Certificate Authority Certificate Maker Tools

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This package provides a small library, built on top of pyOpenSSL, which allows for creating a custom certificate authority certificate, and genereating on-demand dynamic host certs using that CA certificate.

It is most useful for use with a man-in-the-middle HTTPS proxy, for example, for recording or replaying web content.

Trusting the CA created by this tool should be used with caution in a controlled setting to avoid security risks.

CertificateAuthority API

The CertificateAuthority class provides an interface to manage a root CA and generate dynamic host certificates suitable for use with the native Python ssl library as well as pyOpenSSL SSL module.

The class provides several options for storing the root CA and generated host CAs.

File-based Certificate Cache ~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code:: python

ca = CertificateAuthority('My Custom CA', 'my-ca.pem', certcache='/tmp/certs') filename = ca.certfor_host('example.com')

In this configuration, the root CA is stored at my-ca.pem and dynamically generated certs are placed in /tmp/certs. The filename returned would be /tmp/certs/example.com.pem in this example.

This filename can then be used with the Python ssl.load_cert_chain(certfile) <https://docs.python.org/3/library/ssl.html#ssl.SSLContext.load_cert_chain>_ command.

Note that the dynamically created certs are never deleted by certauth, it remains up to the user to handle cleanup occasionally if desired.

In-memory Certificate Cache ~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. code:: python

ca = CertificateAuthority('My Custom CA', 'my-ca.pem', certcache=50) cert, key = ca.loadcert('example.com')

This configuration stores the root CA at my-ca.pem but uses an in-memory certificate cache for dynamically created certs. These certs are stored in an LRU cache, configured to keep at most 50 certs.

The cert and key can then be used with OpenSSL.SSL.Context.use_certificate <http://www.pyopenssl.org/en/stable/api/ssl.html#OpenSSL.SSL.Context.use_certificate>_

.. code:: python

    context = SSl.Context(...)
    context.use_privatekey(key)
    context.use_certificate(cert)

Custom Cache ~~~~~~~~~~~~

A custom cache implementations which stores and retrieves per-host certificates can also be provided:

.. code:: python

ca = CertificateAuthority('My Custom CA', 'my-ca.pem', certcache=CustomCache()) cert, key = ca.loadcert('example.com')

class CustomCache: def setitem(self, host, certstring): # store certstring for host

   def get(self, host):
      # return cached cert_string, if available
      cert_string = ...
      return cert_string

Wildcard Certs ~~~~~~~~~~~~~~

To reduce the number of certs generated, it is convenient to generate wildcard certs.

.. code:: python

cert, key = ca.load_cert('example.com', wildcard=True)

This will generate a cert for *.example.com.

To automatically generate a wildcard cert for parent domain, use:

.. code:: python

cert, key = ca.loadcert('test.example.com', wildcard=True, wildcardfor_parent=True)

This will also generate a cert for *.example.com

Starting with 1.3.0, certauth uses tldextract to determine the tld for a given host, and will not use a parent domain if it is itself a tld suffix.

For example, calling:

.. code:: python

cert, key = ca.loadcert('example.co.uk', wildcard=True, wildcardfor_parent=True)

will now result in a cert for *.example.co.uk, not *.co.uk.

CLI Usage Examples

certauth also includes a simple command-line API for certificate creation and management.

::

usage: certauth [-h] [-c CERTNAME] [-n HOSTNAME] [-d CERTSDIR] [-f] [-w] rootca_cert

positional arguments: rootcacert Path to existing or new root CA file

optional arguments: -h, --help show this help message and exit -c CERTNAME, --certname CERTNAME Name for root certificate -n HOSTNAME, --hostname HOSTNAME Hostname certificate to create -d CERTSDIR, --certs-dir CERTSDIR Directory for host certificates -f, --force Overwrite certificates if they already exist -w, --wildcard_cert add wildcard SAN to host: *.,

To create a new root CA certificate:

certauth myrootca.pem --certname "My Test CA"

To create a host certificate signed with CA certificate in directory certs_dir:

certauth myrootca.pem --hostname "example.com" -d ./certs_dir

If the root cert doesn't exist, it'll be created automatically. If certs_dir, doesn't exist, it'll be created automatically also.

The cert for example.com will be created as certs_dir/example.com.pem. If it already exists, it will not be overwritten (unless -f option is used).

The -w option can be used to create a wildcard cert which has subject alternate names (SAN) for example.com and *.example.com

History

The CertificateAuthority functionality has evolved from certificate management originally found in the man-in-the-middle proxy pymiproxy <https://github.com/allfro/pymiproxy>_ by Nadeem Douba.

It was also extended in warcprox <https://github.com/internetarchive/warcprox>_ by Noah Levitt <https://github.com/nlevitt>_ of Internet Archive.

The CA functionality was also reused in pywb <https://github.com/ikreymer/pywb>_ and finally factored out into this separate package for modularity.

It is now also used by wsgiprox <https://github.com/webrecorder/wsgiprox>_ to provide a generalized HTTPS proxy wrapper to any WSGI application.