Section 1.1: Prerequisites for Certificate Issuance

To issue a certificate, you will need a domain name. This must be a legitimate domain recognized on the public Internet, which means you will need to purchase it from a registrar.

In this guide, we'll refer to a domain I purchased previously for AWS usage, which is currently unused.

I registered this domain through Route53, making it easy to manipulate DNS records. If your domain was obtained via a different registrar, you should still have the capability to add DNS records. Refer to your DNS documentation for specifics.

A crucial component of the ACME DNS challenge is the ability to create a TXT record. This DNS record type allows you to insert custom text, essentially transforming DNS into a small information repository. Let's Encrypt will provide a unique string for this TXT record, validating your domain ownership and enabling certificate issuance.

Section 1.2: Automating Certificate Issuance with Certbot

To streamline the certificate acquisition process from Let's Encrypt, you can use an application called Certbot. For this example, we'll remain application-agnostic since the certificate's usage will not impact the process.

Install the command-line Certbot application on the host from which you will obtain the certificate. Ideally, this should be the same machine where the certificate will be installed.

Once Certbot is installed, execute it with the correct options for a DNS challenge:

sudo certbot certonly

--test-cert

—manual

--preferred-challenges dns

-d yourdomain.com

Here's a breakdown of the command:

1. Sudo: This command requires write access to various log and certificate directories.
2. certonly: This option allows you to receive only the raw certificates, avoiding any installation processes for web servers.
3. --test-cert: This flag directs the request to a staging server, issuing a test certificate to avoid production rate limits.
4. --manual: This indicates that interactive validation is needed, allowing you to manually update DNS records.
5. --preferred-challenges dns: This tells Certbot to utilize DNS validation.

After answering a few prompts, Certbot will provide the necessary DNS challenge record details.

The above video explains the process of using self-signed and Let's Encrypt certificates for local area networks, detailing the steps to successfully set up TLS certificates.

Section 2: Using the Certificates Securely

Upon successful issuance, you will receive two vital files: the certificate and the private key. The certificate includes details like domain names, organizational information, expiration, and issuing authority. The private key is a secret credential that "unlocks" the certificate and must be safeguarded rigorously.

A few key rules regarding private keys:

• They should never be stored online or in public cloud storage.
• Avoid sending them via chat applications or email (even if encrypted).
• They should not traverse the public Internet.

While this may seem overly cautious, it's essential. If your private key is compromised, so is your certificate.

When it comes to utilizing the certificate and private key, you have several options:

• Use them on the original host to keep the private key secure.
• Re-run the issuance on the desired host, generating a new certificate and key.
• Transfer the key and certificate via secure means, though this is less secure than keeping them on the originating host.

Once the certificate and private key are on the appropriate host, you can install them in the application of your choice, whether it’s a web server, database, or RPC client/server library.

This video covers the steps to obtain an SSL certificate from Let's Encrypt, providing clear instructions for securing your applications with TLS.

Section 3: Ensuring Accurate DNS Configuration

It's crucial to ensure that the DNS names on the certificate correspond with the actual DNS name of your application. If they don't match, you may encounter connection errors. To resolve this, consider implementing a split-horizon DNS setup.

When using a public certificate authority like Let's Encrypt, remember that you need a public domain. Let's Encrypt cannot validate internal-only domain names.

If you require a truly offline PKI for internal systems, you should explore establishing a private CA, although this process is significantly more complex.