What is TLS 1.3?
TLS 1.3 is a streamlined protocol version defined in RFC 8446 that reduces handshake latency to one round trip and mandates modern AEAD ciphers.
TLS 1.3 is the fourth major version of the Transport Layer Security protocol. Published as RFC 8446 in August 2018, it replaces TLS 1.2 as the current standard for encrypted communications over TCP. The protocol was redesigned to remove legacy features, simplify the handshake, and eliminate known vulnerabilities from earlier versions.
The most visible change in TLS 1.3 is the handshake. A full handshake now completes in one round trip (1-RTT) instead of two. A zero round trip (0-RTT) mode allows resumption with cached session state, sending application data on the first flight. The cipher suite list was pruned to a small set of AEAD-only algorithms: AES-128-GCM, AES-256-GCM, and ChaCha20-Poly1305. Static RSA key exchange and CBC-mode ciphers were removed entirely. All key agreement uses ephemeral Diffie-Hellman (DHE or ECDHE), providing forward secrecy by default. The protocol also replaced the hash-based PRF with HKDF, and the Finished message now covers the entire handshake transcript, preventing downgrade attacks.
In the protocol stack, TLS 1.3 sits between TCP and the application layer. It is backwards-incompatible with TLS 1.2 at the wire level, so implementations negotiate via the supported_versions extension. Major web browsers and servers adopted TLS 1.3 rapidly after publication. It is mandated by PCI DSS 4.0 and required for HTTP/2 connections by many major platforms. The version does not support renegotiation or compression, and it removed several cryptographic primitives that had been deprecated over the preceding decade.
Key facts
- Published as RFC 8446 in August 2018, replacing TLS 1.2.
- Full handshake completes in one round trip (1-RTT); 0-RTT resumption is optional.
- Only AEAD ciphers (AES-128-GCM, AES-256-GCM, ChaCha20-Poly1305) are allowed.
- All key exchange provides forward secrecy; static RSA and DH key exchange removed.
- Does not support renegotiation, compression, or CBC-mode ciphers.
How it works in practice
Related terms
References
More in TLS & PKI
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Certificate Authority
A Certificate Authority (CA) is a trusted entity that issues digital certificates after verifying that the requester controls the domain or identity named in the certificate.
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Certificate Pinning
A security technique where an application trusts only a specific, pre-selected certificate or public key for a given server, bypassing the standard chain of trust.
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A cipher suite is a named set of cryptographic algorithms negotiated during a TLS handshake, specifying key exchange, authentication, encryption, and integrity protection for secure communications.
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Domain Validation (DV) is the lowest level of certificate validation used in TLS/SSL, where the certificate authority verifies only that the applicant controls the domain name, typically via an HTTP or DNS challenge.
ECH
Encrypted Client Hello (ECH) is a TLS extension that encrypts the Client Hello message, including the Server Name Indication (SNI), to prevent on-path observers from learning the target hostname during the handshake.
Extended Validation
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HSTS
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Intermediate Certificate
An intermediate certificate is a subordinate CA certificate signed by a root CA, used to sign end-entity certificates and enable path validation while the root remains offline.