HTTPS Handshake Optimization: Cutting Latency from 200ms to 50ms

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# Measure timing for each phase with curl
curl -w "@curl-format.txt" -o /dev/null -s https://terra-nas.com

# curl-format.txt:
#   time_namelookup:  %{time_namelookup}s\n
#   time_connect:     %{time_connect}s\n
#   time_appconnect:  %{time_appconnect}s\n
#   time_starttransfer: %{time_starttransfer}s\n
#   time_total:       %{time_total}s\n

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time_namelookup:  0.020s   # DNS
time_connect:     0.060s   # TCP (RTT ≈ 40ms)
time_appconnect:  0.260s   # TLS handshake complete!
time_starttransfer: 0.280s
time_total:       0.350s

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openssl s_client -connect terra-nas.com:443 -status 2>&1 | head -50

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Client                              Server
  |                                    |
  |------- ClientHello --------------->|  RTT 1
  |<------ ServerHello + Cert ---------|  
  |<------ ServerKeyExchange ----------|
  |<------ ServerHelloDone ------------|
  |                                    |
  |------- ClientKeyExchange --------->|  RTT 2
  |------- ChangeCipherSpec ---------->|
  |------- Finished ------------------>|
  |<------ ChangeCipherSpec -----------|
  |<------ Finished -------------------|
  |                                    |
  |======= Application Data ==========>|  Finally can send data!

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Client                              Server
  |                                    |
  |------- ClientHello + KeyShare ---->|  RTT 1
  |<------ ServerHello + KeyShare -----|
  |<------ EncryptedExtensions --------|
  |<------ Certificate ----------------|
  |<------ CertificateVerify ----------|
  |<------ Finished -------------------|
  |------- Finished ------------------>|
  |                                    |
  |======= Application Data ==========>|  Can send data after 1-RTT!

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# After first connection, server sends Session Ticket
# Subsequent connections can send encrypted data immediately

Client                              Server
  |                                    |
  |------- ClientHello + EarlyData --->|  0-RTT!
  |======= Application data already flowing ======>|
  |<------ ServerHello + ... ----------|

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server {
    listen 443 ssl http2;
    
    ssl_protocols TLSv1.2 TLSv1.3;  # Support both 1.2 and 1.3
    ssl_prefer_server_ciphers off;   # Not needed for TLS 1.3
    
    # TLS 1.3 cipher suites
    ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384;
    
    # Enable 0-RTT (use with caution)
    ssl_early_data on;
}

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Traditional flow:
Client --> Server: Get certificate
Client --> CA (OCSP): Is this cert valid?  ← Extra RTT!
CA --> Client: Yes
Client --> Server: Continue handshake

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ssl_stapling on;
ssl_stapling_verify on;
ssl_trusted_certificate /path/to/chain.pem;

# Set OCSP responder
resolver 8.8.8.8 valid=300s;
resolver_timeout 5s;

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openssl s_client -connect terra-nas.com:443 -status 2>&1 | grep -A 15 "OCSP"
# OCSP Response Status: successful

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# Check the certificate chain
openssl s_client -connect terra-nas.com:443 -showcerts 2>/dev/null | grep "s:"
# s:/CN=terra-nas.com
# s:/CN=Let's Encrypt Authority X3  # Intermediate cert
# s:/CN=DST Root CA X3              # Root cert (shouldn't be sent!)

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# Correct certificate file should contain:
# 1. Site certificate
# 2. Intermediate certificate
# (NOT the root certificate)

ssl_certificate /path/to/fullchain.pem;
ssl_certificate_key /path/to/privkey.pem;

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ssl_session_tickets on;
ssl_session_timeout 1d;  # 24 hours

# Custom ticket key (share across servers if needed)
ssl_session_ticket_key /path/to/ticket.key;

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ssl_session_cache shared:SSL:10m;  # 10MB shared cache
ssl_session_timeout 1d;

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# Generate ECDSA private key
openssl ecparam -genkey -name prime256v1 -out privkey.pem

# Generate CSR
openssl req -new -key privkey.pem -out csr.pem

# Request certificate (Let's Encrypt supports ECDSA)
certbot certonly --csr csr.pem

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listen 443 ssl http2;

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# Before optimization
curl -w "TLS: %{time_appconnect}s\n" -o /dev/null -s https://terra-nas.com
# TLS: 0.260s

# After optimization
curl -w "TLS: %{time_appconnect}s\n" -o /dev/null -s https://terra-nas.com
# TLS: 0.050s

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Timing panel:
  DNS Lookup:     20ms
  Initial connection: 50ms  ← Significantly reduced
  SSL:            30ms      ← TLS handshake
  TTFB:           80ms

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# Monitor TLS handshake time
- job_name: 'nginx'
  metrics_path: '/metrics'
  static_configs:
    - targets: ['localhost:9113']

# Alert rule
- alert: HighTLSHandshakeTime
  expr: nginx_http_ssl_handshake_time_seconds_bucket{le="0.1"} / nginx_http_ssl_handshake_time_seconds_count < 0.9
  for: 5m
  labels:
    severity: warning
  annotations:
    summary: "Over 10% of TLS handshakes taking > 100ms"

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server {
    listen 443 ssl http2;
    server_name terra-nas.com;
    
    # Certificates
    ssl_certificate /etc/letsencrypt/live/terra-nas.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/terra-nas.com/privkey.pem;
    
    # Protocol and cipher suites
    ssl_protocols TLSv1.2 TLSv1.3;
    ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305;
    
    # OCSP Stapling
    ssl_stapling on;
    ssl_stapling_verify on;
    ssl_trusted_certificate /etc/letsencrypt/live/terra-nas.com/chain.pem;
    resolver 8.8.8.8 8.8.4.4 valid=300s;
    
    # Session resumption
    ssl_session_cache shared:SSL:10m;
    ssl_session_timeout 1d;
    ssl_session_tickets on;
    
    # 0-RTT (use carefully)
    ssl_early_data on;
    
    # Security headers
    add_header Strict-Transport-Security "max-age=31536000" always;
    
    # ...
}