Moving on from “should we do it?” (with the answer to most real-world scenarios being “yes, and as a bonus it can help block a lot of spambots“), here’s how to restrict several Internet services — Nginx, Apache, Postfix, and Dovecot — to TLSv1.2 or newer.
As usual, these are not complete guides for any of those servers; I’m assuming you already have them working fine (including TLS encryption), and just want to disable any TLS protocols lower than v1.2. (If you need to add TLS to a non-TLS server, see instructions for Nginx, Apache, Postfix, and Dovecot.)
Nginx:
In each virtual host’s server section — or, even better, if you’re using Let’s Encrypt, in /etc/letsencrypt/options-ssl-nginx.conf or its equivalent –, add the following (or replace any existing ssl_protocols entry):
ssl_protocols TLSv1.2 TLSv1.3;
Restart Nginx, and test it on SSL Labs. You should get something like this1:
(Note: if you’re using a very old version of Nginx, it may not accept the “TLSv1.3” parameter and refuse to start; in such a case, remove it — or, better yet, upgrade your system. 🙂 )
Apache:
Similarly to Nginx, you can add one of the following to each Virtual Host, or to the global HTTPS configuration (typically in /etc/httpd/conf.d/ssl.conf), or, if using Let’s Encrypt, to /etc/letsencrypt/options-ssl-apache.conf :
SSLProtocol +TLSv1.2 +TLSv1.3
or:
SSLProtocol all -SSLv2 -SSLv3 -TLSv1 -TLSv1.1
Right now, they’ll do the same thing: allow TLSv1.2 and v1.3 only. Personally, I like the second version (which disables older protocols) better, for two reasons: 1) it’ll work even with some ancient Apache version that doesn’t recognize “TLSv1.3”, and 2) when future TLS versions are added, they’ll be enabled, making it more future-proof.
Again, you can test the new configuration on SSL Labs.
Postfix:
Add the following to /etc/postfix/main.cf (replacing any equivalent entries, if they exist).
After restarting Postfix, you can test its available protocols with Immuniweb’s SSL Security Test (specify something like yourhostname:25, or yourhostname:465 if not using STARTTLS).
Dovecot:
Add the following (or replace it if it exists) to your SSL configuration (typically /etc/dovecot/conf.d/10-ssl.conf):
ssl_min_protocol = TLSv1.2
Restart Dovecot, and test it on Immuniweb’s test (use something like yourhostname:143 , or yourhostname:993 if not using STARTTLS).
TLSv1.0, used not only for HTTPS but also for secure SMTP, IMAP, etc., has been around for a while — 1999, in fact –, and, while not “hopelessly broken” like SSL 2 and 3 are, there have been many successful attacks/exploits against it in the past two decades, and while most implementations (in terms of both servers and clients) have been patched to work around those, there may always be another one just around the corner. Also, TLSv1.0 came from a time where it was desirable to support as many different ciphers as possible, which means that, by default, some ciphers later found to be insecure may still be enabled.
Therefore, the end of TLSv1.0 has been talked about for a while, and, indeed, the main browser vendors — Google, Mozilla, Apple, and Microsoft — have announced that they’ll deprecate TLSv1.0 (and 1.1, which is little more than a revision of 1.0) by early 2020.
Now, until a few days ago I still had TLSv1.0 enabled on my servers (including Nginx, Postfix and Dovecot); my belief then being that some encryption was always better than no encryption, and besides we were mostly talking about public websites, that didn’t ask for user credentials or anything. Furthermore, any modern browsers/email clients default to secure protocols (TLSv1.2 or better), so there would never be, “in real life”, a situation where important/sensitive data (say, me logging on to my own mail server, or to one of my WordPresses) was being transmitted in an insecure way.
On the other hand… doesn’t the above mean that, “in real life”, nobody will really be using TLSv1.0 “legitimately”? Doesn’t it mean that setting up TLSv1.2 as a minimum will have no adverse consequences?
