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calculate constants

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orignal 2019-12-06 14:54:15 -05:00
parent 2877900233
commit e6956d9bb0
2 changed files with 40 additions and 32 deletions
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70
libi2pd/Elligator.cpp
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@ -5,52 +5,60 @@ namespace i2p
{
namespace crypto
{
static const uint8_t p_[32]=
{
0xed, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f
};
static const uint8_t n1_[32] =
{
0xec, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f
};
static const uint8_t n2_[32] =
{
0xeb, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f
};
static const uint8_t u_[32] =
{
0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};
#define decode_bytes(x) { x = BN_new (); BN_bin2bn (x##_, 32, x); } // TODO: endianess
Elligator2::Elligator2 ()
{
decode_bytes (p);
decode_bytes (n1);
decode_bytes (n2);
decode_bytes (u);
A = BN_new (); BN_set_word (A, 486662);
// TODO: share with Ed22519
p = BN_new ();
// 2^255-19
BN_set_bit (p, 255); // 2^255
BN_sub_word (p, 19);
p38 = BN_dup (p); BN_add_word (p38, 3); BN_div_word (p38, 8); // (p+3)/8
p12 = BN_dup (p); BN_sub_word (p12, 1); BN_div_word (p12, 2); // (p-1)/2
n1 = BN_dup (p); BN_sub_word (n1, 1); // p-1
n2 = BN_dup (p); BN_sub_word (n2, 2); // p-2
BN_CTX * ctx = BN_CTX_new ();
A = BN_new (); BN_set_word (A, 486662);
nA = BN_new (); BN_sub (nA, p, A);
BN_CTX * ctx = BN_CTX_new ();
// calculate sqrt(-1)
sqrtn1 = BN_new ();
BN_mod_exp (sqrtn1, n1, p38, p, ctx); // (-1)^((p+3)/8)
auto p14 = BN_dup (p); BN_sub_word (p14, 1); BN_div_word (p14, 4); // (p-1)/4
auto tmp = BN_new (); BN_set_word (tmp, 2);
BN_mod_exp (tmp, tmp, p14, p, ctx); // 2^((p-1)/4
BN_mod_mul (sqrtn1, tmp, sqrtn1, p, ctx); // 2^((p-1)/4 * (-1)^((p+3)/8)
BN_free (p14);
u = BN_new (); BN_bin2bn (u_, 32, u); // TODO: endianess
iu = BN_new (); BN_mod_inverse (iu, u, p, ctx);
// calculate d = -121665*inv(121666)
d = BN_new ();
BN_set_word (tmp, 121666);
BN_mod_inverse (tmp, tmp, p, ctx);
BN_set_word (d, 121665);
BN_set_negative (d, 1);
BN_mod_mul (d, d, tmp, p, ctx);
BN_free (tmp);
//printf ("%s\n", BN_bn2hex (d));
BN_CTX_free (ctx);
}
Elligator2::~Elligator2 ()
{
BN_free (p);
BN_free (n1);
BN_free (n2);
BN_free (A);
BN_free (p); BN_free (p38); BN_free (p12);
BN_free (n1);BN_free (n2); BN_free (sqrtn1);
BN_free (A); BN_free (nA);
BN_free (u); BN_free (iu); BN_free (d);
}
void Elligator2::Encode (const uint8_t * key, uint8_t * encoded) const

2
libi2pd/Elligator.h
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@ -21,7 +21,7 @@ namespace crypto
private:
BIGNUM * p, * n1, * n2, * A, * u, * iu;
BIGNUM * p, * n1, * n2, * p38, * p12, * sqrtn1, * A, * nA, * u, * iu, * d;
};
std::unique_ptr<Elligator2>& GetElligator ();