# Erebus
[](https://github.com/venndr/erebus/actions/workflows/elixir.yml)
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`:
```elixir
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:
```elixir
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:
```elixir
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](https://hex.pm/packages/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:
```elixir
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:
```elixir
defimpl Erebus.Encryption do
def encrypted_fields(_), do: [:first, :second]
end
```
### Usage with local KMS adapter
1. Set the following values in your application config:
```elixir
config :my_app, :erebus,
kms_backend: Erebus.KMS.Local,
keys_base_path: "path_to_directory_containing_a_key_pair",
private_key_password: "1234"
```
2. Generate asymmetric key pairs (named `public.pem` and `private.pem`) in the folder at `keys_base_path`.
### Usage with Google KMS adapter
1. Include [Goth](https://hex.pm/packages/goth) in your application:
```elixir
{:goth, "~> 1.3.0-rc.2"}
```
2. Start Goth in your `application.ex`:
```elixir
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}
]
```
3. Pass the app's `name` in the `google_goth` option to Erebus:
```elixir
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:
- [Cloud KMS CryptoKey Encrypter](https://cloud.google.com/kms/docs/reference/permissions-and-roles#cloudkms.cryptoKeyEncrypter)
- [Cloud KMS CryptoKey Decrypter](https://cloud.google.com/kms/docs/reference/permissions-and-roles#cloudkms.cryptoKeyDecrypter)
- [Cloud KMS CryptoKey Public Key Viewer](https://cloud.google.com/kms/docs/reference/permissions-and-roles#cloudkms.publicKeyViewer)
### Ecto usage full example
```elixir
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.
## Licence
ISC License
Copyright (c) 2024 Music Glue
Permission to use, copy, modify, and/or distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.
THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.
A copy of the licence text is also included in the file LICENSE