So I investigated it a little:
in terms of browsers/clients, requiring TLSv1.2 or above means: 1) no Internet Explorer before version 11; 2) no Safari before 6.x; 3) no default Android browser before Android 4.4.x (but those users can still use Chrome or other non-default browsers). (You can check this out on SSL Labs). I don’t have a way to check email clients that old, but you can assume that anything released after the browsers just mentioned will be OK;
in terms of my own server logs (mostly Nginx, but also Postfix, in terms of opportunistic encryption), apparently, only spambots and such are using TLSv1.0; any “legitimate” email servers use TLSv1.2 or 1.3. The same thing with my websites — any TLSv1.0 entries in my logs are always from some bot (and not one for a “well-known” search engine), not actual visitors. 1
In short: you can probably move to requiring TLSv1.2 or above now (and, indeed, I’ve done so since a few days ago), unless you’re in some very peculiar situation — maybe your site needs to be accessed by users of a company whose IT policy includes not using software newer than 20 years old? Or you have a CEO who’s always refused to upgrade his beloved Symbian phone, but who’d flip out if he couldn’t access your company’s webmail with it? 🙂 Otherwise, my advice is: go TLSv1.2 and don’t look back.
However, and since this post is already quite long, I’ll leave the specific instructions for disabling TLS before 1.2 in Nginx, Apache, Postfix, and Dovecot for the next one…
Some time ago, I noticed something like this on a site (not mine)’s rating on SSL Labs:
According to SSL Labs’ test, that little P means:
(P) This server prefers ChaCha20 suites with clients that don’t have AES-NI (e.g., Android devices)
Naturally, my curiosity was piqued, and a bit of investigating followed…
First (and briefly), the theory:
both AES and ChaCha20 ciphers are thought to be equally secure.
many modern CPUs provide hardware acceleration for AES, in which case it’s faster…
… however, if the CPUÂ doesn’t accelerate AES, then ChaCha20 is faster.
Therefore, setting a web server (or any other kind of server, such as IMAP or SMTP, but those are outside this article’s scope) to use either option all the time means that some clients won’t have the optimal cipher(s) (in terms of performance) for their device. It won’t probably be noticeable in 99% of cases, but, hey, I’m a geek, and geeks optimize stuff for fun, not just for real-world performance. 🙂
Fortunately, as the SSL Labs test shows, it’s possible to configure a server to use/prefer one cipher for non-hardware accelerated devices, and another cipher (or, more precisely, a list of preferred ciphers) for the rest.
(For the curious, the selection process works like this: if the client’s preferred cipher is ChaCha20, then the server assumes it’s a device without hardware AES and uses that. If the client’s top cipher is anything else, then the server uses its own cipher list.)
This guide shows how to do it in Nginx, using Let’s Encrypt certificates. I’m using an Ubuntu 19.04 server, but any relatively recent Nginx should work, as long as you’re using OpenSSL 1.1.0 or newer, or LibreSSL. If your distro still provides only OpenSSL 1.0.x or older by default, you can always compile a newer version to a separate directory, and then compile Nginx to use it: here are instructions for OpenSSL 1.1.x or LibreSSL.
This is actually relatively simple, though some specific distros/servers may require some other changes:
1- Give Nginx a list of ciphers that doesn’t have ChaCha20 in first place (you need to specify some AES ciphers first). The list I’m using (currently specified in /etc/letsencrypt/options-ssl-nginx.conf , since I’m using Let’s Encrypt) is:
2- Edit your OpenSSL/LibreSSL configuration file (in Ubuntu/Debian it’s /etc/ssl/openssl.cnf) and, just before the first section in square brackets (in Ubuntu it’s “[ new_oids ]“), add the following:
3- Restart Nginx, and test it on SSL Labs. If you see the superscript “P” at the right of each ChaCha20 line, everything went well. (Problems? Ask here, and maybe I, or some other reader, can help.)
You can also set up your Nginx to log ciphers (possibly to a separate log file), using something like:
And then access the site with some of your devices, noting what ciphers they use. For instance, both my (2015) i7 laptop and my (2016) ZenFone 3 Android phone use AES (yes, apparently the Snapdragon 625 chip includes AES acceleration), but a 2013 Nexus 7 tablet and a 2015 iPad Pro (Safari, in this case — all other examples used Chrome) went for ChaCha. This shows that everything’s working correctly — the devices that specifically want to use ChaCha are indeed using it, while the rest aren’t. And, yes, this means that the very same browser (in this case, Chrome on Android) has different cipher preference defaults depending on the hardware it’s running on.
