performing-ssl-tls-inspection-configuration

执行 SSL/TLS 检查配置

概述

SSL/TLS 检查（也称为 SSL 解密、HTTPS 检查或 TLS 中断检查）会拦截客户端与服务器之间的加密流量，以检查明文内容中的恶意软件、数据外泄、策略违规以及命令与控制通信。检查设备充当受信任的中间人，终止来自客户端的 TLS 会话，检查明文内容，并与目标服务器建立新的 TLS 会话。如今超过 95% 的 Web 流量已加密，未部署 TLS 检查的组织将面临巨大的盲区。本技能涵盖在下一代防火墙上的 TLS 检查配置、受信任 CA 证书的部署、证书固定应用的豁免管理，以及确保符合隐私法规。

何时使用

• 在进行涉及执行 ssl tls 检查配置的安全评估时
• 在遵循相关安全事件的事件响应流程时
• 在执行定期安全测试或审计活动时
• 在通过动手测试验证安全控制时

前提条件

• 具备 TLS 检查能力的下一代防火墙或安全 Web 网关
• 用于签发检查证书的内部证书颁发机构（CA）
• 端点证书管理（GPO、MDM 或手动部署）
• 针对 TLS 检查范围的隐私与法律审查
• 了解 PKI、X.509 证书和 TLS 握手

核心概念

SSL/TLS 检查模式

模式	方向	描述
SSL 正向代理	出站	拦截客户端到互联网的 HTTPS 连接
SSL 入站检查	入站	解密发往内部服务器的流量
SSH 代理	双向	检查 SSH 隧道流量

正向代理流程

Client                  Firewall/Proxy              Web Server
  │                         │                          │
  │──TLS ClientHello──────→│                          │
  │                         │──TLS ClientHello───────→│
  │                         │←─TLS ServerHello────────│
  │                         │  (real server cert)      │
  │                         │                          │
  │                         │  [Validates server cert]  │
  │                         │  [Generates proxy cert   │
  │                         │   signed by internal CA]  │
  │                         │                          │
  │←─TLS ServerHello───────│                          │
  │  (proxy-signed cert)    │                          │
  │                         │                          │
  │──Encrypted data────────→│  [Decrypt, Inspect]      │
  │                         │──Encrypted data────────→│
  │←─Encrypted data─────────│  [Decrypt, Inspect]      │
  │                         │←─Encrypted data─────────│

证书信任链

Enterprise Root CA
  └── Subordinate CA (SSL Inspection)
        └── Dynamically Generated Server Certificates
             (CN matches requested server)

工作流

步骤 1：为 SSL 检查生成内部 CA

# Create private key for SSL Inspection CA
openssl genrsa -aes256 -out ssl-inspect-ca.key 4096

# Create CA certificate (5 year validity)
openssl req -new -x509 -key ssl-inspect-ca.key \
  -sha256 -days 1825 \
  -out ssl-inspect-ca.crt \
  -subj "/C=US/ST=California/O=Corp Inc/OU=Network Security/CN=Corp SSL Inspection CA" \
  -extensions v3_ca \
  -config <(cat <<EOF
[req]
distinguished_name = req_dn
x509_extensions = v3_ca

[req_dn]

[v3_ca]
basicConstraints = critical,CA:TRUE,pathlen:0
keyUsage = critical,digitalSignature,keyCertSign,cRLSign
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always
EOF
)

# Verify certificate
openssl x509 -in ssl-inspect-ca.crt -text -noout

步骤 2：将 CA 证书部署到端点

Windows（组策略）：

# Import CA cert to trusted root store via GPO
# Computer Configuration > Policies > Windows Settings >
# Security Settings > Public Key Policies > Trusted Root CAs

# Or deploy via PowerShell
Import-Certificate -FilePath "\\server\share\ssl-inspect-ca.crt" `
  -CertStoreLocation "Cert:\LocalMachine\Root"

# Verify deployment
Get-ChildItem Cert:\LocalMachine\Root | Where-Object {
    $_.Subject -like "*SSL Inspection CA*"
}

macOS（MDM 描述文件或手动）：

# Install via command line
sudo security add-trusted-cert -d -r trustRoot \
  -k /Library/Keychains/System.keychain ssl-inspect-ca.crt

Linux：

# Ubuntu/Debian
sudo cp ssl-inspect-ca.crt /usr/local/share/ca-certificates/
sudo update-ca-certificates

# RHEL/CentOS
sudo cp ssl-inspect-ca.crt /etc/pki/ca-trust/source/anchors/
sudo update-ca-trust

步骤 3：配置 Palo Alto SSL 正向代理

# Import CA certificate to firewall
# Device > Certificate Management > Certificates > Import

# Set as Forward Trust CA
set shared certificate SSL-Inspect-CA forward-trust-certificate yes

# Create Decryption Profile
set profiles decryption Corporate-Decrypt ssl-forward-proxy block-expired-certificate yes
set profiles decryption Corporate-Decrypt ssl-forward-proxy block-untrusted-issuer yes
set profiles decryption Corporate-Decrypt ssl-forward-proxy block-unknown-cert yes
set profiles decryption Corporate-Decrypt ssl-forward-proxy restrict-cert-exts yes
set profiles decryption Corporate-Decrypt ssl-forward-proxy strip-alpn no

