Security 3

1
Security 3

• Distributed Systems
• Lecture 16

2
Overview

• Steganography
• Digital Watermarking

3
Steganography
Taken from An Analysis of Steganographic
Techniques by Popa
4
Steganography

• First evidence in 440BC
• Histiaeus persian revolution messages
• Apparently neutral?s protest is thoroughly
  discounted and ignored. Isman hard hit. Blockade
  issue affects for pretext embargo on by-products,
  ejecting suets and vegetable oils.? ?
• Pershing sails for NY June 1? can be retrieved

5
Steganography

• Integrity of hidden information must be preserved
• Stego object must not visibly change
• Changes in the stego object must not affect the
  watermark
• Always assume the presence of watermark is
  well-known

6
Steganography

• Private vs public
• Private Require secret key
• Public Can look at watermark, but cannot tamper
  it
• Private
• Type I Require original and modified objects,
  ouput watermark
• Type II Require Orginal, Modified and Watermark,
  answer yes or no

7
Fingerprinting vs watermarking

• Fingerprints are user specific
• Encrypted checksum user ID
• Watermarks are vendor specific
• Independent of users
• Protect against illegal copies
• Watermarks more feasible for mass produced
  CDs/disks

8
Techniques

• Audio
• Frequency masking
• Temporal masking
• Source codea 5b 7c 9
• Move around unordered statements to to encode a
  detectable pattern
• Useful for binary code as well

9
Techniques

• Text-based techniques
• Line-shift coding
• Word-shift coding
• Feature coding
• White-space
• Content-based

10
Image-based
Visible watermarking taken from Jonathan et al
univ of birmingjam
11
Least-significant bit encoding
Host Pixel 10110001 Secret Pixel 00111111 New
Image Pixel 10110011
12
More techniques

• Image DCT
• Round off coefficient
• Sound
• MP3 use parity bits
• Video
• Lots of room for sneaking in additional
  information

13
Example
Results of StirMark. Taken from Information
Hiding - A Survey by Peticolas et al.
14
Mosaic Attack
15
More attacks

• Intrepretation Attacks
• Confuse the watermark checker
• Implementation Attacks
• Digimarc was compromised by using a debugger to
  crack the ID checking part