# devolutions-crypto
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Cryptographic library used in Devolutions products. It is made to be fast, easy to use and misuse-resistant.
[![crates.io](https://img.shields.io/crates/v/devolutions-crypto.svg)](https://crates.io/crates/devolutions-crypto) 
[Documentation](https://docs.rs/devolutions-crypto/)

# Usage
* [Overview](#overview)
* [Ciphertext Module](#ciphertext)
    * [Symmetric Encryption](#symmetric)
    * [Asymmetric Encryption](#asymmetric)
* [Key Module](#key)
    * [Key Generation/Derivation](#generationderivation)
    * [Key Exchange](#key-exchange)
* [PasswordHash Module](#passwordhash)
* [SecretSharing Module](#secretsharing)
* [Signature Module](#signature)
    * [Generating Key Pairs](#generating-key-pairs)
    * [Signing data](#signing-data)
    * [Signature Verification](#verifying-the-signature)
* [Utils Module](#utils)
    * [Key Generation](#key-generation)
    * [Key Derivation](#key-derivation)

## Overview

The library is splitted into multiple modules, which are explained below. When
dealing with "managed" data, that includes an header and versionning, you deal
with structures like `Ciphertext`, `PublicKey`, etc. 

These all implements `TryFrom<&[u8]>` and `Into<Vec<u8>>` which are the implemented way to serialize and deserialize data.

```rust
use std::convert::TryFrom as _;
use devolutions_crypto::utils::generate_key;
use devolutions_crypto::ciphertext::{ encrypt, CiphertextVersion, Ciphertext };

let key: Vec<u8> = generate_key(32);

let data = b"somesecretdata";

let encrypted_data: Ciphertext = encrypt(data, &key, CiphertextVersion::Latest).expect("encryption shouldn't fail");

// The ciphertext can be serialized.
let encrypted_data_vec: Vec<u8> = encrypted_data.into();

// This data can be saved somewhere, passed to another language or over the network
// ...
// When you receive the data as a byte array, you can deserialize it into a struct using TryFrom

let ciphertext = Ciphertext::try_from(encrypted_data_vec.as_slice()).expect("deserialization shouldn't fail");

let decrypted_data = ciphertext.decrypt(&key).expect("The decryption shouldn't fail");

assert_eq!(decrypted_data, data);
```

## Ciphertext

This module contains everything related to encryption. You can use it to encrypt and decrypt data using either a shared key of a keypair.  
Either way, the encryption will give you a `Ciphertext`, which has a method to decrypt it. 

### Symmetric

```rust
use devolutions_crypto::utils::generate_key;
use devolutions_crypto::ciphertext::{ encrypt, CiphertextVersion, Ciphertext };

let key: Vec<u8> = generate_key(32);

let data = b"somesecretdata";

let encrypted_data: Ciphertext = encrypt(data, &key, CiphertextVersion::Latest).expect("encryption shouldn't fail");

let decrypted_data = encrypted_data.decrypt(&key).expect("The decryption shouldn't fail");

assert_eq!(decrypted_data, data);
```

### Asymmetric
Here, you will need a `PublicKey` to encrypt data and the corresponding 
`PrivateKey` to decrypt it. You can generate them by using `generate_keypair` 
in the [Key module](#key).

```rust
use devolutions_crypto::key::{generate_keypair, KeyVersion, KeyPair};
use devolutions_crypto::ciphertext::{ encrypt_asymmetric, CiphertextVersion, Ciphertext };

let keypair: KeyPair = generate_keypair(KeyVersion::Latest);

let data = b"somesecretdata";

let encrypted_data: Ciphertext = encrypt_asymmetric(data, &keypair.public_key, CiphertextVersion::Latest).expect("encryption shouldn't fail");

let decrypted_data = encrypted_data.decrypt_asymmetric(&keypair.private_key).expect("The decryption shouldn't fail");

assert_eq!(decrypted_data, data);
```

## Key

For now, this module only deal with keypairs, as the symmetric keys are not wrapped yet.

### Generation/Derivation

Using `generate_keypair` will generate a random keypair.

Asymmetric keys have two uses. They can be used to [encrypt and decrypt data](##asymmetric) and to perform a [key exchange](#key-exchange).

