TLS Handshake
The process where a client and server negotiate encryption before exchanging data over HTTPS.
The TLS handshake happens after the TCP connection is established and before any HTTP data is exchanged. During the handshake, the client and server agree on a TLS version and cipher suite, the server presents its SSL certificate, the client verifies the certificate's validity, and both sides generate session keys for encryption. This entire process typically takes one round-trip (TLS 1.3) or two (TLS 1.2). Cloudflare error 525 occurs when this handshake fails between Cloudflare and the origin server.