saymrwulf/curve25519-dalek-source
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byte-oriented x25519 function

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This commit is contained in:
DebugSteven 2018-12-16 11:30:32 -07:00
parent ff0e1f286b
commit d3b7ccf030
3 changed files with 46 additions and 47 deletions
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2
Cargo.toml
View file

@ -20,7 +20,7 @@ exclude = [
travis-ci = { repository = "dalek-cryptography/x25519-dalek", branch = "master"} travis-ci = { repository = "dalek-cryptography/x25519-dalek", branch = "master"}
[dependencies.curve25519-dalek] [dependencies.curve25519-dalek]
version = "^1.0.0-pre.1" version = "1"
default-features = false default-features = false
[dependencies.rand_core] [dependencies.rand_core]

2
benches/x25519.rs
View file

@ -32,7 +32,7 @@ fn bench_diffie_hellman(c: &mut Criterion) {
c.bench_function("diffie_hellman", move |b| { c.bench_function("diffie_hellman", move |b| {
b.iter_with_setup( b.iter_with_setup(
|| EphemeralSecret::new(&mut csprng), || EphemeralSecret::new(&mut csprng),
|alice_secret| EphemeralSecret::diffie_hellman(alice_secret, &bob_public), |alice_secret| alice_secret.diffie_hellman(&bob_public),
) )
}); });
} }

89
src/x25519.rs
View file

@ -22,7 +22,6 @@ use rand_core::RngCore;
use rand_core::CryptoRng; use rand_core::CryptoRng;
/// A DH ephemeral public key. /// A DH ephemeral public key.
#[repr(C)]
pub struct EphemeralPublic(pub (crate) MontgomeryPoint); pub struct EphemeralPublic(pub (crate) MontgomeryPoint);
impl From<[u8; 32]> for EphemeralPublic { impl From<[u8; 32]> for EphemeralPublic {
@ -34,8 +33,6 @@ impl From<[u8; 32]> for EphemeralPublic {
} }
/// A DH ephemeral secret key. /// A DH ephemeral secret key.
#[repr(C)]
#[derive(Default)] // we derive Default in order to use the clear() method in Drop
pub struct EphemeralSecret(pub (crate) Scalar); pub struct EphemeralSecret(pub (crate) Scalar);
/// Overwrite ephemeral secret key material with null bytes when it goes out of scope. /// Overwrite ephemeral secret key material with null bytes when it goes out of scope.
@ -46,13 +43,11 @@ impl Drop for EphemeralSecret {
} }
impl EphemeralSecret { impl EphemeralSecret {
/// The diffie_hellman function performs scalar multipication on a montegomery point. /// Utility function to make it easier to call `x25519()` with
/// This is the implementation for the x25519 function, as specified in RFC7748. /// an ephemeral secret key and montegomery point as input and
/// a shared secret as the output.
pub fn diffie_hellman(self, their_public: &EphemeralPublic) -> SharedSecret { pub fn diffie_hellman(self, their_public: &EphemeralPublic) -> SharedSecret {
let k: Scalar = clamp_scalar(self.0.as_bytes()); SharedSecret(self.0 * their_public.0)
let point: MontgomeryPoint = MontgomeryPoint(*their_public.0.as_bytes());
SharedSecret(k * point)
} }
/// Generate an x25519 `EphemeralSecret` key. /// Generate an x25519 `EphemeralSecret` key.
@ -63,7 +58,7 @@ impl EphemeralSecret {
csprng.fill_bytes(&mut bytes); csprng.fill_bytes(&mut bytes);
EphemeralSecret(clamp_scalar(&bytes)) EphemeralSecret(clamp_scalar(bytes))
} }
} }
@ -78,7 +73,6 @@ impl<'a> From<&'a EphemeralSecret> for EphemeralPublic {
} }
/// A DH SharedSecret /// A DH SharedSecret
#[repr(C)]
pub struct SharedSecret(pub (crate) MontgomeryPoint); pub struct SharedSecret(pub (crate) MontgomeryPoint);
/// Overwrite shared secret material with null bytes when it goes out of scope. /// Overwrite shared secret material with null bytes when it goes out of scope.
