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certbuilder Documentation

certbuilder is a Python library for constructing X.509 certificates. It provides a high-level interface with knowledge of RFC 5280 to produce, valid, correct certificates without terrible APIs or hunting through RFCs.

Since its only dependencies are the asn1crypto and oscrypto libraries, it is easy to install and use on Windows, OS X, Linux and the BSDs.

The documentation consists of the following topics:

Basic Usage

A simple, self-signed certificate can be created by generating a public/private key pair using oscrypto and then passing a dictionary of name information to the CertificateBuilder() constructor:

from oscrypto import asymmetric
from certbuilder import CertificateBuilder, pem_armor_certificate


public_key, private_key = asymmetric.generate_pair('rsa', bit_size=2048)

with open('/path/to/my/env/will_bond.key', 'wb') as f:
    f.write(asymmetric.dump_private_key(private_key, 'password'))

builder = CertificateBuilder(
    {
        'country_name': 'US',
        'state_or_province_name': 'Massachusetts',
        'locality_name': 'Newbury',
        'organization_name': 'Codex Non Sufficit LC',
        'common_name': 'Will Bond',
    },
    public_key
)
builder.self_signed = True
certificate = builder.build(private_key)

with open('/path/to/my/env/will_bond.crt', 'wb') as f:
    f.write(pem_armor_certificate(certificate))

All name components must be unicode strings. Common name keys include:

  • country_name
  • state_or_province_name
  • locality_name
  • organization_name
  • common_name

Less common keys include:

  • organizational_unit_name
  • email_address
  • street_address
  • postal_code
  • business_category
  • incorporation_locality
  • incorporation_state_or_province
  • incorporation_country

See CertificateBuilder.subject for a full list of supported name keys.

CA and End-Entity Certificates

Beyond self-signed certificates lives the world of root CAs, intermediate CAs and end-entity certificates.

The example below will create a root CA and then an end-entity certificate signed by the root. By simply creating another CA certificate signed by the root CA, an intermediate CA certificate could be added.

from oscrypto import asymmetric
from certbuilder import CertificateBuilder, pem_armor_certificate


# Generate and save the key and certificate for the root CA
root_ca_public_key, root_ca_private_key = asymmetric.generate_pair('rsa', bit_size=2048)

with open('/path/to/my/env/root_ca.key', 'wb') as f:
    f.write(asymmetric.dump_private_key(root_ca_private_key, 'password'))

builder = CertificateBuilder(
    {
        'country_name': 'US',
        'state_or_province_name': 'Massachusetts',
        'locality_name': 'Newbury',
        'organization_name': 'Codex Non Sufficit LC',
        'common_name': 'CodexNS Root CA 1',
    },
    root_ca_public_key
)
builder.self_signed = True
builder.ca = True
root_ca_certificate = builder.build(root_ca_private_key)

with open('/path/to/my/env/root_ca.crt', 'wb') as f:
    f.write(pem_armor_certificate(root_ca_certificate))


# Generate an end-entity key and certificate, signed by the root
end_entity_public_key, end_entity_private_key = asymmetric.generate_pair('rsa', bit_size=2048)

with open('/path/to/my/env/will_bond.key', 'wb') as f:
    f.write(asymmetric.dump_private_key(end_entity_private_key, 'password'))

builder = CertificateBuilder(
    {
        'country_name': 'US',
        'state_or_province_name': 'Massachusetts',
        'locality_name': 'Newbury',
        'organization_name': 'Codex Non Sufficit LC',
        'common_name': 'Will Bond',
    },
    end_entity_public_key
)
builder.issuer = root_ca_certificate
end_entity_certificate = builder.build(root_ca_private_key)

with open('/path/to/my/env/will_bond.crt', 'wb') as f:
    f.write(pem_armor_certificate(end_entity_certificate))