# What is the most popular cipher suite used in TLS 1.2 for HTTPS?

I'm trying to do some performance (time) calculations over TLS. I have the data I need for a variety of cipher suites but in order for the calculations to generalize well, I need to know if there is a clear most popular choice for TLS 1.2 cipher suite. Data to back up any answers would be appreciated.

• This is the only ressource I could find after a short search (it's from 2016 but nothing much should have changed since then) and it states that the vast majority of connections to mozilla.org use ECDHE-RSA-AES128-GCM-SHA256, of course that's only the report of one website (which also sits behind a CDN which has disabled DHE)... – SEJPM Jul 10 '18 at 18:59
• Mozilla publish measurements: mzl.la/2vGWAYJ - that's for today, with Firefox Nightly, which is a little biased, but not so badly that the obvious top value, TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, would be wrong. That confirms @SEJPM's answer. – Martin Thomson Aug 6 '18 at 10:38

## 1 Answer

The first web search hit I find is:

https://scotthelme.co.uk/alexa-top-1-million-analysis-february-2018/

This claims that the most widely supported cipher suite among the Alexa top 1m sites is ECDHE-RSA-AES256-GCM-SHA384, supported by 147 985 servers. Raw data and methodology are at the link.

Other links found by a quick search that may have similar data about HTTPS servers:

(This answer will be outdated within a year or two, if not in months.)

If you are trying to decide what cipher suites to configure your HTTPS server to use, based on what browsers you want to support and what software you're running on the server, you should use this tool: https://mozilla.github.io/server-side-tls/ssl-config-generator/

If these don't answer your question, you'll need to be more specific about why the quick web search results aren't what you're looking for.

Beware that AES, GCM, RSA, and ECDH in that cipher suite are likely to be vulnerable to timing side channel attacks if implemented in software!

• Small nitpick: supported != used, I would expect (based on experience) that a AES_128_GCM cipher is actually used a lot more than a AES_256_GCM cipher, even if ciphersuites with AES_256_GCM are more commonly supported by servers. – puzzlepalace Jul 10 '18 at 20:36
• @puzzlepalace The question also says ‘most popular choice’. I didn't know what exactly they meant so I picked something that gave an easy answer with a quick web search. If the original poster wants a clearer answer they can always ask a clearer question! – Squeamish Ossifrage Jul 11 '18 at 0:32