django-pgcrypto-fields

django-pgcrypto-fields is a Django extension which relies upon pgcrypto to encrypt and decrypt data for fields.

django-pgcrypto-fields has 3 kinds of fields:

• hash based fields
• PGP fields
• Symmetric fields

Hash based fields are:

• TextDigestField
• TextHMACField

PGP key fields are:

• EmailPGPPublicKeyField
• IntegerPGPPublicKeyField
• TextPGPPublicKeyField

PGP symmetric fields are:

• EmailPGPSymmetricKeyField
• IntegerPGPSymmetricKeyField
• TextPGPSymmetricKeyField

Requirements

• postgres with pgcrypto

Installation

pip

pip install django-pgcrypto-fields

Fields

TextDigestField

TextDigestField is a hash based field. The value is hashed in the database when saved with the digest pgcrypto function using the sha512 algorithm.

TextHMACField

TextHMACField is a hash based field. The value is hashed in the database when saved with the hmac pgcrypto function using a key and the sha512 algorithm.

key is set in settings.PGCRYPTO_KEY.

EmailPGPPublicKeyField, IntegerPGPPublicKeyField and TextPGPPublicKeyField

Public key encryption. It generates a token generated with a public key to encrypt the data and a private key to decrypt it.

Public and private keys can be set in settings with PUBLIC_PGP_KEY and PRIVATE_PGP_KEY.

Generate GPG keys.

The public key is going to encrypt the message and the private key will be needed to decrypt the content. The following commands have been taken from the pgcrypto documentation (see Generating PGP Keys with GnuPG).

Generating a public and a private key:

$ gpg --gen-key
$ gpg --list-secret-keys

/home/bob/.gnupg/secring.gpg
---------------------------
sec   2048R/21 2014-10-23
uid                  Test Key <example@example.com>
ssb   2048R/42 2014-10-23


$ gpg -a --export 42 > public.key
$ gpg -a --export-secret-keys 21 > private.key

EmailPGPSymmetricKeyField, IntegerPGPSymmetricKeyField and TextPGPSymmetricKeyField

Symmetric key encryption. Encrypt and decrypt the data with settings.PGCRYPTO_KEY.

Django settings

In settings.py:

BASEDIR = os.path.dirname(os.path.dirname(__file__))
PUBLIC_PGP_KEY_PATH = os.path.abspath(os.path.join(BASEDIR, 'public.key'))
PRIVATE_PGP_KEY_PATH = os.path.abspath(os.path.join(BASEDIR, 'private.key'))


# Used by PGPPublicKeyField
PUBLIC_PGP_KEY = open(PUBLIC_PGP_KEY_PATH).read()
PRIVATE_PGP_KEY = open(PRIVATE_PGP_KEY_PATH).read()

# Used by TextHMACField and PGPSymmetricKeyField
PGCRYPTO_KEY='ultrasecret'


# And add 'pgcrypto_fields' to `INSTALLED_APPS` to create the extension for
# pgcrypto (in a migration).
INSTALLED_APPS = (
    ...
    'pgcrypto_fields',
    ...
)

Usage

Model definition

from django.db import models

from pgcrypto_fields import fields

class MyModel(models.Model):
    digest_field = fields.TextDigestField()
    hmac_field = fields.TextHMACField()

    integer_pgp_pub_field = fields.IntegerPGPPublicKeyField()
    pgp_pub_field = fields.TextPGPPublicKeyField()
    integer_pgp_sym_field = fields.IntegerPGPSymmetricKeyField()
    pgp_sym_field = fields.TextPGPSymmetricKeyField()

Encrypting

Data is encrypted when inserted into the database.

Example:

>>> MyModel.objects.create(value='Value to be encrypted...')

Decrypting

PGP fields

When accessing the field name attribute on a model instance we are getting the decrypted value.

Example:

>>> # When using a PGP public key based encryption
>>> my_model = MyModel.objects.get()
>>> my_model.value  # field's proxy
'Value decrypted'

To be able to filter PGP values we first need to use an aggregate method to decrypt the values.

Example when using a PGPPublicKeyField:

>>> from pgcrypto_fields.aggregates import PGPPublicKeyAggregate
>>> my_models = MyModel.objects.annotate(PGPPublicKeyAggregate('pgp_pub_field'))
[<MyModel: MyModel object>, <MyModel: MyModel object>]
>>> my_models.filter(pgp_pub_field__decrypted='Value decrypted')
[<MyModel: MyModel object>]
>>> my_models.first().pgp_pub_field__decrypted
'Value decrypted'

Example when using a PGPSymmetricKeyField:

>>> from pgcrypto_fields.aggregates import PGPSymmetricKeyAggregate
>>> my_models = MyModel.objects.annotate(PGPSymmetricKeyAggregate('pgp_sym_field'))
[<MyModel: MyModel object>, <MyModel: MyModel object>]
>>> my_models.filter(pgp_pub_field__decrypted='Value decrypted')
[<MyModel: MyModel object>]
>>> my_models.first().pgp_sym_field__decrypted
'Value decrypted'

Hash fields

To filter hash based values we need to compare hashes. This is achieved by using a __hash_of lookup.

Example:

>>> my_model = MyModel.objects.filter(digest_field__hash_of='value')
[<MyModel: MyModel object>]
>>> my_model = MyModel.objects.filter(hmac_field__hash_of='value')
[<MyModel: MyModel object>]