TLS / рукопожатие: ментальная модель

Question

Accepted Answer

TLS оборачивает TCP в authenticated encrypted channel: cipher + cert chain + shared symmetric key без передачи ключа по wire. TLS 1.3 — 1 RTT, forward secrecy через ephemeral keys.

## Разбор

Every HTTPS — два nested channels. TCP = reliable pipe; **TLS wraps** — no read/tamper, proof you're on `bank.com`. Handshake настраивает это *before* HTTP.

**Key exchange clever part:** client и server share symmetric key, **never transmitted**. Asymmetric (slow) только для bootstrap; symmetric (fast) для bulk. Asymmetric for handshake, symmetric for data — whole design.

```
TCP handshake        TLS handshake                 Encrypted HTTP
──────────────       ──────────────────────        ──────────────
SYN →                ClientHello →                  GET / ... (all
    ← SYN-ACK            ← ServerHello + cert        encrypted with
ACK →                DONE (key derived)  →           the shared key)
(1 RTT)              (TLS 1.3: 1 RTT)
```

Certificate = identity proof server owns DH key, not encryption of session key.

## Итог

TLS = fast symmetric bulk after slow asymmetric bootstrap; ephemeral DH = past traffic safe if key leaks later.