OpenVPN client self-sign cert, revoke on elsewhere?

Question

I've got myself into a pretty messy situation:

1. I generated a clients self-signed certificate on server A, with server A being the CA.
2. I then copied the self-signed certificate (.crt, .key) to server B, which is also a CA by itself.
3. I started using this self-signed certificate on server B and it worked, so I didn't think too much afterward.

Now, I need to revoke this self-signed certificate, however I cannot do it on server B (it complaints about "name does not match"). I've managed to revoke it on server A which signed it, but how can I let server B know that this certificate has indeed been revoked?

I tried to copy the revoked cert over to server B but it doesn't really work...

Platform:

• server A: Ubuntu server 10.10, openssl version 0.9.8o
• server B: CentOS 4.4, openssl version 0.9.7a

If there's anything else I can provide please let me know.

Hope my explanation makes sense, if not, please leave me a msg. Any help would be very much appreciated!

Answer 1

To set up this trust, the clients must trust the root of the server’s certificate. This means, clients have to possess the certificate of the certification authority that issued the server certificate in their Trusted Root Certification Authorities store. You can observe this store via the Certificates snap-in.

The process is mandatory if you are using a certificate not issued by a third part vendor.

Important To install the server root certificate, do the following on the client.

To install the root Certificate on the client

1. Open the Certificates snap-in console. If you have not previously added in the Certificates snap-in console, you can achieve this by doing the following: • Click Start, select Run, type mmc, and then tap OK. • On the File menu, choose Add/Remove Snap-in. • In the Add or Remove Snap-ins dialog box, in the Available snap-ins file, choose Certificates, and then click Add. • In the Certificates snap-in dialog box, select Computer account, and at that time click Next. • In the Select Computer dialog box, click Local computer: (the computer this console is running on), followed by selecting Finish. • In the Add or Remove snap-ins dialog box, click OK.

2. In the Certificates snap-in console, in the console tree, double click to show more items on Certificates (Local Computer), repeat previous step with Trusted Root Certification Authorities, right-click Certificates, and focus on All Tasks, followed by selecting Import.

3. Once you get to the Welcome to the Certificate Import Wizard page, select Next.
4. On the File to Import page, in the File name box, indicate the title of the server root certificate, then select Next.
5. On the Password page, if you created a pass phrase for the private key linked with the certificate previously, enter the pass phrase.
6. On the Certificates Store page, allow the default selection (Place all certificates in the following store – Trusted Root Certification Authorities), followed by choosing Next.

7. On the Completing the Certificate Import Wizard page, verify that the certificate settings appear as followed: • Certificate Store Selected by User: Trusted Root Certification Authorities • Content: Certificate • File Name: FilePath\, where is the name of the server root certificate.

8. Select Finish.

9. Once the certificate upload has successfully concluded, a confirmation message will show up proving the import was successful. Select OK.
10. With Certificates chosen in the console hierarchy, in the detail panel, confirm that the root certificate of the server has become visible in the file of certificates on the client.

This process can be modified on client computers to use website certificates, remote desktop certificates, and Exchange certificates.

Answer 2

You must have copied the server and client certificates from A to B if the same client certs still work when authenticating to B. Is this not the case? If you only moved the client certs, and not the server cert, but you can still authenticate to B with client certs from A, then you must have the same CA on A and B.

You don't need to copy the revoked cert to B, you just need to add the cert to B's revocation list. Normally, as long as the server and client certs are signed by the same CA, authentication will proceed. Revocation works by adding entries to a text file. When you authenticate with a cert, OpenVPN will check your Certificate Revocation List (CRL) to see if the cert has been revoked. You're not making any changes to the actual cert.