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2 changed files with 6 additions and 179 deletions
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@ -15,6 +15,9 @@ dataDir = "data"
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layoutDir = "layouts"
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publishDir = "public"
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[author]
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name = "Melora Hugues"
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[taxonomies]
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category = "blog"
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tags = "tags"
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@ -53,9 +56,6 @@ author = true
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logoText = "Hello there!"
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logoHomeLink = "/"
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[params.author]
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name = "Melora Hugues"
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[[params.social]]
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name = "git"
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url = "https://git.faercol.me"
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@ -142,185 +142,12 @@ server for that.
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### Configuring the DNS server
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The first step is configuring the DNS server. For this, I'll just use a [bind](https://bind9.readthedocs.io/en/v9.18.27/)
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server installed from my usual package manager.
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```bash
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# example on Debian 12
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sudo apt install bind9
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```
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Most of the configuration happens in the `/etc/bind` directory, mostly in `/etc/bind/named.conf.local`
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```text
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root@dns-server: ls /etc/bind/
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bind.keys db.127 db.empty named.conf named.conf.local rndc.key
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db.0 db.255 db.local named.conf.default-zones named.conf.options zones.rfc1918
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```
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Let's declare a first zone, for `internal.example.com`. Add the following config to
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`/etc/bind/named.conf.local`
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```text
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zone "internal.example.com." IN {
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type master;
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file "/var/lib/bind/internal.example.com.zone";
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```
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This simply declares a new zone which is described in the file `/var/lib/bind/internal.example.com.zone`
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Let's now create the zone itself. A DNS zone has a base structure that you must follow
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```dns
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$ORIGIN .
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$TTL 7200 ; 2 hours
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internal.example.com IN SOA ns.internal.example.com. admin.example.com. (
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2024070301 ; serial
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3600 ; refresh (1 hour)
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600 ; retry (10 minutes)
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86400 ; expire (1 day)
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600 ; minimum (10 minutes)
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)
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NS ns.internal.example.com.
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$ORIGIN internal.example.com.
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ns A 1.2.3.4
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test A 192.168.1.2
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```
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This file declares a zone `internal.example.com` which master is `ns.internal.example.com`.
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It also sets the parameters (time to live for the records, and the current serial for the
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zone config).
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Finally, two (2) A records are created, associating the name `ns.internal.example.com` to
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the IP address `1.2.3.4`, and `test.internal.example.com` (the domain for which we want
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a certificate) to a local IP address `192.168.1.2`.
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A simple `systemctl restart bind9` would be enough to apply the modification, but we still
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have one thing to do, which is allowing remote modifications to the zone.
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### Enabling remote DNS zone modification
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To allow remote modification of our DNS zone, we are going to use [TSIG](https://www.ibm.com/docs/en/aix/7.3?topic=ssw_aix_73/network/bind9_tsig.htm)
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which stands for **Transaction signature**. It's a way to secure server to server operations
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to edit a DNS zone, and is preferred to access control based on IP addresses.
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Let's start with creating a key using the command `tsig-keygen <keyname>`
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```shell
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➜ tsig-keygen letsencrypt
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key "letsencrypt" {
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algorithm hmac-sha256;
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secret "oK6SqKRvGNXHyNyIEy3hijQ1pclreZw4Vn5v+Q4rTLs=";
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};
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```
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This creates a key with the given name using the default algorithm (which is `hmac-sha256`).
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The entire output of this command is actually a code block that you can add to your bind9
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configuration.
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Finally, using `update-policy`, allow this key to be used to update the zone.
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```text
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update-policy {
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grant letsencrypt. zonesub txt;
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};
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```
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{{< callout type="note" >}}
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Doing so allows users to update everything in your zone using this key. In fact
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you would only need to update `_acme-challenge.test.internal.example.com` as seen
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in the DNS challenge description.
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If you want a better restriction, then you can use the following configuration instead
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```text
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update-policy {
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grant letsencrypt. name _acme-challenge.test.internal.example.com. txt;
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};
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```
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{{< /callout >}}
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This means your entire `named.conf.local` would become something like this
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```text
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key "letsencrypt" {
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algorithm hmac-sha256;
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secret "oK6SqKRvGNXHyNyIEy3hijQ1pclreZw4Vn5v+Q4rTLs=";
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};
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zone "internal.example.com." IN {
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type master;
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file "/var/lib/bind/internal.example.com.zone";
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update-policy {
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grant letsencrypt. zonesub txt;
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};
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};
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```
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{{< callout type="warning" >}}
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Be **very cautious** about the `.` at the end of the zone name and the key name, they are
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easy to miss, and forgetting them will cause issues that would be hard to detect.
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{{< /callout >}}
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With that being done, you can restart the DNS server and everything is ready server side,
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the only remaining thing to do would be the DNS challenge itself.
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### Performing the challenge
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Start by installing the certbot with the RFC2136 plugin (to perform the DNS challenge).
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```shell
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apt install python3-certbot-dns-rfc2136
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```
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It's handled using a `.ini` configuration file, let's put it in `/etc/certbot/credentials.ini`
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```ini
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dns_rfc2136_server = <you_dns_ip>
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dns_rfc2136_port = 53
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dns_rfc2136_name = letsencrypt.
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dns_rfc2136_secret = oK6SqKRvGNXHyNyIEy3hijQ1pclreZw4Vn5v+Q4rTLs=
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dns_rfc2136_algorithm = HMAC-SHA512
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```
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Finally, run the challenge using certbot (if it's the first time you're using certbot on
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that machine, it might ask for an email to handle admin stuff).
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```shell
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root@toolbox:~# certbot certonly --dns-rfc2136 --dns-rfc2136-credentials /etc/certbot/credentials.ini -d 'test.internal.example.com'
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Saving debug log to /var/log/letsencrypt/letsencrypt.log
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Requesting a certificate for test.internal.example.com
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Waiting 60 seconds for DNS changes to propagate
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Successfully received certificate.
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Certificate is saved at: /etc/letsencrypt/live/test.internal.example.com/fullchain.pem
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Key is saved at: /etc/letsencrypt/live/test.internal.example.com/privkey.pem
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This certificate expires on 2024-09-30.
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These files will be updated when the certificate renews.
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Certbot has set up a scheduled task to automatically renew this certificate in the background.
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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If you like Certbot, please consider supporting our work by:
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* Donating to ISRG / Let's Encrypt: https://letsencrypt.org/donate
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* Donating to EFF: https://eff.org/donate-le
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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```
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And that's done, you have a certificate, and a no point in time did you need to
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actually expose your application to the outside world.
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Now because I like to go way too far, I can propose two (2) improvements to this
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setup:
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- Using ACL in addition to the TSIG key to secure operations on the DNS server
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- Using a second DNS server only locally accessible for your private records, and
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using the public server to only perform challenges
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## Bonus 1: adding a second layer of authentication to connect to the DNS
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## Bonus 2: completely hiding your private domains from outside
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## Bonus: completely hiding your private domains from outside
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