

      • May lose error resilience and scalability

      • Require much computation power

      • Exploring MM property in encryption is desired

    • How to distinguish changes introduced by compression vs. malicious tampering?

      • Bit-by-bit accuracy is not always desired authenticity criterion for MM

    • Protection from encryption vanishes once data is decrypted

      • Still want establish ownership and restrict illegal re-distributions

Min Wu @ U. Maryland 2002


Visible digital watermarks l.jpg
Visible Digital Watermarks

from IBM Watson web page“Vatican Digital Library”

Min Wu @ U. Maryland 2002


Invisible watermark l.jpg
Invisible Watermark

  • human visual model for imperceptibility: protect smooth areas and sharp edges

  • 1st & 30th Mpeg4.5Mbps frame of original, marked, and their luminance difference

Min Wu @ U. Maryland 2002


Data hiding for annotating binary line drawings l.jpg
Data Hiding for Annotating Binary Line Drawings

pixel-wise difference

marked w/ “01/01/2000”

original

Min Wu @ U. Maryland 2002


Multimedia fingerprinting trace traitors l.jpg

original media

Customer: Eve

Sell Content

= Fingerprint

101101 …

compress

embed

Fingerprint Tracing:

Candidate

Fingerprint

= Suspicious

Search

Database

extract

101101 …

Customer: Eve

Multimedia Fingerprinting: Trace Traitors

Min Wu @ U. Maryland 2002


16 bit anti collusion code acc example for detecting 3 colluders l.jpg

( -1, 1, 1, 1, 1, 1, …, -1, 1, 1, 1 ) User#4

User#1 ( -1,-1, -1, -1, 1, 1, 1, 1, …, 1 )

Collude by Averaging

Uniquely Identify User 1 & 4

Extracted fingerprint code ( -1, 0, 0, 0, 1, …, 0, 0, 0, 1, 1, 1 )

16-bit Anti-Collusion Code (ACC) Example for Detecting 3 Colluders

Min Wu @ U. Maryland 2002


Conveying one bit through noisy channel l.jpg
Conveying One-bit Through Noisy Channel

  • Optimal detection ~ minimize prob. of error

    MAP ~ maximize posterior probability

    => ML ~ maximum likelihood detector [for equal prior]

    => Minimum distance detector [for iid Gaussian noise]

    => Maximum correlation detector [for equal-energy sig.]

  • Detection statistics

    • [correlator] i yi si

      • Prob. distribution under each hypothesis ~ N( ||s||2 , ||s||2d 2)

    • [correlator with unit-variance] i yi si/ [(i si 2) d 2]1/2 ~ N( ||s||/d ,1)

Min Wu @ U. Maryland 2002


Performance of optimal detector l.jpg
Performance of Optimal Detector

  • Probability of detection error = Q (||s||/d )

    • Q (x) is monotonically decreasing for non-negative x

    • Signal-to-noise ratio (SNR) ~ (||s||2/n) / d 2

  • Communications under very low SNR

    • Choose large n

      • collect info. (energy) from many signal components

      • a basic idea behind “spread spectrum communications”

  • Useful in invisible watermarking (data hiding)

    • Adding or subtracting a weak signal to convey one-bit hidden info.

    • Will go into more details next time

  • Extension for non-i.i.d. Gaussian noise

Min Wu @ U. Maryland 2002


Add security layers to communications l.jpg
Add Security Layers to Communications

  • Confidentiality =>

    • Messages for “your eyes” only

  • Integrity

    • Message is what sender intended to deliver at this moment

  • Threats and Attacks on information

    (1) Use limited info. to find out ways to decipher confidential msg.

    • Prefer a system s.t. the best attack strategy is guessing and exhaustive search

      => unbreakable within reasonable time period

      (2) Altering a message s.t. authentication system still regard it as unaltered

      (3) Replaying an old message as if it is being sent by sender right now

Min Wu @ U. Maryland 2002


Useful crypto tools building blocks l.jpg
Useful Crypto Tools/Building-Blocks

  • Crypto’ly strong one-way function f(x)

    • Easy to compute f(x) given x, but difficult to find x when given f(x)

    • Given a set of (xi, f(xi)) and f(x), difficult to find x

    • SHA (Secure Hash Algorithm) and DES are popular choice for one-way function

  • “Low-cost” crypto’ly strong random number generator

    • Generating truly random seq. via natural randomness ~ flip coins, etc.

