Mailinglist Archive: opensuse (2912 mails)

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Re: [SLE] How to avoid copying/scanning printed paper ?
  • From: "Carlos E. R." <robin1.listas@xxxxxxxxxx>
  • Date: Sat, 19 Feb 2005 23:01:53 +0100 (CET)
  • Message-id: <Pine.LNX.4.58.0502192243110.8157@xxxxxxxxxxxxxxxx>

The Saturday 2005-02-19 at 09:43 -0800, Randall R Schulz wrote:

> (*) I still don't know what you mean by an "ordinary" watermark or what
> varieties of watermarks you know of. As I mentioned earlier, the
> original meaning of watermark is a mark embedded in the paper itself,
> not part of the image printed upon it, as is the meaning of the term as
> appropriated by the computer industry.

It must be a special watermark designed to interfere with the scanner
matrix. The document can be scanned, but the quality is bad, and OCR does
not work. The design is most probably proprietary.

There are also some special fonts designed so that the human eye can read
it, but they can't be read by scanning the radio waves emitted by the CRT
monitor - believe me, there are businesses very paranoid about such
things. For example, PGP for windows support it:

Secure Viewer. Select this option to protect the data from TEMPEST
attacks upon decryption. If you select this option, the decrypted
data is displayed in a special TEMPEST attack prevention font that
is unreadable to radiation capturing equipment, and cannot be
saved in decrypted format. For more information about TEMPEST
attacks, see the section on vulnerabilities in An Introduction to
Cryptography.


--
Cheers,
Carlos Robinson

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