Signed SSL certificate

If you're not going to be the only person using the ZNC instance, you may want to consider using signed SSL certificates. Signed SSL certificates are generated by third-party companies, such as Let's Encrypt, PositiveSSL, VeriSign, or others, and will not cause "self-signed certificate" errors when used with an IRC client.

General advice

znc.pem must contain everything in order from the "most private" to the "most public" entries, except for the root certificate.

E.g. it may be something like this:

cat your-certificate-private.key > znc.pem
cat your-certificate.crt >> znc.pem
cat intermediate-certificate-of-ca.crt >> znc.pem  # If your certificate wasn't signed by CA root certificate directly.
# cat ca-root.crt >> znc.pem  # Possible, but useless. If client knows this CA, this is redundant. If client doesn't know this CA, it's not trusted anyway.

You should also generate the Diffie–Hellman key exchange parameters, also appended to znc.pem:

openssl dhparam -out dhparam.pem 2048
cat dhparam.pem >> znc.pem

The dhparam file doesn't have to be kept secret, and can be used multiple times; substitute 2048 for your private key's bit size.

To apply this new certificate file to ZNC, just put (replace) it in ZNC's work folder.
As of 1.6.2, ZNC will reload znc.pem each time a client connects, but it'll be fixed in future.

Below you may find more specific instructions how to configure certs from few CAs, contributed by various people.

CA-specific application of the general advice above

Why this section is even needed?... --DarthGandalf (talk) 09:11, 4 December 2015 (UTC)

PositiveSSL

This is how I (Wayne_Arthurton) created a Positive SSL certificate for znc.

1. openssl req -nodes -newkey rsa:2048 -keyout myserver.key -out server.csr
2. Submit server.csr to PositiveSSL
3. Once you receive your SSL Bundle zip, uncompress
4. cat myserver.key > ~/.znc/znc.pem
5. cat host_domain_com.crt >> ~/.znc/znc.pem
6. cat PositiveSSLCA2.crt >> ~/.znc/znc.pem
7. cat AddTrustExternalCARoot.crt >> ~/.znc/znc.pem

That should do it. Drop a note on my Wiki Page if you need any more help.

To use a PositiveSSL, this seemed to be the recipe

LetsEncrypt

Caveat: Let's Encrypt does not currently support IP addresses, if you want to use a Let's Encrypt certificate you'll need to be on a (sub-)domain. Additionally, they have a 90-day expiry, so it's a good idea to set up a cron job to reissue a cert every so often (monthly works).

Official Client

If you're using the official Let's Encrypt client, assuming you have your certificate in /etc/letsencrypt/live/example.org/, here is how you can make a znc.pem from it (concatenate the 3 files together):

cat /etc/letsencrypt/live/example.org/{privkey,cert,chain}.pem > znc.pem

You need to repeat this every time you obtain a new certificate.

Caddy

Caddy is a web server (alike Apache or nginx) with automatic HTTPS through LetsEncrypt. The certificate files generated through Caddy can be used for ZNC, although they have to be concatenated just like with the official client.

Here's how you can make a znc.pem from them:

cat /etc/ssl/caddy/.caddy/acme/acme-v01.api.letsencrypt/sites/example.org/example.org.{key,crt} > /var/lib/znc/znc.pem

Just like with the official client, you will need to repeat this every time Caddy obtains a new certificate. This can be automated to copy every month using a cronjob, like so:

0 0 1 * * cat /etc/ssl/caddy/.caddy/acme/acme-v01.api.letsencrypt/sites/example.org/example.org.{key,crt} > /var/lib/znc/znc.pem

Alternative Setup

This is a very quick install using a small, dependency-free, auditable python script: acme-tiny. I recommend working in a separate directory, and then moving/symlinking the final cert into the config file afterward.

First, generate some RSA keys. The account key is your letsencrypt account, and can be reused for multiple domain keys if you're managing a lot of servers. For a private install it's easiest to just generate a new throwaway. Do replace yoursite.com with the appropriate value, here.

openssl genrsa 4096 > account.key
openssl genrsa 4096 > domain.key
openssl req -new -sha256 -key domain.key -subj "/CN=yoursite.com" > domain.csr

Next, we need to set up a challenge-response folder available from port 80. If your server has a web server available you'll need to hook into it temporarily (see the docs on the acme-tiny repo). If you do not have a web server, you can spin up a temporary one with python:

mkdir -p .well-known/acme-challenge/
sudo python -m SimpleHTTPServer 80 &

Now, download that script (and audit it if you're paranoid about malicious code), and run it get your signed cert. Then, we pull down the cross-signed cert to build our certificate chain, and smush all the files together for our final znc.pem:

python acme_tiny.py \
  --account-key ./account.key \
  --csr ./domain.csr \
  --acme-dir ./.well-known/acme-challenge/ \
  > ./signed.crt

wget https://letsencrypt.org/certs/lets-encrypt-x3-cross-signed.pem
cat domain.key signed.crt lets-encrypt-x3-cross-signed.pem > znc.pem

Don't forget to kill the temporary web server if you started it up, and then copy/symlink the certificate into place.

If you want/need to set up automatic renewals, you'll probably need to set up a permanent web server hosting the acme-challenge folder, and otherwise the shell script is identical to the last code block above, except with absolute paths.