Hardening TLS

Protocol versions

TLS 1.2 and 1.3. Nothing else.

ssl_protocols TLSv1.2 TLSv1.3;

1.0 and 1.1 are deprecated, fail compliance scans and are not needed by any browser in current use. SSLv3 has been broken for a decade.

Ciphers

TLS 1.3 handles this itself; its cipher suites are all good. For 1.2, a short modern list:

ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305;

ssl_prefer_server_ciphers off;

Forward secrecy only, AEAD only. Letting the client choose is now the better default: a phone without AES hardware picks ChaCha20 and is faster for it.

Sessions and stapling

ssl_session_cache shared:SSL:10m;
ssl_session_timeout 1d;
ssl_session_tickets off;

Tickets off unless you rotate the keys, because a static ticket key undermines forward secrecy.

ssl_stapling on;
ssl_stapling_verify on;

Stapling means your server presents the revocation status itself, so the client does not make a separate request to the CA. Faster, and more private for your visitors.

HSTS, deliberately

add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;

This tells browsers never to use plain HTTP for your domain again, and it is hard to undo — a visitor's browser remembers it for a year. Enable it only once every subdomain genuinely works over HTTPS. Start with a short max-age if you are unsure.

And remember that one add_header in a location block cancels inherited headers; see nginx pitfalls.

Test from outside

Do not trust the configuration file. Check what is actually negotiated:

openssl s_client -connect example.com:443 -tls1_1 — should fail

echo | openssl s_client -connect example.com:443 -servername example.com 2>/dev/null | openssl x509 -noout -subject -enddate

A public SSL testing service gives you the full picture including chain problems. Be sceptical of anything reporting a protocol as enabled when a handshake actually failed — a “Cipher is (NONE)” result means refused, not supported.

The chain and the renewal

Serve the full chain, not just the leaf: browsers forgive a missing intermediate, many API clients and mobile apps do not. And the most common TLS outage is not a weak cipher, it is an expired certificate — monitor the expiry date and test the renewal, as TLS certificates describes.

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