StrongSwan (简体中文)

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翻译状态: 本文是英文页面 StrongSwan翻译,最后翻译时间:2016-06-07,点击这里可以查看翻译后英文页面的改动。

IPSec 是一个加密和认证标准,可以组建安全虚拟专用网路(VPN).

Linux kernel 已经支持这个标准,但是用户需要配置加密密钥。IPSec VPN 使用 IKE 协议自动协商密钥的交换,交换方式包括认证、提前共享或同时使用。

通常用服务器上的一个后台进程实现,strongSwan 是一个完全支持 IKEv1 和 IKEv2 的 IKE 后台进程。大部分现代的客户端都支持,包括 Linux, Windows 7, Apple iOS, Mac OSX, FreeBSD and BlackBerry OS.

安装

安装软件包 strongswanAUR

证书

第一步是生成 X.509 认证,包括一个认证机构(CA)证书,一个服务器证书和至少一个客户端证书。

认证机构

首先创建一个自己签名的根 CA 证书:

生成 4096 位 RSA 私钥 strongswanKey.pem:

$ cd /etc/ipsec.d/
$ ipsec pki --gen --type rsa --size 4096 --outform pem > private/strongswanKey.pem
$ chmod 600 private/strongswanKey.pem

生成自签名的 CA 证书 strongswanCert.pem,期限是 10 年(3650天),用 PEM 编码格式保存:

$ ipsec pki --self --ca --lifetime 3650 --in private/strongswanKey.pem --type rsa --dn "C=CH, O=strongSwan, CN=strongSwan Root CA" \
	   --outform pem > cacerts/strongswanCert.pem

可以根据需要修改 Distinguished Name (DN),country (C), organization (O), and common name (CN)。

通过下面命令查看新生成的证书:

$ ipsec pki --print --in cacerts/strongswanCert.pem

输出:

cert:      X509
subject:  "C=CH, O=strongSwan, CN=strongSwan Root CA"
issuer:   "C=CH, O=strongSwan, CN=strongSwan Root CA"
validity:  not before Nov 22 11:55:41 2013, ok
           not after  Nov 20 11:55:41 2023, ok (expires in 3649 days)
serial:    65:39:93:df:a0:f8:40:03
flags:     CA CRLSign self-signed
authkeyId: 45:30:11:da:a4:0e:0b:0a:a3:41:a5:81:41:ab:d8:04:7a:40:6c:c0
subjkeyId: 45:30:11:da:a4:0e:0b:0a:a3:41:a5:81:41:ab:d8:04:7a:40:6c:c0
pubkey:    RSA 4096 bits
keyid:     dc:15:91:95:04:07:a5:13:69:5f:77:65:26:d7:02:3f:60:ec:73:c8
subjkey:   45:30:11:da:a4:0e:0b:0a:a3:41:a5:81:41:ab:d8:04:7a:40:6c:c0
警告: CA 的私钥 /etc/ipsec.d/private/strongswanKey.pem 必须保存在安全位置,最好放在一个没有网络访问的签名专用服务器。如果此密钥泄露,整个公钥系统就土崩瓦解了。

主机证书

此证书被用来认证 VPN 服务器,运行下面命令:

生成 2048 位 RSA 私钥:

$ cd /etc/ipsec.d/
$ ipsec pki --gen --type rsa --size 2048 --outform pem > private/vpnHostKey.pem
$ chmod 600 private/vpnHostKey.pem

导出公钥并生成被 CA 签名的 vpnHostCert.pem,证书有效期是两年(730天),使用完整域名 vpn.example.com 作为身份

$ ipsec pki --pub --in private/vpnHostKey.pem --type rsa | \
	 ipsec pki --issue --lifetime 730 \
	  --cacert cacerts/strongswanCert.pem \
	  --cakey private/strongswanKey.pem \
	  --dn "C=CH, O=strongSwan, CN=vpn.example.com" \
	  --san vpn.example.com \
	  --flag serverAuth --flag ikeIntermediate \
	  --outform pem > certs/vpnHostCert.pem

后面的客户端连接配置中,会使用 VPN 服务器的域名或 IP 地址,必须将其加入 Distinguished Name 或 Alternative Name (line11), 最好都包含。请注意把 vpn.example.com 修改为 VPN 的主机名 - 否则客户端和服务器的连接会失败。