This post should be titled “How to get a 100% score on SSL Labs (Nginx, Let’s Encrypt) as of April 2018“, since SSL Labs‘s test evolves all the time (and a good thing it does, too.) But that would be too long a title. 🙂
The challenge:
As we’ve seen before, it’s relatively easy to get an A+ rating on SSL Labs. However, even that configuration will only give a score like this:
Zurgl.com’s current SSL Labs score
Certainly more than good enough (and, incidentally, almost certainly much better than whatever home banking site you use…), but your weirdo of a host can’t look at those less-than-100% bars and not see a challenge. 🙂
First, note that all of the following will be just for fun, as the settings to get 100% will demand recent browsers (and, in some cases, recent operating systems/devices), so you probably don’t want this in a world-accessible site. It would be more applicable, say, for a webmail used by you alone, or by half a dozen people. But the point here isn’t real-world use, it’s fun (OK, OK, and learning something new). So, let’s begin.
Getting that perfect SSL Labs score:
For this example, I’ll be using a just-installed Debian 9 server, in which I did something like:
apt -y install nginx
echo "deb http://ftp.debian.org/debian stretch-backports main" >> /etc/apt/sources.list.d/stretch-backports.list # if you don't have this repository active already
apt -y install python-certbot-nginx -t stretch-backports
(The reason for the above extra complexity is the fact that the default certbot in Debian Stretch is too old and tries to authenticate new certificates in an obsolete way, but there’s a newer one in stretch-backports.)
I also created a simple index.html file on /var/www/html/ that just says “Hello world!”. Right now, the site doesn’t even have HTTPS.
So, let’s create a new certificate and configure the HTTPS server in Nginx:
Testing it on SSL Labs, it gives… exactly the same bars as in the image above, but with an A rating instead of A+. Right, we need HSTS to get A+ (and currently certbot doesn’t support configuring it automatically in Nginx), so we add this to the virtual host’s server section:
(Note: remove “includeSubDomains;” if you have HTTP sites on any subdomain. Also, HSTS makes your site HTTPS-only, so you can’t use it if you want to keep an HTTP version — in which case you can’t get better than an A rating.)
This upgrades the rating to A+, as expected, but the bars still didn’t change. Let’s make them grow, shall we?
Certificate:
It’s already at 100%, so yay. 🙂
Protocol Support:
Just disable any TLS lower than 1.2. In this case, edit /etc/letsencrypt/options-ssl-nginx.conf and replace the ssl_protocols line (or comment it and add a new one) with:
ssl_protocols TLSv1.2;
WARNING: any change you make to the file above will affect all virtual hosts on this Nginx server. If you need some of them to support older protocols, it’s better to just comment out that option in that file, and then include it in each virtual host’s server section.
EDIT: actually, it turns out that ssl_protocols affects the entire server, with the first option Nginx finds (first in /etc/nginx.conf, then in the default website (which possibly includes /etc/letsencrypt/options-ssl-nginx.conf)) taking precedence. So just choose whether you want TLS 1.0 to 1.2 (maximum compatibility) or just 1.2 only (maximum security/rating); if you need both, use two separate servers.
Key Exchange:
We’ve already created the new certificate with a 4096-bit key (with “—rsa-key-size 4096“, see above), and according to SSL Labs’ docs this should be enough… but it isn’t. After some googling, I found out that you also need to add the following option inside the server section in Nginx:
ssl_ecdh_curve secp384r1;
Since the default Nginx+OpenSSL/LibreSSL setting, either “X25519” or “secp256r1” (actually “prime256v1“), also lowers the score.
EDIT: again, ssl_ecdh_curve affects the entire server, so you can’t use different default curves for each virtual host. So I’d suggest (in /etc/letsencrypt/options-ssl-nginx.conf):
ssl_ecdh_curve secp384r1:X25519:prime256v1;
if you want the 100% rating, or:
ssl_ecdh_curve X25519:prime256v1:secp384r1:
otherwise. This one doesn’t affect compatibility, by the way; it’s just a question of the preferred order.
The certificate’s key size (4096 or 2048) is, like the certificate itself, specific to each virtual host.
