Re: Digital Watermarks for copy protection in recent Billboard

[tcmay@got.net (Timothy C. May)]

At 11:19 AM 7/22/96, Alex F wrote:

>This is probably yet another case of people not thinking ahead.  As
>usual.  People buying CDs at a garage sale & getting arrested for
>piracy.  Wonderful.

Arrests like this are uncommon. Even buying "cheap bikes" and other "cheap"
(= probably stolen and fenced) merchandise almost never subjects the
purchaser to criminal sanctions. I think the legal types would call it
"scienter" (direct knowledge of the act), with a dollop of "provenance"
(the paper trail) thrown in.

For example, finding a piece of paper with my name on it by the side of the
road does not prove I littered, as the paper could've gotten there by
blowing off a trash truck, by being thrown there with others who found it
(perhaps at the trash site), and so on. Scienter, provenance, etc.
("Alice's Restaurant" not to the contrary; the confession to Officer Obie
cinched his fate.)

So, purchasers from garage sales need have no fear that the Copyright
Police will arrest them. If anything, the garage sale folks might get a
visit, assuming they were dealing in large enough volumes to indicate they
were links in a chain of pirates. This is in fact what most of the "piracy"
cases have involved.

>Actually, this would be quite easy.  The "watermark" would be a
>signal that plays inband, but out of our hearing range during the
>entire CD.  The human ear can only hear in the 20-20,000 (Hz, KHZ?,
>whatever) range.  It would be trivial to add a digital ID signal at,
>say 30,000 or 15 or something like that.  This could then be decoded,

Doubtful. The existing CD standard tops out at a Nyquist limit of about
20KHz, with the actual sampling at 44 KHz--but there is simply "nothing" at
above 20-22KHz. Putting a signal in at "30 KHz" is simply not possible,
given the Nyquist Theorem and the CD sampling rate.

Placing a nominally "inaudible" signal in at, say, 15 KHz, was in fact the
first proposal for the DAT market, circa 1986-88. The signal was in fact
detectable by many, and was dropped in favor of SCMS (pronounced "Scums,"
but standing for Serial Copy Management System). SCMS does not involve
actual changes to the audio stream. It is easily defeated--I have access to
one for making DAT-to-DAT transfers.

The larger issue of watermarks in digital data is an interesting one. Some
of the proposals people talk about have actually been spoofs (esp. the Bart
Nagel "announcement" in "Mondo 2000" a couple of years ago, which still
gets cited as an actual technique, about the same way the "Infoworld" spoof
about how the NSA got viruses planted in equipment bound for Iraq got
picked up by some as an example of "infowar.")

--Tim May

Boycott "Big Brother Inside" software!
We got computers, we're tapping phone lines, we know that that ain't allowed.
---------:---------:---------:---------:---------:---------:---------:----
Timothy C. May              | Crypto Anarchy: encryption, digital money,
tcmay@got.net  408-728-0152 | anonymous networks, digital pseudonyms, zero
W.A.S.T.E.: Corralitos, CA  | knowledge, reputations, information markets,
Licensed Ontologist         | black markets, collapse of governments.
"National borders aren't even speed bumps on the information superhighway."