Packet flow

1. TCP SYN-ACK Handshake:

• Client: Sends a TCP SYN packet to the server, indicating it wants to initiate a connection.
• Server: Responds with a TCP SYN-ACK packet, acknowledging the client’s SYN and sending its own SYN for data transfer.
• Client: Acknowledges the server’s SYN-ACK with a TCP ACK packet. (3-way handshake complete)

2. TLS Handshake:

• Client: Sends a Client Hello message, specifying supported TLS versions, ciphers, and session resumption data (if applicable).
• Server: Responds with a Server Hello message, choosing a cipher suite and potentially requesting client certificate authentication.
• (Optional) Client Certificate Exchange: If requested, the client sends its certificate and potentially a certificate chain.
• Server Key Exchange: The server sends its public key certificate.
• Server Hello Done: The server signals the end of its messages.
• Client Certificate Verify (Optional): The client may send a message verifying the server’s certificate.
• Premaster Secret: The client generates a random secret and encrypts it with the server’s public key, sending it in the encrypted Premaster Secret message.
• Change Cipher Spec (Client & Server): Both parties indicate they’re switching to the negotiated cipher suite.
• Finished (Client & Server): Both parties send a Finished message containing a hash of the handshake messages to verify data integrity. (Handshake complete, secure connection established)

3. Application Data Flow:

• Client: Sends an HTTP request message containing headers (method, URL, etc.) and potentially an encrypted payload.
• Server: Responds with an HTTP response message containing headers (status code, etc.) and potentially an encrypted payload.
• This data exchange can occur multiple times during the API call.

4. FIN-ACK Termination:

• Client: Sends a TCP FIN packet, indicating it wants to close the connection.
• Server: Acknowledges the FIN with a TCP ACK packet.
• Server: Sends its own TCP FIN packet to close its end.
• Client: Acknowledges the server’s FIN with a TCP ACK packet. (Connection closed)