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Redacting with Confidence: How to Safely Publish Sanitized Reports Converted From Word to PDF

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Report # I333-015R-2005
Date 12/13/2005
Redacting with Confidence: How to Safely Publish
Sanitized Reports Converted From Word to PDF
Architectures and Applications Division
of the
Systems and Network Attack Center (SNAC)
Information Assurance Directorate
National Security Agency
ATTN: I333
9800 Savage Rd. STE 6704
Ft. Meade, MD 20755-6704
(410) 854-6191 commercial
(410) 854-6510 facsimile
W2Kguides@nsa.gov
CLASSIFICATION//X1
This page intentionally left blank.
1
Abstract
There are a number of pitfalls for the person attempting to sanitize a Word document for release.
This paper describes the issue, and gives a step-by-step description of how to do it with
confidence that inappropriate material will not be released.
SUMMARY
Both the Microsoft Word document format (MS Word) and Adobe Portable Document (PDF) are
complex, sophisticated computer data formats. They can contain many kinds of information
such as text, graphics, tables, images, meta-data, and more all mixed together. The complexity
makes them potential vehicles for exposing information unintentionally, especially when
downgrading or sanitizing classified materials. Although the focus is on MS Word, the general
guidance applies to other word processors and office tools, such as WordPerfect, PowerPoint,
Excel, Star Office, etc.
This document does not address all the issues that can arise when distributing or downgrading
original document formats such as MS Word or MS PowerPoint. Using original source formats,
such as MS Word, for downgrading can entail exceptional risks; the lengthy and complicated
procedures for mitigating such risks are outside the scope of this note.
DETAILS
MS Word is used throughout the DoD and the Intelligence Community (IC) for preparing
documents, reports, notes, and other formal and informal materials. Commonly used versions of
MS Word include Word 2000, Word XP, and Word 2003.
Adobe PDF is used very extensively by all parts of the U.S. Government and military services
for disseminating and distributing documents of all kinds. PDF provides excellent fidelity and
portability, and allows easy distribution of documents over computer networks and the Internet.
PDF files are usually produced using commercial conversion software (so-called “distillers”) that
accept source formats such as Postscript or MS Word, and output PDF. PDF is often used as the
format for downgraded or sanitized documents.
As numerous people have learned to their chagrin, merely converting an MS Word document to
PDF does not remove all metadata automatically. In addition, Adobe Distiller and the
PDFMaker Add-in to MS Word (the most common way to convert) convert much of the layering
complexity from one format to the next. For example, images placed on top of text in MS Word
will be copied verbatim to PDF with the same layout.
Typical Kinds of Exposures
When attempting to sanitize a document, analysts commit three common mistakes with MS
Word and PDF that lead to most cases of unintentional exposure.
1. Redaction of Text and Diagrams – Covering text, charts, tables, or diagrams with black
rectangles, or highlighting text in black, is a common and effective means of redaction
for hardcopy printed materials. It is not effective, in general, for computer documents
distributed across computer networks (i.e. in “softcopy” format). The most common
mistake is covering text with black.
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2. Redaction of Images – Covering up parts of an image with separate graphics such as
black rectangles, or making images ‘unreadable’ by reducing their size, has also been
used for redaction of hardcopy printed materials. It is generally not effective for
computer documents distributed in softcopy form.
3. Meta-data and Document Properties – In addition to the visible content of a document,
most office tools, such as MS Word, contain substantial hidden information about the
document. This information is often as sensitive as the original document, and its
presence in downgraded or sanitized documents has historically led to compromise.
Note that many of these mistakes can also occur inadvertently in document composition. For
example, sensitive information in an embedded image can be overlaid with another image during
format. Such hidden data can be difficult to be spot during manual review of the softcopy.
Application Tools and Settings for Removing Data
Microsoft Word XP/2003: Microsoft has attempted to remedy certain issues with Metadata in
Office XP and up by including a menu option to remove personal information (metadata). There
is also a tool available for free from MS, Remove Hidden Data 1.0 (for XP) and 1.1 (for Office
2003), hereafter referred to as RHD, that allows batch removal information from Word
documents. None of these will remove sensitive information from the main document; neither
will they remove all metadata of possible concern. And RHD 1.0 suffered from stability issues.
Reliance of these tools may give a false sense of security.