#### `generate_keypair`
```rust
use devolutions_crypto::key::{generate_keypair, KeyVersion, KeyPair};

let keypair: KeyPair = generate_keypair(KeyVersion::Latest);
```

### Key Exchange

The goal of using a key exchange is to get a shared secret key between
two parties without making it possible for users listening on the conversation
to guess that shared key.
1. Alice and Bob generates a `KeyPair` each.
2. Alice and Bob exchanges their `PublicKey`.
3. Alice mix her `PrivateKey` with Bob's `PublicKey`. This gives her the shared key.
4. Bob mixes his `PrivateKey` with Alice's `PublicKey`. This gives him the shared key.
5. Both Bob and Alice has the same shared key, which they can use for symmetric encryption for further communications.

```rust
use devolutions_crypto::key::{generate_keypair, mix_key_exchange, KeyVersion, KeyPair};

let bob_keypair: KeyPair = generate_keypair(KeyVersion::Latest);
let alice_keypair: KeyPair = generate_keypair(KeyVersion::Latest);

let bob_shared = mix_key_exchange(&bob_keypair.private_key, &alice_keypair.public_key).expect("key exchange should not fail");

let alice_shared = mix_key_exchange(&alice_keypair.private_key, &bob_keypair.public_key).expect("key exchange should not fail");

// They now have a shared secret!
assert_eq!(bob_shared, alice_shared);
```

## PasswordHash
You can use this module to hash a password and validate it afterward. This is the recommended way to verify a user password on login.
```rust
use devolutions_crypto::password_hash::{hash_password, PasswordHashVersion};

let password = b"somesuperstrongpa$$w0rd!";

let hashed_password = hash_password(password, 10000, PasswordHashVersion::Latest);

assert!(hashed_password.verify_password(b"somesuperstrongpa$$w0rd!"));
assert!(!hashed_password.verify_password(b"someweakpa$$w0rd!"));
```

## SecretSharing
This module is used to generate a key that is splitted in multiple `Share`
and that requires a specific amount of them to regenerate the key.  
You can think of it as a "Break The Glass" scenario. You can
generate a key using this, lock your entire data by encrypting it
and then you will need, let's say, 3 out of the 5 administrators to decrypt
the data. That data could also be an API key or password of a super admin account.

```rust
use devolutions_crypto::secret_sharing::{generate_shared_key, join_shares, SecretSharingVersion, Share};

// You want a key of 32 bytes, splitted between 5 people, and I want a 
// minimum of 3 of these shares to regenerate the key.
let shares: Vec<Share> = generate_shared_key(5, 3, 32, SecretSharingVersion::Latest).expect("generation shouldn't fail with the right parameters");

assert_eq!(shares.len(), 5);
let key = join_shares(&shares[2..5]).expect("joining shouldn't fail with the right shares");
```

## Signature
This module is used to sign data using a keypair to certify its authenticity. 

###  Generating Key Pairs
```rust
use devolutions_crypto::signing_key::{generate_signing_keypair, SigningKeyVersion, SigningKeyPair, SigningPublicKey};

let keypair: SigningKeyPair = generate_signing_keypair(SigningKeyVersion::Latest);
```
### Signing Data
```rust
use devolutions_crypto::signature::{sign, Signature, SignatureVersion};

let signature: Signature = sign(b"this is some test data", &keypair, SignatureVersion::Latest);
```

### Verifying the signature
```rust
use devolutions_crypto::signature::{sign, Signature, SignatureVersion};

assert!(signature.verify(b"this is some test data", &public_key));
```

## Utils

These are a bunch of functions that can
be useful when dealing with the library.

### Key Generation

This is a method used to generate a random key. In almost all case, the `length` parameter should be 32.

```rust
use devolutions_crypto::utils::generate_key;

let key = generate_key(32);
assert_eq!(32, key.len());
```

### Key Derivation

This is a method used to generate a key from a password or another key. Useful for password-dependant cryptography. Salt should be a random 16 bytes array if possible and iterations should be 10000 or configurable by the user.

```rust
use devolutions_crypto::utils::{generate_key, derive_key};
let key = b"this is a secret password";
let salt = generate_key(16);
let iterations = 10000;
let length = 32;

let new_key = derive_key(key, &salt, iterations, length);

assert_eq!(32, new_key.len());
```

# Underlying algorithms
As of the current version:
 * Symmetric cryptography uses XChaCha20Poly1305
 * Asymmetric cryptography uses Curve25519.
 * Asymmetric encryption uses ECIES.
 * Key exchange uses x25519, or ECDH over Curve25519
 * Password Hashing uses PBKDF2-HMAC-SHA2-256
 * Secret Sharing uses Shamir Secret sharing over GF256