TELECOM Digest OnLine - Sorted: Re: Privacy Worries? Don't Orint in color

Re: Privacy Worries? Don't Orint in color

Dan Lanciani (
Wed, 26 Oct 2005 05:14:45 EDT

> Of course, the same technique can be used to identify anything else
> from the printer. But Zahren says privacy-conscious citizens have
> nothing to fear. "You only have to worry about it identifying you if
> you have partaken in illegal activity," he said.

The flurry of messages I've seen on this subject seem to be missing a
larger problem. The encoding scheme disclosed by the EFF does not
incorporate any kind of cryptographic signature of the page image. As
far as I can see, printers don't even sign their time/date stamps.
This suggests that if you have any sample page from a printer (or
perhaps just its serial number) you can potentially forge many pages
that appear to have come from that printer.

Supposedly there is already a firmware hack available to disable the
watermark in the described printer. If this is so I wouldn't be
surprised to see a version that lets you set the serial number in the
watermark to whatever you want (or maybe randomize it). Regardless,
the manufacturer obviously has the ability to do this already and
likely so do various law enforcement agencies.

Given the above I would hope that matching watermarks would be treated
only as very weak evidence, not even on the level of actual
handwriting comparisons and old-style typewriter font matching. Yet I
fear that because it's digital and new and "the computer says so" a
watermark match will be taken as conclusive evidence that the pages
came from the indicated printer.

Dan Lanciani

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