Watercast: watermarking multicast media

Watercasting: Distributed Watermarking of Multicast Media Ian Brown, Colin Perkins and Jon Crowcroft

Introduction
Watermarking
Working with multicast - watercast
Applications

Watermarking
LSBs, compression parameters etc. changed to imperceptibly mark image
Images courtesy of Bernard Clarisse and Fabien Petitcolas

Why is watermarking important?
Cryptography can only protect data in transit - customers need keys.
Cannot rely on ends to enforce access control in mass market - SDMI, DVD.
Watermarks can’t prevent illegal redistribution, but allow miscreants to be traced.

Watermarking and multicast
Sending differently marked data streams to each client rules out multicast.
Even if bandwidth was available, marking algorithms don’t scale.

Watercasting: marking data
Server watermarks and multicasts n versions of each packet, where n  tree depth
Routers drop one packet version based on next hop’s IP address
Last-hop router passes on only one packet version based on receiver and router identification key

Example
Source creates 5 versions of each packet
Each router drops one version
Last-hop router passes on one version to client

Implementation
PGM application-layer filters could be used at routers, but have extra security requirements
Reverse SPMs require special support
Client only needs way to obtain security parameters from server - no media tool alteration is necessary

Source requirements
Provide each client with media decryption keys after receiving valid reverse SPM
Store original media, client details and tree topology for as long as content needs to be traced

Tracing traitors
Classify recovered clip’s packets - ACCEDBADABCD
Simulate network behaviour during that period
Calculate users and routers who individually or in collusion are most likely to have produced clip

Reducing resource requirements
Each router forwards only minimum number of packet versions
Only mark selected packets - tradeoff between bandwidth used and quality of ripped-off data

Applications
Information value and customer resources may not justify retail versions.
But very appropriate for wholesale distribution - digital films, Blockbuster, in-flight entertainment etc.

Conclusions
Watermarking is an essential technology for digital content protection.
Our scheme makes marking scalable, processor and bandwidth-wise.
Now busy ironing out design wrinkles ready for implementation.

Watercast: watermarking multicast media

by Ian Brown on Sep 07, 2008

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Watercast: watermarking multicast media — Presentation Transcript