Senior LevelREST APIs & Web Services
How does TLS 1.3 0-RTT (Zero Round-Trip Time) session resumption accelerate mobile API connections?
❓ Interview Prompt: Explain TLS 1.3 handshake optimization, 1-RTT full handshake, 0-RTT session resumption using Pre-Shared Keys (PSK), and replay attack risks.
TLS 1.3 reduces initial connection establishment latency from 2 round-trips down to 1 round-trip. For returning mobile clients, 0-RTT (Zero Round-Trip Time) allows sending data immediately:
0-RTT Mechanics:
Using a Pre-Shared Key (PSK) derived from a previous session ticket, the client encrypts and includes the HTTP API request payload inside the very first TLS 'ClientHello' packet!
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Security Warning: 0-RTT HTTP payloads are vulnerable to Replay Attacks! API Gateways MUST allow 0-RTT ONLY for idempotent 'GET' requests, rejecting 0-RTT on 'POST'/'PUT'.
Code Implementation Example
http
// TLS 1.3 0-RTT Early Data Header sent on resumption:
GET /api/v1/user/profile HTTP/1.1
Host: api.example.com
Early-Data: 1💡TLS 1.3 0-RTT Early Data HTTP request header.
🎯 Interview Key Takeaway
TLS 1.3 0-RTT sends encrypted HTTP request payloads inside the initial TLS handshake, but must be restricted to idempotent GET requests to prevent replay attacks.
#TLS 1.3#0-RTT#Latency#Performance#Senior
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