Cocoon

Cocoon is a protected container to wrap sensitive data with strong encryption and format validation. A format of Cocoon is developed for the following practical cases:

1. As a file format to organize simple secure storage:
   1. Key store.
   2. Password store.
   3. Sensitive data store.
2. For encrypted data transfer:
   • As a secure in-memory container.

Cocoon is developed with security in mind. It aims to do the only one thing and do it flawlessly. It has a minimal set of dependencies and a minimalist design to simplify control over security aspects. It's a pure Rust implementation, and all dependencies are pure Rust packages with disabled default features.

Problem

Whenever you need secure storage you reinvent the wheel: you have to take care of how to encrypt data properly, how to store and transmit randomly generated buffers, then to get data back, parse, and decrypt securely. Instead, you can use Cocoon.

Basic Usage

📌 Wrap/Unwrap

One party wraps private data into a container using Cocoon::wrap. Another party (or the same one, or whoever knows the password) unwraps a private data out of the container using Cocoon::unwrap.

let cocoon = Cocoon::new(b"password");

let wrapped = cocoon.wrap(b"my secret data")?;
assert_ne!(&wrapped, b"my secret data");

let unwrapped = cocoon.unwrap(&wrapped)?;
assert_eq!(unwrapped, b"my secret data");

📌 Dump/Parse

You can store data to file. Put data into Vec container, the data is going to be encrypted in place and stored in a file using the "cocoon" format.

let mut data = b"my secret data".to_vec();
let cocoon = Cocoon::new(b"password");

cocoon.dump(data, &mut file)?;

let data = cocoon.parse(&mut file)?;
assert_eq!(&data, b"my secret data");

📌 Encrypt/Decrypt

You can encrypt data in place and avoid re-allocations. The method operates with a detached meta-data (a container format prefix) in the array on the stack. It is suitable for "no_std" build and whenever you want to evade re-allocations of a huge amount of data. You have to care about how to store and transfer a data length and a container prefix though.

let mut data = "my secret data".to_owned().into_bytes();
let cocoon = Cocoon::from_crypto_rng(b"password", good_rng);

let detached_prefix = cocoon.encrypt(&mut data)?;
assert_ne!(data, b"my secret data");

cocoon.decrypt(&mut data, &detached_prefix)?;
assert_eq!(data, b"my secret data");

Study Case

You implement a database of secrets that must be stored in an encrypted file using a user password. There are a lot of ways how your database can be represented in memory and how it could be serialized. You handle these aspects on your own, e.g. you can use HashMap to manage data and use borsh, or bincode, to serialize the data. You can even compress a serialized buffer before encryption.

In the end, you use Cocoon to put the final image into an encrypted container.

use borsh::BorshSerialize;
use cocoon::{Cocoon, Error};

use std::collections::HashMap;
use std::fs::File;

// Your data can be represented in any way.
#[derive(BorshSerialize)]
struct Database {
    inner: HashMap<String, String>,
}

fn main() -> Result<(), Error> {
    let mut file = File::create("target/test.db")?;
    let mut db = Database { inner: HashMap::new() };

    // Over time you collect some kind of data.
    db.inner.insert("my.email@example.com".to_string(), "eKPV$PM8TV5A2".to_string());

    // You can choose how to serialize data. Also, you can compress it.
    let encoded = db.try_to_vec().unwrap();

    // Finally, you want to store your data secretly.
    // Supply some password to Cocoon: password is any byte array, basically.
    // Don't use a hard-coded password in real life!
    // It could be a user-supplied password.
    let cocoon = Cocoon::new(b"secret password");

    // Dump the serialized database into a file as an encrypted container.
    let container = cocoon.dump(encoded, &mut file)?;

    Ok(())
}

Cryptography

256-bit cryptography is chosen as a Cocoon baseline.

• Key: 256-bit.
• Salt for KDF: random 128-bit + predefined part.
• Nonce for encryption: random 96-bit.

Key derivation parameters comply with NIST SP 800-132 recommendations (salt, iterations), and cipher parameters (key, nonce, length) fit requirements of a particular cipher. AEAD is chosen in order to authenticate encrypted data together with an unencrypted header.

Zeroization

Encryption key is wrapped into zeroizing container (provided by zeroize crate), which means that the key is erased automatically once it is dropped.

How It Works

See more implementation details on , e.g.

1. the process of container creation,
2. customizable crate features,
3. and of course API.