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//! # Key exchange functions
//!
//! [`Session`] implements libsodium's key exchange functions, which use a
//! combination of Curve25519, Diffie-Hellman, and Blake2b to generate shared
//! session keys between two parties who know each other's public keys.
//!
//! You should use [`Session`] when you want to:
//!
//! * derive shared secrets between two parties
//! * use public-key cryptography, but do so with another cipher that only
//! supports pre-shared secrets
//! * create a session key or token that can't be used to derive the original
//! inputs should it become compromised
//!
//! # Rustaceous API example
//!
//! ```
//! use dryoc::kx::*;
//!
//! // Generate random client/server keypairs
//! let client_keypair = KeyPair::gen();
//! let server_keypair = KeyPair::gen();
//!
//! // Compute client session keys, into default stack-allocated byte array
//! let client_session_keys =
//! Session::new_client_with_defaults(&client_keypair, &server_keypair.public_key)
//! .expect("compute client failed");
//!
//! // Compute server session keys, into default stack-allocated byte array
//! let server_session_keys =
//! Session::new_server_with_defaults(&server_keypair, &client_keypair.public_key)
//! .expect("compute client failed");
//!
//! let (client_rx, client_tx) = client_session_keys.into_parts();
//! let (server_rx, server_tx) = server_session_keys.into_parts();
//!
//! // Client Rx should match server Tx keys
//! assert_eq!(client_rx, server_tx);
//! // Client Tx should match server Rx keys
//! assert_eq!(client_tx, server_rx);
//! ```
//!
//! ## Additional resources
//!
//! * See <https://doc.libsodium.org/key_exchange> for additional details on key
//! exchange
#[cfg(feature = "serde")]
use serde::{Deserialize, Serialize};
use zeroize::Zeroize;
use crate::classic::crypto_kx::{crypto_kx_client_session_keys, crypto_kx_server_session_keys};
use crate::constants::{
CRYPTO_KX_PUBLICKEYBYTES, CRYPTO_KX_SECRETKEYBYTES, CRYPTO_KX_SESSIONKEYBYTES,
};
use crate::error::Error;
use crate::types::*;
/// Stack-allocated session key type alias
pub type SessionKey = StackByteArray<CRYPTO_KX_SESSIONKEYBYTES>;
/// Stack-allocated public key type alias
pub type PublicKey = StackByteArray<CRYPTO_KX_PUBLICKEYBYTES>;
/// Stack-allocated secret key type alias
pub type SecretKey = StackByteArray<CRYPTO_KX_SECRETKEYBYTES>;
/// Stack-allocated keypair type alias
pub type KeyPair = crate::keypair::KeyPair<PublicKey, SecretKey>;
#[cfg_attr(
feature = "serde",
derive(Zeroize, Clone, Debug, Serialize, Deserialize)
)]
#[cfg_attr(not(feature = "serde"), derive(Zeroize, Clone, Debug))]
/// Key derivation implemantation based on Curve25519, Diffie-Hellman, and
/// Blake2b. Compatible with libsodium's `crypto_kx_*` functions.
pub struct Session<SessionKey: ByteArray<CRYPTO_KX_SESSIONKEYBYTES> + Zeroize> {
rx_key: SessionKey,
tx_key: SessionKey,
}
/// Stack-allocated type alias for [`Session`]. Provided for convenience.
pub type StackSession = Session<SessionKey>;
#[cfg(any(feature = "nightly", all(doc, not(doctest))))]
#[cfg_attr(all(feature = "nightly", doc), doc(cfg(feature = "nightly")))]
pub mod protected {
//! # Protected memory type aliases for [`Session`]
//!
//! This mod provides re-exports of type aliases for protected memory usage
//! with [`Session`]. These type aliases are provided for
//! convenience.
//!
//! ## Example
//!
//! ```
//! use dryoc::kx::protected::*;
//! use dryoc::kx::Session;
//!
//! // Generate random client/server keypairs
//! let client_keypair =
//! LockedROKeyPair::gen_readonly_locked_keypair().expect("couldn't generate client keypair");
//! let server_keypair =
//! LockedROKeyPair::gen_readonly_locked_keypair().expect("couldn't generate server keypair");
//!
//! // Compute client session keys, into default stack-allocated byte array
//! let client_session_keys: LockedSession =
//! Session::new_client(&client_keypair, &server_keypair.public_key)
//! .expect("compute client failed");
//!
//! // Compute server session keys, into default stack-allocated byte array
//! let server_session_keys: LockedSession =
//! Session::new_server(&server_keypair, &client_keypair.public_key)
//! .expect("compute client failed");
//!
//! let (client_rx, client_tx) = client_session_keys.into_parts();
//! let (server_rx, server_tx) = server_session_keys.into_parts();
//!