注意: 如果要使用 Win7 内置的 VPN 客户端,必须按上面例子在主机证书中添加 serverAuth 标记。OS X 10.7.3 和更早的版本需要 ikeIntermediate 标记。这些标记不影响其它功能,可以放心使用。

查看新生成的证书:

$ ipsec pki --print --in certs/vpnHostCert.pem

Output:

cert:      X509
subject:  "C=CH, O=strongSwan, CN=vpn.example.com"
issuer:   "C=CH, O=strongSwan, CN=strongSwan Root CA"
validity:  not before Nov 22 21:16:51 2013, ok
           not after  Nov 22 21:16:51 2015, ok (expires in 729 days)
serial:    0c:05:d7:d5:57:0e:d9:48
altNames:  vpn.zeitgeist.se
flags:     serverAuth iKEIntermediate 
authkeyId: 9b:57:35:fb:cd:9e:2d:20:37:1d:61:4c:e7:c4:5b:5e:dc:64:ad:fc
subjkeyId: 5f:12:c2:06:ee:2b:1e:cc:5f:78:54:ff:f0:f3:7b:a0:2b:c0:b4:d6
pubkey:    RSA 2048 bits
keyid:     6f:a7:99:60:27:27:09:96:02:c1:b9:d9:7d:c1:b0:10:e3:e1:d5:45
subjkey:   5f:12:c2:06:ee:2b:1e:cc:5f:78:54:ff:f0:f3:7b:a0:2b:c0:b4:d6

客户端证书

客户端需要个人证书再能使用 VPN. 和生成主机证书类似,只是这里用客户端的电子邮件而不是主机名:

生成 2048 位 RSA 私钥:

$ cd /etc/ipsec.d/
$ ipsec pki --gen --type rsa --size 2048 --outform pem > private/ClientKey.pem
$ chmod 600 private/ClientKey.pem

导出公钥并用 CA 签名,证书时间是两年。

$ ipsec pki --pub --in private/ClientKey.pem --type rsa | \
	 ipsec pki --issue --lifetime 730 \
	  --cacert cacerts/strongswanCert.pem \
	  --cakey private/strongswanKey.pem \
	  --dn "C=CH, O=strongSwan, CN=myself@example.com" \
	  --san myself@example.com \
	  --outform pem > certs/ClientCert.pem

将所有证书和密钥用密码打包成 PKCS#12 文件,以方便客户端使用。

$ openssl pkcs12 -export -inkey private/ClientKey.pem \
	  -in certs/ClientCert.pem -name "My own VPN client certificate" \
	  -certfile cacerts/strongswanCert.pem \
	  -caname "strongSwan Root CA" \
	  -out Client.p12

不同的 VPN 模式

最简单的配置方式是用隧道模式运行 IPSec。

IPSec 隧道模式

可以在 /etc/ipsec.conf 找到 VPN 配置,下面配置包含了基本 VPN 服务器需要的选项:

/etc/ipsec.conf
# ipsec.conf - strongSwan IPsec configuration file
config setup

  # By default only one client can connect at the same time with an identical
  # certificate and/or password combination. Enable this option to disable
  # this behavior.
  # uniqueids=never

  # Slightly more verbose logging. Very useful for debugging.
  charondebug="cfg 2, dmn 2, ike 2, net 2"

# Default configuration options, used below if an option is not specified.
# See: https://wiki.strongswan.org/projects/strongswan/wiki/ConnSection
conn %default

  # Use IKEv2 by default
  keyexchange=ikev2

  # Prefer modern cipher suites that allow PFS (Perfect Forward Secrecy)
  ike=aes128-sha256-ecp256,aes256-sha384-ecp384,aes128-sha256-modp2048,aes128-sha1-modp2048,aes256-sha384-modp4096,aes256-sha256-modp4096,aes256-sha1-modp4096,aes128-sha256-modp1536,aes128-sha1-modp1536,aes256-sha384-modp2048,aes256-sha256-modp2048,aes256-sha1-modp2048,aes128-sha256-modp1024,aes128-sha1-modp1024,aes256-sha384-modp1536,aes256-sha256-modp1536,aes256-sha1-modp1536,aes256-sha384-modp1024,aes256-sha256-modp1024,aes256-sha1-modp1024!
  esp=aes128gcm16-ecp256,aes256gcm16-ecp384,aes128-sha256-ecp256,aes256-sha384-ecp384,aes128-sha256-modp2048,aes128-sha1-modp2048,aes256-sha384-modp4096,aes256-sha256-modp4096,aes256-sha1-modp4096,aes128-sha256-modp1536,aes128-sha1-modp1536,aes256-sha384-modp2048,aes256-sha256-modp2048,aes256-sha1-modp2048,aes128-sha256-modp1024,aes128-sha1-modp1024,aes256-sha384-modp1536,aes256-sha256-modp1536,aes256-sha1-modp1536,aes256-sha384-modp1024,aes256-sha256-modp1024,aes256-sha1-modp1024,aes128gcm16,aes256gcm16,aes128-sha256,aes128-sha1,aes256-sha384,aes256-sha256,aes256-sha1!