Figure A: PDFMaker Settings in MS Word
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Adobe Acrobat 5.0/6.0: The use of PDF conversion tools on a Word document does guarantee
the removal of a great deal of data, such as version information and change tracking. These tools
also convert embedded objects such as Excel spreadsheets into images so that only the viewable
face of the object remains. Adobe’s conversion tool for within Word, PDFMaker, is an add-in
that works in connection with Adobe Distiller. Distiller is a robust PostScript to PDF application
whose operation can be modified by Conversion Settings selectable within Distiller or
PDFMaker (Select Adobe PDF->Change Conversion Settings->Advanced Settings). Most of
these tweak the size and resolution of the resulting PDF. PDFMaker itself has a number of
Word-specific settings as shown in Figure A, two of which are relevant to the sanitizer. The
checkbox “Convert Document Information” controls the conversion of MS Word metadata to
PDF and is checked by default. “Attach source file to Adobe PDF” does just what it suggest: it
inserts a copy of the original Word document inside the output file, almost certainly not what
was intended by the analyst. It is unchecked by default. Unselecting “Convert Document
Information” removes one avenue of metadata leakage, but will not stop the other sources of
leakage.
Deletion not Redaction
The key concept for understanding the issues that lead to the inadvertent exposure is that
information hidden or covered in a computer document can almost always be recovered. The
way to avoid exposure is to ensure that sensitive information is not just visually hidden or made
illegible, but is actually removed from the original document. Thus any sensitive information
must be removed from the document through deletion. The procedures detailed below discuss
some of the ways to maintain formatting during the process.
Section 2: Procedures to Sanitize a Word Document
The following steps were tested with MS Word 2000 and Acrobat 5.0 and 6.0. Other recent
versions should work similarly. While time-consuming, these steps give the highest confidence
that sensitive information is not hidden in the released document. Copying the text and images
into a blank document is a good way to manually review a sensitive document, since sections can
be copied over one at a time as they are reviewed.
Pictorial Outline of Procedure–
Original Report.doc
Original Word
Sensitive
Document with
Data
Sensitive Data
Copy of Original
Report.doc
Save a copy of the
original document and
edit this document instead.
The original remains as a
backup.
4
Copy of Word
Document with
Sensitive Data
Redacted Report.doc
Review document and delete sensitive text,
diagrams, tables and images using the techniques
described. Turn off Track Changes, Comments,
and other visible markups. Rename document to
remove sensitive information and to indicate
manual redaction has been completed.
Redacted Copy of
Original Document
(sensitive metadata)
New Redacted
Report.doc
Open new blank Word document, and select and
copy data into it. This step removes residual
document composition information (except data
associated with the default template!). Selecting
and copying section by section is a good way to
verify that redaction was done correctly.
New Document
with Redacted Copy
(metadata reset)
New Redacted
Report.pdf
Convert Word document to PDF (here using
PDFMaker). Review final output PDF for
missed redactions, or formatting issues.
5
Final Redacted
Output.
Detailed Procedure
Create a new copy of the document.
1. Open the document and select
File->SaveAs from the top menu bar;
give the file a new name. Make sure the
new name is not itself sensitive. Do all
redacting work with the new copy,
preserving the original as a backup.
Turn Off Track Changes
2. The Track Changes feature is a toggle.
Selecting Tools->Track Changes from
the top menu bar toggles the feature on
or off. The quickest way to determine if
Track Changes is on or off is by looking
at the bottom status bar. The letters TRK
are dimmed if Track Changes is off and
bold if Track Changes is on.
Review and Delete Sensitive Content
3. Select each chart, diagram, image or
segment of text to be redacted and delete
that item. Delete all comments.
Figure 1 – Original Document
Resizing an image, covering a section
with a black box, or changing the color
of a font to make it invisible will not
work. The item must be deleted. If
deleting an item changes the format or
structure of the document in an
unacceptable way, replace the item with
meaningless content of a size that keeps
the formatting correct. If the redacted
item is text, replace the text with copies
of a single character such as all As or all
Xs. If the redacted item is an image or a
chart, replace the item with a gray
rectangle of the same size.
Example: Redacting text. Figure 1 on
the right shows a page of a document
before redaction. Figure 2 shows the
same page after deleting some text (the
area marked by the large black arrows at
the top of the figures).
Figure 2 – Text deleted from original changes
formatting
6
Notice that the chart and a paragraph
from the next page move up in the
document because deleting the text has
shifted the subsequent text (the area
marked by the large black arrow at the
bottom of figure 2).
Because of this shift, subsequent pages
may need to be reformatted to ensure
figures stay with certain text, or that
page breaks are in the correct place, or
that other such formatting issues do not
adversely alter the appearance of the
document. This could be time
consuming for a large document. If
formatting changes are a concern,
replace the text with meaningless
content of the same size rather than
delete it. Figure 3 shows a before and
after close-up of the replaced text.
Notice that the paragraph following the
replaced text did not shift position thus
preserving the formatting of the rest of
the document.
Figure 3—Replacing deleted text with an equal
amount of meaningless text.
Example: Redacting a chart, image, or
other object. Figure 4 shows the page
from Figure 1 after redacting some text
and deleting the chart. In this case, the
chart is an image. Notice that some text
and part of a table have shifted onto the
page. To preserve the formatting, insert a
gray rectangle the same size as the chart
(or image) into the vacant space as
detailed in the following steps:
a. Before deleting the image, determine
its size: select the image, select
Format->Picture from the top
menu bar, and then select the Size
tab in the Format Picture dialog box.
