How to use digital Signatures

1. Where to get a Certificate

First of all you need a valid digital certificate. You can get one for free by various Security Providers, for Germany especially for people from Hamburg, you can get such a certificate from the Trustcenter ([1]), other people may have a look at Thawte ([2]). These companies offer such a certificate for free with an expiration time of one year. After that you have to renew it if you like. If not you will not be able to sign documents any longer.

If you do not trust these companies or want a higher Class Certificate you need to pay some money and the company will validate your personal data to make sure that you are the one you say you are. Such companies are Globalsign ([3]), Verisign ([4]) and also Trustcenter and Thawte. In combination with a Freemail Account you can get a digital certificate for Germany at Web.de ([5]).

1.1 How to make a certificate useable for StarOffice

If you follow the process to get a certificate this will be installed into the keystore of your Browser. Mozilla users will find it under Privacy & Security in the Option dialog of their Browser. Firefox user will find it at a similar place. The few people using Microsoft's Internet Explorer will find it under Start-Settings-Control Panel-Internet Options-Content-Certificates.

This information is needed as StarOffice / OpenOffice.org relies on the Crypto engine used on the users system. On Windows the Microsoft Crypto API is used, therefore nothing has to be done if the Internet Explorer was used to get the Certificate. In case you've used Mozilla or Firefox, you have to export your certificate into a file from the Mozilla Certificate store and import it into the Microsoft keystore. To do so, just go to your settings dialog in Mozilla and choose :

-Manage Certificates from it.
-Select the Certificate to export and click on the button Backup
-Find a place were you can save the file and name it
-Follow the instructions given by Mozilla 
-To import the Certificate into the Microsoft Cryptoengine, do the following:
 -travel to the location of the now exported file by using your preferred file manager and 
 -double click the file. 
 -Follow the instructions and that's it. 
 -You have transferred your certificate into the Microsoft keystore of your Windows installation.

For Linux and Solaris this procedure may be used the other way to get a certificate from Windows into the keystores of Mozilla, Thunderbird or Firefox.

1.1.1 Prerequisites on Linux / Solaris

To use your Certificate for digital signing of documents on Linux or Solaris we need some prerequisites :

- A certificate (obtained from a Certificate Authority)
- A Thunderbird, Mozilla or Firefox profile to store the certificate

StarOffice / OpenOffice.org is looking for a certificate in the mentioned profiles according to the following search order :

a.) The environment variable MOZILLA_CERTIFICATE_FOLDER
b.) The Thunderbird profile
c.) The Mozilla suite profile
d.) The Firefox profile.

This is especially useful to know as Debian and maybe Fedora Linux Installations seem to set the profile names in an other way as suggested by the Mozilla developers. In this case the Certificates are not shown in the digital signature dialog of the Office suite. In this case, locate the appropriate profile folder and set the Environment Variable MOZILLA_CERTIFICATE_FOLDER accordingly. See Certificate Detection

1.1.2 Prerequisites on Windows

As you need only a valid certificate located in the keystore of the Windows Crypto API and we have installed it under Chapter 1.1, there are no more Prerequisites for Windows.

2. How to sign a document

Edit the document you want to sign and save it. Now select Digital Signatures from the File Menu. If you get a warning about a missing Mozilla profile, have a look at chapter 1.1.1 please. You probably use a Debian or Fedora Linux and haven't set the environment variable in the correct way.

If all is properly set, you get the digital signatures dialog and can click on the Add button. On Linux and Solaris you're asked for the password for accessing the used keystore, on Windows it depends on the settings made on importing the certificate. Now your stored certificates are shown. Please select the one you want to use and than click on Ok. After that you will be back in StarOffice / OpenOffice.org Digital Signatures dialog. This dialog will show a small icon in front of the textual representation of the certificate used to sign the Document.

2.1 How to sign a Macro

To sign a Macro you have two possible ways.

1.)Use Tools – Macro – Digital Signature
2.)Use File – Digital Signature within the BASIC Editor of StarOffice / OpenOffice.org

The procedure of adding a certificate to the Macro is the same as used for documents.

3. Error messages and visual aids

3.1 Error messages on loading of documents

You only get a message on loading the document if the signature of the document and / or the signature of the containing macros is broken. In this case the execution of macros is stopped and you can only activate macros by setting the security level to low and re-loading the document. But this is not recommended. Or remove the broken signature from the document and reload it. In this case make sure the macros contained in the document are not malicious.

3.2 Visual Aids

We have four visual aids for the possible states of a document signature.

A sheet with a stylised red seal stating that the document signature(s) are OK and no alteration of the document occurred since the last signing.

The addition (signed) to the title bar of an opened signed document.

A sheet with a stylised red seal and a small yellow triangle with exclamation mark stating that the document signature(s) are OK and no alteration of the document occurred since the last signing but at least one of the used certificates could not be validated. This can be caused by a not available root certificate from the Issuer of one of the certificates used or a not possible connection to the server containing the Revocation List for the Certificate Issuer. This is just an informal message, the document itself isn't changed after signing. But the decision on how far you can trust this document is up to you. The used certificate is maybe outdated or revoked.

A yellow triangle with black exclamation mark showing that the document signature is broken. So this document has been altered in some way and therefore you should not trust it's content.

These visual aids will be displayed in the digital signature dialog and the status bar. For the '(signed)' text, this one is shown in the title bar of the document window next to the file name.