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RE: Validating SSL certificates
From: "William Madell" <bill.madell () trustis com>
Date: Thu, 5 Jul 2012 09:43:22 +0100

Hi Erki,

Yes, the great majority of applications need the ability to build the 'trust chain' from the end-entity certificate (in 
this case, the cert used on the client app) to the trust anchor (the 'root' cert).  

In many cases, Root CAs are maintained in an 'offline' state in order to provide an additional level of protection to 
the Root CA signing key - in those instances, an online Subordinate CA is created (signed by the Root CA) in order to 
issue the end-entity certificates.  If you create this type of multi-tiered PKI, you'll need to install both the Root 
CA certificate as well as the Subordinate CA (leaf) certificate to the application in order to build the chain from the 
end-entity cert.

Cheers,
Bill

-----Original Message-----
From: listbounce () securityfocus com [mailto:listbounce () securityfocus com] On Behalf Of Erki Männiste
Sent: 04 July 2012 18:38
To: security-basics () securityfocus com
Subject: Validating SSL certificates

Hi

We are developing a software and it is going to be used offline. We have to somehow check if the user’s licence is 
still valid and for that, we have decided to use X.509 certificates. So we would create a self-signed root CA and 
inherit client certificates from that certificate. So in our program we are able to check if the client cert is still 
valid (expiration date attributes) and also that the client cert is a leaf of our root CA. My first question is – is it 
enough, moreover, is it a good idea?
I’ve been googeling around the internet but i have not found a good source that explains the magic behind this in less 
than 100 pages. So i ask some more questions :
a) do i have to include the root CA also to the program to verify the chain or does the client certificate somehow know 
who's it's root CA, so i could only hardcode the root CA's thumbprint for verification?
b) if i need the root CA, do i have to install it to certificate store to perform the validation or can i just use it? 
It really wouldn't be a problem to store as a line of bytes to the database (without primary key), but the less the 
better. I ask this because my validation code failed, when the root CA was not in trusted root store, but passed when 
it was. Perhaps my code was wrong.

Thanks
erki



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