Make a note of the height and width
of the image.
b. Select the image and delete it.
Figure 4
7
c. Insert a rectangle in the same space:
select
Insert->Picture->Autoshapes
from the top menu bar (this opens
the AutoShapes toolbar). Select the
rectangle from the Autoshapes
toolbar as in Figure 5. Left click the
rectangle which creates a drawing
canvas. Move the cursor somewhere
on the drawing canvas, left click
again to drop a rectangle on the
canvas.
Figure 5
d. resize the rectangle: select the
rectangle, move it to the upper left
corner of the drawing canvas, right
click, select Format AutoShape
from the menu as in Figure 6 (this
opens the Format AutoShape dialog
box), select the Size tab, enter the
desired height and width of the
rectangle and hit OK.
Figure 6
8
e. Fill the rectangle with gray: select
the paint bucket on the bottom
toolbar which brings up the Fill
toolbar shown in Figure 7. Left click
on one of the gray colors.
Figure 7
f. Figure 8 shows the page after
redacting the text and the chart;
Notice that the format and page
layout of the subsequent text in the
document is preserved.
Figure 8
9
Doublecheck Redacted Document
4. Carefully read over the document to
ensure that all material to be redacted
has been deleted and if necessary
replaced with innocuous filler. Check all
headers, footers, captions, section titles,
footnotes, endnotes, labels, etc. Verify
that all comments have been deleted.
To easily flip through the document, use
Word’s “Browse By” feature for some of
the different objects. By default, the
arrows at the bottom of the right scroll
bar browse through the document by
page when clicked. To change this, hit
the dot at the bottom of the scroll bar
that is shown in figure 9. This brings up
a toolbar with the “Browse By” options,
including Browse By Comment, Browse
By Footnote, Browse By Graphic, etc. as
shown in figure 10. Select one of the
options. Now use the double arrows on
top and bottom of the dot to flip through
the document to each instance of that
type of object. This is a quick way to
make sure all comments are deleted, all
images have been redacted correctly, all
footnotes have been checked, etc.
Figure 9
Select and Copy the Contents of the
Document to a New File
Figure 10
5. Select the entire contents of the
document using Edit->Select All
from the top menu bar. Copy the
selected contents using Edit->Copy
from the top menu bar. This will copy
the contents, the formatting, the headers
and footers and all necessary
information into Word’s buffer.
Open a new Word document using
File->New from the top menu bar. Paste
the redacted document contents into this
new document using Edit->Paste from
the top menu bar.
10
Save the document with a new name
using File->SaveAs from the top menu
bar.
Ensure Adobe PDF settings are correct.
6. One reason to convert a Word document
to PDF is that the conversion redacts
some information or hidden data from
the document that is intrinsic to the
Word format. However, some PDF
software has the ability to automatically
copy document meta-data and properties
from Word to PDF. This feature, among
others, must be disabled when
downgrading or sanitizing documents.
This section of the paper will describe
the most common way to disable the
features and convert a document, but
other methods are suitable as long as the
PDF software is configured to prevent
converting anything but the visible
contents of the file.
Figure 11
Figure 12
The most common configuration for
PDFMaker in Acrobat 6.0 is to run from
the menu bar of Word as in Figure 11 (if
Adobe PDF is not on the menu bar, see
the system administrator). There is also a
configuration tool that allows the user to
change numerous settings for PDF
conversions. This step describes which
options must be set for converting
redacted Word documents, and these
options must be verified for each
document conversion.
Select Adobe PDF->Change
Conversion Settings from the menu
bar as in Figure 12. This opens the
Acrobat PDFMaker dialog shown in
Figure 13. There are four tabs labeled
Settings, Security, Word, and
Bookmarks. On the Settings tab,
ensure that Convert Document
Information and Attach Source File
to Adobe PDF are both unchecked as
shown in Figure 13.
Figure 13
11
On the Word Tab, shown in the close-up
in Figure 14, uncheck Convert
Comments to Notes and hit OK.
7. Convert the document to PDF by
selecting Adobe PDF ->Convert to
Adobe PDF from the menu bar.
8. Lastly, review the output PDF for
formatting issues and omissions.
Figure 14
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References and Further Reading
1. How to minimize metadata in Office documents – Microsoft, January 28, 2005,
available at support.microsoft.com.
2. Avoiding Information Compromise When Using Microsoft Word and Adobe
Acrobat PDF – NSIRC- Advisory
3. Metadata – Are you Protected? – Donna Payne, Payne Consulting Group, Law
Technology News, August 2004. Discussion of PDF issues.
13

About author
A #globalrevolution enthusiast. Twitter: @AliceKhatib
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