i2pd/Signature.cpp
2015-04-08 16:18:16 -04:00

90 lines
2.4 KiB
C++

#include <cryptopp/integer.h>
#include <cryptopp/eccrypto.h>
#include "Log.h"
#include "Signature.h"
namespace i2p
{
namespace crypto
{
class Ed25519
{
public:
Ed25519 ()
{
q = CryptoPP::Integer::Power2 (255) - CryptoPP::Integer (19); // 2^255-19
l = CryptoPP::Integer::Power2 (252) + CryptoPP::Integer ("27742317777372353535851937790883648493");
// 2^252 + 27742317777372353535851937790883648493
d = CryptoPP::Integer (-121665) * CryptoPP::Integer (121666).InverseMod (q); // -121665/121666
I = a_exp_b_mod_c (CryptoPP::Integer::Two (), (q - CryptoPP::Integer::One ()).DividedBy (4), q);
}
private:
CryptoPP::ECP::Point Sum (const CryptoPP::ECP::Point& p1, const CryptoPP::ECP::Point& p2)
{
CryptoPP::Integer m = d*p1.x*p2.x*p1.y*p2.y,
x = a_times_b_mod_c (p1.x*p2.y + p2.x*p1.y, (CryptoPP::Integer::One() + m).InverseMod (q), q),
y = a_times_b_mod_c (p1.y*p2.y + p1.x*p2.x, (CryptoPP::Integer::One() - m).InverseMod (q), q);
return CryptoPP::ECP::Point {x, y};
}
CryptoPP::ECP::Point Mul (const CryptoPP::ECP::Point& p, const CryptoPP::Integer& e)
{
CryptoPP::ECP::Point res {0, 1};
if (!e.IsZero ())
{
auto bitCount = e.BitCount ();
for (int i = bitCount - 1; i >= 0; i--)
{
res = Sum (res, res);
if (e.GetBit (i)) res = Sum (res, p);
}
}
return res;
}
bool IsOnCurve (const CryptoPP::ECP::Point& p)
{
auto x2 = p.x.Squared(), y2 = p.y.Squared ();
return (y2 - x2 - CryptoPP::Integer::One() - d*x2*y2).Modulo (q).IsZero ();
}
CryptoPP::Integer RecoverX (const CryptoPP::Integer& y)
{
auto y2 = y.Squared ();
auto xx = (y2 - CryptoPP::Integer::One())*(d*y2 + CryptoPP::Integer::One()).InverseMod (q);
auto x = a_exp_b_mod_c (xx, (q + CryptoPP::Integer (3)).DividedBy (8), q);
if (!(x.Squared () - xx).Modulo (q).IsZero ())
x = a_times_b_mod_c (x, I, q);
if (x.IsOdd ()) x = q - x;
return x;
}
CryptoPP::ECP::Point DecodePoint (const CryptoPP::Integer& y)
{
auto x = RecoverX (y);
CryptoPP::ECP::Point p {x, y};
if (!IsOnCurve (p))
{
LogPrint (eLogError, "Decoded point is not on 25519");
return CryptoPP::ECP::Point {0, 1};
}
return p;
}
private:
CryptoPP::Integer q, l, d, I;
};
bool EDDSAVerifier::Verify (const uint8_t * buf, size_t len, const uint8_t * signature) const
{
return true; // TODO:
}
}
}