mirror of https://github.com/bsnes-emu/bsnes.git
56 lines
1.3 KiB
C++
56 lines
1.3 KiB
C++
#pragma once
|
|
|
|
#if defined(EC_REFERENCE)
|
|
#include <nall/elliptic-curve/modulo25519-reference.hpp>
|
|
#else
|
|
#include <nall/elliptic-curve/modulo25519.hpp>
|
|
#endif
|
|
|
|
namespace nall { namespace EllipticCurve {
|
|
|
|
struct Curve25519 {
|
|
auto sharedKey(uint256_t secretKey, uint256_t basepoint = 9) const -> uint256_t {
|
|
secretKey &= ((0_u256 - 1) >> 2) - 7;
|
|
secretKey |= 1_u256 << 254;
|
|
basepoint &= (0_u256 - 1) >> 1;
|
|
|
|
point p = scalarMultiply(secretKey, modP(basepoint));
|
|
return p.x * p.z.reciprocal();
|
|
}
|
|
|
|
private:
|
|
using field = Modulo25519;
|
|
struct point { field x, z; };
|
|
|
|
inline auto montgomeryAdd(point p, point q, field b) const -> point {
|
|
return {
|
|
(p.x * q.x - p.z * q.z).square(),
|
|
(p.x * q.z - p.z * q.x).square() * b
|
|
};
|
|
}
|
|
|
|
inline auto montgomeryDouble(point p) const -> point {
|
|
field a = (p.x + p.z).square();
|
|
field b = (p.x - p.z).square();
|
|
field c = a - b;
|
|
field d = a + c * 121665;
|
|
return {a * b, c * d};
|
|
}
|
|
|
|
inline auto scalarMultiply(uint256_t e, field b) const -> point {
|
|
point p{1, 0}, q{b, 1};
|
|
for(uint n : rrange(255)) {
|
|
bool bit = e >> n & 1;
|
|
cswap(bit, p.x, q.x);
|
|
cswap(bit, p.z, q.z);
|
|
q = montgomeryAdd(p, q, b);
|
|
p = montgomeryDouble(p);
|
|
cswap(bit, p.x, q.x);
|
|
cswap(bit, p.z, q.z);
|
|
}
|
|
return p;
|
|
}
|
|
};
|
|
|
|
}}
|