Patent History Rich For Blu-ray’s Cinavia/Verance Watermarks
After February, all new Blu-ray players under the Advanced Access Content System copy protection license must incorporate a Cinavia/Verance watermark detector that can block playback of unauthorized copy discs or downloads. Our practical tests have shown that the Cinavia/Verance watermark system works, but that few Blu-ray players and movies are using it.
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Since technical details of the system have been very sketchy, we traced its technology trail and patent history. Verance was formed in November 1999 by the merger of two companies, Aris Technologies of Cambridge, Mass., and Solana Technology Corp. of San Diego. Aris and Solana had both developed and patented watermarking techniques and their joint Verance system was selected for use with DVD-Audio to control copying and by the recording industry’s Secure Digital Music Initiative (SDMI) to control music downloads. SDMI soon folded and DVD-Audio was a commercial failure.
We found about 50 U.S. applications and granted patents filed by Verance, many naming Rade Petrovic and Joseph Winograd from Aris as key inventors. The most recent Verance filings claim high level mathematical details of encryption key techniques used. Some (US 6,430,301; 7,616,776; 7,024,018; and 8,005,258) advocate the of multiple watermarks to minimize detection errors. Others describe noise suppression (US 6,122,610) and phase modulation (US 6,145,081) to foil hackers who mount collusion attacks by comparing, averaging or cutting and splicing multiple copies of the same content. Many of these patents stem from documents filed earlier by Aris and Solana.
In 1995 and 1996, Solana was developing systems based on spread spectrum or “colored noise,” in which the mark is added to a sound signal as a smear of quiet and subtly varying noise that’s inaudible to the human ear (US 5,822,360; 6,154, 484; 5,940, 429; 5,719,937; and 5,937,000).
Aris then was working along similar lines with spread spectrum coding (US 5,774,452 and 6,005,501). But in 1997, even before the SDMI rejected the idea of adding coded noise to music, Aris changed course and developed a completely different technique that relies on slightly altering the levels of peak sounds in a coded pattern. Verance followed this line of development. Early patents (US 5,828,325; 6,175,627; 6,683,958; 7,606,366; and International filings WO 98/53565 and 97/37448) variously filed by Rade Petrovic, Kanaan Jemili, Joseph Winograd, Jack Wolosewicz and Eric Metois offer a clear and reasonably plain English explanation of the basic technique.
The encoder holds a library of symbols, or digitally coded letters of the alphabet and numbers, which are represented by pre-determined patterns of a musical waveform. These can be peaks within a limited range of heights, which occur within a fixed period of time. The encoder analyses the sound, looking for peak patterns that are similar to the library patterns. When a close match is found for a symbol that is to be buried in the music, the encoder modifies the musical peaks so they exactly match the library symbol.
In the player’s decoder resides a library of symbol representations like those in the encoder. When it finds a matching pattern in the music, it triggers the appropriate symbol. Together the symbols build up a copyright message. The symbol data rate varies depending on the audio content, but is typically between 10 and 100 bits per second. So it takes only a few seconds for the decoder to recognize all the symbols needed for a copyright message or copy-control signal.
Much like Dolby tape noise reduction, the Aris/Verance system relies on psychoacoustic masking, with weak sounds made inaudible by louder sounds of similar frequency. The patent documents variously claim the system “has minimal impact on human perception” and is “completely imperceptible to the ordinary listener.”