# Minimum TLS version
set profiles decryption Corporate-Decrypt ssl-protocol-settings min-version tls1-2
set profiles decryption Corporate-Decrypt ssl-protocol-settings max-version max

# Decryption policy - decrypt outbound HTTPS
set rulebase decryption rules Decrypt-Outbound from Trust to Untrust
set rulebase decryption rules Decrypt-Outbound source any
set rulebase decryption rules Decrypt-Outbound destination any
set rulebase decryption rules Decrypt-Outbound service any
set rulebase decryption rules Decrypt-Outbound action decrypt
set rulebase decryption rules Decrypt-Outbound type ssl-forward-proxy
set rulebase decryption rules Decrypt-Outbound profile Corporate-Decrypt

步骤 4：配置豁免

某些应用和类别必须排除在 TLS 检查之外：

# Exempt certificate-pinned applications
set rulebase decryption rules No-Decrypt-Pinned from Trust to Untrust
set rulebase decryption rules No-Decrypt-Pinned application [ apple-update microsoft-update dropbox-base ]
set rulebase decryption rules No-Decrypt-Pinned action no-decrypt

# Exempt privacy-sensitive categories
set rulebase decryption rules No-Decrypt-Privacy from Trust to Untrust
set rulebase decryption rules No-Decrypt-Privacy category [ health-and-medicine financial-services ]
set rulebase decryption rules No-Decrypt-Privacy action no-decrypt

# Exempt specific high-trust domains
set rulebase decryption rules No-Decrypt-Trusted from Trust to Untrust
set rulebase decryption rules No-Decrypt-Trusted destination [ bank-of-america.com chase.com healthcare.gov ]
set rulebase decryption rules No-Decrypt-Trusted action no-decrypt

步骤 5：为内部服务器配置入站检查

# Import server certificate and private key
# Device > Certificate Management > Certificates > Import

# Inbound inspection policy
set rulebase decryption rules Inspect-WebServers from Untrust to DMZ
set rulebase decryption rules Inspect-WebServers destination [ 10.0.20.10 10.0.20.11 ]
set rulebase decryption rules Inspect-WebServers service service-https
set rulebase decryption rules Inspect-WebServers action decrypt
set rulebase decryption rules Inspect-WebServers type ssl-inbound-inspection
set rulebase decryption rules Inspect-WebServers profile Corporate-Decrypt

步骤 6：验证 SSL 检查

# Test from client - verify certificate issuer is internal CA
openssl s_client -connect www.google.com:443 -servername www.google.com 2>/dev/null | \
  openssl x509 -noout -issuer -subject

# Expected output (with inspection active):
# issuer= /C=US/O=Corp Inc/OU=Network Security/CN=Corp SSL Inspection CA
# subject= /CN=www.google.com

# Verify no certificate errors in browser
# Check firewall decryption logs for errors

# Test with curl
curl -v https://www.example.com 2>&1 | grep "issuer"

# Check decryption statistics on firewall
show system setting ssl-decrypt memory
show system setting ssl-decrypt certificate-cache
show counter global filter category ssl

性能考量

因素	影响	缓解措施
CPU 开销	每个会话增加 50-80%	硬件 SSL 加速、专用解密设备
吞吐量下降	通常 40-60%	按峰值加密流量为解密硬件选型
延迟增加	增加 1-5ms	将检查设备部署在靠近用户的位置
TLS 1.3 0-RTT	无法检查 0-RTT 数据	阻止 0-RTT 或接受风险
证书固定	检查失败	添加到豁免列表
QUIC/HTTP3	绕过传统代理	阻止 QUIC，强制使用 HTTP/2

合规与隐私

• 员工告知 - 告知用户网络流量会受到检查
• 隐私豁免 - 排除医疗、金融和受法律特权保护的流量
• 数据处理 - 检查后的明文不得被不必要地记录或存储
• GDPR 合规 - 记录处理加密个人数据的合法依据
• 证书固定 - 为使用 HPKP 或内置固定的应用维护豁免列表

最佳实践

• 从日志记录开始 - 先以仅检测模式部署，以识别使用证书固定的应用程序
• 维护豁免列表 - 保留一份需要绕过解密的应用程序精选列表
• 阻止 QUIC - 阻止 UDP/443，以强制 HTTP/2 通过 TLS 检查
• 监控证书错误 - 在防火墙日志中跟踪解密错误
• 最低 TLS 1.2 - 强制最低版本为 TLS 1.2；阻止 SSLv3 和 TLS 1.0/1.1
• 密钥保护 - 在生产环境中将检查 CA 私钥存储在 HSM 中
• 定期轮换 CA - 在到期前规划 CA 证书轮换

参考资料

• Palo Alto SSL Decryption
• Cisco SSL/TLS Proxy
• NIST SP 800-52 Rev 2 - TLS Configuration
• US-CERT Alert on HTTPS Inspection