為什麼 curl 需要根證書和中間證書才能安全地連接到 HTTP 伺服器？

November 13, 2018

我創建了一個根證書、一個中間證書和一個伺服器證書：

root (ca.cert.pem)
|
+---intermediate (intermediate/certs/intermediate.cert.pem)
   |
   +---www.example.com
       ↳ certificate: (intermediate/certs/www.example.com.cert.pem)
       ↳ private key: (intermediate/private/www.example.com.key.pem)

我使用私鑰和公共證書www.example.com來使用 Node 創建一個 HTTPS 伺服器：

var tls = require('tls');
var fs = require('fs');

var options = {
 key: fs.readFileSync('intermediate/private/www.example.com.key.pem'),
 cert: fs.readFileSync('intermediate/certs/www.example.com.cert.pem')
};

tls.createServer(options, function (s) {
 s.write("welcome!\n");
 s.pipe(s);
}).listen(8000);

我想驗證如果客戶端有權訪問根證書 ( ca.cert.pem)，它可以成功地向https://www.example.com:8000.

如果我嘗試：

$ curl -v --cacert certs/ca.cert.pem https://www.example.com:8000

它失敗並顯示錯誤消息：

* Rebuilt URL to: https://www.example.com:8000/
*   Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to www.example.com (127.0.0.1) port 8000 (#0)
* ALPN, offering h2
* ALPN, offering http/1.1
* successfully set certificate verify locations:
*   CAfile: /certs/ca.cert.pem
 CApath: /etc/ssl/certs
* TLSv1.2 (OUT), TLS handshake, Client hello (1):
* TLSv1.2 (IN), TLS handshake, Server hello (2):
* NPN, no overlap, use HTTP1.1
* TLSv1.2 (IN), TLS handshake, Certificate (11):
* TLSv1.2 (OUT), TLS alert, Server hello (2):
* SSL certificate problem: unable to get local issuer certificate
* stopped the pause stream!
* Closing connection 0
curl: (60) SSL certificate problem: unable to get local issuer certificate
More details here: https://curl.haxx.se/docs/sslcerts.html

curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.

但是，如果我創建一個證書鏈：

$ cat intermediate/certs/intermediate.cert.pem \
     certs/ca.cert.pem &gt; intermediate/certs/ca-chain.cert.pem

並將其用作 curl 的--cacert，一切都按預期工作：

$ curl -v --cacert intermediate/certs/ca-chain.cert.pem   https://www.example.com:8000
* Rebuilt URL to: https://www.example.com:8000/
*   Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to www.example.com (127.0.0.1) port 8000 (#0)
* ALPN, offering h2
* ALPN, offering http/1.1
* successfully set certificate verify locations:
*   CAfile: /intermediate/certs/ca-chain.cert.pem
 CApath: /etc/ssl/certs
* TLSv1.2 (OUT), TLS handshake, Client hello (1):
* TLSv1.2 (IN), TLS handshake, Server hello (2):
* NPN, no overlap, use HTTP1.1
* TLSv1.2 (IN), TLS handshake, Certificate (11):
* TLSv1.2 (IN), TLS handshake, Server key exchange (12):
* TLSv1.2 (IN), TLS handshake, Server finished (14):
* TLSv1.2 (OUT), TLS handshake, Client key exchange (16):
* TLSv1.2 (OUT), TLS change cipher, Client hello (1):
* TLSv1.2 (OUT), TLS handshake, Unknown (67):
* TLSv1.2 (OUT), TLS handshake, Finished (20):
* TLSv1.2 (IN), TLS handshake, Finished (20):
* SSL connection using TLSv1.2 / ECDHE-RSA-AES128-GCM-SHA256
* ALPN, server did not agree to a protocol
* Server certificate:
*  subject: C=AU; ST=Victoria; L=Melbourne; O=ACME; OU=ACME Web; CN=www.example.com; emailAddress=web@example.com
*  start date: Nov 12 11:32:59 2018 GMT
*  expire date: Nov 22 11:32:59 2019 GMT
*  common name: www.example.com (matched)
*  issuer: C=AU; ST=Victoria; O=ACME; OU=ACME Certificate Authority; CN=ACME Intermediate CA; emailAddress=contact2@example.com
*  SSL certificate verify ok.
> GET / HTTP/1.1
> Host: www.example.com:8000
> User-Agent: curl/7.58.0
> Accept: */*
> 
welcome!
GET / HTTP/1.1
Host: www.example.com:8000
User-Agent: curl/7.58.0
Accept: */*

如果我沒看錯的話，和瀏覽器類似，curl應該只需要根證書來驗證SSL證書的簽名即可www.example.com。那麼，為什麼curl需要根證書和中間證書才能驗證它確實與正確的伺服器通信呢？

PEM 文件

以下是此設置中使用的 PEM 文件的內容（丟棄的未加密 PEM 文件）：

`ca.cert.pem`

`intermediate.cert.pem`

`www.example.com.cert.pem`

`www.example.com.key.pem`

(0) 這與加密無關，可能在 security.SX 上會更好，它有很多關於證書連結和 HTTPS 瀏覽器和伺服器使用的問題，但是……
(1) 雖然現在 AIA 的使用比過去更多，並且可能是一種可接受的解決方法，但官方的標準解決方案是伺服器必鬚髮送包含中間證書的鏈，但不一定包括根證書，請參閱https://www.rfc-editor.org/rfc/rfc5246#section-7.4.2 et pred（注意：TLS1.3 rfc8446 對此略有改變）或熊史詩 https://security.stackexchange.com/questions/ 20803/how-does-ssl-tls-work在標題證書和身份驗證，以及…
（2）幾個Stack上有很多關於如何配置各種伺服器按要求發送證書鏈的Q；對於 nodejs，以
https://stackoverflow.com/questions/19104215/node-js-express-js-chain-certificate-not-working
https://stackoverflow.com/questions/16224064/running-ssl-node-js開頭-server-with-godaddy-gd-bundle-crt
https://stackoverflow.com/questions/32777760/how-to-fix-missing-an-intermediate-chain-certificate-in-nodejs

引用自：https://crypto.stackexchange.com/questions/63907

為什麼 curl 需要根證書和中間證書才能安全地連接到 HTTP 伺服器？

PEM 文件

`ca.cert.pem`

`intermediate.cert.pem`

`www.example.com.cert.pem`

`www.example.com.key.pem`

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