Cert Hero

Python Stand-alone Library to Download the SSL Certificate for Any Host™

• Documentation: https://cert-hero.readthedocs.io.

---

Why Use?

• This library always returns the SSL certificate, if a server has one. This works for expired and self-signed certificate, whereas the builtin ssl library returns an empty dict if verification fails for any reason (source).

• The only dependency is asn1crypto (with over 300 stars on GitHub), which is ~94% more lightweight and robust than a solution with pyOpenSSL (chart).

• If a host redirects to another URL, this info is captured in Location and Status.

• Convenience methods such as __repr__() to make output more human-readable.

Core Exports

• cert_please - Retrieve the SSL certificate for a given hostname.

• certs_please - Retrieve (concurrently) the SSL certificate(s) for a list of hostnames.

• set_expired - Helper function to check (at runtime) if a cert is expired or not.

Install

$ pip install cert-hero

Usage

Fetch the SSL certificate for a host with cert_please():

import cert_hero

cert = cert_hero.cert_please('google.com')

print('Cert is Valid Till:', cert.not_after_date.isoformat())

# To get the output as a JSON string, use `str(cert)` or remove `!r` from below
print(f'Cert -> \n{cert!r}')

cert_hero.set_expired(cert)
print(f'Validity ->\n{cert["Validity"]}')

Output (Sample)

Cert is Valid Till: 2023-10-28
Cert ->
CertHero(
  {
    "Cert Status": "SUCCESS",
    "Serial": "753DD6FF20CB1B4510CB4C1EA27DA2EB",
    "Subject Name": {
      "Common Name": "*.google.com"
    },
    "Issuer Name": {
      "Country": "US",
      "State/Province": "California",
      "Organization": "Zscaler Inc.",
      "Organization Unit": "Zscaler Inc.",
      "Common Name": "Zscaler Intermediate Root CA (zscalerthree.net) (t) "
    },
    "Validity": {
      "Not After": "2023-10-28",
      "Not Before": "2023-10-14"
    },
    "Wildcard": true,
    "Signature Algorithm": "SHA256WITHRSA",
    "Key Algorithm": "RSA-2048",
    "Subject Alt Names": [
      "*.google.com",
      "*.appengine.google.com",
      "youtu.be",
      "*.youtube.com",
      ...
    ],
    "Location": "https://www.google.com/",
    "Status": 301
  }
)
Validity ->
{'Not After': '2023-10-28', 'Not Before': '2023-10-14', 'Expired': False}

Fetch (concurrently) the SSL certificates for multiple hosts with certs_please():

import cert_hero

host_to_cert = cert_hero.certs_please(['google.com', 'cnn.com', 'www.yahoo.co.in', 'youtu.be'])
cert_hero.set_expired(host_to_cert)

for host, cert in host_to_cert.items():
    print(f'=== {host.center(17)} ===')
    # To get the output as a JSON string, use `str(cert)` or remove `!r` from below
    print(f'{cert!r}')
    print()

Output (Sample)

===     google.com    ===
CertHero(
  {
    "Cert Status": "SUCCESS",
    "Serial": "753DD6FF20CB1B4510CB4C1EA27DA2EB",
    "Subject Name": {
      "Common Name": "*.google.com"
    },
    ...
  }
)

===      cnn.com      ===
CertHero(
  {
    "Cert Status": "SUCCESS",
    "Serial": "7F2F3E5C350554D71A6784CCFE6E8315",
    "Subject Name": {
      "Common Name": "cnn.com"
    },
    ...
  }
)

===  www.yahoo.co.in  ===
CertHero(
  {
    "Cert Status": "SUCCESS",
    "Serial": "7D7FD7B7C2EE7146B4D4E43E36908B72",
    "Subject Name": {
      "Common Name": "src1.yahoo.com"
    },
    ...
  }
)

===      youtu.be     ===
CertHero(
  {
    "Cert Status": "SUCCESS",
    "Serial": "753DD6FF20CB1B4510CB4C1EA27DA2EB",
    "Subject Name": {
      "Common Name": "*.google.com"
    },
    ...
  }
)

Usage as a CLI

After the installation step you can use cert-hero just typing ch in your terminal window.

The ch command allows you to retrieve the SSL certificate(s) for one or more given host.

For example:

ch google.com cnn.com

You can get help about the main command using:

ch --help

Rationale

The builtin Python module ssl can be used to retrieve a certificate from a server via getpeercert, but it’ll work only if the certificate of interest can be successfully verified (source).

If, for any reason, verification fails, like, for example, with expired or a self-signed certificate, we’ll get ssl.SSLCertVerificationError instead of the requested info.

We can work around this by asking for the certificate in the binary form:

getpeercert(binary_form=True)

But now we have to convert it, and thus we can use a third party asn1crypto module, instead of the (bulkier) cryptography module.

Credits

This package was created with Cookiecutter and the rnag/cookiecutter-pypackage project template.