为什么要给网站启用SSL

Author： Neosey
发布时间：March 22, 2020
1139views
No comments
5431 words
Categories：代码项

# 什么是 SSL？

SSL协议位于TCP/IP协议与各种应用层协议之间，为数据通讯提供安全支持。SSL协议可分为两层： SSL记录协议（SSL Record Protocol）：它建立在可靠的传输协议（如TCP）之上，为高层协议提供数据封装、压缩、加密等基本功能的支持。 SSL握手协议（SSL Handshake Protocol）：它建立在SSL记录协议之上，用于在实际的数据传输开始前，通讯双方进行身份认证、协商加密算法、交换加密密钥等。

![SSL 网络模型](https://i.loli.net/2020/03/22/OhQvIrGL1ilUw8t.png)

SSL 作为 `HTTPS` 的基础最早由网景于 1994 年提出。虽然 HTTP 协议本身提供了基本认证和摘要认证（后来提出）两种客户端认证方案，但是毕竟除了用户名和密码外的所有数据仍然是明文传输的（甚至基本认证只对密码信息做了 Base64 编码），要保证传输的安全性还得依靠 SSL。SSL 本身是一种二进制协议，避免了随随便便一个代理就能读取/修改数据的问题。

随着技术发展，SSL 本身也在不断改进。从 SSL 1.0、SSL 2.0 到 SSL 3.0，再到标准化后的 TLS（目前 TLS 1.3 刚刚定稿），这个协议本身也在完善当中。在本文中，我们按照一般惯例使用 SSL 一词同时指代 SSL 和 TLS 两种协议。

---

# 什么是 HTTPS？

首先我们把A 看作客户端，通常情况下也就是浏览器，B 看作服务器，E 看作网络链路上某台邪恶的代理，C 是一位公正的第三方，顺便，我们把 C 交给 B 的那段含有一些基本信息和 B 的公钥的密文叫做数字证书。现在，我们可以把 C 叫做证书颁发机构。
在真实情况下，数字证书会包含一些加密的基本信息。毕竟数字证书并没有统一的标准，这些加密信息会用来告诉 A 如何解密数字证书。当然这些信息不会被加密，不然 A 完全无法解密数字证书。因此现实情况下，C 会对数字证书包含的所有内容建立一个摘要（你可以把它当做简介），然后只对这个摘要用自己的私钥进行加密。这个过程叫做签名。当 A 收到证书后，会解密这段摘要，然后自己通过相同的算法独立算出证书的摘要——如果是一样的，那就没问题了。
![HTTPS 模型](https://i.loli.net/2020/03/22/cFOh2uzH7XwSKAQ.png)
那么现在开始连接。A 向 B 发出了一个请求。在建立连接后，B 会将数字证书发送给 A。A 会验证数字证书（甚至会询问 C 确保这张证书没有作废）。如果成功，A 会利用从证书中取得的 B 的公钥在加密环境下协商出一个一致的临时密钥，接下来双方会用这个密钥进行**对称加密**来互相交流。
这就完成了！现在 A 和 B 可以使用相同的密钥进行对称加密通信在这个基础上，A 和 B 可以使用标准的 HTTP 协议进行交流。同时由于没能截获密钥，可怜的 E 同学再次扑了个空。我们成功完成了一次加密的 HTTPS 通信。

---

# 如何给域名申请SSL 加密证书

部署 HTTPS 的第一步是挑选符合要求的证书签发机构和合适的证书种类。不同的签发机构之间，以及同一机构签发的不同种类的证书之间，所需的价格是不同的。

> 证书种类是什么？真实的情况的确比上文提到的情况要再复杂一点。总的来说，证书分为 DV、OV、EV 三类。DV 证书只能提供最基本的加密功能，价格最低；而 OV 和 EV 证书会在签发前验证申请者的身份，流程更繁琐，价格也更高，但是这类证书可以提供验证网站身份的功能（比如浏览器会对不同种类的证书提供视觉上的差异，见下图），而且在出现安全问题时（比如签发机构的私钥泄露，虽然几率很小，但是有可能）的赔付金额也更高。

