TLS/SSL certificate verification

Question

I am new to TLS/SSL so this might be a very basic question, but I've been searching a lot an could not find an answer.

I am trying to implement a TLS/SSL client. This client will run on an embedded unit with Windows OS on it (XPe or WES7). My implementation uses GnuTLS.

How do I get the list of trusted authorities to my unit so my client can verify the server's certificate? Is it supposed to be a file stored on the client side, that the client is responsible for keeping up to date? Or can my client somehow get this list from the internet each time it is needed and not maintain it locally?

Answer 1

The Certificating Authority (CA) master certificates are stored client side and the client is responsible for keeping them up to date. Keeping them up to date isn't as hard as it sounds, as CA certificates aren't changed that often - most are valid for 5-10 years at least.

Client side storage is necessary because any given internet site your application uses might be compromised.

To get a list, you might start by looking at the CA certificates distributed with a browser or at the cacerts file distributed with Java. Before releasing your code, you'll probably want to check that the certs you use are genuine by checking them against information provided by the CA.

Answer 2

Go to any Windows machine and run "certman.msc" from command-line. Export each CA certificate (Intermediate Certificates, Trusted Authorities) to file (BER, PEM), then import these certificates into your embedded software. Now you can validate email certificates, the same way Windows does (i.e. using various x.509 related RFCs and CRLs)