uecc_EccPoint_mult() about micro-ecc HOT 1 CLOSED

No. Rx[0] and Ry[0] are initialized by XYcZ_initial_double(). Also,
bitcount_t is signed, so adding a check to see if p_numBits > 2 is
unnecessary.

On Fri, Feb 27, 2015 at 2:37 AM, azahido [email protected] wrote:

hello,
please I detect a bug in the function:
EccPoint_mult(EccPoint * RESTRICT p_result, EccPoint * RESTRICT p_point,
const uECC_word_t * RESTRICT p_scalar, const uECC_word_t * RESTRICT
p_initialZ, bitcount_t p_numBits),

the issue are, missed an initialization for Rx[0] and Ry[0] :
the solution proposed is to add the Rx[0] initial value:
vli_set(Rx[0], p_point->x);//Rx[0]
vli_set(Ry[0], p_point->y); //Rx[0]
we should add a test for p_numBits because there as an 2

P are added in the result , please find the code modified below, now it
work fine and the result compared with others calculators now we can
compute the multiplication points successfully. code corrected: static void
EccPoint_mult(EccPoint * RESTRICT p_result, EccPoint * RESTRICT p_point,
const uECC_word_t * RESTRICT p_scalar, const uECC_word_t * RESTRICT
p_initialZ, bitcount_t p_numBits) { / R0 and R1 */
uECC_word_t Rx[2][uECC_WORDS];
uECC_word_t Ry[2][uECC_WORDS];
uECC_word_t A[1][uECC_WORDS];
uECC_word_t t;
uECC_word_t z[uECC_WORDS];

bitcount_t i;
uECC_word_t nb;

vli_set(Rx[1], p_point->x);//Rx[1]
vli_set(Ry[1], p_point->y); //Rx[1]
vli_set(Rx[0], p_point->x);//Rx[0]
vli_set(Ry[0], p_point->y); //Rx[0]
if((p_numBits)>=2)
{
XYcZ_initial_double(Rx[1], Ry[1], Rx[0], Ry[0], p_initialZ);
for(i = p_numBits - 2; i > 0; --i)
{
nb =! vli_testBit(p_scalar, i);//=!
XYcZ_addC(Rx[1-nb], Ry[1-nb], Rx[nb], Ry[nb]);
XYcZ_add(Rx[nb], Ry[nb], Rx[1-nb], Ry[1-nb]);
}
nb =! vli_testBit(p_scalar, 0);//=!
XYcZ_addC(Rx[1-nb], Ry[1-nb], Rx[nb], Ry[nb]);
vli_modSub_fast(z, Rx[1], Rx[0]); /* X1 - X0 /
vli_modMult_fast(z, z, Ry[1-nb]); / Yb * (X1 - X0) /
vli_modMult_fast(z, z, p_point->x); / xP * Yb * (X1 - X0) /
vli_modInv(z, z, curve_p); / 1 / (xP * Yb * (X1 - X0)) /
vli_modMult_fast(z, z, p_point->y); / yP / (xP * Yb * (X1 - X0)) /
vli_modMult_fast(z, z, Rx[1-nb]); / Xb * yP / (xP * Yb * (X1 - X0)) /
/ End 1/Z calculation */

XYcZ_add(Rx[nb], Ry[nb], Rx[1-nb], Ry[1-nb]);
apply_z(Rx[0], Ry[0], z);

/* Find final 1/Z value. */

}

vli_set(p_result->x, Rx[0]);
vli_set(p_result->y, Ry[0]);

}

good luck

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