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One of the goals of Cloudflare is to give our customers the necessary knobs to enable security in a way that fits their needs. In the realm of SSL/TLS, we offer two key controls: setting the minimum TLS version, and restricting the list of supported cipher suites. Previously, these settings applied to the entire domain, resulting in an “all or nothing” effect. While having uniform settings across the entire domain is ideal for some users, it sometimes lacks the necessary granularity for those with diverse requirements across their subdomains.
It is for that reason that we’re excited to announce that as of today, customers will be able to set their TLS settings on a per-hostname basis.
The trade-off with using modern protocols
In an ideal world, every domain could be updated to use the most secure and modern protocols without any setbacks. Unfortunately, that's not the case. New standards and protocols require adoption in order to be effective. TLS 1.3 was standardized by the IETF in April 2018. It removed the vulnerable cryptographic algorithms that TLS 1.2 supported and provided a performance boost by requiring only one roundtrip, as opposed to two. For a user to benefit from TLS 1.3, they need their browser or device to support the new TLS version. For modern browsers and devices, this isn’t a problem - these operating systems are built to dynamically update to support new protocols. But legacy clients and devices were, obviously, not built with the same mindset. Before 2015, new protocols and standards were developed over decades, not months or years, so the clients were shipped out with support for one standard — the one that was used at the time.
If we look at Cloudflare Radar, we can see that about 62.9% of traffic uses TLS 1.3. That’s quite significant for a protocol that was only standardized 5 years ago. But that also means that a significant portion of the Internet continues to use TLS 1.2 or lower.
The same trade-off applies for digital signature algorithms. ECDSA for TLS was standardized in 2006, years after RSA. It offers a higher level of security than RSA and uses shorter key lengths, which adds a performance boost for every request. To use ECDSA, a domain owner needs to obtain and serve an ECDSA certificate and the connecting client needs to support cipher suites that use elliptical curve cryptography (ECC). While most publicly trusted certificate authorities now support ECDSA-based certificates, the slow rate of adoption has led many legacy systems to only support RSA, which means that restricting applications to only support ECC-based algorithms could prevent access from those that use older clients and devices.
Balancing the trade-offs
When it comes to security and accessibility, it’s important to find the right middle ground for your business.
To maintain brand, most companies deploy all of their assets under one domain. It’s common for the root domain (e.g. example.com) to be used as a marketing website to provide information about the company, its mission, and the products and services it offers. Then, under the same domain, you might have your company blog (e.g. blog.example.com), your management portal (e.g. dash.example.com), and your API gateway (e.g. api.example.com).
The marketing website and the blog are similar in that they’re static sites that don’t collect information from the accessing users. On the other hand, the management portal and API gateway collect and present sensitive data that needs to be protected.
When you’re thinking about which settings to deploy, you want to consider the data that’s exchanged and the user base. The marketing website and blog should be accessible to all users. You can set them up to support modern protocols for the clients that support them, but you don’t necessarily want to restrict access for users that are accessing these pages from old devices.
The management portal and API gateway should be set up in a manner that provides the best protection for the data exchanged. That means dropping support for less secure standards with known vulnerabilities and requiring new, secure protocols to be used.
To be able to achieve this setup, you need to be able to configure settings for every subdomain within your domain individually.
Per hostname TLS settings - now available!
Customers that use Cloudflare’s Advanced Certificate Manager can configure TLS settings on individual hostnames within a domain. Customers can use this to enable HTTP/2, or to configure the minimum TLS version and the supported ciphers suites on a particular hostname. Any settings that are applied on a specific hostname will supersede the zone level setting. The new capability also allows you to have different settings on a hostname and its wildcard record; which means you can configure example.com to use one setting, and *.example.com to use another.
Let’s say that you want the default min TLS version for your domain to be TLS 1.2, but for your dashboard and API subdomains, you want to set the minimum TLS version to be TLS 1.3. In the Cloudflare dashboard, you can set the zone level minimum TLS version to 1.2 as shown below. Then, to make the minimum TLS version for the dashboard and API subdomains TLS 1.3, make a call to the per-hostname TLS settings API endpoint with the specific hostname and setting.
This is all available, starting today, through the API endpoint! And if you’d like to learn more about how to use our per-hostname TLS settings, please jump on over to our developer documentation.