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reduce number of precalculated points

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orignal 2015-11-27 13:19:45 -05:00
parent 9bc477e1b6
commit 7bfb499549
1 changed files with 35 additions and 9 deletions
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44
Signature.cpp
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@ -56,22 +56,26 @@ namespace crypto
BN_mod (By, By, q, ctx); // % q
// precalculate Bi16 table
Bi16[0][0] = { Bx, By }; // B
Bi16Carry = { Bx, By }; // B
for (int i = 0; i < 64; i++)
{
if (i) Bi16[i][0] = Sum (Bi16[i-1][14], Bi16[i-1][0], ctx);
for (int j = 1; j < 15; j++)
Bi16[i][0] = Bi16Carry;
for (int j = 1; j < 8; j++)
Bi16[i][j] = Sum (Bi16[i][j-1], Bi16[i][0], ctx); // (16+j+1)^i*B
Bi16Carry = Bi16[i][7];
for (int j = 8; j < 16; j++)
Bi16Carry = Sum (Bi16Carry, Bi16[i][0], ctx);
}
BN_CTX_free (ctx);
}
Ed25519 (const Ed25519& other): q (BN_dup (other.q)), l (BN_dup (other.l)),
d (BN_dup (other.d)), I (BN_dup (other.I)), two_252_2 (BN_dup (other.two_252_2))
d (BN_dup (other.d)), I (BN_dup (other.I)), two_252_2 (BN_dup (other.two_252_2)),
Bi16Carry (other.Bi16Carry)
{
for (int i = 0; i < 64; i++)
for (int j = 0; j < 15; j++)
for (int j = 0; j < 8; j++)
Bi16[i][j] = other.Bi16[i][j];
}
@ -251,20 +255,40 @@ namespace crypto
return res;
}
EDDSAPoint MulB (const uint8_t * e, BN_CTX * ctx) const // B*e. e is 32 bytes Little Endian
EDDSAPoint MulB (const uint8_t * e, BN_CTX * ctx) const // B*e, e is 32 bytes Little Endian
{
BIGNUM * zero = BN_new (), * one = BN_new ();
BN_zero (zero); BN_one (one);
EDDSAPoint res {zero, one};
bool carry = false;
for (int i = 0; i < 32; i++)
{
uint8_t x = e[i] & 0x0F; // 4 low bits
if (carry) { x++; if (x <= 15) carry = false; else x = 0; };
if (x > 0)
res = Sum (res, Bi16[i*2][x-1], ctx);
{
if (x <= 8)
res = Sum (res, Bi16[i*2][x-1], ctx);
else
{
res = Sum (res, -Bi16[i*2][15-x], ctx); // -Bi[16-x]
carry = true;
}
}
x = e[i] >> 4; // 4 high bits
if (carry) { x++; if (x <= 15) carry = false; else x = 0; };
if (x > 0)
res = Sum (res, Bi16[i*2+1][x-1], ctx);
{
if (x <= 8)
res = Sum (res, Bi16[i*2+1][x-1], ctx);
else
{
res = Sum (res, -Bi16[i*2+1][15-x], ctx); // -Bi[16-x]
carry = true;
}
}
}
if (carry) res = Sum (res, Bi16Carry, ctx);
return res;
}
@ -391,8 +415,10 @@ namespace crypto
BIGNUM * q, * l, * d, * I;
// transient values
BIGNUM * two_252_2; // 2^252-2
EDDSAPoint Bi16[64][15]; // per 4-bits, Bi16[i][j] = (16+j+1)^i*B, we don't store zeroes
EDDSAPoint Bi16[64][8]; // per 4-bits, Bi16[i][j] = (16+j+1)^i*B, we don't store zeroes
// if j > 8 we use 16 - j and carry 1 to next 4-bits
// Bi16[0][0] = B, base point
EDDSAPoint Bi16Carry; // Bi16[64][0]
};
static std::shared_ptr<Ed25519> g_Ed25519;