OpenOffice.org OpenOffice - 3.2 User's Guide download pdf (Page 255)

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.

On Windows operating systems, the Windows features of validating a

signature are used. On Solaris and Linux systems, files that are

supplied by Thunderbird, Mozilla or Firefox are used. For a more

detailed description of how to get and manage a certificate, and

signature validation, see “Using Digital Signatures” in the OOo Help.

To sign a document:

1) Choose File > Digital Signatures.

2) If you have not saved the document since the last change, a

message appears. Click Yes to save the file.

3) After saving, you see the Digital Signatures dialog box. Click Add

to add a public key to the document.

4) In the Select Certificate dialog box, select your certificate and

click OK.

5) You see again the Digital Signatures dialog box, where you can

add more certificates if you want. Click OK to add the public key

to the saved file.

A signed document shows an icon in the status bar. You can

double-click the icon to view the certificate.

Chapter 10 Printing, e-mailing, exporting, and saving slide shows 255

1 2 ... 250 251 252 253 254 255 256 257 258 259 260 ... 290 291

No comments

OpenOffice.org OpenOffice - 3.2 User's Guide Page 255