OpenOffice.org OpenOffice - 3.0 Quick Start Guide Page 335

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Figure 296: Sending a document as an email message
Digital signing of documents
To sign a document digitally, you need a personal key, the certificate. A
personal key is stored on your computer as a combination of a private
key, which must be kept secret, and a public key, which you add to your
documents when you sign them. You can get a certificate from a
certification authority, which may be a private company or a
governmental institution.
When you apply a digital signature to a document, a kind of checksum
is computed from the document’s content plus your personal key. The
checksum and your public key are stored together with the document.
When someone later opens the document on any computer with a
recent version of OpenOffice.org, the program will compute the
checksum again and compare it with the stored checksum. If both are
the same, the program will signal that you see the original, unchanged
document. In addition, the program can show you the public key
information from the certificate. You can compare the public key with
the public key that is published on the web site of the certificate
authority.
Whenever someone changes something in the document, this change
breaks the digital signature.
Chapter 10 Printing, Exporting, and E-mailing 335
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