TLS 1.2 Protocol

RFC 5246 defines Transport Layer Security Version 1.2, providing cryptographic privacy and data integrity across computer networks.

Compatibility in HTTPX

HTTPX uses TLS 1.2 for interoperability on the standard-library HTTPS/1.1 client transport, for legacy servers and enterprise load balancers that do not yet support TLS 1.3.

• Cipher Suites: Supports AES-128-GCM, AES-256-GCM, and ChaCha20-Poly1305 authenticated encryption.
• Handshake: 2-RTT handshake negotiating symmetric session keys and verifying X.509 certificate chains.
• SNI: Supported by the standard-library HTTPS/1.1 transport.
• ALPN: Not available on the TLS 1.2 path. Native ALPN negotiation uses TLS 1.3.

Handshake Flow

Client                                               Server
ClientHello (TLS 1.2, SNI)  -------------->
                                              ServerHello
                                              Certificate
                                              ServerKeyExchange
                                  <--------   ServerHelloDone
ClientKeyExchange
[ChangeCipherSpec]
Finished                          -------->
                                              [ChangeCipherSpec]
                                  <--------   Finished
Application Data                  <------->   Application Data

Related

• Protocol: TLS 1.3
• Guide: TLS
• Security: TLS