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# -*- coding: utf-8 -*-
import warnings
import six
from django import forms
from django.conf import settings
from django.core.exceptions import ImproperlyConfigured
from django.db import models
try:
from keyczar import keyczar
except ImportError:
raise ImportError('Using an encrypted field requires the Keyczar module. '
'You can obtain Keyczar from http://www.keyczar.org/.')
class EncryptionWarning(RuntimeWarning):
pass
class BaseEncryptedField(models.Field):
prefix = 'enc_str:::'
def __init__(self, *args, **kwargs):
if not hasattr(settings, 'ENCRYPTED_FIELD_KEYS_DIR'):
raise ImproperlyConfigured('You must set the settings.ENCRYPTED_FIELD_KEYS_DIR '
'setting to your Keyczar keys directory.')
crypt_class = self.get_crypt_class()
self.crypt = crypt_class.Read(settings.ENCRYPTED_FIELD_KEYS_DIR)
# Encrypted size is larger than unencrypted
self.unencrypted_length = max_length = kwargs.get('max_length', None)
if max_length:
kwargs['max_length'] = self.calculate_crypt_max_length(max_length)
super(BaseEncryptedField, self).__init__(*args, **kwargs)
def calculate_crypt_max_length(self, unencrypted_length):
# TODO: Re-examine if this logic will actually make a large-enough
# max-length for unicode strings that have non-ascii characters in them.
# For PostGreSQL we might as well always use textfield since there is little
# difference (except for length checking) between varchar and text in PG.
return len(self.prefix) + len(self.crypt.Encrypt('x' * unencrypted_length))
def get_crypt_class(self):
"""
Get the Keyczar class to use.
The class can be customized with the ENCRYPTED_FIELD_MODE setting. By default,
this setting is DECRYPT_AND_ENCRYPT. Set this to ENCRYPT to disable decryption.
This is necessary if you are only providing public keys to Keyczar.
Returns:
keyczar.Encrypter if ENCRYPTED_FIELD_MODE is ENCRYPT.
keyczar.Crypter if ENCRYPTED_FIELD_MODE is DECRYPT_AND_ENCRYPT.
Override this method to customize the type of Keyczar class returned.
"""
crypt_type = getattr(settings, 'ENCRYPTED_FIELD_MODE', 'DECRYPT_AND_ENCRYPT')
if crypt_type == 'ENCRYPT':
crypt_class_name = 'Encrypter'
elif crypt_type == 'DECRYPT_AND_ENCRYPT':
crypt_class_name = 'Crypter'
else:
raise ImproperlyConfigured(
'ENCRYPTED_FIELD_MODE must be either DECRYPT_AND_ENCRYPT '
'or ENCRYPT, not %s.' % crypt_type)
return getattr(keyczar, crypt_class_name)
def to_python(self, value):
if isinstance(self.crypt.primary_key, keyczar.keys.RsaPublicKey):
retval = value
elif value and (value.startswith(self.prefix)):
if hasattr(self.crypt, 'Decrypt'):
retval = self.crypt.Decrypt(value[len(self.prefix):])
if six.PY2 and retval:
retval = retval.decode('utf-8')
else:
retval = value
else:
retval = value
return retval
def from_db_value(self, value, expression, connection, context):
return self.to_python(value)
def get_db_prep_value(self, value, connection, prepared=False):
if value and not value.startswith(self.prefix):
# We need to encode a unicode string into a byte string, first.
# keyczar expects a bytestring, not a unicode string.
if six.PY2:
if type(value) == six.types.UnicodeType:
value = value.encode('utf-8')
# Truncated encrypted content is unreadable,
# so truncate before encryption
max_length = self.unencrypted_length
if max_length and len(value) > max_length:
warnings.warn("Truncating field %s from %d to %d bytes" % (
self.name, len(value), max_length), EncryptionWarning
)
value = value[:max_length]
value = self.prefix + self.crypt.Encrypt(value)
return value
def deconstruct(self):
name, path, args, kwargs = super(BaseEncryptedField, self).deconstruct()
kwargs['max_length'] = self.unencrypted_length
return name, path, args, kwargs
class EncryptedTextField(BaseEncryptedField):
def get_internal_type(self):
return 'TextField'
def formfield(self, **kwargs):
defaults = {'widget': forms.Textarea}
defaults.update(kwargs)
return super(EncryptedTextField, self).formfield(**defaults)
class EncryptedCharField(BaseEncryptedField):
def __init__(self, *args, **kwargs):
super(EncryptedCharField, self).__init__(*args, **kwargs)
def get_internal_type(self):
return "CharField"
def formfield(self, **kwargs):
defaults = {'max_length': self.max_length}
defaults.update(kwargs)
return super(EncryptedCharField, self).formfield(**defaults)
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