use curve25519_dalek::constants::ED25519_BASEPOINT_TABLE;
use curve25519_dalek::montgomery::MontgomeryPoint;
use curve25519_dalek::scalar::Scalar;
use rand_core::CryptoRng;
use rand_core::RngCore;
use zeroize::Zeroize;
#[cfg_attr(feature = "serde", serde(crate = "our_serde"))]
#[cfg_attr(
feature = "serde",
derive(our_serde::Serialize, our_serde::Deserialize)
)]
#[derive(Copy, Clone, Debug)]
pub struct PublicKey(pub(crate) MontgomeryPoint);
impl From<[u8; 32]> for PublicKey {
fn from(bytes: [u8; 32]) -> PublicKey {
PublicKey(MontgomeryPoint(bytes))
}
}
impl PublicKey {
#[inline]
pub fn as_bytes(&self) -> &[u8; 32] {
self.0.as_bytes()
}
}
#[derive(Zeroize)]
#[zeroize(drop)]
pub struct EphemeralSecret(pub(crate) Scalar);
impl EphemeralSecret {
pub fn diffie_hellman(self, their_public: &PublicKey) -> SharedSecret {
SharedSecret(self.0 * their_public.0)
}
pub fn new<T>(csprng: &mut T) -> Self
where
T: RngCore + CryptoRng,
{
let mut bytes = [0u8; 32];
csprng.fill_bytes(&mut bytes);
EphemeralSecret(clamp_scalar(bytes))
}
}
impl<'a> From<&'a EphemeralSecret> for PublicKey {
fn from(secret: &'a EphemeralSecret) -> PublicKey {
PublicKey((&ED25519_BASEPOINT_TABLE * &secret.0).to_montgomery())
}
}
#[cfg_attr(feature = "serde", serde(crate = "our_serde"))]
#[cfg_attr(
feature = "serde",
derive(our_serde::Serialize, our_serde::Deserialize)
)]
#[derive(Clone, Zeroize)]
#[zeroize(drop)]
pub struct StaticSecret(
#[cfg_attr(feature = "serde", serde(with = "AllowUnreducedScalarBytes"))] pub(crate) Scalar,
);
impl StaticSecret {
pub fn diffie_hellman(&self, their_public: &PublicKey) -> SharedSecret {
SharedSecret(&self.0 * their_public.0)
}
pub fn new<T>(csprng: &mut T) -> Self
where
T: RngCore + CryptoRng,
{
let mut bytes = [0u8; 32];
csprng.fill_bytes(&mut bytes);
StaticSecret(clamp_scalar(bytes))
}
pub fn to_bytes(&self) -> [u8; 32] {
self.0.to_bytes()
}
}
impl From<[u8; 32]> for StaticSecret {
fn from(bytes: [u8; 32]) -> StaticSecret {
StaticSecret(clamp_scalar(bytes))
}
}
impl<'a> From<&'a StaticSecret> for PublicKey {
fn from(secret: &'a StaticSecret) -> PublicKey {
PublicKey((&ED25519_BASEPOINT_TABLE * &secret.0).to_montgomery())
}
}
#[derive(Zeroize)]
#[zeroize(drop)]
pub struct SharedSecret(pub(crate) MontgomeryPoint);
impl SharedSecret {
#[inline]
pub fn as_bytes(&self) -> &[u8; 32] {
self.0.as_bytes()
}
}
fn clamp_scalar(mut scalar: [u8; 32]) -> Scalar {
scalar[0] &= 248;
scalar[31] &= 127;
scalar[31] |= 64;
Scalar::from_bits(scalar)
}
pub fn x25519(k: [u8; 32], u: [u8; 32]) -> [u8; 32] {
(clamp_scalar(k) * MontgomeryPoint(u)).to_bytes()
}
pub const X25519_BASEPOINT_BYTES: [u8; 32] = [
9, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
];