Cipher Strength:
For 100% here, you need to disable not only any old protocols, but also any 128-bit ciphers. I started from Mozilla’s SSL tool (with the “Modern” option selected), then removed anything with “128” in its name, then moved ChaCha20 to the front just because, and ended up with this line, which I added to /etc/letsencrypt/options-ssl-nginx.conf (replacing the current setting with the same name):
(This time, this setting can indeed be specified for each virtual host, though you’d need to comment it out in the file above (which affects all virtual hosts with Let’s Encrypt certificates) if you want to do so, otherwise they’ll conflict.)
The result:
As said near the beginning, this is not something you likely want to do (yet) for a production, world-accessible site, as it will require relatively modern browsers, and you typically can’t control what visitors use1. According to SSL Labs’ list, it’s not actually that bad: all versions of Chrome, Firefox, or Safari from the past couple of years are fine, but no Microsoft browser older than IE11 will work, nor will Android’s default browser before 7.0 (Chrome on Android, which is not the same thing, will do fine.) I’d suggest it for a site where you can “control” the users, such as a small or medium-sized company’s webmail or employee portal (where you, as a sysadmin, can and should demand up-to-date security from your users).
But the main point of this exercise was, of course, to see if I could do it. Challenging yourself is always good. 🙂 And if you can share what you learned with others, so much the better.
(Yes, you read the title correctly. For extra fun, and to prevent this blog from being too focused on Ubuntu/Debian, this time I’ll be using Red Hat Enterprise Linux / CentOS (and, I assume, Fedora as well.) Later on, I may post a Debian-based version.)
Configuring a basic HTTP site on Nginx
(Note: if you already have a working HTTP site, you can skip to the next section (“Adding encryption…”))
Yes, the post title mentions an “existing” website, which I believe will be the case in most “real world” situations, but installing a new one is actually very easy on CentOS1. First, do:
yum -y install epel-release; yum -y install nginx
Then create a very basic configuration file for the (non-HTTPS) site, as /etc/nginx/conf.d/mysite.conf :
Then, of course, create the /var/www/mysite directory (CentOS doesn’t use /var/www by default, but I’m far too used to it to change. 🙂 ) If you’d like, create an index.html text file in that directory, restart nginx (“service nginx restart” or “systemctl restart nginx“, depending on your system’s major version), and try browsing to http://mysite.mydomain.com . If it works, congratulations, you have a running web server and a basic site.
Adding encryption to the site (not using Let’s Encrypt):
Second, edit the site’s configuration file (in the “starting from scratch” example above, it’s “/etc/nginx/conf.d/mysite.conf“), and copy the entire server section so that it appears twice on that text file (one after the other). Pick either the original or the copy (not both!), and, inside it, change the line:
listen 80;
to:
listen 443 ssl http2;
(Note: the “http2” option is only available in Nginx 1.9.5 or newer. If your version complains about it, just remove it, or upgrade.)
This should be enough — restart Nginx and you should have an HTTPS site as well as the HTTP one.
And what if you want to disable HTTP for that site and use HTTPS only? Just edit the same configuration file, look for the server section you didn’t change (the one that still includes “listen 80;“), and replace the inside of that section with:
(replacing “mysite.mydomain.com” with yours, of course.)
Answer the questions it asks you: a contact email, whether you agree with the terms (you need to say yes to this one), if you want to share your email with the EFF, and finally if you want “No redirect” (i.e. keep the HTTP site) or “Redirect” (make your site HTTPS only).
And that’s it (almost — see the next paragraph) — when you get the shell prompt back, certbot will already have reconfigured Nginx in the way you chose in the paragraph above, and restarted it so that it’s running the new configuration. You may want to add “http2” to the “listen 443 ssl;” line in the configuration file (it’ll probably be the default someday, but as of this post’s date it isn’t), and don’t forget your options for improved security and security headers.
Only one thing is missing: automatically renewing certificates. Strangely, the certbot package configures that automatically on Ubuntu, but not on CentOS, from what I’ve seen (please correct me if I’m wrong). The official Let’s Encrypt docs recommend adding this (which includes some randomization so that entire timezones don’t attempt to renew their certificates at precisely the same time) to root’s crontab:
(Note: It’s possible to use Let’s Encrypt to create ECDSA certificates, but as of this writing you have to do most of the work manually (creating a CSR, etc.), and you lose the automatic renewal, so for the moment I suggest using RSA certificates. I hope this changes in the future.)
