What the padlock means
How your browser decides a site is who it claims to be and keeps the conversation private: certificates, revocation, automated issuance, TLS and HSTS.
- 01
A certificate says who you are X.509
A website proves its identity with a certificate that binds its name to a public key and is signed by a certificate authority. X.509 defines the format and how a chain of signatures is checked.
- 02
The name must match Service identity
Having a valid certificate is not enough. The client also checks that the name in the certificate matches the site it meant to reach.
- 03
Is it still good? Revocation
A certificate can be revoked before it expires. OCSP lets a client ask a responder about a certificate's status instead of downloading a full revocation list.
- 04
Getting a certificate automatically ACME
ACME lets a server prove it controls a domain and obtain a certificate without a human, which is what made short-lived certificates and free HTTPS practical.
- 05
Encrypt the connection TLS 1.3
TLS agrees on keys, authenticates the server and encrypts everything that follows. TLS 1.3 was published as RFC 8446 and has since been revised as RFC 9846; the older TLS 1.0 and 1.1 are deprecated.
RFC 9846 TLS 1.3 (current)RFC 8446 TLS 1.3 (original)RFC 8996 Deprecating TLS 1.0 and 1.1
- 06
Never fall back to plain HTTP HSTS and https
A site can tell browsers to use only HTTPS for it from now on. The padlock also depends on how HTTP defines the https scheme.