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 to 2.2.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 <example@example.com>
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:
- Connect locally or use SSL connections.
- 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.