@ -105,7 +99,7 @@ impl SharedSecret {
/// # Returns /// # Returns
/// ///
/// A `Scalar`. /// A `Scalar`.
fn clamp_scalar(scalar: &[u8; 32]) -> Scalar { fn clamp_scalar(scalar: [u8; 32]) -> Scalar {
let mut s: [u8; 32] = scalar.clone(); let mut s: [u8; 32] = scalar.clone();
s[0] &= 248; s[0] &= 248;
@ -115,58 +109,63 @@ fn clamp_scalar(scalar: &[u8; 32]) -> Scalar {
Scalar::from_bits(s) Scalar::from_bits(s)
} }
/// The x25519 function, as specified in RFC7748.
pub fn x25519(k: [u8; 32], u: [u8; 32]) -> [u8; 32] {
(clamp_scalar(k) * MontgomeryPoint(u)).to_bytes()
}
#[cfg(test)] #[cfg(test)]
mod test { mod test {
use super::*; use super::*;
fn do_rfc7748_ladder_test1(input_scalar: &Scalar, fn do_rfc7748_ladder_test1(input_scalar: [u8; 32],
input_point: &MontgomeryPoint, input_point: [u8; 32],
expected: &[u8; 32]) { expected: [u8; 32]) {
let result = EphemeralSecret::diffie_hellman(EphemeralSecret(*input_scalar), &EphemeralPublic(*input_point)); let result = x25519(input_scalar, input_point);
assert_eq!(result.0, MontgomeryPoint(*expected)); assert_eq!(result, expected);
} }
#[test] #[test]
fn rfc7748_ladder_test1_vectorset1() { fn rfc7748_ladder_test1_vectorset1() {
let input_scalar: Scalar = Scalar::from_bits([ let input_scalar: [u8; 32] = [
0xa5, 0x46, 0xe3, 0x6b, 0xf0, 0x52, 0x7c, 0x9d, 0xa5, 0x46, 0xe3, 0x6b, 0xf0, 0x52, 0x7c, 0x9d,
0x3b, 0x16, 0x15, 0x4b, 0x82, 0x46, 0x5e, 0xdd, 0x3b, 0x16, 0x15, 0x4b, 0x82, 0x46, 0x5e, 0xdd,
0x62, 0x14, 0x4c, 0x0a, 0xc1, 0xfc, 0x5a, 0x18, 0x62, 0x14, 0x4c, 0x0a, 0xc1, 0xfc, 0x5a, 0x18,
0x50, 0x6a, 0x22, 0x44, 0xba, 0x44, 0x9a, 0xc4, ]); 0x50, 0x6a, 0x22, 0x44, 0xba, 0x44, 0x9a, 0xc4, ];
let input_point: MontgomeryPoint = MontgomeryPoint([ let input_point: [u8; 32] = [
0xe6, 0xdb, 0x68, 0x67, 0x58, 0x30, 0x30, 0xdb, 0xe6, 0xdb, 0x68, 0x67, 0x58, 0x30, 0x30, 0xdb,
0x35, 0x94, 0xc1, 0xa4, 0x24, 0xb1, 0x5f, 0x7c, 0x35, 0x94, 0xc1, 0xa4, 0x24, 0xb1, 0x5f, 0x7c,
0x72, 0x66, 0x24, 0xec, 0x26, 0xb3, 0x35, 0x3b, 0x72, 0x66, 0x24, 0xec, 0x26, 0xb3, 0x35, 0x3b,
0x10, 0xa9, 0x03, 0xa6, 0xd0, 0xab, 0x1c, 0x4c, ]); 0x10, 0xa9, 0x03, 0xa6, 0xd0, 0xab, 0x1c, 0x4c, ];
let expected: [u8; 32] = [ let expected: [u8; 32] = [
0xc3, 0xda, 0x55, 0x37, 0x9d, 0xe9, 0xc6, 0x90, 0xc3, 0xda, 0x55, 0x37, 0x9d, 0xe9, 0xc6, 0x90,
0x8e, 0x94, 0xea, 0x4d, 0xf2, 0x8d, 0x08, 0x4f, 0x8e, 0x94, 0xea, 0x4d, 0xf2, 0x8d, 0x08, 0x4f,
0x32, 0xec, 0xcf, 0x03, 0x49, 0x1c, 0x71, 0xf7, 0x32, 0xec, 0xcf, 0x03, 0x49, 0x1c, 0x71, 0xf7,
0x54, 0xb4, 0x07, 0x55, 0x77, 0xa2, 0x85, 0x52, ]; 0x54, 0xb4, 0x07, 0x55, 0x77, 0xa2, 0x85, 0x52, ];
do_rfc7748_ladder_test1(&input_scalar, &input_point, &expected); do_rfc7748_ladder_test1(input_scalar, input_point, expected);
} }
#[test] #[test]
