Individually Watermarked Information Distributed Scalable by Modified Transforms.

摘要

Distribution of secret information in audio, video or images to known recipients are made secure by encryption. The weak part of such distribution scheme is after the decryption of the content, since if the media deliberately or by mistake is redistributed the cryptology no longer is effective. One way to discourage deliberate re-distribution is to embed the information with individual watermarks (sometimes called fingerprinting) for each recipient. If for example a copy of an illegally redistributed image is obtained the individual watermark can be retrieved and identify the redistribution source. After the source is traced an investigation must be made to decide if the re-distribution was made deliberately or by mistake, or if the image somehow has been stolen from the original recipient. The problem with distribution of individually watermarked information is that to distribute a unique content by unicast to each recipient requires a large bandwidth and much power at the distributor. This is especially apparent if the number or recipients are large. Therefore scalable methods, with a bandwidth need that do not expand drastically for even large number of recipient, are needed for distribution of individually marked content. Previous methods for solving the scalable distribution problem either use special networks with active routers or split the content into a shared non watermarked part and a watermarked part. The watermarked part can be unique for each recipient or in part be shared with other recipients. All of these methods will need a larger bandwidth and complex embedding at the distributor or in the network. Another type of methods distributes the same content to all recipients but some type of descrambling is needed at the recipient to be able to use the content.