Like any web server, Nginx logs all accesses/hits by default, and if you have some kind of log-based analytics tool (such as AWstats) you probably have it already set to ignore hits from the host itself (usually by skipping both localhost (127.0.0.1) and the server’s public IP address). If you don’t do so, then your statistics will probably be inflated (“wow, my newly created site is surprisingly popular!“), and, unless your site has many regular users, the IP address at the top of the “visitors” table will almost certainly be your own. Local hits can come from several culprits: for instance, some web software such as WordPress or MyBB use special URLs as a form of cron replacement, and also you may have yourself be monitoring your site in some way (such as, in my case, benchmarking a particular URL and MRTGing the access speed).
OK, so your analytics don’t show it anymore — but what about the log files themselves? Maybe you don’t want a large percentage of them being composed of internal hits (especially in the case of those “let’s measure the average response speed for 100 hits every 5 minutes” benchmarks, which for that site made up some 95% of its access logs…). Maybe it even interferes with some other tools you’re using, such as something like DenyHosts or Fail2ban, to detect some abuse patterns, even after whitelisting your external IP. How about having the option not to log them at all? 1
On Nginx, this is actually pretty easy to do.
1- in the Nginx main configuration file, add the following:
Replacing YOUR_EXTERNAL_IP with… you can probably guess. 🙂
Important: if your virtual hosts’ configurations are in another directory that is “included” from nginx.conf, take care to add the above before the include lines (e.g. include /etc/nginx/conf.d/*.conf) . Otherwise, the virtual hosts won’t have the “$notlocal” variable defined yet, and Nginx won’t start because of it.
2- for each virtual host where you want to stop logging local hits, edit the access_log line, changing it from something like:
Note the addition of “combined“. “combined” is the default format for Nginx access logs, so specifying it isn’t usually needed, but apparently if you want to specify the “if” condition, it must come after the log format option (otherwise, I guess Nginx thinks you want a log format of “if“, which of course doesn’t exist and will prevent the server from starting.)
That it! Restart Nginx, and enjoy your much cleaner/smaller logs.
Some time ago, I wrote about how to set up Nginx to get an A+ rating on SSL Labs (focusing specifically on an ECDSA certificate, but you can certainly achieve the same with a (more common) RSA certificate). SSL Labs' test is very comprehensive, warning the user of most potential problems, including SSL/TLS implementation bugs (update your software!), misconfigurations, problems with the certificate itself, etc.. But there is another similar tool, securityheaders.io, which focuses on something different: security-related headers. Such headers are sent by the web server (such as Nginx or Apache) and affect browsers' security in several ways, unrelated to encryption, protocols or the certificate used (these are tested by SSL Labs).
For more details about those headers, I'd suggest you navigate to securityheaders.io itself, and then check your site in it, then follow the links for each suggestion. Meanwhile, if your site uses Nginx, here's a "quick and dirty" guide for getting an A rating (and, yes, I'll mention what you'd need for an A+ rating, and also why I choose not to try for one).
 Forces TLS (don't use if you still need to provide HTTP); prevents mixed content warnings. NOTE: again, this is not the most secure setting; see below.
You're probably wondering about the last two settings. I choose to send referring information to other sites for a simple reason: I like to see where my own visitors come from (I don't sell, share or monetize that in any way, it's just for curiosity's sake), and I'm a firm believer in treating others as I want to be treated. If you don't care about that, you may want to change this to "no-referrer-when-downgrade", or "strict-origin".
As for the Content Security Policy, anything more "secure" than the above prevents (or at least makes it a lot more headache-inducing) the use of inline scripts and/or external scripts, which would mean no external tools/scripts/content (or at least a lot of work in adding every external domain to a list of exceptions), and a lot of hacking on software such as WordPress (seriously: add the setting, but then remove the "unsafe-*" options and see what stops working...). You might use the most paranoid settings for an internally developed, mostly static site, but I fail to see the point. So, this and the paragraph above are the reasons for an A rating, instead of an A+.
