C

cam

Command-line tool to manage a Certification Authority.

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cam - minimal X509 Certification Authority management

cam is a tiny Python program that can be used to manage a X509 Certification Authority for a small organization. It can only create server certificates, so it is not going to be useful to manage an X509-based client authentication infrastructure.

The intended usage involves describing the list of certificates to generate in a configuration file, and using the cam tool to create and renew them.

Installation

cam has few requirements:

  • A moderately recent version of Python 2;
  • OpenSSL (>=1.0.0) - specifically, the openssl binary.

Once you have downloaded the source code, system-wide installation is simply a matter of:

$ sudo python setup.py install

Configuration

The configuration file uses a standard INI-like syntax, consisting of a number of sections. There are two special sections: ca and global, any other section is interpreted as a certificate definition.

The ca section contains the attributes of the CA itself, see the example configuration file to see which attributes are supported.

The global section contains configuration parameters for cam. The only configuration parameter supported is root_dir, which is where all the CA private data will be stored.

Certificates are identified by a tag (the section name), so for example given the following configuration snippet:

[web]
cn = www.domain.org

you would use the following command to generate it:

$ cam --config=my.config gen web

Global

The global section contains options that affect the behavior of the cam tool itself. You can usually leave this out altogether.

Available options:

root_dir
This is where the CA private data will be stored. If you leave this parameter empty, or if you don't define a global section at all, this will default to the directory containing the configuration file.

Certification Authority

The ca section specifies parameters for the Certification Authority. Some of these are mandatory as they uniquely identify each CA.

The following parameters specify options of the CA certificate itself. They are only used once, at CA initialization time (when running cam init). Subsequent changes to these options will be ignored.

cn
Value of the Common Name (CN) field in the X509 Subject.
org
Value of the Organization (O) field in the X509 Subject.
country
Value of the Country (C) field in the X509 Subject.
email
Contact email, added to the X509 CA certificate.
days
Number of days that the CA certificate will be valid for (default: 3650, or 10 years).
crl_url
Public URL where the CA Certificate Revocation List will be accessible (optional).

Other options:

default_days
Number of days that a new certificate will be valid for (default: 365).
bits
Size of the RSA key for the CA certificate, and also default key size for all newly created certificates (default: 2048).
signature_algorithm
Digest algorithm to use for CA signatures (default: sha256).

Certificates

Every other section defines options for a certificate. Some of these options can be left unset, in which case a default value will be provided by the ca section. cn must be always specified.

The following options are available:

days
Number of days that this certificate will be valid for. If unset, will use ca.default_days.
cn
Common Name (CN) for the X509 Subject.
ou
Organizational Unit (OU) for the X509 Subject (optional).
alt_names
Space-separated list of alternate names for this certificate. These will be encoded as DNS entries in the certificate's X509v3 Subject Alternative Name field.

Usage

Once you have created a configuration file, initialize the CA by running:

$ cam --config=my.config init

This will create the CA certificate and private key, and it will ask you to set a passphrase for the key. Pick something secure.

Once this is done, you will be able to generate the certificates described in the configuration using the cam gen command. For example, if the configuration defines a certificate with a tag of web:

$ cam --config=my.config gen web

The tool will ask you for the CA passphrase, and it will create a certificate and a private key in the CA private data directory. You can obtain their path with:

$ cam --config=my.config files web
/your/ca/dir/public/certs/web.pem
/your/ca/dir/private/web.key

At any time you can inspect the status of the configured certificates (and see which ones are about to expire) using the cam list command:

$ cam --config=my.config list

Standalone Install

The CA private keys are very sensitive information, so you'll want to store them in some encrypted removable storage. You can bundle the cam application itself with the CA data by using virtualenv:

$ virtualenv --no-site-packages /secure/cam
$ virtualenv --relocatable /secure/cam
$ (cd /tmp ; git clone https://git.autistici.org/ai/cam.git \
   && /secure/cam/bin/python setup.py install)

Then you can simply mount your encrypted image wherever there is a Python interpreter available (well, with the same architecture/OS too) and run:

$ /secure/cam/bin/cam --config=/secure/ca/my.config ...