[CentOS] VPN suggestions centos 6, 7

Paul Heinlein heinlein at madboa.com
Mon Apr 18 16:09:19 UTC 2016

On Mon, 18 Apr 2016, david wrote:

> I had lots of suggestions, and the most persuasive was to try 
> OpenVPN.  I already had a CA working, so issuing certificates was 
> easy.  The HOW-TO guides were less helpful than I could hope, but 
> comparing several of them, applying common sense, and trying things 
> out, I arrived at a dead-end. Here's essentially what happened:
> - None of the HOW-TOs were very clear about the need to add some attributes 
> to a certificate, keyUsage and extendedKeyUsage.  They had different values 
> for server and client.  OpenSSL documentation was a big vague on how to add 
> them, but I think I did - the print out of the entity certificates showed the 
> values.  The attempt to connect failed.  The client log is below.  I think 
> it's complaining that the CA certificate doesn't have the ke Usage extension, 
> which makes no sense to me.  Such an extension should be in the end-entity 
> certificate, not the CA's, unless I'm wrong.  I checked the server and really 
> think that the certificates are in the right place.

Here's how I managed that in my openssl.cnf file. Lots of bits ellided 
for clarity's sake:

### start ###
[ ca ]
default_ca = CA_default

[ CA_default ]
x509_extensions = server_cert

[ server_cert ]
keyUsage = nonRepudiation, dataEncipherment, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth, clientAuth
nsCertType = server, client
### end ###

I think the nsCertType directive may be unnecessary these days, but I 
keep it around because it doesn't hurt anything.

The important bit is the extendedKeyUsage line; I'm pretty sure that 
an OpenVPN server needs the serverAuth extension. For instance, here 
is the X509 extensions configuration for a server used by EasyRSA:

   basicConstraints = CA:FALSE
   subjectKeyIdentifier = hash
   authorityKeyIdentifier = keyid,issuer:always
   extendedKeyUsage = serverAuth,clientAuth
   keyUsage = digitalSignature,keyEncipherment

You can ask openssl to tell you the purpose of a certificate:

[bash]$ openssl x509 -noout -purpose -in cert.pem  | grep SSL
SSL client : Yes
SSL client CA : No
SSL server : Yes
SSL server CA : No
Netscape SSL server : Yes
Netscape SSL server CA : No

Anyway, those are the extensions that should do away with these 

> Mon Apr 18 05:34:50 2016 VERIFY OK: depth=1, C=US, ST=California, L=San 
> Francisco, OU=Certificate Authority, O=XXXX, CN=X.X.X
> Mon Apr 18 05:34:50 2016 Certificate does not have key usage extension

Paul Heinlein <> heinlein at madboa.com <> http://www.madboa.com/

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