TLS Handshake

TLS Handshake

TLS (Transport Layer Security) provides encryption, authentication, and integrity for network communication. HTTPS = HTTP + TLS. The TLS handshake establishes a secure connection before any application data is exchanged.

TLS 1.2 Handshake Steps

Client                              Server
  │                                   │
  │── ClientHello ──────────────────>│  (supported ciphers, random)
  │                                   │
  │<──────────────── ServerHello ────│  (chosen cipher, random)
  │<──────────────── Certificate ────│  (server's public key)
  │<──────────── ServerHelloDone ────│
  │                                   │
  │── ClientKeyExchange ────────────>│  (pre-master secret)
  │── ChangeCipherSpec ─────────────>│
  │── Finished ─────────────────────>│
  │                                   │
  │<─────────── ChangeCipherSpec ────│
  │<──────────────────── Finished ───│
  │                                   │
  │       SECURE CONNECTION          │

Key Concepts

• Cipher Suite: Combination of key exchange, encryption, and MAC algorithms (e.g., TLS_RSA_WITH_AES_256_CBC_SHA256)
• Pre-Master Secret: Random value encrypted with server's public key
• Master Secret: Derived from pre-master secret + client random + server random
• Session Keys: Derived from master secret, used for symmetric encryption

Your Task

Implement simulateTLSHandshake(clientCiphers, serverCiphers, serverCert) that simulates a TLS handshake:

1. Client sends supported ciphers and a random value
2. Server picks the first matching cipher and sends its random + certificate
3. Client generates a pre-master secret, derives a master secret (simplified: XOR of all three values)
4. Both sides derive session keys

Return an array of handshake message objects with step, from, to, and data.

Also implement deriveSessionKey(preMaster, clientRandom, serverRandom) that returns a simplified "key" (sum mod 256).