import binascii
import random
import string
 
from django import forms
from django.db import models
from django.conf import settings
 
class BaseEncryptedField(models.Field):
    '''This code is based on the djangosnippet #1095
You can find the original at http://www.djangosnippets.org/snippets/1095/'''
 
    def __init__(self, *args, **kwargs):
        cipher = kwargs.pop('cipher', 'AES')
        imp = __import__('Crypto.Cipher', globals(), locals(), [cipher], -1)
        self.cipher = getattr(imp, cipher).new(settings.SECRET_KEY[:32])
        self.prefix = '$%s$' % cipher
 
        max_length = kwargs.get('max_length', 40)
        mod = max_length % self.cipher.block_size
        if mod > 0:
            max_length += self.cipher.block_size - mod
        kwargs['max_length'] = max_length * 2 + len(self.prefix)
 
        models.Field.__init__(self, *args, **kwargs)
 
    def _is_encrypted(self, value):
        return isinstance(value, basestring) and value.startswith(self.prefix)
 
    def _get_padding(self, value):
        mod = len(value) % self.cipher.block_size
        if mod > 0:
            return self.cipher.block_size - mod
        return 0
 
 
    def to_python(self, value):
        if self._is_encrypted(value):
            return self.cipher.decrypt(binascii.a2b_hex(value[len(self.prefix):])).split('\0')[0]
        return value
 
    def get_db_prep_value(self, value):
        if value is not None and not self._is_encrypted(value):
            padding = self._get_padding(value)
            if padding > 0:
                value += "\0" + ''.join([random.choice(string.printable) for index in range(padding-1)])
            value = self.prefix + binascii.b2a_hex(self.cipher.encrypt(value))
        return value
 
class EncryptedTextField(BaseEncryptedField):
    __metaclass__ = models.SubfieldBase
 
    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):
    __metaclass__ = models.SubfieldBase
 
    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))

from encryption import EncryptedCharField
...
class Example(models.Model):
    secret = EncryptedCharField(max_length=255)
 
    class Meta:
        ordering = ('secret',)
 
    def __unicode__(self):
        return self.secret