相对来说，个人网站建立SSL是昂贵的，而且往往过程繁琐。一个标准的2048位证书费用至少150美元/年，网站除了要支付一笔昂贵的费用、重新配置Web服务器，并需要解决大量的配置错误。这让广大中小网站望而生畏。

然而，Let‘s Encrypt免费证书的开放，极大推进了国内 HTTPS 的进程。Let‘s Encrypt 真正的意义在于，它推动了 HTTPS 在小型网站和个人网站中的应用，加速全面 HTTPS 时代的到来。Let‘s Encrypt 的最大贡献是它的 ACME 协议，第一份全自动服务器身份验证协议，以及配套的基础设施和客户端。这是为了解决一直以来 HTTPS TLS X.509 PKI 信任模型，即证书权威（Certificate Authority, CA）模型缺陷的一个起步。

Let‘sEncrypt的工作原理

看图：

ACME 解决了私钥持有者验证自己身份这一过程的自动化问题。

在CentOS6，CentOS7上安装Let‘s Encrypt

非营利组织电子前沿基金会的CertBot是一个很好的工具,我们使用它来安装Let‘s Encrypt

一、升级系统

1. # yum -y update

二、安装EPEL库，为CertBot提供最新的Python包。

1. # yum -y install epel-release

三、下载CertBot

1、CentOS7:

1. # yum -y install python-certbot-apache

2、CentOS6:

1. # wget https://dl.eff.org/certbot-auto
2. # chmod 755 certbot-auto

四、Apache下配置Let‘s Encrypt

执行下条命令

1. # ./certbot-auto --apache

根据提示操作

1. /root/.local/share/letsencrypt/lib/python2.6/site-packages/cryptography/__init__.py:26: DeprecationWarning: Python 2.6 is no longer supported by the Python core team, please upgrade your Python. A future version of cryptography will drop support for Python 2.6
2. DeprecationWarning
3. Saving debug log to /var/log/letsencrypt/letsencrypt.log
4. Enter email address (used for urgent renewal and security notices) (Enter ‘c‘ to
5. cancel):输入管理员邮箱
6.  
7. -------------------------------------------------------------------------------
8. Please read the Terms of Service at
9. https://letsencrypt.org/documents/LE-SA-v1.1.1-August-1-2016.pdf. You must agree
10. in order to register with the ACME server at
11. https://acme-v01.api.letsencrypt.org/directory
12. -------------------------------------------------------------------------------
13. (A)gree/(C)ancel: A
14.  
15. -------------------------------------------------------------------------------
16. Would you be willing to share your email address with the Electronic Frontier
17. Foundation, a founding partner of the Let‘s Encrypt project and the non-profit
18. organization that develops Certbot? We‘d like to send you email about EFF and
19. our work to encrypt the web, protect its users and defend digital rights.
20. -------------------------------------------------------------------------------
21. (Y)es/(N)o: Y
22.  
23. Which names would you like to activate HTTPS for?
24. -------------------------------------------------------------------------------
25. 1: www.xi-chuang.com
26. -------------------------------------------------------------------------------
27. Select the appropriate numbers separated by commas and/or spaces, or leave input
28. blank to select all options shown (Enter ‘c‘ to cancel):1
29. Obtaining a new certificate

成功后，在/etc/letsencrypt/live/www.xi-chuang.com/下生成4个证书：

1. cert.pem ->
2. chain.pem ->
3. fullchain.pem ->
4. privkey.pem ->

五、打开防火墙iptables的443端口

1. -A INPUT -m state --state NEW -m tcp -p tcp --dport 443 -j ACCEPT
2. #service iptables restart

六、编辑ssl.conf

vi /etc/httpd/conf.d/ssl.conf

1. # General setup for the virtual host, inherited from global configuration
2. DocumentRoot "/var/www/html/xi-chuang.com"
3. ServerName www.xi-chuang.com:443
4. .
5. .
6. .
7. SSLCertificateFile /etc/letsencrypt/live/www.xi-chuang.com/fullchain.pem
8. .
9. .
10. .
11. SSLCertificateKeyFile /etc/letsencrypt/live/www.xi-chuang.com/privkey.pem
12. .
13. .
14. .

service httpd restart

七、这个时候网站HTTPS已经能够访问了，试一下

最后，通过.htaccess进行301转向

1. RewriteEngine On
2. RewriteCond %{SERVER_PORT} 80
3. RewriteRule ^(.*)$ https://www.xi-chuang.com/$1 [R=301,L]
4. RewriteCond %{HTTP_HOST} !^www.xi-chuang.com$ [NC]
5. RewriteRule ^(.*)$ https://www.xi-chuang.com/$1 [L,R=301]

八、大功告成

注意：Let‘sEncrypt的证书有效期为90天，因此，建议使用cron作业在证书到期前一周将证书renew

在CentOS6,CentOS7安装 Let'sEncrypt 免费SSL安全证书