Watercast: watermarking multicast media

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Presented at Networked Group Communications in Pisa, 1999

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Watercast: watermarking multicast media

  1. 1. Watercasting: Distributed Watermarking of Multicast Media Ian Brown, Colin Perkins and Jon Crowcroft
  2. 2. Introduction <ul><li>Watermarking </li></ul><ul><li>Working with multicast - watercast </li></ul><ul><li>Applications </li></ul>
  3. 3. Watermarking <ul><li>LSBs, compression parameters etc. changed to imperceptibly mark image </li></ul>Images courtesy of Bernard Clarisse and Fabien Petitcolas
  4. 4. Why is watermarking important? <ul><li>Cryptography can only protect data in transit - customers need keys. </li></ul><ul><li>Cannot rely on ends to enforce access control in mass market - SDMI, DVD. </li></ul><ul><li>Watermarks can’t prevent illegal redistribution, but allow miscreants to be traced. </li></ul>
  5. 5. Watermarking and multicast <ul><li>Sending differently marked data streams to each client rules out multicast. </li></ul><ul><li>Even if bandwidth was available, marking algorithms don’t scale. </li></ul>
  6. 6. Watercasting: marking data <ul><li>Server watermarks and multicasts n versions of each packet, where n  tree depth </li></ul><ul><li>Routers drop one packet version based on next hop’s IP address </li></ul><ul><li>Last-hop router passes on only one packet version based on receiver and router identification key </li></ul>
  7. 7. Example <ul><li>Source creates 5 versions of each packet </li></ul><ul><li>Each router drops one version </li></ul><ul><li>Last-hop router passes on one version to client </li></ul>
  8. 8. Implementation <ul><li>PGM application-layer filters could be used at routers, but have extra security requirements </li></ul><ul><li>Reverse SPMs require special support </li></ul><ul><li>Client only needs way to obtain security parameters from server - no media tool alteration is necessary </li></ul>
  9. 9. Source requirements <ul><li>Provide each client with media decryption keys after receiving valid reverse SPM </li></ul><ul><li>Store original media, client details and tree topology for as long as content needs to be traced </li></ul>
  10. 10. Tracing traitors <ul><li>Classify recovered clip’s packets - ACCEDBADABCD </li></ul><ul><li>Simulate network behaviour during that period </li></ul><ul><li>Calculate users and routers who individually or in collusion are most likely to have produced clip </li></ul>
  11. 11. Reducing resource requirements <ul><li>Each router forwards only minimum number of packet versions </li></ul><ul><li>Only mark selected packets - tradeoff between bandwidth used and quality of ripped-off data </li></ul>
  12. 12. Applications <ul><li>Information value and customer resources may not justify retail versions. </li></ul><ul><li>But very appropriate for wholesale distribution - digital films, Blockbuster, in-flight entertainment etc. </li></ul>
  13. 13. Conclusions <ul><li>Watermarking is an essential technology for digital content protection. </li></ul><ul><li>Our scheme makes marking scalable, processor and bandwidth-wise. </li></ul><ul><li>Now busy ironing out design wrinkles ready for implementation. </li></ul>

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