SSL/TLS 证书

概述

证书申请、配置、自动续期技能。

OpenSSL 基础

生成私钥

# RSA 私钥
openssl genrsa -out private.key 2048
openssl genrsa -out private.key 4096

# 带密码保护
openssl genrsa -aes256 -out private.key 2048

# ECDSA 私钥
openssl ecparam -genkey -name prime256v1 -out private.key

生成 CSR

# 交互式
openssl req -new -key private.key -out request.csr

# 非交互式
openssl req -new -key private.key -out request.csr \
    -subj "/C=CN/ST=Beijing/L=Beijing/O=Company/CN=example.com"

# 带 SAN
openssl req -new -key private.key -out request.csr \
    -config <(cat <<EOF
[req]
distinguished_name = req_distinguished_name
req_extensions = v3_req

[req_distinguished_name]
CN = example.com

[v3_req]
subjectAltName = @alt_names

[alt_names]
DNS.1 = example.com
DNS.2 = www.example.com
DNS.3 = api.example.com
EOF
)

自签名证书

# 一步生成
openssl req -x509 -nodes -days 365 -newkey rsa:2048 \
    -keyout private.key -out certificate.crt \
    -subj "/CN=example.com"

# 从已有私钥
openssl req -x509 -key private.key -days 365 -out certificate.crt

查看证书

# 查看证书信息
openssl x509 -in certificate.crt -text -noout

# 查看 CSR
openssl req -in request.csr -text -noout

# 查看私钥
openssl rsa -in private.key -text -noout

# 验证证书链
openssl verify -CAfile ca.crt certificate.crt

# 检查远程证书
openssl s_client -connect example.com:443 -servername example.com

格式转换

# PEM 转 DER
openssl x509 -in cert.pem -outform DER -out cert.der

# DER 转 PEM
openssl x509 -in cert.der -inform DER -out cert.pem

# PEM 转 PKCS12
openssl pkcs12 -export -out cert.p12 -inkey private.key -in cert.pem

# PKCS12 转 PEM
openssl pkcs12 -in cert.p12 -out cert.pem -nodes

Let's Encrypt

Certbot 安装

# Debian/Ubuntu
apt install certbot python3-certbot-nginx

# CentOS/RHEL
yum install certbot python3-certbot-nginx

申请证书

# Nginx 插件
certbot --nginx -d example.com -d www.example.com

# Apache 插件
certbot --apache -d example.com

# Standalone
certbot certonly --standalone -d example.com

# Webroot
certbot certonly --webroot -w /var/www/html -d example.com

# DNS 验证（通配符）
certbot certonly --manual --preferred-challenges dns -d "*.example.com"

管理证书

# 查看证书
certbot certificates

# 续期测试
certbot renew --dry-run

# 手动续期
certbot renew

# 删除证书
certbot delete --cert-name example.com

自动续期

# Cron
0 0 * * * certbot renew --quiet

# Systemd timer
systemctl enable certbot.timer
systemctl start certbot.timer

Nginx 配置

基础 HTTPS

server {
    listen 443 ssl http2;
    server_name example.com;
    
    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;
    
    ssl_protocols TLSv1.2 TLSv1.3;
    ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256;
    ssl_prefer_server_ciphers off;
}

HTTP 重定向

server {
    listen 80;
    server_name example.com;
    return 301 https://$server_name$request_uri;
}

安全加固

ssl_session_timeout 1d;
ssl_session_cache shared:SSL:50m;
ssl_session_tickets off;

ssl_stapling on;
ssl_stapling_verify on;
resolver 8.8.8.8 8.8.4.4 valid=300s;

add_header Strict-Transport-Security "max-age=63072000" always;

常见场景

场景 1：创建 CA

# 生成 CA 私钥
openssl genrsa -out ca.key 4096

# 生成 CA 证书
openssl req -x509 -new -nodes -key ca.key -sha256 -days 3650 \
    -out ca.crt -subj "/CN=My CA"

# 签发证书
openssl x509 -req -in server.csr -CA ca.crt -CAkey ca.key \
    -CAcreateserial -out server.crt -days 365 -sha256

场景 2：检查证书过期

#!/bin/bash
DOMAIN=$1
DAYS=30

EXPIRY=$(echo | openssl s_client -connect ${DOMAIN}:443 -servername ${DOMAIN} 2>/dev/null | \
    openssl x509 -noout -enddate | cut -d= -f2)

EXPIRY_EPOCH=$(date -d "$EXPIRY" +%s)
NOW_EPOCH=$(date +%s)
DIFF=$(( (EXPIRY_EPOCH - NOW_EPOCH) / 86400 ))

if [ $DIFF -lt $DAYS ]; then
    echo "WARNING: ${DOMAIN} 证书将在 ${DIFF} 天后过期"
fi

场景 3：批量续期

#!/bin/bash
certbot renew --deploy-hook "systemctl reload nginx"

故障排查

问题	排查方法
证书不信任	检查证书链、CA
域名不匹配	检查 CN、SAN
证书过期	检查有效期、续期
握手失败	检查协议、密码套件

# 测试 SSL
openssl s_client -connect example.com:443

# 检查证书链
openssl s_client -connect example.com:443 -showcerts

# SSL Labs 测试
curl https://api.ssllabs.com/api/v3/analyze?host=example.com