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//! Pure Rust implementation of the [`crypto_box`] public-key authenticated //! encryption scheme from [NaCl]-family libraries (e.g. libsodium, TweetNaCl) //! which combines the [X25519] Diffie-Hellman function and the //! [XSalsa20Poly1305] authenticated encryption cipher into an Elliptic Curve //! Integrated Encryption Scheme ([ECIES]). //! //! # Introduction //! //! Imagine Alice wants something valuable shipped to her. Because it's //! valuable, she wants to make sure it arrives securely (i.e. hasn't been //! opened or tampered with) and that it's not a forgery (i.e. it's actually //! from the sender she's expecting it to be from and nobody's pulling the old //! switcheroo). //! //! One way she can do this is by providing the sender (let's call him Bob) //! with a high-security box of her choosing. She provides Bob with this box, //! and something else: a padlock, but a padlock without a key. Alice is //! keeping that key all to herself. Bob can put items in the box then put the //! padlock onto it, but once the padlock snaps shut, the box cannot be opened //! by anyone who doesn't have Alice's private key. //! //! Here's the twist though, Bob also puts a padlock onto the box. This padlock //! uses a key Bob has published to the world, such that if you have one of //! Bob's keys, you know a box came from him because Bob's keys will open Bob's //! padlocks (let's imagine a world where padlocks cannot be forged even if you //! know the key). Bob then sends the box to Alice. //! //! In order for Alice to open the box, she needs two keys: her private key //! that opens her own padlock, and Bob's well-known key. If Bob's key doesn't //! open the second padlock then Alice knows that this is not the box she was //! expecting from Bob, it's a forgery. //! //! # Usage //! //! ```rust //! use crypto_box::{Box, PublicKey, SecretKey, aead::Aead}; //! //! // //! // Encryption //! // //! //! // Generate a random secret key. //! // NOTE: It can be serialized as bytes by calling `secret_key.to_bytes()` //! let mut rng = rand::thread_rng(); //! let alice_secret_key = SecretKey::generate(&mut rng); //! //! // Get the public key for the secret key we just generated //! let alice_public_key_bytes = alice_secret_key.public_key().as_bytes().clone(); //! //! // Obtain your recipient's public key. //! let bob_public_key = PublicKey::from([ //! 0xe8, 0x98, 0xc, 0x86, 0xe0, 0x32, 0xf1, 0xeb, //! 0x29, 0x75, 0x5, 0x2e, 0x8d, 0x65, 0xbd, 0xdd, //! 0x15, 0xc3, 0xb5, 0x96, 0x41, 0x17, 0x4e, 0xc9, //! 0x67, 0x8a, 0x53, 0x78, 0x9d, 0x92, 0xc7, 0x54, //! ]); //! //! // Create a `Box` by performing Diffie-Hellman key agreement between //! // the two keys. //! let alice_box = Box::new(&bob_public_key, &alice_secret_key); //! //! // Get a random nonce to encrypt the message under //! let nonce = crypto_box::generate_nonce(&mut rng); //! //! // Message to encrypt //! let plaintext = b"Top secret message we're encrypting"; //! //! // Encrypt the message using the box //! let ciphertext = alice_box.encrypt(&nonce, &plaintext[..]).unwrap(); //! //! // //! // Decryption //! // //! //! // Either side can encrypt or decrypt messages under the Diffie-Hellman key //! // they agree upon. The example below shows Bob's side. //! let bob_secret_key = SecretKey::from([ //! 0xb5, 0x81, 0xfb, 0x5a, 0xe1, 0x82, 0xa1, 0x6f, //! 0x60, 0x3f, 0x39, 0x27, 0xd, 0x4e, 0x3b, 0x95, //! 0xbc, 0x0, 0x83, 0x10, 0xb7, 0x27, 0xa1, 0x1d, //! 0xd4, 0xe7, 0x84, 0xa0, 0x4, 0x4d, 0x46, 0x1b //! ]); //! //! // Deserialize Alice's public key from bytes //! let alice_public_key = PublicKey::from(alice_public_key_bytes); //! //! // Bob can compute the same Box as Alice by performing the reciprocal //! // key exchange operation. //! let bob_box = Box::new(&alice_public_key, &bob_secret_key); //! //! // Decrypt the message, using the same randomly generated nonce //! let decrypted_plaintext = bob_box.decrypt(&nonce, &ciphertext[..]).unwrap(); //! //! assert_eq!