django-pgcrypto-fields

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

Requirements

• postgres with pgcrypto
• Supports Django 1.11.x, 2.2.x, and 3.0.x
• Compatible with Python 3 only

Last version of this library that supports Django 1.8.x, 1.9.x, 1.10.x was django-pgcrypto-fields 2.2.0.

Installation

Install package

pip install django-pgcrypto-fields

Django settings

Our library support different crypto keys for multiple databases by defining the keys in your DATABASES settings.

In settings.py:

import os
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 used by default if not specified by the db
PUBLIC_PGP_KEY = open(PUBLIC_PGP_KEY_PATH).read()
PRIVATE_PGP_KEY = open(PRIVATE_PGP_KEY_PATH).read()

# Used by TextHMACField and PGPSymmetricKeyField if not specified by the db
PGCRYPTO_KEY='ultrasecret'

DIFF_PUBLIC_PGP_KEY_PATH = os.path.abspath(
    os.path.join(BASEDIR, 'tests/keys/public_diff.key')
)
DIFF_PRIVATE_PGP_KEY_PATH = os.path.abspath(
    os.path.join(BASEDIR, 'tests/keys/private_diff.key')
)

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

DATABASES = {
    # This db will use the default keys above
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': 'pgcryto_fields',
        'USER': 'pgcryto_fields',
        'PASSWORD': 'xxxx',
        'HOST': 'psql.test.com',
        'PORT': 5432,
        'OPTIONS': {
            'sslmode': 'require',
        }
    },
    'diff_keys': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': 'pgcryto_fields_diff',
        'USER': 'pgcryto_fields_diff',
        'PASSWORD': 'xxxx',
        'HOST': 'psqldiff.test.com',
        'PORT': 5432,
        'OPTIONS': {
            'sslmode': 'require',
        },
        'PGCRYPTO_KEY': 'djangorocks',
        'PUBLIC_PGP_KEY': open(DIFF_PUBLIC_PGP_KEY_PATH, 'r').read(),
        'PRIVATE_PGP_KEY': open(DIFF_PRIVATE_PGP_KEY_PATH, 'r').read(),
    },
}

Generate GPG keys if using Public Key Encryption

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 (The preferred key type is "DSA and Elgamal".):

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

/home/bob/.gnupg/secring.gpg
---------------------------
sec   2048R/21 2014-10-23
uid                  Test Key <[email protected]>
ssb   2048R/42 2014-10-23


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

Limitations

This library currently does not support Public Key Encryption private keys that are password protected yet. See Issue #89 to help implement it.

Upgrading to 2.4.0 from previous versions

The 2.4.0 version of this library received a large rewrite in order to support auto-decryption when getting encrypted field data as well as the ability to filter on encrypted fields without using the old PGPCrypto aggregate functions available in previous versions.

The following items in this library have been removed and therefore references in your application to these items need to be removed as well:

• managers.PGPManager
• admin.PGPAdmin
• aggregates.*

Fields

django-pgcrypto-fields has 3 kinds of fields:

• Hash based fields
• Public Key (PGP) fields
• Symmetric fields

Hash Based Fields

Supported hash based fields are:

• TextDigestField
• TextHMACField

TextDigestField is hashed in the database using the digest pgcrypto function using the sha512 algorithm.

TextHMACField is hashed in the database using the hmac pgcrypto function using a key and the sha512 algorithm. This is similar to the digest version however the hash can only be recalculated knowing the key. This prevents someone from altering the data and also changing the hash to match.

Public Key Encryption Fields

Supported PGP public key fields are:

• CharPGPPublicKeyField
• EmailPGPPublicKeyField
• TextPGPPublicKeyField
• DatePGPPublicKeyField
• DateTimePGPPublicKeyField
• TimePGPPublicKeyField
• IntegerPGPPublicKeyField
• DecimalPGPPublicKeyField
• FloatPGPPublicKeyField

Public key encryption creates 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.

Symmetric Key Encryption Fields

Supported PGP symmetric key fields are:

• CharPGPSymmetricKeyField
• EmailPGPSymmetricKeyField
• TextPGPSymmetricKeyField
• DatePGPSymmetricKeyField
• DateTimePGPSymmetricKeyField
• TimePGPSymmetricKeyField
• IntegerPGPSymmetricKeyField
• DecimalPGPSymmetricKeyField
• FloatPGPSymmetricKeyField

Encrypt and decrypt the data with settings.PGCRYPTO_KEY which acts like a password.

Django Model Field Equivalents

Django Field	Public Key Field	Symmetric Key Field
CharField	CharPGPPublicKeyField	CharPGPSymmetricKeyField
EmailField	EmailPGPPublicKeyField	EmailPGPSymmetricKeyField
TextField	TextPGPPublicKeyField	TextPGPSymmetricKeyField
DateField	DatePGPPublicKeyField	DatePGPSymmetricKeyField
DateTimeField	DateTimePGPPublicKeyField	DateTimePGPSymmetricKeyField
TimeField	TimePGPPublicKeyField	TimePGPSymmetricKeyField
IntegerField	IntegerPGPPublicKeyField	IntegerPGPSymmetricKeyField
DecimalField	DecimalPGPPublicKeyField	DecimalPGPSymmetricKeyField
FloatField	FloatPGPPublicKeyField	FloatPGPSymmetricKeyField

Other Django model fields are not currently supported. Pull requests are welcomed.

