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I was just curious about TLS1.3 which Cloudflare is one of the companies leading the implementation. I then visited blog.cloudflare.com and turned on my Wireshark. I am not 100% clear about all technical details of TLS1.3, but one of the new features that I was particularly interested in is Encrypted-SNI, which aims to hide the intended visiting domain name.

I check the pcap, saw both Client Hello and Server Hello as follow: enter image description here

I was surprised to see TLS1.2 was wrapped in the TLS1.3 packet, and the SNI part of TLS1.2 is still there, exposing the server name.

cl

So I wonder whether this is the implementation error or I have been downgraded, or am I missing something? Note that I already configure my Firefox browser to force TLS1.3 only, thus it's not the issue of my browser as you can see in the supported_versions extension.

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  • I'm not an expert either, but I'm pretty sure that the handshake version (the way the client and server prove their identity, and the way the session key is established) is independent of the overall protocol version. For example, I've seen TLS 1.2 with an SSLv3-style handshake. – Mike Ounsworth Jan 18 '19 at 02:06
  • *"....details of TLS1.3, but one of the new features that I was particularly interested in is Encrypted-SNI..."* - ESNI is not part of TLS 1.3 even if it was originally planned this way. It is a separate draft (no standard yet) - see https://datatracker.ietf.org/doc/draft-ietf-tls-esni/ – Steffen Ullrich Jan 18 '19 at 06:07

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Your question about the version numbers in TLS 1.3 ClientHello -- note the record version is 1.0 (wire 0301) and message version is 1.2 (wire 0303), and as you note only the supported_versions extension says 1.3 (0304) -- is a crossdupe of https://serverfault.com/questions/907347/tls-1-3-client-server-hello-version-1-2 and now that RFC8446 is official is explained there.

It appears your actual concern might be that your connection attempt -- which is in fact 1.3 -- is not using ESNI. If so, the obvious answer is that the domain blog.cloudflare.com does not support ESNI, at least as defined in the draft; specifically it does not publish any TXT RR(s) at _esni.blog.cloudflare.com as required. The only domain I know cloudflare has announced to support ESNI is encryptedsni.com, and _esni.encrypted.com does have TXT RR containing ESNIKeys, although I didn't go to the trouble of installing Firefox nightly to test if it actually works. You might try that.

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