Field-Level Encryption via Custom Model Field Descriptors

from cryptography.fernet import Fernet
from django.conf import settings
from django.db import models
 
class EncryptedFieldDescriptor:
    def __init__(self, field):
        self.field = field
 
    def __get__(self, instance, owner=None):
        if instance is None:
            return self
        value = instance.__dict__.get(self.field.name)
        if value is None or not isinstance(value, str):
            return value
        if value.startswith('gAAAAA'):
            cipher = Fernet(settings.SECRET_KEY.encode()[:32].ljust(32, b'='))
            return cipher.decrypt(value.encode()).decode()
        return value
 
    def __set__(self, instance, value):
        if value is not None and isinstance(value, str):
            cipher = Fernet(settings.SECRET_KEY.encode()[:32].ljust(32, b'='))
            encrypted = cipher.encrypt(value.encode()).decode()
            instance.__dict__[self.field.name] = encrypted
        else:
            instance.__dict__[self.field.name] = value
 
class EncryptedCharField(models.CharField):
    def contribute_to_class(self, cls, name, **kwargs):
        super().contribute_to_class(cls, name, **kwargs)
        setattr(cls, name, EncryptedFieldDescriptor(self))