Update Joar has posted a very nice page on this at: Getting a certificate for Mail
Panther’s Mail.app supports certificate based signing and encryption of email. Mail’s help mentions this and the fact that you need a certificate on your keychain, but no instructions on how to get a certificate.
So after some research and help from friends, we have some (partial) instructions on how to get your own certificate. There are several ways, this is a free method.
First off, you must use Mozilla. Not Internet Explorer, not Safari, not Omniweb, but Mozilla.
Go to: http://www.thawte.com/
Click on the “Secure your email link”
Give them the info they need including the EMAIL YOU WANT TO SIGN AND ENCRYPT FROM. Has to be one you use with Panther Mail. I used email@example.com. Tell them you are not interested in any other products, uncheck the spam boxes and click Submit.
On the next page, Click Join. In the popup window , click Next
Enter your last name, first name, and date of birth. Click Next.
On the next page, for your USA National ID, use your drivers license, and click the Driver’s license button. Then enter your email address again and press next.
I forget the next step (sorry) but uou’ll be asked at some point for a password and five questions for security purposes. The site will email you a ping code. Take that url and use Mozilla to load it, and enter your ping data. Then you’ll be on a page to request a certificate.
Once you do that, follow the instructions. Then it will take 5 mins or so. Keep refreshing the View Certificate Status page and when it says it is oked, then click the link to show your certificates. There will be a fetch button. Once you click Fetch, your certificate is stored inside Mozilla.
Now open Mozilla Preferences. Turn down Private and Security. Click Certificates. Click Manage Certificates. Select the Certificate (it is the indented one) and click backup. Now enter a password for this file (like 12345) and save to your desktop as somethihng like firstname.lastname@example.org
Now double click that file on the desktop. Keychain Assistant will ask for the backup password. When you get it right, your certificate will now be in keychain.
Now when you open mail and make a new messagae, you’ll see a little star icon to the right of the address selection popup. If that is checked, your email will be signed. People will get an attachment. If EVERYONE (not just some) of the people in your to/cc/bcc fifleds has sent you their certificate, then you will also see a lock icon, allowing you to encrypt the email! Sweet.