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use std::convert::TryFrom;
const SIGNING_KEY_LEN: usize = 32;
const ENCRYPTION_KEY_LEN: usize = 32;
const COMBINED_KEY_LENGTH: usize = SIGNING_KEY_LEN + ENCRYPTION_KEY_LEN;
// Statically ensure the numbers above are in-sync.
#[cfg(feature = "signed")]
const_assert!(crate::secure::signed::KEY_LEN == SIGNING_KEY_LEN);
#[cfg(feature = "private")]
const_assert!(crate::secure::private::KEY_LEN == ENCRYPTION_KEY_LEN);
/// A cryptographic master key for use with `Signed` and/or `Private` jars.
///
/// This structure encapsulates secure, cryptographic keys for use with both
/// [`PrivateJar`](crate::PrivateJar) and [`SignedJar`](crate::SignedJar). A
/// single instance of a `Key` can be used for both a `PrivateJar` and a
/// `SignedJar` simultaneously with no notable security implications.
#[cfg_attr(all(nightly, doc), doc(cfg(any(feature = "private", feature = "signed"))))]
#[derive(Clone)]
pub struct Key([u8; COMBINED_KEY_LENGTH /* SIGNING | ENCRYPTION */]);
impl PartialEq for Key {
fn eq(&self, other: &Self) -> bool {
use subtle::ConstantTimeEq;
self.0.ct_eq(&other.0).into()
}
}
impl Key {
// An empty key structure, to be filled.
const fn zero() -> Self {
Key([0; COMBINED_KEY_LENGTH])
}
/// Creates a new `Key` from a 512-bit cryptographically random string.
///
/// The supplied key must be at least 512-bits (64 bytes). For security, the
/// master key _must_ be cryptographically random.
///
/// # Panics
///
/// Panics if `key` is less than 64 bytes in length.
///
/// For a non-panicking version, use [`Key::try_from()`] or generate a key with
/// [`Key::generate()`] or [`Key::try_generate()`].
///
/// # Example
///
/// ```rust
/// use cookie::Key;
///
/// # /*
/// let key = { /* a cryptographically random key >= 64 bytes */ };
/// # */
/// # let key: &Vec<u8> = &(0..64).collect();
///
/// let key = Key::from(key);
/// ```
#[inline]
pub fn from(key: &[u8]) -> Key {
Key::try_from(key).unwrap()
}
/// Derives new signing/encryption keys from a master key.
///
/// The master key must be at least 256-bits (32 bytes). For security, the
/// master key _must_ be cryptographically random. The keys are derived
/// deterministically from the master key.
///
/// # Panics
///
/// Panics if `key` is less than 32 bytes in length.
///
/// # Example
///
/// ```rust
/// use cookie::Key;
///
/// # /*
/// let master_key = { /* a cryptographically random key >= 32 bytes */ };
/// # */
/// # let master_key: &Vec<u8> = &(0..32).collect();
///
/// let key = Key::derive_from(master_key);
/// ```
#[cfg(feature = "key-expansion")]
#[cfg_attr(all(nightly, doc), doc(cfg(feature = "key-expansion")))]
pub fn derive_from(master_key: &[u8]) -> Self {
if master_key.len() < 32 {
panic!("bad master key length: expected >= 32 bytes, found {}", master_key.len());
}
// Expand the master key into two HKDF generated keys.
const KEYS_INFO: &[u8] = b"COOKIE;SIGNED:HMAC-SHA256;PRIVATE:AEAD-AES-256-GCM";
let mut both_keys = [0; COMBINED_KEY_LENGTH];
let hk = hkdf::Hkdf::<sha2::Sha256>::from_prk(master_key).expect("key length prechecked");
hk.expand(KEYS_INFO, &mut both_keys).expect("expand into keys");
Key::from(&both_keys)
}
/// Generates signing/encryption keys from a secure, random source. Keys are
/// generated nondeterministically.
///
/// # Panics
///
/// Panics if randomness cannot be retrieved from the operating system. See
/// [`Key::try_generate()`] for a non-panicking version.
///
/// # Example
///
/// ```rust
/// use cookie::Key;
///
/// let key = Key::generate();
/// ```
pub fn generate() -> Key {
Self::try_generate().expect("failed to generate `Key` from randomness")
}
/// Attempts to generate signing/encryption keys from a secure, random
/// source. Keys are generated nondeterministically. If randomness cannot be
/// retrieved from the underlying operating system, returns `None`.
