I had to install an OpenVPN service onto a fresh, disconnected computer, but the keys and certs were delivered through an insecure computer with a highly suspect connection.

Let's assume that the TLS Auth Key, CA Cert, Public Client Cert, and Public Client Key were all intercepted during delivery--wouldn't that render the VPN connection pointless? If I must manually enter or copy-paste these keys and certs into fields during VPN installation, how should I securely obtain the keys and certs?

The VPN has the following specs:


AES-256-CBC with HMAC-SHA1 for authentication


AES-256-GCM with HMAC-SHA384 for authentication

AES-256-CBC with HMAC-SHA1 for authentication

4096 bit RSA keys size

4096 bit Diffie-Hellman keys size


TLS additional authorization layer key: 2048 bit

Perfect Forward Secrecy through Diffie-Hellman key exchange DHE. After the initial key negotiation, re-keying is performed every 60 minutes (this value can be lowered unilaterally by the client)


I think you're using non standard terminologies and that is making things confusing for you. I'll define the terms here:

  1. Private key: a string that need to be kept secret, used in cryptographic operations to authenticate or encrypt
  2. Public key: a string that are mathematically bound to the private key, not a secret. Used in certificate to decrypt and identify signatures that matches a private key
  3. Certificate: public key + optional associated data + signature of the CA binding the key with the associated data. Not a secret. Each side in the communication uses the associated data in the certificate to identify its peer.

TLS Auth Key, the client private key, and server private key are the only data that should be keep private by the client and server respectively.

In the normal operation of x.509 authentication, the server doesn't need to know the client's private key, and vice versa the client doesn't need to know the server's key. You only need to deliver your public keys to the CA in a way that the CA can verify that they are signing the right public key for the right entity for the right purposes.

The CA's root certificate, the server's public key and certificate, and the client's public key and certificate are all non secret. The security properties of PKI does not rely on the secrecy of public key and certificates. An attacker can intercept these and that won't help them decipher your communication with the server.

An attacker that can passively intercept your communication with the CA would not be able to intercept your communication to the server either. To intercept your communication with the server, the attacker would need to actively modify your communication with the CA, throughout the entire verification process and throughout all your communication with the server.

In short, yes, insecure delivery of certificate signing request to the CA can make PKI useless. Insecure delivery of the certificate to communication peer though, is not an issue as all the information exchanged are public.

  • Thanks for the detailed answer. So, if I'm understanding this correctly, the TLS Auth Key is the only thing that should be kept secret because it's my private key. Because my key is known, that makes delivery of the certificate signing request insecure. Because of that, my communication with the server could be compromised? Sorry, I'm not an IT guy and I've had a long day. – MeatBlimp May 13 '16 at 16:06

All the cert and keys you are presenting are necessary information for a working openvpn service for the client side.

It is nothing wrong to give them in public. The only security weakness is the username:password (if it is weak) and your IP (ddos attacks).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.