The initial communication in a HTTPS connection relies on a traditional D-H key exchange – which will serve as symmetric encryption key for the rest of the HTTPS conversation.
The outline of the handshake is:
– client/server hello: list the available encryption algorithms
– certificate exchange
– certificate validation
– key exchange
Here is the process explained in layman words:
1. Client sends a
Client hellomessage to the server with some metadata (TLS version, cipher algorithms, compression methods)
2. The server replies with a
Server hellomessage to the client with the corresponding metadata + the Server public certificate signed by a CA.
3. The client verifies the server digital certificate and cipher a symmetric cryptography key using an asymmetric cryptography algorithm, attaching the server public key and an encrypted message for verification purposes.
4. The server decrypts the key using its private key and decrypts the verification message with it, then replies with the verification message decrypted and signed with its private key
5. The client confirm the server identity, cipher the agreed key and sends a
finishedmessage to the server, attaching the encrypted agreed key.
6. The server sends a
finishedmessage to the client, encrypted with the agreed key.
From now on the TLS session communicates information encrypted with the agreed key
The same process – explained in full details.
Note: Excepting the initial TLS handshake, the other HTTPS content (headers + payload) is encrypted with the key agreed during the TLS handshake.
Written by Dorin Moise (Published articles: 264)