  # Dead Peer Discovery
  dpdaction=clear
  dpddelay=300s

  # Do not renegotiate a connection if it is about to expire
  rekey=no

  # Server side
  left=%any
  leftsubnet=0.0.0.0/0
  leftcert=vpnHostCert.pem

  # Client side
  right=%any
  rightdns=8.8.8.8,8.8.4.4
  rightsourceip=%dhcp

# IKEv2: Newer version of the IKE protocol
conn IPSec-IKEv2
  keyexchange=ikev2
  auto=add

# IKEv2-EAP
conn IPSec-IKEv2-EAP
  also="IPSec-IKEv2"
  rightauth=eap-mschapv2
  rightsendcert=never
  eap_identity=%any

# IKEv1 (Cisco-compatible version)
conn CiscoIPSec
  keyexchange=ikev1
  # forceencaps=yes
  rightauth=pubkey
  rightauth2=xauth
  auto=add

IPSec in transport mode

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Need to better explain the differences, advantages and inconvenients, then write a tutorial. (Discuss in Talk:StrongSwan (简体中文)#)

IPSec/L2TP

L2TP/IPsec VPN client setup 页面包含了如何建立一个连接到 IPSec/L2TP 服务器的客户端。这种 IPSec VPN 和纯 IPSec 相比,可以将隧道用于非 IP 包,缺点是需要运行一个额外的 L2TP 后台进程。

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Need to better explain the differences, advantages and inconvenients, then write a tutorial. (Discuss in Talk:StrongSwan (简体中文)#)

Secrets

strongSwan 需要知道哪些客户端是允许连接到 VPN 的,通过 /etc/ipsec.secrets 文件进行配置:

/etc/ipsec.secrets
# This file holds shared secrets or RSA private keys for authentication.

# RSA private key for this host, authenticating it to any other host
# which knows the public part.  Suitable public keys, for ipsec.conf, DNS,
# or configuration of other implementations, can be extracted conveniently
# with "ipsec showhostkey".

: RSA ClientKey.pem
user1 : EAP "topsecretpassword"
user2 : XAUTH "evenmoretopsecretpassword"

当 strongSwan 运行时,如果编辑了 /etc/ipsec.secrets,需要重新加载:

$ ipsec rereadsecrets

Networking

需要执行下面设备让 VPN 服务器正常的进行 VPN 隧道传输:

/etc/sysctl.d/10-net-forward.conf
# VPN
net.ipv4.ip_forward = 1
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.send_redirects = 0

上面的 VPN 配置用 DHCP 自动给客户端分配 IP 地址,所以需要一个 DHCP 服务,如果这个服务是运行在 strongSwan 相同的服务器上,需要编辑 /etc/strongswan.d/charon/dhcp.conf:

/etc/strongswan.d/charon/dhcp.conf
dhcp {
 force_server_address = yes
 server = 192.168.0.255
}

在防火墙中开放如下协议:

  • ESP (Encrypted Secure Payload): Standard IPSec traffic
  • UDP 4500: IPSec traffic in "NAT Traversal" mode
  • UDP 500: Key exchanges (IKE)

最后,startenable strongswan 服务。

在容器中运行 Strongswan

要在容器中运行 strongswan,比如在 systemd-nspawn 中,需要类似下面的服务文件:

/etc/systemd/system/systemd-nspawn@.service.d/override.conf}
[Service]
ExecStart=
ExecStart=/usr/bin/systemd-nspawn --quiet --keep-unit --boot --link-journal=try-guest --settings=override --machine=%I --capability=CAP_NET_ADMIN --network-veth 

Troubleshooting

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Need to explain at least ip xfrm and common issues (Discuss in Talk:StrongSwan (简体中文)#)

参阅