You can encrypt a document or add a security password to a document, but those measures don’t provide the recipient with a guarantee that the document they receive is from you. Unless you want to physically hand the user the document, the best way to let that user know the document is from you is to add your digital signature to it.

This is a great DIY task for anyone who wants more security for their office suite, but doesn’t want to have to pay someone to make it so. For this tutorial, I focus on adding digital signatures to LibreOffice documents. Once you complete the steps required to set this up, the signing of documents is very easy.

Requirements

  • The most recent release of LibreOffice, which as of this writing is 3.5.
  • A digital certificate
  • Firefox web browser

Older releases of LibreOffice will not work because of the way Firefox handles user profiles. I recommend downloading the latest installation file from the LibreOffice website, removing your current installed application, and installing the newer version.

As for your digital certification, I highly recommend you either get a free certificate from a service like CAcert.org or use a tool such as TinyCA for the creation. If you create your certificate using TinyCA, you need to create your CA and then create a client certificate. Then you need to export the certificate (right-click the listing in the Certificates tab), select PKCS#12 (Figure A), and click OK. The exported certificate will be in the form jack@adorkabledesigns.net-cert.p12. You can rename this if you like — just remember what you name it and where you save it.
Figure A

Click the image to enlarge.

The next step is to make the certificate available to LibreOffice. Believe it or not, this is not handled through LibreOffice; instead, you make the certificate available with the help of Firefox. Here’s how:

1. Open Firefox and go to Edit | Preferences.

2. Click the Advanced tab and then click the Encryption tab.

3. Click the View Certificates button.

4. Click the Import button (Figure B) and back up your certificate authorities from this window.
Figure B

5. Navigate to where you saved the certificate, select the certificate, and click Open.

6. Enter the password for the certificate.

Now that we finally have the digital certificates available to this system, the rest is simple… with a catch: You can only sign file formats native to LibreOffice (.odt, .ods, etc.).

1. When your document is open (and saved), go to File | Digital Signatures.

2. From this new window, click Sign Document to open a listing of the available signatures (Figure C).
Figure C

3. Click View Certificate to get more information on the certificate to be used.

4. Select the certificate you want to use and then click OK to sign the document. Your document is digitally signed.

When you send a signed document, the receiver can go to File | Digital Signatures to see that it has been signed. The receiver can then click View Certificate to see who the certificate was issued to and who issued the certificate.