(&plaintext[..], &decrypted_plaintext[..]); //! ``` //! //! ## In-place Usage (eliminates `alloc` requirement) //! //! This crate has an optional `alloc` feature which can be disabled in e.g. //! microcontroller environments that don't have a heap. //! //! The [`Aead::encrypt_in_place`] and [`Aead::decrypt_in_place`] //! methods accept any type that impls the [`aead::Buffer`] trait which //! contains the plaintext for encryption or ciphertext for decryption. //! //! Note that if you enable the `heapless` feature of this crate, //! you will receive an impl of `aead::Buffer` for [`heapless::Vec`] //! (re-exported from the `aead` crate as `aead::heapless::Vec`), //! which can then be passed as the `buffer` parameter to the in-place encrypt //! and decrypt methods. //! //! A `heapless` usage example can be found in the documentation for the //! `xsalsa20poly1305` crate: //! //! <https://docs.rs/xsalsa20poly1305/latest/xsalsa20poly1305/#in-place-usage-eliminates-alloc-requirement> //! //! [NaCl]: https://nacl.cr.yp.to/ //! [`crypto_box`]: https://nacl.cr.yp.to/box.html //! [X25519]: https://cr.yp.to/ecdh.html //! [XSalsa20Poly1305]: https://nacl.cr.yp.to/secretbox.html //! [ECIES]: https://en.wikipedia.org/wiki/Integrated_Encryption_Scheme //! [`heapless::Vec`]: https://docs.rs/heapless/latest/heapless/struct.Vec.html #![no_std] #![doc(html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo_small.png")] #![warn(missing_docs, rust_2018_idioms)] pub use x25519_dalek::PublicKey; pub use xsalsa20poly1305::aead; use aead::generic_array::{ typenum::{U0, U16, U24}, GenericArray, }; use aead::{Aead, Buffer, Error, NewAead}; use core::fmt::{self, Debug}; use rand_core::{CryptoRng, RngCore}; use salsa20::hsalsa20; use xsalsa20poly1305::{Tag, XSalsa20Poly1305}; /// Size of a `crypto_box` public or secret key in bytes. pub const KEY_SIZE: usize = 32; /// Generate a random nonce: every message MUST have a unique nonce! /// /// Do *NOT* ever reuse the same nonce for two messages! pub fn generate_nonce<T>(csprng: &mut T) -> GenericArray<u8, U24> where T: RngCore + CryptoRng, { let mut nonce = GenericArray::default(); csprng.fill_bytes(&mut nonce); nonce } /// `crypto_box` secret key #[derive(Clone)] pub struct SecretKey(x25519_dalek::StaticSecret); impl SecretKey { /// Generate a random [`SecretKey`]. pub fn generate<T>(csprng: &mut T) -> Self where T: RngCore + CryptoRng, { SecretKey(x25519_dalek::StaticSecret::new(csprng)) } /// Get the [`PublicKey`] which corresponds to this [`SecretKey`] pub fn public_key(&self) -> PublicKey { self.into() } /// Get the serialized bytes for this [`SecretKey`] pub fn to_bytes(&self) -> [u8; KEY_SIZE] { self.0.to_bytes() } } impl From<[u8; KEY_SIZE]> for SecretKey { fn from(bytes: [u8; KEY_SIZE]) -> SecretKey { SecretKey(bytes.into()) } } impl Debug for SecretKey { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { f.write_str("SecretKey(...)") } } impl From<&SecretKey> for PublicKey { fn from(secret_key: &SecretKey) -> PublicKey { PublicKey::from(&secret_key.0) } } /// Alias for [`SalsaBox`]. pub type Box = SalsaBox; /// Public-key encryption scheme based on the [X25519] Elliptic Curve /// Diffie-Hellman function and the [XSalsa20Poly1305] authenticated encryption /// cipher. /// /// This type impls the [`aead::Aead`] trait, and otherwise functions as a /// symmetric Authenticated Encryption with Associated Data (AEAD) cipher /// once instantiated. /// /// [X25519]: https://cr.yp.to/ecdh.html /// [XSalsa20Poly1305]: https://github.com/RustCrypto/AEADs/tree/master/xsalsa20poly1305 pub struct SalsaBox(XSalsa20Poly1305); impl SalsaBox { /// Create a new [`SalsaBox`], performing X25519 Diffie-Hellman to derive /// a shared secret from the provided public and secret keys. pub fn new(public_key: &PublicKey, secret_key: &SecretKey) -> Self { let shared_secret = secret_key.0.diffie_hellman(public_key); // Use HSalsa20 to create a uniformly random key from the shared secret let key = hsalsa20( &GenericArray::clone_from_slice(shared_secret.as_bytes()), &GenericArray::default(), ); SalsaBox(XSalsa20Poly1305::new(key)) } } impl Aead for SalsaBox { type NonceSize = U24; type TagSize = U16; type CiphertextOverhead = U0; fn encrypt_in_place( &self, nonce: &GenericArray<u8, Self::NonceSize>, associated_data: &[u8], buffer: &mut impl Buffer, ) -> Result<(), Error> { self.0.encrypt_in_place(nonce, associated_data, buffer) } fn encrypt_in_place_detached( &self, nonce: &GenericArray<u8, Self::NonceSize>, associated_data: &[u8], buffer: &mut [u8], ) -> Result<Tag, Error> { self.0 .encrypt_in_place_detached(nonce, associated_data, buffer) } fn decrypt_in_place( &self, nonce: &GenericArray<u8, Self::NonceSize>, associated_data: &[u8], buffer: &mut impl Buffer, ) -> Result<(), Error> { self.0.decrypt_in_place(nonce, associated_data, buffer) } fn decrypt_in_place_detached( &self, nonce: &GenericArray<u8, Self::NonceSize>, associated_data: &[u8], buffer: &mut [u8], tag: &Tag, ) -> Result<(), Error> { self.0 .decrypt_in_place_detached(nonce, associated_data, buffer, tag) } }