#[cfg_attr(feature = "serde", serde(crate = "our_serde"))]
#[cfg_attr(
feature = "serde",
derive(our_serde::Serialize, our_serde::Deserialize)
)]
#[cfg_attr(feature = "serde", serde(remote = "Scalar"))]
struct AllowUnreducedScalarBytes(
#[cfg_attr(feature = "serde", serde(getter = "Scalar::to_bytes"))] [u8; 32],
);
impl From<AllowUnreducedScalarBytes> for Scalar {
fn from(bytes: AllowUnreducedScalarBytes) -> Scalar {
clamp_scalar(bytes.0)
}
}
#[cfg(test)]
mod test {
use super::*;
use rand_core::OsRng;
#[test]
fn alice_and_bob() {
let alice_secret = EphemeralSecret::new(&mut OsRng);
let alice_public = PublicKey::from(&alice_secret);
let bob_secret = EphemeralSecret::new(&mut OsRng);
let bob_public = PublicKey::from(&bob_secret);
let alice_shared_secret = alice_secret.diffie_hellman(&bob_public);
let bob_shared_secret = bob_secret.diffie_hellman(&alice_public);
assert_eq!(alice_shared_secret.as_bytes(), bob_shared_secret.as_bytes());
}
#[test]
fn byte_basepoint_matches_edwards_scalar_mul() {
let mut scalar_bytes = [0x37; 32];
for i in 0..32 {
scalar_bytes[i] += 2;
let result = x25519(scalar_bytes, X25519_BASEPOINT_BYTES);
let expected = (&ED25519_BASEPOINT_TABLE * &clamp_scalar(scalar_bytes))
.to_montgomery()
.to_bytes();
assert_eq!(result, expected);
}
}
#[test]
#[cfg(feature = "serde")]
fn serde_bincode_public_key_roundtrip() {
use bincode;
let public_key = PublicKey::from(X25519_BASEPOINT_BYTES);
let encoded = bincode::serialize(&public_key).unwrap();
let decoded: PublicKey = bincode::deserialize(&encoded).unwrap();
assert_eq!(encoded.len(), 32);
assert_eq!(decoded.as_bytes(), public_key.as_bytes());
}
#[test]
#[cfg(feature = "serde")]
fn serde_bincode_public_key_matches_from_bytes() {
use bincode;
let expected = PublicKey::from(X25519_BASEPOINT_BYTES);
let decoded: PublicKey = bincode::deserialize(&X25519_BASEPOINT_BYTES).unwrap();
assert_eq!(decoded.as_bytes(), expected.as_bytes());
}
#[test]
#[cfg(feature = "serde")]
fn serde_bincode_static_secret_roundtrip() {
use bincode;
let static_secret = StaticSecret(clamp_scalar([0x24; 32]));
let encoded = bincode::serialize(&static_secret).unwrap();
let decoded: StaticSecret = bincode::deserialize(&encoded).unwrap();
assert_eq!(encoded.len(), 32);
assert_eq!(decoded.to_bytes(), static_secret.to_bytes());
}
#[test]
#[cfg(feature = "serde")]
fn serde_bincode_static_secret_matches_from_bytes() {
use bincode;
let expected = StaticSecret(clamp_scalar([0x24; 32]));
let clamped_bytes = clamp_scalar([0x24; 32]).to_bytes();
let decoded: StaticSecret = bincode::deserialize(&clamped_bytes).unwrap();
assert_eq!(decoded.to_bytes(), expected.to_bytes());
}
fn do_rfc7748_ladder_test1(input_scalar: [u8; 32], input_point: [u8; 32], expected: [u8; 32]) {
let result = x25519(input_scalar, input_point);
assert_eq!(result, expected);
}
#[test]
fn rfc7748_ladder_test1_vectorset1() {
let input_scalar: [u8; 32] = [
0xa5, 0x46, 0xe3, 0x6b, 0xf0, 0x52, 0x7c, 0x9d, 0x3b, 0x16, 0x15, 0x4b, 0x82, 0x46,
0x5e, 0xdd, 0x62, 0x14, 0x4c, 0x0a, 0xc1, 0xfc, 0x5a, 0x18, 0x50, 0x6a, 0x22, 0x44,
0xba, 0x44, 0x9a, 0xc4,
];
let input_point: [u8; 32] = [
0xe6, 0xdb, 0x68, 0x67, 0x58, 0x30, 0x30, 0xdb, 0x35, 0x94, 0xc1, 0xa4, 0x24, 0xb1,
0x5f, 0x7c, 0x72, 0x66, 0x24, 0xec, 0x26, 0xb3, 0x35, 0x3b, 0x10, 0xa9, 0x03, 0xa6,
0xd0, 0xab, 0x1c, 0x4c,
];
let expected: [u8; 32] = [
0xc3, 0xda, 0x55, 0x37, 0x9d, 0xe9, 0xc6, 0x90, 0x8e, 0x94, 0xea, 0x4d, 0xf2, 0x8d,
0x08, 0x4f, 0x32, 0xec, 0xcf, 0x03, 0x49, 0x1c, 0x71, 0xf7, 0x54, 0xb4, 0x07, 0x55,
0x77, 0xa2, 0x85, 0x52,
];
do_rfc7748_ladder_test1(input_scalar, input_point, expected);
}
#[test]
fn rfc7748_ladder_test1_vectorset2() {
let input_scalar: [u8; 32] = [
0x4b, 0x66, 0xe9, 0xd4, 0xd1, 0xb4, 0x67, 0x3c, 0x5a, 0xd2, 0x26, 0x91, 0x95, 0x7d,
0x6a, 0xf5, 0xc1, 0x1b, 0x64, 0x21, 0xe0, 0xea, 0x01, 0xd4, 0x2c, 0xa4, 0x16, 0x9e,
0x79, 0x18, 0xba, 0x0d,
];
let input_point: [u8; 32] = [
0xe5, 0x21, 0x0f, 0x12, 0x78, 0x68, 0x11, 0xd3, 0xf4, 0xb7, 0x95, 0x9d, 0x05, 0x38,
0xae, 0x2c, 0x31, 0xdb, 0xe7, 0x10, 0x6f, 0xc0, 0x3c, 0x3e, 0xfc, 0x4c, 0xd5, 0x49,
0xc7, 0x15, 0xa4, 0x93,
];
let expected: [u8; 32] = [
0x95, 0xcb, 0xde, 0x94, 0x76, 0xe8, 0x90, 0x7d, 0x7a, 0xad, 0xe4, 0x5c, 0xb4, 0xb8,
0x73, 0xf8, 0x8b, 0x59, 0x5a, 0x68, 0x79, 0x9f, 0xa1, 0x52, 0xe6, 0xf8, 0xf7, 0x64,
0x7a, 0xac, 0x79, 0x57,
];
do_rfc7748_ladder_test1(input_scalar, input_point, expected);
}
#[test]
#[ignore]
fn rfc7748_ladder_test2() {
use curve25519_dalek::constants::X25519_BASEPOINT;
let mut k: [u8; 32] = X25519_BASEPOINT.0;
let mut u: [u8; 32] = X25519_BASEPOINT.0;
let mut result: [u8; 32];
macro_rules! do_iterations {
($n:expr) => {
for _ in 0..$n {
result = x25519(k, u);
u = k.clone();
k = result;
}
};
}
do_iterations!(1);
assert_eq!(
k,
[
0x42, 0x2c, 0x8e, 0x7a, 0x62, 0x27, 0xd7, 0xbc, 0xa1, 0x35, 0x0b, 0x3e, 0x2b, 0xb7,
0x27, 0x9f, 0x78, 0x97, 0xb8, 0x7b, 0xb6, 0x85, 0x4b, 0x78, 0x3c, 0x60, 0xe8, 0x03,
0x11, 0xae, 0x30, 0x79,
]
);
do_iterations!(999);
assert_eq!(
k,
[
0x68, 0x4c, 0xf5, 0x9b, 0xa8, 0x33, 0x09, 0x55, 0x28, 0x00, 0xef, 0x56, 0x6f, 0x2f,
0x4d, 0x3c, 0x1c, 0x38, 0x87, 0xc4, 0x93, 0x60, 0xe3, 0x87, 0x5f, 0x2e, 0xb9, 0x4d,
0x99, 0x53, 0x2c, 0x51,
]
);
do_iterations!(999_000);
assert_eq!(
k,
[
0x7c, 0x39, 0x11, 0xe0, 0xab, 0x25, 0x86, 0xfd, 0x86, 0x44, 0x97, 0x29, 0x7e, 0x57,
0x5e, 0x6f, 0x3b, 0xc6, 0x01, 0xc0, 0x88, 0x3c, 0x30, 0xdf, 0x5f, 0x4d, 0xd2, 0xd2,
0x4f, 0x66, 0x54, 0x24,
]
);
}
}