//! // Client Rx should match server Tx keys
//! assert_eq!(client_rx.as_slice(), server_tx.as_slice());
//! // Client Tx should match server Rx keys
//! assert_eq!(client_tx.as_slice(), server_rx.as_slice());
//! ```
use super::*;
pub use crate::keypair::protected::*;
pub use crate::protected::*;
pub use crate::types::*;
/// Heap-allocated, paged-aligned session key type alias for use with
/// protected memory
pub type SessionKey = HeapByteArray<CRYPTO_KX_SESSIONKEYBYTES>;
/// Heap-allocated, paged-aligned public key type alias for use with
/// protected memory
pub type PublicKey = HeapByteArray<CRYPTO_KX_PUBLICKEYBYTES>;
/// Heap-allocated, paged-aligned secret key type alias for use with
/// protected memory
pub type SecretKey = HeapByteArray<CRYPTO_KX_SECRETKEYBYTES>;
/// Heap-allocated, paged-aligned keypair type alias for use with
/// protected memory
pub type LockedKeyPair = crate::keypair::KeyPair<Locked<PublicKey>, Locked<SecretKey>>;
/// Heap-allocated, paged-aligned keypair type alias for use with
/// protected memory
pub type LockedROKeyPair = crate::keypair::KeyPair<LockedRO<PublicKey>, LockedRO<SecretKey>>;
/// Locked session keys type alias, for use with protected memory
pub type LockedSession = Session<Locked<SessionKey>>;
}
impl<SessionKey: NewByteArray<CRYPTO_KX_SESSIONKEYBYTES> + Zeroize> Session<SessionKey> {
/// Computes client session keys, given `client_keypair` and
/// `server_public_key`, returning a new session upon success.
pub fn new_client<
PublicKey: ByteArray<CRYPTO_KX_PUBLICKEYBYTES> + Zeroize,
SecretKey: ByteArray<CRYPTO_KX_SECRETKEYBYTES> + Zeroize,
>(
client_keypair: &crate::keypair::KeyPair<PublicKey, SecretKey>,
server_public_key: &PublicKey,
) -> Result<Self, Error> {
let mut rx_key = SessionKey::new_byte_array();
let mut tx_key = SessionKey::new_byte_array();
crypto_kx_client_session_keys(
rx_key.as_mut_array(),
tx_key.as_mut_array(),
client_keypair.public_key.as_array(),
client_keypair.secret_key.as_array(),
server_public_key.as_array(),
)?;
Ok(Self { rx_key, tx_key })
}
/// Computes server session keys, given `server_keypair` and
/// `client_public_key`, returning a new session upon success.
pub fn new_server<
PublicKey: ByteArray<CRYPTO_KX_PUBLICKEYBYTES> + Zeroize,
SecretKey: ByteArray<CRYPTO_KX_SECRETKEYBYTES> + Zeroize,
>(
server_keypair: &crate::keypair::KeyPair<PublicKey, SecretKey>,
client_public_key: &PublicKey,
) -> Result<Self, Error> {
let mut rx_key = SessionKey::new_byte_array();
let mut tx_key = SessionKey::new_byte_array();
crypto_kx_server_session_keys(
rx_key.as_mut_array(),
tx_key.as_mut_array(),
server_keypair.public_key.as_array(),
server_keypair.secret_key.as_array(),
client_public_key.as_array(),
)?;
Ok(Self { rx_key, tx_key })
}
}
impl Session<SessionKey> {
/// Returns a new client session upon success using the default types for
/// the given `client_keypair` and `server_public_key`. Wraps
/// [`Session::new_client`], provided for convenience.
pub fn new_client_with_defaults<
PublicKey: ByteArray<CRYPTO_KX_PUBLICKEYBYTES> + Zeroize,
SecretKey: ByteArray<CRYPTO_KX_SECRETKEYBYTES> + Zeroize,
>(
client_keypair: &crate::keypair::KeyPair<PublicKey, SecretKey>,
server_public_key: &PublicKey,
) -> Result<Self, Error> {
Self::new_client(client_keypair, server_public_key)
}
/// Returns a new server session upon success using the default types for
/// the given `server_keypair` and `client_public_key`. Wraps
/// [`Session::new_server`], provided for convenience.
pub fn new_server_with_defaults<
PublicKey: ByteArray<CRYPTO_KX_PUBLICKEYBYTES> + Zeroize,
SecretKey: ByteArray<CRYPTO_KX_SECRETKEYBYTES> + Zeroize,
>(
server_keypair: &crate::keypair::KeyPair<PublicKey, SecretKey>,
client_public_key: &PublicKey,
) -> Result<Self, Error> {
Self::new_server(server_keypair, client_public_key)
}
}
impl<SessionKey: ByteArray<CRYPTO_KX_SESSIONKEYBYTES> + Zeroize> Session<SessionKey> {
/// Moves the rx_key and tx_key out of this instance, returning them as a
/// tuple with `(rx_key, tx_key)`.
pub fn into_parts(self) -> (SessionKey, SessionKey) {
(self.rx_key, self.tx_key)
}
/// Returns a reference to a slice of the Rx session key.
#[inline]
pub fn rx_as_slice(&self) -> &[u8] {
self.rx_key.as_slice()
}
/// Returns a reference to a slice of the Tx session key.
#[inline]
pub fn tx_as_slice(&self) -> &[u8] {
self.tx_key.as_slice()
}
/// Returns a reference to an array of the Rx session key.
#[inline]
pub fn rx_as_array(&self) -> &[u8; CRYPTO_KX_SESSIONKEYBYTES] {
self.rx_key.as_array()
}
/// Returns a reference to an array of the Tx session key.
#[inline]
pub fn tx_as_array(&self) -> &[u8; CRYPTO_KX_SESSIONKEYBYTES] {
self.tx_key.as_array()
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_kx() {
let client_keypair = KeyPair::gen();
let server_keypair = KeyPair::gen();
let client_session_keys =
Session::new_client_with_defaults(&client_keypair, &server_keypair.public_key)
.expect("compute client failed");
let server_session_keys =
Session::new_server_with_defaults(&server_keypair, &client_keypair.public_key)
.expect("compute client failed");
let (client_rx, client_tx) = client_session_keys.into_parts();
let (server_rx, server_tx) = server_session_keys.into_parts();
assert_eq!(client_rx, server_tx);
assert_eq!(client_tx, server_rx);
}
}