TLS Handshake
The TLS handshake is the negotiation at the start of an HTTPS connection where client and server agree on encryption and the server proves its identity with a certificate.
A slow or failing handshake — caused by an expired certificate, an incomplete chain, or a protocol mismatch — blocks the connection before any content loads. It is a common, hard-to-spot cause of "the site is down".
Related terms
SSL/TLS CertificateAn SSL/TLS certificate is a digital credential that enables encrypted HTTPS connections and proves a site owns its domain.HSTSHSTS (HTTP Strict Transport Security) is a response header that tells browsers to only ever connect to a site over HTTPS, never plain HTTP.Certificate ChainA certificate chain is the sequence of certificates linking your site's SSL certificate to a trusted root certificate authority.
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