Configuring tls 1 3 for secure communications

Skill henriquescastilho/my-claude/.claude/skills/configuring-tls-1-3-for-secure-communications

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SKILL.md

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Configuring TLS 1.3 for Secure Communications

Overview

TLS 1.3 (RFC 8446) is the latest version of the Transport Layer Security protocol, providing significant improvements over TLS 1.2 in both security and performance. It reduces handshake latency to 1-RTT (and 0-RTT for resumed sessions), removes obsolete cipher suites, and mandates perfect forward secrecy. This skill covers configuring TLS 1.3 on servers, validating configurations, and testing for common misconfigurations.

When to Use

When deploying or configuring configuring tls 1 3 for secure communications capabilities in your environment
When establishing security controls aligned to compliance requirements
When building or improving security architecture for this domain
When conducting security assessments that require this implementation

Prerequisites

Familiarity with cryptography concepts and tools
Access to a test or lab environment for safe execution
Python 3.8+ with required dependencies installed
Appropriate authorization for any testing activities

Objectives

Configure TLS 1.3 on nginx and Apache web servers
Implement TLS 1.3 in Python applications using the ssl module
Validate TLS configurations with openssl and testssl.sh
Understand TLS 1.3 cipher suites and key exchange mechanisms
Configure 0-RTT early data with appropriate protections
Disable legacy TLS versions (1.0, 1.1) and weak cipher suites

Key Concepts

TLS 1.3 Cipher Suites

Cipher Suite	Key Exchange	Authentication	Encryption	Hash
TLS_AES_256_GCM_SHA384	ECDHE/DHE	Certificate	AES-256-GCM	SHA-384
TLS_AES_128_GCM_SHA256	ECDHE/DHE	Certificate	AES-128-GCM	SHA-256
TLS_CHACHA20_POLY1305_SHA256	ECDHE/DHE	Certificate	ChaCha20-Poly1305	SHA-256

TLS 1.3 vs 1.2 Improvements

1-RTT Handshake: Full handshake completes in one round trip (vs 2 in TLS 1.2)
0-RTT Resumption: Resumed connections can send data immediately
No RSA Key Exchange: Only ephemeral Diffie-Hellman (mandatory PFS)
Simplified Cipher Suites: Removed CBC, RC4, 3DES, static RSA, SHA-1
Encrypted Handshake: Server certificate is encrypted after ServerHello

Key Exchange Groups

x25519: Curve25519 ECDH (preferred, fast)
secp256r1: NIST P-256 ECDH (widely supported)
secp384r1: NIST P-384 ECDH (higher security margin)
x448: Curve448 ECDH (highest security)

Workflow

Verify OpenSSL version supports TLS 1.3 (1.1.1+)
Generate or obtain TLS certificate and private key
Configure server to use TLS 1.3 cipher suites
Disable TLS 1.0 and 1.1 (optionally keep 1.2 for compatibility)
Set preferred key exchange groups
Enable OCSP stapling for certificate validation
Test configuration with openssl s_client and testssl.sh
Configure HSTS header for HTTP Strict Transport Security

Security Considerations

0-RTT data is vulnerable to replay attacks; limit to idempotent requests
Always include TLS 1.2 fallback if legacy client support is required
Use ECDSA certificates for better performance (vs RSA)
Enable OCSP stapling to improve client certificate validation
Set HSTS header with long max-age and includeSubDomains
Monitor for certificate transparency logs

Validation Criteria

TLS 1.3 handshake completes successfully
Only approved cipher suites are offered
Perfect forward secrecy is enforced
TLS 1.0 and 1.1 are rejected
OCSP stapling is functional
Certificate chain is valid and complete
testssl.sh reports no vulnerabilities

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