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Secure Multimedia CommunicationPowerPoint Presentation

Secure Multimedia Communication

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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

Curtsey of Professor Min Wu Electrical & Computer EngineeringUniv. 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
- 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

- 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.?

- 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

(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

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

- 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

- Directly apply conventional encryption to compressed MM bitstream?

Min Wu @ U. Maryland 2002

Visible Digital Watermarks

from IBM Watson web page“Vatican Digital Library”

Min Wu @ U. Maryland 2002

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

pixel-wise difference

marked w/ “01/01/2000”

original

Min Wu @ U. Maryland 2002

Customer: Eve

Sell Content

= Fingerprint

101101 …

compress

embed

Fingerprint Tracing:

Candidate

Fingerprint

= Suspicious

Search

Database

extract

101101 …

Customer: Eve

Multimedia Fingerprinting: Trace TraitorsMin Wu @ U. Maryland 2002

( -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 ColludersMin Wu @ U. Maryland 2002

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||2d 2)

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

- [correlator] i yi si

Min Wu @ U. Maryland 2002

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”

- Choose large n
- 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

- 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

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

Min Wu @ U. Maryland 2002

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( )”

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

Min Wu @ U. Maryland 2002

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

- One-way “compression” function

Min Wu @ U. Maryland 2002

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

- 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

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

- Security strength based on discrete log problem

Min Wu @ U. Maryland 2002

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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