From: InfoSec News (alertsinfosecnews.org)
Date: Fri Dec 11 2009 - 04:21:33 CST

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http://gcn.com/articles/2009/12/09/tsa-breach-pdf-redaction-refresher.aspx

By Kevin McCaney
GCN.com
Dec 09, 2009

News that the Transportation Security Administration (TSA) accidentally
posted secret information detailing its airline screening practices may
have had a familiar ring to feds. The information was exposed because of
inadequate redaction procedures.

TSA's operating manual had been posted on a procurement Web site in the
spring in redacted form. But anyone who copied the document and pasted
it into another format, such as Microsoft Word or Windows Notepad, could
read the redacted sections. Some of those sections included the settings
for X-ray machines and explosives detectors, as well as procedures for
dealing with diplomats, CIA employees and law enforcement officers.

Information breaches due to improper redaction are not new. In 2005, the
Multi-National Force-Iraq ran into a similar problem when a memo with
redacted classified information about a shooting was posted on the Web
[1]. The classified information, however, wasn't actually redacted so
much as blacked out, and the information could be revealed by copying
and pasting it into a different format.

The White House, Justice Department and United Nations also have
encountered similar slip-ups.

In wake of those embarrassments, the National Security Agency issued
guidance [2] to federal agencies, titled "Redacting with Confidence: How
to Safely Publish Sanitized Reports Converted From Word to PDF."

In the guidance, NSA identified the three most common mistakes analysts
make in redacting documents intended for the Web, all of them
essentially the result of thinking that what works for a print copy
works for a digital copy. The three most common mistakes:

    * Covering text, charts, tables, or diagrams with black rectangles,
      or highlighting text in black. most common mistake is covering
      text with black (or changing the background to black).

    * Covering up parts of an image with separate graphics such as black
      rectangles, or making images .unreadable. by reducing their size.
      As with text, this works only on printed copies.

    * Failing to remove metadata and documents properties, which is
      often as sensitive as the original document; its presence in
      downgraded or sanitized documents has historically led to
      compromise.

A few tips NSA offers on how to properly redact a document:

    * Save a copy of the original document; make changes to the copy and
      keep the original.

    * Delete, rather than black-out, sensitive text, diagrams, tables
      and images.

    * Turn off track changes, comments and other visible markups, which
      can contain potentially compromising hidden data.

    * Rename the document to show that manual redaction is complete.

    * Create a new Word document, and copy and paste the edited text.

    * Convert a Word document to PDF and review final output for missed
      redactions or formatting issues.

Metadata and recorded, but often not visible, changes to a document are
potential dangers because they often go unnoticed by the user. Knowing
how to find that data is the key to removing it.

[1] http://gcn.com/articles/2005/05/13/pdf-user-slipup-gives-dod-lesson-in-protecting-classified-information.aspx
[2] http://www.fas.org/sgp/othergov/dod/nsa-redact.pdf

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