16 октября, 2017

How to: LetsEncrypt HTTPS on OpenWRT with uhttpd

My old router TP Link WRN740N hosting my homepage stokito.name and it’s too small to handle full LetsEncrypt certbot installer and OpenSSL. So if you want to enable HTTPS you have to run certbot on some other machine and then upload to router.
Here I would like to show how I did that.

Manual installation

The fisrt step is to use manual certs installation from my laptop and renew them after 3 month. Actually this can be automated too latter.

Now, lets generate certs for your domain:

$ sudo certbot certonly --manual --preferred-challenges http

Answer all the questions and it will ask you to upload a file to your router:

-------------------------------------------------------------------------------
Create a file containing just this data:

1Fyw2Q3IARaG0G6RVUJS587HG_Ou6pKpBLZC-_KuC8g.OKKBaAC2SgfXHQyvgKrLkn3zyCNH82xHgKsMg9OQQJE

And make it available on your web server at this URL:

http://www.stokito.name/.well-known/acme-challenge/1Fyw2Q3IARaG0G6RVUJS587HG_Ou6pKpBLZC-_KuC8g

-------------------------------------------------------------------------------
Press Enter to Continue

You need to create the folder on router:

# mkdir -p ./.well-known/acme-challenge

Then upload the files via SCP from your computer to router:

$ echo "1Fyw2Q3IARaG0G6RVUJS587HG_Ou6pKpBLZC-_KeC4g.OKKBaAC2SgfXHQyvgKrLkn3zyCNH82xHgKsMg9OQQJE" > 1Fyw2Q3IARaG0G6RVUJS587HG_Ou6pKpBLZC-_KeC4g

$ scp ./1Fyw2Q3IARaG0G6RVUJS587HG_Ou6pKpBLZC-_KeC4g root@192.168.1.1:/www/.well-known/acme-challenge/1Fyw2Q3IARaG0G6RVUJS587HG_Ou6pKpBLZC-_KeC4g

BTW, there is no any analogue of WinSCP for Linux but you can try to run it on Wine.

Then go back to certbot and press Enter. It will check that files are in place and accessible from web.

 - Congratulations! Your certificate and chain have been saved at:
   /etc/letsencrypt/live/stokito.name/fullchain.pem
   Your key file has been saved at:
   /etc/letsencrypt/live/stokito.name/privkey.pem
   Your cert will expire on 2018-01-13. To obtain a new or tweaked
   version of this certificate in the future, simply run certbot
   again.

It generated two files: privkey.pem and fullchain.pem (which is not public key!)

Finally, you need to convert the private key and the certificate from the ASCII-armored PEM format to the more economical binary DER format used by uhttpd:

openssl rsa -in privkey.pem -outform DER -out uhttpd.key
openssl x509 -in fullchain.pem -outform DER -out uhttpd.crt

Upload them to the router

$ scp uhttpd.crt root@192.168.1.1:/etc/uhttpd.crt
$ scp uhttpd.key root@192.168.1.1:/etc/uhttpd.key

On the router you need to install uhttpd-mod-tls:

# opkg update
# opkg install uhttpd-mod-tls

edit /etc/config/uhttpd as described in docs i.e. like this

config uhttpd 'stokito.name'
    list listen_http '31.172.137.103:80'
    list listen_https '31.172.137.103:443'
    option redirect_https '1'
    option home '/www'
    option rfc1918_filter '0'
    option cert '/etc/uhttpd.crt'
    option key '/etc/uhttpd.key'

Here 31.172.137.103 is my public static IP.
Note that 443 port should be opened in /etc/config/firewall:

config rule
    option target 'ACCEPT'
    option src 'wan'
    option proto 'tcp'
    option dest_port '443'
    option name 'HTTPS'

Then restart the firewall and uhttpd server:

# /etc/init.d/firewall restart
# /etc/init.d/uhttpd restart

Now try your site in browser. But please check your site latter: I noticed that uhttpd was down but after restart it worked well.

Renewing cert

… So it passed 3 months and my cert got expired and I need to renew it. It’s funny that today is an Old New Year and from window I hear some concert on my street.
This time I decided not to use manual mode and use standalone mode instead: certbot starts itself an https server on 443 port and I need to shut down webserver on my router and enable 443 port forwarding from router to my laptop.

So let’s do that:
1. Connect to router and stop uhttpd service:

$ ssh root@192.168.1.1
# /etc/init.d/uhttpd stop

Enable 443 port forwarding. Download firewall config from router:

$ scp root@192.168.1.1:/etc/config/firewall ./

Edit and comment out current rule for 443 port. If you used that one that I mentioned before then:

# temporarry comment out the rule
#config rule
#  option target 'ACCEPT'
#  option src 'wan'
#  option proto 'tcp'
#  option dest_port '443'
#  option name 'HTTPS'

Then add a HTTPS forwarding rule:

config 'redirect'
    option 'name' 'HTTPS_to_laptop'
    option 'src' 'wan'
    option 'proto' 'tcp'
    option 'src_dport' '443'
    option 'dest_ip' '192.168.1.144'
    option 'dest_port' '443'
    option 'target' 'DNAT'
    option 'dest' 'lan'

Where 192.168.1.144 is the ip of the your laptop. Run ifconfig to see it.

Upload the new firewall config to router:

$ scp ./firewall root@192.168.1.1:/etc/config/

Now restart firewall service on router:

# /etc/init.d/firewall restart

Now your laptop’s 443 port is exposed to the world. So lets tun certbot:

$ sudo certbot certonly --standalone --preferred-challenges tls-sni --cert-name=stokito.name

Then convert the keys do DER format and upload to router as was described above. Then disable forwardind firewall rule and rollback previous and restart firewall and uhttpd.

Now you certs was renewed.