Transport Layer Security: comparing TLS 1.2 vs 1.3 handshakes, and step-by-step connection walkthroughs.

1. Comparison: TLS 1.2 vs. TLS 1.3

Feature	TLS 1.2 Handshake	TLS 1.3 Handshake
Round Trips (RTT)	2-RTT (requires 2 round trips before sending encrypted data).	1-RTT (requires only 1 round trip, reducing latency).
Key Exchange	Supports RSA, Static DH, and Ephemeral DH.	Mandates Ephemeral DH (ECDHE/DHE) to guarantee Forward Secrecy.
0-RTT Mode	Not supported.	Supported (allows returning clients to send encrypted data on the first request).
Cipher Suites	Supports old, weak ciphers (RC4, 3DES, CBC mode).	Only supports highly secure AEAD ciphers (AES-GCM, ChaCha20-Poly1305).

2. TLS 1.3 Handshake Sequence

Client                                                              Server
  |                                                                   |
  |---- ClientHello (Supported ciphers, DH key share A=g^a mod p) --->|
  |                                                                   |
  |                                 [Server selects cipher suite]     |
  |                                 [Calculates Shared Secret]        |
  |<--- ServerHello (Selected cipher, DH key share B=g^b mod p) ------|
  |<--- Server Certificate & Signature (Signed with CA Private Key) --|
  |<--- Finished (Encrypted validation tag) --------------------------|
  |                                                                   |
  | [Client verifies Server Certificate]                              |
  | [Calculates Shared Secret]                                        |
  |---- Finished (Encrypted validation tag) ------------------------->|
  |                                                                   |
  |<================== Encrypted Application Data ===================>|