Most people who maintain web servers (or email servers, or…) have probably had to deal with SSL/TLS certificates in the past, but the process is, in my opinion, typically more complex than it should be, and not that well documented, typically forcing the user to consult several tutorials on the web so that they can adapt parts of each for their needs. Since I had to renew a couple of certificates last week, I thought about writing a quick and easy tutorial for a particular case: HTTPS on Nginx (although the certificate itself could, of course, be used for other services; right now I have one I’m using for IMAP (Dovecot) and SMTP (Postfix) as well). For extra fun, I’ll be creating/using an ECDSA certificate with an EC key, instead of the more usual RSA type; ECDSA is more modern and is theoretically more secure even with smaller keys.
A few notes:
There are alternatives (e.g. key sizes, etc.) for basically every parameter I’m using, but I’m not going into those. This is supposed to be as quick and easy as possible, after all.
Similarly, I’m not going into Let’s Encrypt; instead, I’m assuming a “normal” certificate authority such as Comodo (which supports ECDSA certificates; if you choose another, you should make sure of that in advance). If you do use Let’s Encrypt, just use it to create the certificate instead of the “send the CSR to the certification authority” part.
The certificate (and server) will be compatible with most browsers, but that “most” won’t include any Microsoft browsers on Windows XP (Firefox or Chrome on that abomination of an OS will still work).
If you already have a certificate (whether ECDSA or not, whether from Let’s Encrypt or not) and you’re here just for the A+ rating on SSL Labs, skip to “Setting up Nginx” below.
Generating the key and the Certificate Signing Request (CSR):
The second command will ask you for details about your server/company (location, etc.). You should fill in every field, although the only mandatory one is “Common Name” (CN), which must match your server’s public name (not necessarily the machine’s name, but the host name people will type in the browser, such as “zurgl.com“. Note that a certificate for “domain.com” also includes “www.domain.com” (so don’t include the “www.” in the CN), but if the server is reached at “subdomain.domain.com“, then that’s what the CN needs to be.
Ordering and receiving the new certificate:
Now go to a certification authority (CA), order a new certificate, and when asked for a CSR, send them (usually you can just copy and paste it to a text entry window) that myserver.csr file.
If everything went well, then the CA should email you the new certificate in a short while. Typically they send you two files: the certificate itself, and a couple of “intermediate” certificates. Only the first is really needed, but I’ve had best results with concatenating your certificate (first) and the intermediate certs (last) into a single file, which you might call myserver-full.crt . Put it somewhere Nginx can access (e.g. /etc/nginx), and also the key you generated earlier (in this example, myserver.key). You don’t need the CSR there, by the way; it was just needed for ordering the new certificate.
Setting up Nginx:
This is, of course, not a complete Nginx tutorial (that would take a lot more space than a single post), just a simple recipe for configuring an HTTPS site with your new certificate, and have it be secure (and get a great score at SSL Labs, too). I’m assuming you can take care of all the non-HTTPS bits.
So, inside a virtual host, you need the server section:
server {
listen 443 ssl http2; # if your nginx complains about 'http2', remove it, or (better yet) upgrade to a recent version
server_name mysite.com # replace with your site, obviously
# all the non-HTTPS bits (directories, log paths, etc.) go here
# the rest of the recipe -- see below -- can go here
}
See the last comment? OK, let’s begin adding stuff there (I won’t indent any configuration lines from now on, but they look better if aligned with the rest of the configuration inside the { } ).
ssl_certificate /etc/nginx/myserver-full.crt; # the certificate and the intermediate certs, as seen above...
ssl_certificate_key /etc/nginx/myserver.key; # ... and the key
ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
ssl_ciphers 'ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES256-SHA:ECDHE-ECDSA-DES-CBC3-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:DES-CBC3-SHA:!DSS:!3DES';
# the above comes from Mozilla's Server Side TLS guide
add_header X-Content-Type-Options nosniff;
ssl_session_cache shared:SSL:10m;
ssl_session_timeout 5m; # basic defaults.
Great, you now have a basic HTTPS server! I suggest you try it now: save the configuration, restart Nginx, and test it. Access the URL with a browser (and check if the browser doesn’t complain about the certificate: if it did, something went wrong), and run it through SSL Labs’ Server Test. Check if it complains about something; if so, something needs fixing (ask in the comments, maybe I or someone else can help).