对于签发机构，我推荐选择 Let’s Encrypt，这是由 Mozilla、思科、Akamai、IdenTrust 和 EFF 等组织发起的公共、免费的 SSL 项目。它所签发的 DV 证书完全免费，而且支持通配符和多域名。唯一的缺点是它只支持 3 个月的有效期，不过到期后可以免费续期。

> 什么是通配符？浏览器在验证证书时，会确保证书中指定的域名和当前访问的域名相符，而根域名（a.com）和子域名（b.a.com）会被当做不同的域名来处理，不同的子域名（b.a.com 和 c.a.com）也会被当做不同的域名。通配符证书（*.a.com）可以同时匹配不同的子域名，减少了所需签发证书的数量。但是，根域名和通配符子域名不会匹配，都需要签发证书。同时，Let’s Encrypt 支持的多域名可以在同一张证书中包含多个域名，大大减少了所需证书的数量。像图中这样，该域名下的所有二级域名都可以使用此证书。

![SSL Example](https://i.loli.net/2020/03/22/qX8CY2I3FtpemHR.png#shadow)

要使用 **Let’s Encrypt** 签发，我们可以使用 [acme.sh](https://github.com/acmesh-official/acme.sh)，这是一个基于 Let’s Encrypt 接口封装的开源命令行工具，支持多域名/通配符的申请，也支持自动续期。

- 安装 **acme.sh**: `curl https://get.acme.sh | sh`
- 创建 一个 bash 的 alias, 方便你的使用: `alias acme.sh=~/.acme.sh/acme.sh`
- 申请证书: `acme.sh --issue --dns dns_he -d abc.com -d *.abc.com`

申请证书例子中，使用了dns_he API部署，你可以在完整文档中使用你域名解析商的API
</div>

稍等片刻，当证书签发下来，我们往往会得到两个文件，一个是你的私钥，一个是证书。

这时，我们就可以把证书放到服务器上了，然后配置服务器来开启 HTTPS。不同服务器的配置过程通常不同，我也不再赘述了。如果你使用 Nginx，可以使用如下配置。

`````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````bash
server{
    listen 80;
    listen 443 ssl http2;
    # 其他配置...
    # 如果是 HTTP 就跳转到 HTTPS
    if ($server_port !~ 443){
        rewrite ^(/.*)$ https://$host$1 permanent;
    }
    # 证书和私钥路径
    ssl_certificate /path/to/fullchain.pem;
    ssl_certificate_key /path/to/privkey.pem;
    # SSL 参数
    ssl_protocols TLSv1 TLSv1.1 TLSv1.2 TLSv1.3;
    ssl_ciphers TLS13-AES-256-GCM-SHA384:TLS13-CHACHA20-POLY1305-SHA256:TLS13-AES-128-GCM-SHA256:TLS13-AES-128-CCM-8-SHA256:TLS13-AES-128-CCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE:ECDH:AES:HIGH:!NULL:!aNULL:!MD5:!ADH:!RC4:!DH:!DHE;
    ssl_prefer_server_ciphers on;
    ssl_session_timeout 1d;
    ssl_session_cache builtin:1000 shared:SSL:10m;
    ssl_buffer_size 1400;
    ssl_stapling on;
    ssl_stapling_verify on;
    # 其他配置...
}
`````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````

当然，如果是面板之类的…大多有 SSL 的管理入口，依照提示部署证书即可。

最后，我们还需要对网页文件进行修改，尤其是页面上所有引用的资源必须同样使用 HTTPS，否则浏览器就不会显示安全小绿锁。

---

参考: [村通网之也谈 HTTPS](https://flyhigher.top/develop/1093.html)

Last modification：July 27th, 2020 at 01:07 pm

如果觉得我的文章对你有用，请随意赞赏