use curve25519_dalek::constants::ED25519_BASEPOINT_TABLE;
use curve25519_dalek::montgomery::MontgomeryPoint;
use curve25519_dalek::scalar::Scalar;
#[cfg(feature = "std")]
use rand::Rng;
fn decode_scalar(scalar: &[u8; 32]) -> Scalar {
let mut s: [u8; 32] = scalar.clone();
s[0] &= 248;
s[31] &= 127;
s[31] |= 64;
Scalar::from_bits(s)
}
#[cfg(feature = "std")]
pub fn generate_secret<T: Rng>(csprng: &mut T) -> [u8; 32] {
let mut bytes = [0u8; 32];
csprng.fill_bytes(&mut bytes);
bytes
}
pub fn generate_public(secret: &[u8; 32]) -> MontgomeryPoint {
(&decode_scalar(secret) * &ED25519_BASEPOINT_TABLE).to_montgomery()
}
pub fn x25519(scalar: &Scalar, point: &MontgomeryPoint) -> MontgomeryPoint {
let k: Scalar = decode_scalar(scalar.as_bytes());
(&k * point)
}
pub fn diffie_hellman(my_secret: &[u8; 32], their_public: &[u8; 32]) -> [u8; 32] {
x25519(&Scalar::from_bits(*my_secret), &MontgomeryPoint(*their_public)).to_bytes()
}
#[cfg(test)]
mod test {
use super::*;
fn do_rfc7748_ladder_test1(input_scalar: &Scalar,
input_point: &MontgomeryPoint,
expected: &[u8; 32]) {
let result = x25519(&input_scalar, &input_point);
assert_eq!(result.0, *expected);
}
#[test]
fn rfc7748_ladder_test1_vectorset1() {
let input_scalar: Scalar = Scalar::from_bits([
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: MontgomeryPoint = MontgomeryPoint([
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: Scalar = Scalar::from_bits([
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: MontgomeryPoint = MontgomeryPoint([
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: Scalar = Scalar::from_bits(X25519_BASEPOINT.0);
let mut u: MontgomeryPoint = X25519_BASEPOINT;
let mut result: MontgomeryPoint;
macro_rules! do_iterations {
($n:expr) => (
for _ in 0..$n {
result = x25519(&k, &u);
u = MontgomeryPoint(k.as_bytes().clone());
k = Scalar::from_bits(result.to_bytes());
}
)
}
do_iterations!(1);
assert_eq!(k.as_bytes(), &[ 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.as_bytes(), &[ 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.as_bytes(), &[ 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, ]);
}
}