If all went well, you probably got a decent score, maybe even an A. But how to get an A+, like I promised at the beginning?
An A+ score on SSL Labs’ Server Test:
As of now (September 2017), SSL Labs only asks for one more thing: “HTTP Strict Transport Security (HSTS) with long duration”. HSTS is a mechanism to tell browsers: “this site should be accessed through HTTPS only; if you attempt to connect through normal HTTP, then deny access”. This information is actually cached by the browser, it’s not the server that refuses HTTP connections (though it’s, of course, possible to configure Nginx to do just that — or simply do 301 redirects to the equivalent HTTPS URL. But I digress…). In short, it protects against downgrade attacks. As for the “with long duration” part, that’s simply the time that browsers should cache that information.
IMPORTANT: don’t proceed until you have the basic HTTPS site running, and SSL Labs reporting no problems (see the previous section)!
ALSO IMPORTANT: if you *do* want your site to be accessible through both HTTP and HTTPS, stop here, as the rest of the configuration will make it HTTPS-only! That means, however, giving up on the A+ score.
Restart Nginx, try SSL Labs’ test again. Did you get an A+?
If not, or you have any questions, feel free to ask.
For extra fun: have your Nginx use LibreSSL or OpenSSL 1.1.x, and enjoy a few more modern ciphers (look for “ChaCha20” on SSL Labs) without any configuration changes from the above.
So, let’s say you have a Ubuntu or Debian server, using one or more of Nginx, Postfix, and Dovecot, and you’d like to have them link to OpenSSL 1.1.x instead of the default OpenSSL (as of Ubuntu 17.04, it’s version 1.0.2g). (Reasons may include wanting to use modern ciphers such as ChaCha20, or trying out support for the most recent TLS 1.3 draft. Also, if you want to try out LibreSSL instead of OpenSSL 1.1, please check out the previous post.)
So, here’s a relatively simple way, that doesn’t change the system’s default OpenSSL (believe me, that wouldn’t be a good idea, unless you recompiled everything):
./config --prefix=/usr/local/openssl11 --openssldir=/usr/local/openssl11 && make && make install
Install Nginx:
rm -rf /usr/local/src/nginx-openssl11
mkdir /usr/local/src/nginx-openssl11
cd /usr/local/src/nginx-openssl11
apt-get source nginx # ignore the permissions error at the end
edit nginx-<version>/debian/rules: Â add
–with-openssl=/usr/local/src/openssl-
to the beginning of the common_configure_flags option (note that that’s the source directory you used to compile OpenSSL 1.1.x, not where you installed it to);
debuild -uc -us -b
install the required packages in the parent directory with “dpkg -i ” (do dpkg -l | grep nginx to see which you have installed; typically you’ll want to install the newly created versions of those);
apt-mark hold nginx* # to prevent nginx from being updated from Ubuntu / Debian updates
Done! You can now play around with the Mozilla TLS Guide to add support for modern ciphers to your Nginx’s configuration, and use SSLLabs’s SSL Server Test tool to check if they are correctly enabled.
Install Postfix:
It’s just like Nginx (replacing “nginx” with “postfix” in every command / directory name, of course), except that the changes to debian/rules are these:
find -DHAS_SSL, add -I/usr/include/openssl11/include/openssl in front of it;
find AUXLIBS += , add -L/usr/local/openssl11/lib in front of it
find the line with dh_shlibdeps -a, add –dpkg-shlibdeps-params=–ignore-missing-info to it
don’t forget the apt-mark hold postfix* at the end.
Install Dovecot:
Again, use the Nginx instructions, using “dovecot” instead of “nginx” everywhere, except that the changes to debian/rules should be:
override_dh_makeshlibs:
# Do not add an ldconfig trigger; none of the dovecot shared libraries
# are public.
dh_makeshlibs -n
add:
override_dh_shlibdeps:
    dh_shlibdeps --dpkg-shlibdeps-params=--ignore-missing-info
NOTE: the indentation in the second line needs to be a tab, don’t use spaces.
Again, remember to apt-mark hold dovecot* after installation.