      • slow and difficult to store/transmit efficiently

      • prefer low cost in both computation and storage/delivery

    • Use “pseudo-random” generator that can

      • Given a subset of output bits, the rest are unpredictable

      • Produce output using a small secret ~ say, a small set of parameters

      • Produce output fast and be easily implementation, say, in software

    • Use one-way function to generate unpredictable bits Xj = f( s + j )

      • seed “s”, one-way function “f( )”

Min Wu @ U. Maryland 2002


Useful crypto tools building blocks17 l.jpg
Useful Crypto Tools/Building-Blocks

  • Crypto’ly strong hash or digest function H( )

    • One-way “compression” function

      • M-bit input to N-bit output often with fixed N and M >> N

      • Often used to produce a short ID for identifying the input

    • Properties to be satisfied:

      1) Given a message m, H(m) can be calculated very quickly

      2) Given a digest y, it is computationally infeasible to find a message m s.t. H(m) = y (i.e., H is one-way)

      3) It is computationally infeasible to find messages m1 & m2 s.t. H(m1) = H(m2) (i.e. H is strongly collision-free)

    • Keyed Hash:

      • H( k, m ) = Hash( concatenated string derived from k & m )

    • Commonly used crypto hash

      • 160-bit SHA (Secure Hash Algorithm) by NIST

      • 128-bit MD4 and MD5 by Rivest

Min Wu @ U. Maryland 2002


Encryption ciphers l.jpg
Encryption / Ciphers

  • Examples <=

    • Shift cipher: e.g. “plaintext” => “sodlqwhaw” (shift by +3)

    • Substitution cipher ~ equiv. to apply a permutation of alphabet to plaintext

    • Stream cipher using XOR ~ Xi Ki = Yi

      • one-time pad with key size as large as the message

    • Block cipher

      • encrypt a large block of data at a time to make freq. attack difficult

      • many modern ciphers are block ciphers

  • Attacks

    • A small number of searches/guesses

    • Cipher-text and Plaintext attack

      • use some knowns to find/guess unknowns ~ solving equation arrays

    • Frequency analysis (esp. when plaintext is natural language)

Min Wu @ U. Maryland 2002


Encryption keys l.jpg
Encryption Keys

  • Symmetric

    • Encryption and decryption share the same key

    • Key establishment and update are often non-trivial

  • Asymmetric (public-key crypto)

    • Different keys for encryption and decryption

    • Difficult to derive one key from the other key

    • Useful for confidentiality, identity verification, key establishment, etc.

    • Message for Bob’s eye

      • Alice encrypts a msg using Bob’s public key

      • only private key holder can decrypt a ciphertext encrypted by the corresponding public key

    • Message only Bob can produce

      • Bob encrypts a msg using his private key

      • only private key holder can produce a ciphertext decryptable by the corresponding public key

Min Wu @ U. Maryland 2002


A few widely used ciphers l.jpg

K

F1

K

F2

A Few Widely Used Ciphers

  • DES and new AES

    • A building block (“Feistel”) scrambles the input

    • Apply a given number of rounds of Feistel blocks

    • Extensive cryptanalysis

      • A good crypto system should not rely on the secrecy of the algorithm

  • RSA (public-key encryption):

    • Security strength based on discrete log problem

      • Fix a large prime p, let nonzero integer a and b (mod p) s.t. b = a x=> difficult to find x

    • Encryption and Decryption perform exponential modulo operation with different exponents

      • slow

Min Wu @ U. Maryland 2002


Data integrity verification data authentication l.jpg
Data Integrity Verification (data authentication)

  • Authentication is always “relative”

    • with respect to a reference

  • How to establish and use a reference

    [Method-1] Give a “genuine” copy to a trusted 3rd party

    [Method-2] Append “check bits”

    • Want hard to find a different meaningful msg. with same “check bits”=> use crypto’ly strong hash

    • Want tamper-proof if hash func. is public

      • Encrypt concatenated version of message and hash

      • Keyed Hash (Message Authentication Code) ~ no extra encryption needed

  • Digital signature algo. (using public-key crypto)

    • Signed Msg|Hash ~ i.e., encrypt by private key s.t. others can’t forge

Min Wu @ U. Maryland 2002


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