///
/// # Example
///
/// ```rust
/// use cookie::Key;
///
/// let key = Key::try_generate();
/// ```
pub fn try_generate() -> Option<Key> {
use crate::secure::rand::RngCore;
let mut rng = crate::secure::rand::thread_rng();
let mut key = Key::zero();
rng.try_fill_bytes(&mut key.0).ok()?;
Some(key)
}
/// Returns the raw bytes of a key suitable for signing cookies. Guaranteed
/// to be at least 32 bytes.
///
/// # Example
///
/// ```rust
/// use cookie::Key;
///
/// let key = Key::generate();
/// let signing_key = key.signing();
/// ```
pub fn signing(&self) -> &[u8] {
&self.0[..SIGNING_KEY_LEN]
}
/// Returns the raw bytes of a key suitable for encrypting cookies.
/// Guaranteed to be at least 32 bytes.
///
/// # Example
///
/// ```rust
/// use cookie::Key;
///
/// let key = Key::generate();
/// let encryption_key = key.encryption();
/// ```
pub fn encryption(&self) -> &[u8] {
&self.0[SIGNING_KEY_LEN..]
}
/// Returns the raw bytes of the master key. Guaranteed to be at least 64
/// bytes.
///
/// # Example
///
/// ```rust
/// use cookie::Key;
///
/// let key = Key::generate();
/// let master_key = key.master();
/// ```
pub fn master(&self) -> &[u8] {
&self.0
}
}
/// An error indicating an issue with generating or constructing a key.
#[cfg_attr(all(nightly, doc), doc(cfg(any(feature = "private", feature = "signed"))))]
#[derive(Debug)]
#[non_exhaustive]
pub enum KeyError {
/// Too few bytes (`.0`) were provided to generate a key.
///
/// See [`Key::from()`] for minimum requirements.
TooShort(usize),
}
impl std::error::Error for KeyError { }
impl std::fmt::Display for KeyError {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
KeyError::TooShort(n) => {
write!(f, "key material is too short: expected >= {} bytes, got {} bytes",
COMBINED_KEY_LENGTH, n)
}
}
}
}
impl TryFrom<&[u8]> for Key {
type Error = KeyError;
/// A fallible version of [`Key::from()`].
///
/// Succeeds when [`Key::from()`] succeds and returns an error where
/// [`Key::from()`] panics, namely, if `key` is too short.
///
/// # Example
///
/// ```rust
/// # use std::convert::TryFrom;
/// use cookie::Key;
///
/// # /*
/// let key = { /* a cryptographically random key >= 64 bytes */ };
/// # */
/// # let key: &Vec<u8> = &(0..64).collect();
/// # let key: &[u8] = &key[..];
/// assert!(Key::try_from(key).is_ok());
///
/// // A key that's far too short to use.
/// let key = &[1, 2, 3, 4][..];
/// assert!(Key::try_from(key).is_err());
/// ```
fn try_from(key: &[u8]) -> Result<Self, Self::Error> {
if key.len() < COMBINED_KEY_LENGTH {
Err(KeyError::TooShort(key.len()))
} else {
let mut output = Key::zero();
output.0.copy_from_slice(&key[..COMBINED_KEY_LENGTH]);
Ok(output)
}
}
}
#[cfg(test)]
mod test {
use super::Key;
#[test]
fn from_works() {
let key = Key::from(&(0..64).collect::<Vec<_>>());
let signing: Vec<u8> = (0..32).collect();
assert_eq!(key.signing(), &*signing);
let encryption: Vec<u8> = (32..64).collect();
assert_eq!(key.encryption(), &*encryption);
}
#[test]
fn try_from_works() {
use core::convert::TryInto;
let data = (0..64).collect::<Vec<_>>();
let key_res: Result<Key, _> = data[0..63].try_into();
assert!(key_res.is_err());
let key_res: Result<Key, _> = data.as_slice().try_into();
assert!(key_res.is_ok());
}
#[test]
#[cfg(feature = "key-expansion")]
fn deterministic_derive() {
let master_key: Vec<u8> = (0..32).collect();
let key_a = Key::derive_from(&master_key);
let key_b = Key::derive_from(&master_key);
assert_eq!(key_a.signing(), key_b.signing());
assert_eq!(key_a.encryption(), key_b.encryption());
assert_ne!(key_a.encryption(), key_a.signing());
let master_key_2: Vec<u8> = (32..64).collect();
let key_2 = Key::derive_from(&master_key_2);
assert_ne!(key_2.signing(), key_a.signing());
assert_ne!(key_2.encryption(), key_a.encryption());
}
#[test]
fn non_deterministic_generate() {
let key_a = Key::generate();
let key_b = Key::generate();
assert_ne!(key_a.signing(), key_b.signing());
assert_ne!(key_a.encryption(), key_b.encryption());
}
}