How to check if your new installations of Postfix and/or Dovecot are using OpenSSL 1.1.x instead of the default OpenSSL 1.0.x? You could use ldd to check what SSL / TLS libraries your binaries and/or libraries link to, but the best way is probably to use a tool such as sslscan, which you can use to check what ciphers your SMTP, IMAP, etc. support (including with STARTTLS). If you see ChaCha20 in there, everything is fine. 🙂
If you ever want to go back to “normal” versions of these servers, just do apt-mark unhold nginx* (for instance).
So, let’s say you have a Ubuntu or Debian server, using one or more of Nginx, Postfix, and Dovecot, and you’d like to have them link to LibreSSL instead of the default OpenSSL. (I won’t go much into the possible reasons for it; maybe you’re bothered because modern distros are still sticking with OpenSSL 1.0.x, which is ancient and doesn’t support modern ciphers such as ChaCha20, or you trust the OpenBSD developers more than you trust the OpenSSL ones, or — and there’s nothing wrong with that — you want to do it just for fun. You could also use OpenSSL 1.1.x — check out this (very similar) post.)
So, here’s a relatively simple way, that doesn’t change the system’s default OpenSSL (believe me, that wouldn’t be a good idea, unless you recompiled everything):
./configure --prefix=/usr/local/libressl --with-openssldir=/usr/local/libressl && make && make install
Install Nginx:
rm -rf /usr/local/src/nginx-libressl
mkdir /usr/local/src/nginx-libressl
cd /usr/local/src/nginx-libressl
apt-get source nginx # ignore the permissions error at the end
edit the file nginx-<versão>/debian/rules:  add
-I/usr/local/libressl/include
to the line beginning with “debian_cflags:=“, and:
-L/usr/local/libressl/lib
to the line that begins with “debian_ldflags:“. After that, enter the nginx-<version>Â directory and compile the packages with the command:
debuild -uc -us -b
install the required packages in the parent directory with “dpkg -i <package names>” (do “dpkg -l | grep nginx” to see which you have installed; typically you’ll want to install the newly created versions of those);
apt-mark hold nginx* # to prevent nginx from being updated from Ubuntu / Debian updates
Done! You can now play around with the Mozilla TLS Guide to add support for modern ciphers to your Nginx’s configuration, and use SSL Labs’s SSL Server Test tool to check if they are correctly enabled.
Install Postfix:
It’s just like Nginx (replacing “nginx” with “postfix” in every command / directory name, of course), except that the changes to debian/rules are these:
find -DHAS_SSL, add -I/usr/include/libressl/include/openssl in front of it;
find AUXLIBS += , add -L/usr/local/libressl/lib in front of it
find the line with dh_shlibdeps -a, add –dpkg-shlibdeps-params=–ignore-missing-info to it
don’t forget the apt-mark hold postfix* at the end.
Install Dovecot:
Again, use the Nginx instructions, using “dovecot” instead of “nginx” everywhere, except that the changes to debian/rules should be:
override_dh_makeshlibs:
# Do not add an ldconfig trigger; none of the dovecot shared libraries
# are public.
dh_makeshlibs -n
add:
override_dh_shlibdeps:
    dh_shlibdeps --dpkg-shlibdeps-params=--ignore-missing-info
NOTE: the indentation in the second line needs to be a tab, don’t use spaces.
Again, remember to apt-mark hold dovecot* after installation.
How to check if your new installations of Postfix and/or Dovecot are using LibreSSL instead of the default OpenSSL? You could use ldd to check what SSL / TLS libraries your binaries and/or libraries link to, but the best way is probably to use a tool such as sslscan, which you can use to check what ciphers your SMTP, IMAP, etc. support (including with STARTTLS). If you see ChaCha20 in there, everything is fine. 🙂
If you ever want to go back to “normal” versions of these servers, just do apt-mark unhold nginx* (for instance).
I’ve also added /usr/local/libressl/bin to the beginning of my PATH environment variable, so that the LibreSSL binaries are used by default (e.g. to generate keys, CSRs, etc.), although this isn’t necessary for Nginx, etc. to work.
So, let’s say you have a Ubuntu or Debian server, using one or more of 
So, let’s say you have a Ubuntu or Debian server, using one or more of