如何使用python解码SSL证书？

Question

如何使用Python解码经过pem编码的（base64）证书？例如，这来自github.com：

-----BEGIN CERTIFICATE-----
MIIHKjCCBhKgAwIBAgIQDnd2il0H8OV5WcoqnVCCtTANBgkqhkiG9w0BAQUFADBp
MQswCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3
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n2Xkw9dJh1tybLEvrG8=
-----END CERTIFICATE-----

根据ssl-shopper的说法，应该是这样的：

Common Name: github.com
Subject Alternative Names: github.com, www.github.com
Organization: GitHub, Inc.
Locality: San Francisco
State: California
Country: US
Valid From: May 26, 2011
Valid To: July 29, 2013

如何使用python获取此纯文本？

Answer 1

Python的标准库，即使是最新版本，也不包含任何可解码X.509证书的内容。但是，附加cryptography软件包确实支持此功能。引用文档中的示例：

>>> from cryptography import x509
>>> from cryptography.hazmat.backends import default_backend
>>> cert = x509.load_pem_x509_certificate(pem_data, default_backend())
>>> cert.serial_number
2

另一个可选的附加软件包是pyopenssl。这是围绕OpenSSL C
API的精简包装，这意味着有 可能 做您想做的事情，但是希望花几天的时间来整理文档。

如果您无法安装Python附加软件包，但确实有openssl命令行实用程序，

import subprocess
cert_txt = subprocess.check_output(["openssl", "x509", "-text", "-noout", 
                                    "-in", certificate])

应该会产生与您从中的Web实用工具获得的大致相同的东西cert_txt。

顺便说一句，直接进行base64解码会产生二进制gobbledygook的原因是这里有两层编码。
X.509证书是ASN.1数据结构，序列化为X.690
DER
格式，然后，由于DER是二进制格式，因此使用base64铠装以便于文件传输。（在这方面的许多标准都是在90年代编写的，当时您只能可靠地发送7位ASCII码，否则无法可靠地发送任何东西。）