How HTTPS works

In brief

HTTPS is HTTP over TLS. During the handshake, client and server agree on cryptographic parameters, the server proves control of the domain with a certificate, and both sides derive a shared session key with Diffie–Hellman. The browser padlock means the connection to the domain owner is encrypted; it does not prove the site itself is trustworthy.

Key points

• 0:48HTTPS = HTTP over TLS: encryption, integrity and server authentication.
• 2:40A TLS 1.3 handshake takes one round trip.
• 4:45A certificate binds a domain name to a public key and is signed by a certificate authority.
• 6:42The browser validates the certificate chain up to a trusted root certificate.
• 9:00The session key is derived with Diffie–Hellman; it is not sent over the network.
• 11:30Forward secrecy means a leaked server key does not reveal past sessions.
• 14:40The padlock means “encrypted connection to the domain owner,” not “this site is honest.”

Chapters

1. 0:00What HTTPS provides
2. 2:40TLS 1.3 handshake
3. 4:45Certificates and chain of trust
4. 9:00Key exchange
5. 11:30Forward secrecy
6. 14:40What the padlock means

Terms

TLS 0:48

A protocol that encrypts a connection and authenticates its peer.

Certificate authority 4:45

An organisation that signs certificates for domain names.

Forward secrecy 11:30

A property that keeps old sessions safe even if the server key is later compromised.

Takeaways

• Inspect certificate warnings before entering passwords or payment details.
• A padlock is not a trust seal for the site’s content.
• Disable obsolete TLS versions on servers you operate.

Check yourself

1. How many round trips does a TLS 1.3 handshake require?

   OneTwoThree
2. Is the session key sent over the network?

   Yes, but encryptedNo, both sides derive itOnly on the first connection
3. What does the browser padlock guarantee?

   The site is not fraudulentAn encrypted connection to the domain ownerThe browser reviewed the site

Questions about the video