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Erebus is an implementation of the envelope encryption paradigm.
Erebus
Erebus is an implementation of the envelope encryption paradigm. It uses a separate key (called DEK, short for data encryption key) for each encrypted struct. The key is regenerated on each save, making key encryption barely necessary. During each encryption, the DEK is encrypted using the KEK (key encryption key).
The DEK is a symmetric key (Erebus uses AES-256 with Galois mode (AES-GCM) with AEAD), which guarantees both the security and the integrity of the data. The KEK is an asymmetric key – Erebus uses the public key for encryption (for performance reasons when using external key storage) and the private key for decryption. The specific implementation depends on the backend.
Currently, there are three supported backend implementations:
-
Erebus.KMS.Google
- Google KMS key storage. Means that your private key never leaves Google infrastructure, which is the most secure option -
Erebus.KMS.Local
- private/public key pair stored on your hard drive. Please note that it makes them prone to leakage -
Erebus.KMS.Dummy
- base64 as encryption for DEK. Never use it in production
Please note that you need to provide config for the operations and explicitly invoke them, providing the config on every call.
Installation
Erebus can be installed by adding erebus
to your list of dependencies in mix.exs
:
def deps do
[
{:erebus, "~> 0.2.0-rc.3"}
]
end
Usage
To use Erebus you need to wrap it to provide your backend configuration. Create a module like the example below in your app:
defmodule MyApp.Erebus do
def encrypt(struct, handle, version) do
opts = Application.get_env(:my_app, :erebus)
Erebus.encrypt(struct, handle, version, opts)
end
def decrypt(struct, fields) do
opts = Application.get_env(:my_app, :erebus)
Erebus.decrypt(struct, fields, opts)
end
end
In an encrypted struct, Erebus requires several fields for each encrypted property. Follow the example below to define your structs:
defmodule SecureModel
@type t :: %__MODULE__{
# `first` is an encrypted field
first: String.t(),
# `second` is another encrypted field
second: String.t(),
# this field contains the ciphertext for the `first` field
first_encrypted: binary(),
# this field contains the ciphertext for the `second` field
second_encrypted: binary(),
# this field contains a hashed version of the unencrypted `first` field
first_hash: String.t(),
# this field contains a hashed version of the unencrypted `second` field
second_hash: String.t(),
# this field contains the DEK (data encryption key)
dek: map()
}
end
In this example first
and second
are the names of the encryptable fields. The unsuffixed fields are virtual, meaning they are only used for encrypting (before write), or are populated after decrypting the equivalent *_encrypted
fields – only suffixed fields are written to the database. The dek
field contains the DEK.
The *_hash
suffixed fields are hashed (using SHA512) versions of the plain text field content. They can be used for finding exact matches without having to decrypt the content.
When using Ecto, fields are defined using the hashed_encrypted_field(:field_name)
and data_encryption_key()
macros, which create all the necessary auxiliary fields for you:
use Erebus.Schema
embedded_schema "table" do
hashed_encrypted_field(:first)
hashed_encrypted_field(:second)
data_encryption_key()
end
Additionally you must implement the Erebus.Encryption
protocol to mark the fields which should be encrypted:
defimpl Erebus.Encryption do
def encrypted_fields(_), do: [:first, :second]
end
Usage with local KMS adapter
- Set the following values in your application config:
config :my_app, :erebus, kms_backend: Erebus.KMS.Local, keys_base_path: "path_to_directory_containing_a_key_pair", private_key_password: "1234"
- Generate asymmetric key pairs (named
public.pem
andprivate.pem
) in the folder atkeys_base_path
.
Usage with Google KMS adapter
- Include Goth in your application:
{:goth, "~> 1.3.0-rc.2"}
- Start Goth in your
application.ex
:credentials = "GCP_KMS_CREDENTIALS_PATH" |> System.fetch_env!() |> File.read!() |> Jason.decode!() scopes = ["https://www.googleapis.com/auth/cloudkms"] source = {:service_account, credentials, scopes: scopes} children = [ {Goth, name: MyApp.Goth, source: source} ]
- Pass the app's
name
in thegoogle_goth
option to Erebus:config :my_app, :erebus, kms_backend: Erebus.KMS.Google, google_project: "someproject", google_region: "someregion", google_keyring: "some_keyring", google_goth: MyApp.Goth
Please note that if you're using Google KMS, your key must have access to the following roles:
Ecto usage full example
defmodule EncryptedStuff do
use Ecto.Schema
import Ecto.Changeset
use Erebus.Schema
embedded_schema do
hashed_encrypted_field(:first)
hashed_encrypted_field(:second)
data_encryption_key()
field(:other, :string)
end
def changeset(stuff, attrs) do
changes =
stuff
|> cast(attrs, [
:first,
:second
])
encrypted_data =
changes
|> MyApp.Erebus.encrypt("handle", 1)
Ecto.Changeset.change(changes, encrypted_data)
end
defimpl Erebus.Encryption do
def encrypted_fields(_), do: [:first, :second]
end
end
If you don't need multiple encryption keys, provide at hard-coded in MyApp.Erebus
.
Currently Erebus only supports encoding and decoding data using Ecto changeset.