Usage

Model Definition

from django.db import models

from pgcrypto import fields

class MyModel(models.Model):
    digest_field = fields.TextDigestField()
    digest_with_original_field = fields.TextDigestField(original='pgp_sym_field')
    hmac_field = fields.TextHMACField()
    hmac_with_original_field = fields.TextHMACField(original='pgp_sym_field')

    email_pgp_pub_field = fields.EmailPGPPublicKeyField()
    integer_pgp_pub_field = fields.IntegerPGPPublicKeyField()
    pgp_pub_field = fields.TextPGPPublicKeyField()
    date_pgp_pub_field = fields.DatePGPPublicKeyField()
    datetime_pgp_pub_field = fields.DateTimePGPPublicKeyField()
    time_pgp_pub_field = fields.TimePGPPublicKeyField()
    decimal_pgp_pub_field = fields.DecimalPGPPublicKeyField()
    float_pgp_pub_field = fields.FloatPGPPublicKeyField()
    
    email_pgp_sym_field = fields.EmailPGPSymmetricKeyField()
    integer_pgp_sym_field = fields.IntegerPGPSymmetricKeyField()
    pgp_sym_field = fields.TextPGPSymmetricKeyField()
    date_pgp_sym_field = fields.DatePGPSymmetricKeyField()
    datetime_pgp_sym_field = fields.DateTimePGPSymmetricKeyField()
    time_pgp_sym_field = fields.TimePGPSymmetricKeyField()
    decimal_pgp_sym_field = fields.DecimalPGPSymmetricKeyField()
    float_pgp_sym_field = fields.FloatPGPSymmetricKeyField()

Encrypting

Data is automatically encrypted when inserted into the database.

Example:

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

Hash fields can have hashes auto updated if you use the original attribute. This attribute allows you to indicate another field name to base the hash value on.

from django.db import models

from pgcrypto import fields

class User(models.Model):
    first_name = fields.TextPGPSymmetricKeyField(max_length=20, verbose_name='First Name')
    first_name_hashed = fields.TextHMACField(original='first_name') 

In the above example, if you specify the optional original attribute it would take the unencrypted value from the first_name model field as the input value to create the hash. If you did not specify an original attribute, the field would work as it does now and would remain backwards compatible.

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
'Value decrypted'

Filtering encrypted values is now handled automatically as of 2.4.0. And aggregate methods are not longer supported and have been removed from the library.

Also, auto-decryption is support for select_related() models.

from django.db import models

from pgcrypto import fields


class EncryptedFKModel(models.Model):
    fk_pgp_sym_field = fields.TextPGPSymmetricKeyField(blank=True, null=True)


class EncryptedModel(models.Model):
    pgp_sym_field = fields.TextPGPSymmetricKeyField(blank=True, null=True)
    fk_model = models.ForeignKey(
        EncryptedFKModel, blank=True, null=True, on_delete=models.CASCADE
    )

Example:

>>> import EncryptedModel
>>> my_model = EncryptedModel.objects.get().select_releated('fk_model')
>>> my_model.pgp_sym_field
'Value decrypted'
>>> my_model.fk_model.fk_pgp_sym_field
'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>]

Limitations

.distinct('encrypted_field_name')

Due to a missing feature in the Django ORM, using distinct() on an encrypted field does not work for Django 2.0.x and lower.

The normal distinct works on Django 2.1.x and higher:

items = EncryptedFKModel.objects.filter(
    pgp_sym_field__startswith='P'
).only(
    'id', 'pgp_sym_field', 'fk_model__fk_pgp_sym_field'
).distinct(
    'pgp_sym_field'
)

Workaround for Django 2.0.x and lower:

from django.db import models

items = EncryptedFKModel.objects.filter(
    pgp_sym_field__startswith='P'
).annotate(
    _distinct=models.F('pgp_sym_field')
).only(
    'id', 'pgp_sym_field', 'fk_model__fk_pgp_sym_field'
).distinct(
    '_distinct'
)

This works because the annotated field is auto-decrypted by Django as a F field and that field is used in the distinct().

Security Limitations

Taken direction from the PostgreSQL documentation:

https://www.postgresql.org/docs/9.6/static/pgcrypto.html#AEN187024

All pgcrypto functions run inside the database server. That means that all the data and passwords move between pgcrypto and client applications in clear text. Thus you must:

1. Connect locally or use SSL connections.
2. Trust both system and database administrator.

If you cannot, then better do crypto inside client application.

The implementation does not resist side-channel attacks. For example, the time required for a pgcrypto decryption function to complete varies among ciphertexts of a given size.