Encryption in Transit (TLS)

Encryption in Transit: Securing Data on the Wire

Encryption in transit protects data as it moves between systems — from browser to server, server to database, or service to service. The primary protocol for this is TLS (Transport Layer Security), which secures HTTPS, email, VPN connections, and more.

What TLS Protects Against

1. Eavesdropping — Attackers on the same network cannot read the data
2. Tampering — Modified packets are detected and rejected
3. Impersonation — Certificates verify the server's identity

The TLS 1.3 Handshake

TLS 1.3 simplified the handshake to just 1 round trip (1-RTT), compared to TLS 1.2's 2 round trips:

Client                                Server
  │                                     │
  ├── ClientHello + KeyShare ──────────▶│
  │                                     │
  │◀──── ServerHello + KeyShare ────────┤
  │◀──── EncryptedExtensions ───────────┤
  │◀──── Certificate ───────────────────┤
  │◀──── CertificateVerify ────────────┤
  │◀──── Finished ─────────────────────┤
  │                                     │
  ├── Finished ────────────────────────▶│
  │                                     │
  ├════ Encrypted Application Data ═══▶│

Key Exchange

TLS 1.3 uses ephemeral key exchange exclusively:

• X25519 — Elliptic curve Diffie-Hellman on Curve25519 (most common)
• P-256 — NIST elliptic curve (ECDHE)
• Kyber — Post-quantum key encapsulation (experimental, in Chrome/Firefox)

Ephemeral means a new key pair is generated for every connection, providing forward secrecy — even if the server's private key is later compromised, past sessions cannot be decrypted.

Cipher Suites

TLS 1.3 dramatically reduced the number of cipher suites to just five:

Cipher Suite	Key Exchange	Encryption	Hash
TLS_AES_128_GCM_SHA256	ECDHE/DHE	AES-128-GCM	SHA-256
TLS_AES_256_GCM_SHA384	ECDHE/DHE	AES-256-GCM	SHA-384
TLS_CHACHA20_POLY1305_SHA256	ECDHE/DHE	ChaCha20-Poly1305	SHA-256
TLS_AES_128_CCM_SHA256	ECDHE/DHE	AES-128-CCM	SHA-256
TLS_AES_128_CCM_8_SHA256	ECDHE/DHE	AES-128-CCM-8	SHA-256

All five use AEAD encryption — CBC-based suites were removed entirely.

TLS 1.2 vs TLS 1.3

Feature	TLS 1.2	TLS 1.3
Handshake RTT	2	1 (0-RTT resumption)
Key exchange	RSA or ECDHE	ECDHE only
Forward secrecy	Optional	Mandatory
Cipher suites	300+	5
CBC support	Yes	Removed
RSA key transport	Yes	Removed

Certificate Validation

TLS certificates (X.509) verify server identity:

1. Client receives the server's certificate chain
2. Validates the chain up to a trusted root CA
3. Checks the certificate is not expired
4. Verifies the domain name matches (Subject or SAN)
5. Checks revocation status (OCSP or CRL)

Common Configuration Mistakes

• Self-signed certificates in production — Browsers will show security warnings
• Expired certificates — Causes connection failures; use automated renewal (Let's Encrypt + Certbot)
• Allowing TLS 1.0/1.1 — Known vulnerabilities; disable in server configuration
• Weak cipher suites — Disable RC4, 3DES, and CBC-based suites where possible