fn rfc7748_ladder_test1_vectorset2() { fn rfc7748_ladder_test1_vectorset2() {
let input_scalar: Scalar = Scalar::from_bits([ let input_scalar: [u8; 32] = [
0x4b, 0x66, 0xe9, 0xd4, 0xd1, 0xb4, 0x67, 0x3c, 0x4b, 0x66, 0xe9, 0xd4, 0xd1, 0xb4, 0x67, 0x3c,
0x5a, 0xd2, 0x26, 0x91, 0x95, 0x7d, 0x6a, 0xf5, 0x5a, 0xd2, 0x26, 0x91, 0x95, 0x7d, 0x6a, 0xf5,
0xc1, 0x1b, 0x64, 0x21, 0xe0, 0xea, 0x01, 0xd4, 0xc1, 0x1b, 0x64, 0x21, 0xe0, 0xea, 0x01, 0xd4,
0x2c, 0xa4, 0x16, 0x9e, 0x79, 0x18, 0xba, 0x0d, ]); 0x2c, 0xa4, 0x16, 0x9e, 0x79, 0x18, 0xba, 0x0d, ];
let input_point: MontgomeryPoint = MontgomeryPoint([ let input_point: [u8; 32] = [
0xe5, 0x21, 0x0f, 0x12, 0x78, 0x68, 0x11, 0xd3, 0xe5, 0x21, 0x0f, 0x12, 0x78, 0x68, 0x11, 0xd3,
0xf4, 0xb7, 0x95, 0x9d, 0x05, 0x38, 0xae, 0x2c, 0xf4, 0xb7, 0x95, 0x9d, 0x05, 0x38, 0xae, 0x2c,
0x31, 0xdb, 0xe7, 0x10, 0x6f, 0xc0, 0x3c, 0x3e, 0x31, 0xdb, 0xe7, 0x10, 0x6f, 0xc0, 0x3c, 0x3e,
0xfc, 0x4c, 0xd5, 0x49, 0xc7, 0x15, 0xa4, 0x93, ]); 0xfc, 0x4c, 0xd5, 0x49, 0xc7, 0x15, 0xa4, 0x93, ];
let expected: [u8; 32] = [ let expected: [u8; 32] = [
0x95, 0xcb, 0xde, 0x94, 0x76, 0xe8, 0x90, 0x7d, 0x95, 0xcb, 0xde, 0x94, 0x76, 0xe8, 0x90, 0x7d,
0x7a, 0xad, 0xe4, 0x5c, 0xb4, 0xb8, 0x73, 0xf8, 0x7a, 0xad, 0xe4, 0x5c, 0xb4, 0xb8, 0x73, 0xf8,
0x8b, 0x59, 0x5a, 0x68, 0x79, 0x9f, 0xa1, 0x52, 0x8b, 0x59, 0x5a, 0x68, 0x79, 0x9f, 0xa1, 0x52,
0xe6, 0xf8, 0xf7, 0x64, 0x7a, 0xac, 0x79, 0x57, ]; 0xe6, 0xf8, 0xf7, 0x64, 0x7a, 0xac, 0x79, 0x57, ];
do_rfc7748_ladder_test1(&input_scalar, &input_point, &expected); do_rfc7748_ladder_test1(input_scalar, input_point, expected);
} }
#[test] #[test]
@ -174,14 +173,14 @@ mod test {
fn rfc7748_ladder_test2() { fn rfc7748_ladder_test2() {
use curve25519_dalek::constants::X25519_BASEPOINT; use curve25519_dalek::constants::X25519_BASEPOINT;
let mut k: Scalar = Scalar::from_bits(X25519_BASEPOINT.0); let mut k: [u8; 32] = X25519_BASEPOINT.0;
let mut u: MontgomeryPoint = X25519_BASEPOINT; let mut u: [u8; 32] = X25519_BASEPOINT.0;
let mut result: SharedSecret; let mut result: [u8; 32];
macro_rules! do_iterations { macro_rules! do_iterations {
($n:expr) => ( ($n:expr) => (
for _ in 0..$n { for _ in 0..$n {
result = EphemeralSecret::diffie_hellman(EphemeralSecret(k), &EphemeralPublic(u)); result = x25519(k, u);
// OBVIOUS THING THAT I'M GOING TO NOTE ANYWAY BECAUSE I'VE // OBVIOUS THING THAT I'M GOING TO NOTE ANYWAY BECAUSE I'VE
// SEEN PEOPLE DO THIS WITH GOLANG'S STDLIB AND YOU SURE AS // SEEN PEOPLE DO THIS WITH GOLANG'S STDLIB AND YOU SURE AS
// HELL SHOULDN'T DO HORRIBLY STUPID THINGS LIKE THIS WITH // HELL SHOULDN'T DO HORRIBLY STUPID THINGS LIKE THIS WITH
@ -190,8 +189,8 @@ mod test {
// NEVER EVER TREAT SCALARS AS POINTS AND/OR VICE VERSA. // NEVER EVER TREAT SCALARS AS POINTS AND/OR VICE VERSA.
// //
// ↓↓ DON'T DO THIS ↓↓ // ↓↓ DON'T DO THIS ↓↓
u = MontgomeryPoint(k.as_bytes().clone()); u = k.clone();
k = Scalar::from_bits(result.0.to_bytes()); k = result;
} }
) )
} }
@ -204,19 +203,19 @@ mod test {
// 7c3911e0ab2586fd864497297e575e6f3bc601c0883c30df5f4dd2d24f665424 // 7c3911e0ab2586fd864497297e575e6f3bc601c0883c30df5f4dd2d24f665424
do_iterations!(1); do_iterations!(1);
assert_eq!(k.as_bytes(), &[ 0x42, 0x2c, 0x8e, 0x7a, 0x62, 0x27, 0xd7, 0xbc, assert_eq!(k, [ 0x42, 0x2c, 0x8e, 0x7a, 0x62, 0x27, 0xd7, 0xbc,
0xa1, 0x35, 0x0b, 0x3e, 0x2b, 0xb7, 0x27, 0x9f, 0xa1, 0x35, 0x0b, 0x3e, 0x2b, 0xb7, 0x27, 0x9f,
0x78, 0x97, 0xb8, 0x7b, 0xb6, 0x85, 0x4b, 0x78, 0x78, 0x97, 0xb8, 0x7b, 0xb6, 0x85, 0x4b, 0x78,
0x3c, 0x60, 0xe8, 0x03, 0x11, 0xae, 0x30, 0x79, ]); 0x3c, 0x60, 0xe8, 0x03, 0x11, 0xae, 0x30, 0x79, ]);
do_iterations!(999); do_iterations!(999);
assert_eq!(k.as_bytes(), &[ 0x68, 0x4c, 0xf5, 0x9b, 0xa8, 0x33, 0x09, 0x55, assert_eq!(k, [ 0x68, 0x4c, 0xf5, 0x9b, 0xa8, 0x33, 0x09, 0x55,
0x28, 0x00, 0xef, 0x56, 0x6f, 0x2f, 0x4d, 0x3c, 0x28, 0x00, 0xef, 0x56, 0x6f, 0x2f, 0x4d, 0x3c,
0x1c, 0x38, 0x87, 0xc4, 0x93, 0x60, 0xe3, 0x87, 0x1c, 0x38, 0x87, 0xc4, 0x93, 0x60, 0xe3, 0x87,
0x5f, 0x2e, 0xb9, 0x4d, 0x99, 0x53, 0x2c, 0x51, ]); 0x5f, 0x2e, 0xb9, 0x4d, 0x99, 0x53, 0x2c, 0x51, ]);
do_iterations!(999_000); do_iterations!(999_000);
assert_eq!(k.as_bytes(), &[ 0x7c, 0x39, 0x11, 0xe0, 0xab, 0x25, 0x86, 0xfd, assert_eq!(k, [ 0x7c, 0x39, 0x11, 0xe0, 0xab, 0x25, 0x86, 0xfd,
0x86, 0x44, 0x97, 0x29, 0x7e, 0x57, 0x5e, 0x6f, 0x86, 0x44, 0x97, 0x29, 0x7e, 0x57, 0x5e, 0x6f,
0x3b, 0xc6, 0x01, 0xc0, 0x88, 0x3c, 0x30, 0xdf, 0x3b, 0xc6, 0x01, 0xc0, 0x88, 0x3c, 0x30, 0xdf,
0x5f, 0x4d, 0xd2, 0xd2, 0x4f, 0x66, 0x54, 0x24, ]); 0x5f, 0x4d, 0xd2, 0xd2, 0x4f, 0x66, 0x54, 0x24, ]);
} }
} }