TLS 1.3

TLS 1.3 (RFC 8446, published in 2018) is the latest version of the Transport Layer Security protocol. It cut the handshake to a single round trip, removed legacy algorithms and encrypted more of the handshake itself.

Why it matters

Compared with TLS 1.2, version 1.3 is both faster and safer. Features removed include static RSA key exchange, CBC-mode ciphers, RC4, SHA-1 signatures, compression and renegotiation. Every connection has forward secrecy. Because fewer options exist, there are fewer ways to misconfigure a server.

It also supports a 0-RTT mode that lets a returning client send data in its first flight. That data can be replayed by an attacker, so it should be accepted only for idempotent requests, if at all. HTTP/3 requires TLS 1.3.

Example

Enable it in nginx and verify:

ssl_protocols TLSv1.2 TLSv1.3;

openssl s_client -connect example.com:443 -tls1_3 </dev/null 2>/dev/null | grep -E "Protocol|Cipher"

You should see TLSv1.3 and a suite like TLS_AES_256_GCM_SHA384.

Common mistakes

• Running an old OpenSSL build that cannot offer it.
• Disabling TLS 1.2 before checking your visitor and API client mix.
• Turning on 0-RTT without thinking about replay.

Related

• TLS handshake
• Forward secrecy
• Cipher suite
• टूल: TLS version checker

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