Re: using multiple digital certificates

[Scott Klement <midrange-l@xxxxxxxxxxxxxxxx>]

> Is it possible to assign multiple digital certificates to a single
> apache web server instance? We host one secure name now for three
> different sites but want to switch to using three different names each
> with their own certificate.
Others have explained that you can't do it with name-based virtual hosts, 
you have to use IP-based virtual hosts...  I'll attempt to explain why 
that is...
Name based virtual hosting works by looking at the hostname sent by the 
browser in it's GET or POST request. For example, a browser will send 
something like this:
GET /apps/payables/pendinginvoices?invno=12345&acct=4321 HTTP/1.1
Host: ais.pct.edu:443

Apache looks at the Host: keyword and uses it to decide which virtual host 
the request is for.  In this case, the browser sent "ais.pct.edu" so the 
server knows to look for a virtual host with that name.
But this can't be used to determine the SSL certificate...

Why not?  Because the SSL session, certificates and encryption are 
established BEFORE that GET request was sent.  It has to be!  You want the 
data on the GET request (in this example, an invoice number and account 
number) to be encrypted.  What if you sent a credit card number?  Or some 
other sensitive information?  The encryption needs to be activated before 
that GET request was sent.
If the GET request hasn't been sent yet, there's no possible way for the 
host: keyword that's part of that request to be used in establishing 
certificates.
Instead, you need to use IP-based virtual hosts. The IP address is known 
before the SSL session is established, and therefore can be used to decide 
which certificate to send.  Unfortunately, this means that you have to 
have a separate IP address for each certificate.