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Elligator decode

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orignal 2019-12-09 16:11:46 -05:00
parent 3100d587d1
commit c38298c06e
2 changed files with 67 additions and 1 deletions
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67
libi2pd/Elligator.cpp
View file

@ -45,7 +45,14 @@ namespace crypto
BN_CTX * ctx = BN_CTX_new ();
BN_CTX_start (ctx);
BIGNUM * x = BN_CTX_get (ctx); BN_bin2bn (key, 32, x);
uint8_t key1[32];
for (size_t i = 0; i < 16; i++) // from Little Endian
{
key1[i] = key[15 - i];
key1[15 - i] = key[i];
}
BIGNUM * x = BN_CTX_get (ctx); BN_bin2bn (key1, 32, x);
BIGNUM * xA = BN_CTX_get (ctx); BN_add (xA, x, A); // x + A
BN_sub (xA, p, xA); // p - (x + A)
@ -56,6 +63,64 @@ namespace crypto
SquareRoot (r, r, ctx);
bn2buf (r, encoded, 32);
for (size_t i = 0; i < 16; i++) // To Little Endian
{
uint8_t tmp = encoded[i];
encoded[i] = encoded[15 - i];
encoded[15 - i] = tmp;
}
BN_CTX_end (ctx);
BN_CTX_free (ctx);
}
void Elligator2::Decode (const uint8_t * encoded, uint8_t * key) const
{
BN_CTX * ctx = BN_CTX_new ();
BN_CTX_start (ctx);
uint8_t encoded1[32];
for (size_t i = 0; i < 16; i++) // from Little Endian
{
encoded1[i] = encoded[15 - i];
encoded1[15 - i] = encoded[i];
}
BIGNUM * r = BN_CTX_get (ctx); BN_bin2bn (encoded1, 32, r);
// v=-A/(1+u*r^2)
BIGNUM * v = BN_CTX_get (ctx); BN_mod_sqr (v, r, p, ctx);
BN_mod_mul (v, v, u, p, ctx);
BN_add_word (v, 1);
BN_mod_inverse (v, v, p, ctx);
BN_mod_mul (v, v, nA, p, ctx);
BIGNUM * vpA = BN_CTX_get (ctx);
BN_add (vpA, v, A); // v + A
// t = v^3+A*v^2+v = v^2*(v+A)+v
BIGNUM * t = BN_CTX_get (ctx); BN_mod_sqr (t, v, p, ctx);
BN_mod_mul (t, t, vpA, p, ctx);
BN_mod_add (t, t, v, p, ctx);
int legendre = 0; // TODO:
BIGNUM * x = BN_CTX_get (ctx);
if (legendre == 1)
BN_copy (x, v);
else
{
BN_sub (x, p, v);
BN_mod_sub (x, x, A, p, ctx);
}
bn2buf (x, key, 32);
for (size_t i = 0; i < 16; i++) // To Little Endian
{
uint8_t tmp = key[i];
key[i] = key[15 - i];
key[15 - i] = tmp;
}
BN_CTX_end (ctx);
BN_CTX_free (ctx);

1
libi2pd/Elligator.h
View file

@ -18,6 +18,7 @@ namespace crypto
~Elligator2 ();
void Encode (const uint8_t * key, uint8_t * encoded) const;
void Decode (const uint8_t * encoded, uint8_t * key) const;
private: