/* Elliptic curve scalar-point multiplication. Computes R(x, y) = k1 * G +
* k2 * P(x, y), where G is the generator (base point) of the group of
* points on the elliptic curve. Allows k1 = NULL or { k2, P } = NULL.
* Uses mixed Jacobian-affine coordinates. Input and output values are
* assumed to be NOT field-encoded. Uses algorithm 15 (simultaneous
* multiple point multiplication) from Brown, Hankerson, Lopez, Menezes.
* Software Implementation of the NIST Elliptic Curves over Prime Fields. */
mp_err
ec_GFp_pts_mul_jac(const mp_int *k1, const mp_int *k2, const mp_int *px,
const mp_int *py, mp_int *rx, mp_int *ry,
const ECGroup *group)
{
mp_err res = MP_OKAY;
mp_int precomp[4][4][2];
mp_int rz;
const mp_int *a, *b;
unsigned int i, j;
int ai, bi, d;
for (i = 0; i < 4; i++) {
for (j = 0; j < 4; j++) {
MP_DIGITS(&precomp[i][j][0]) = 0;
MP_DIGITS(&precomp[i][j][1]) = 0;
}
}
MP_DIGITS(&rz) = 0;
ARGCHK(group != NULL, MP_BADARG);
ARGCHK(!((k1 == NULL)
&& ((k2 == NULL) || (px == NULL)
|| (py == NULL))), MP_BADARG);
/* if some arguments are not defined used ECPoint_mul */
if (k1 == NULL) {
return ECPoint_mul(group, k2, px, py, rx, ry);
} else if ((k2 == NULL) || (px == NULL) || (py == NULL)) {
return ECPoint_mul(group, k1, NULL, NULL, rx, ry);
}
/* initialize precomputation table */
for (i = 0; i < 4; i++) {
for (j = 0; j < 4; j++) {
MP_CHECKOK(mp_init(&precomp[i][j][0]));
MP_CHECKOK(mp_init(&precomp[i][j][1]));
}
}
/* fill precomputation table */
/* assign {k1, k2} = {a, b} such that len(a) >= len(b) */
if (mpl_significant_bits(k1) < mpl_significant_bits(k2)) {
a = k2;
b = k1;
if (group->meth->field_enc) {
MP_CHECKOK(group->meth->
field_enc(px, &precomp[1][0][0], group->meth));
MP_CHECKOK(group->meth->
field_enc(py, &precomp[1][0][1], group->meth));
} else {
MP_CHECKOK(mp_copy(px, &precomp[1][0][0]));
MP_CHECKOK(mp_copy(py, &precomp[1][0][1]));
}
MP_CHECKOK(mp_copy(&group->genx, &precomp[0][1][0]));
MP_CHECKOK(mp_copy(&group->geny, &precomp[0][1][1]));
} else {
a = k1;
b = k2;
MP_CHECKOK(mp_copy(&group->genx, &precomp[1][0][0]));
MP_CHECKOK(mp_copy(&group->geny, &precomp[1][0][1]));
if (group->meth->field_enc) {
MP_CHECKOK(group->meth->
field_enc(px, &precomp[0][1][0], group->meth));
MP_CHECKOK(group->meth->
field_enc(py, &precomp[0][1][1], group->meth));
} else {
MP_CHECKOK(mp_copy(px, &precomp[0][1][0]));
MP_CHECKOK(mp_copy(py, &precomp[0][1][1]));
}
}
/* precompute [*][0][*] */
mp_zero(&precomp[0][0][0]);
mp_zero(&precomp[0][0][1]);
MP_CHECKOK(group->
point_dbl(&precomp[1][0][0], &precomp[1][0][1],
&precomp[2][0][0], &precomp[2][0][1], group));
MP_CHECKOK(group->
point_add(&precomp[1][0][0], &precomp[1][0][1],
&precomp[2][0][0], &precomp[2][0][1],
&precomp[3][0][0], &precomp[3][0][1], group));
/* precompute [*][1][*] */
for (i = 1; i < 4; i++) {
MP_CHECKOK(group->
point_add(&precomp[0][1][0], &precomp[0][1][1],
&precomp[i][0][0], &precomp[i][0][1],
&precomp[i][1][0], &precomp[i][1][1], group));
}
/* precompute [*][2][*] */
MP_CHECKOK(group->
point_dbl(&precomp[0][1][0], &precomp[0][1][1],
&precomp[0][2][0], &precomp[0][2][1], group));
for (i = 1; i < 4; i++) {
MP_CHECKOK(group->
point_add(&precomp[0][2][0], &precomp[0][2][1],
&precomp[i][0][0], &precomp[i][0][1],
&precomp[i][2][0], &precomp[i][2][1], group));
}
/* precompute [*][3][*] */
MP_CHECKOK(group->
point_add(&precomp[0][1][0], &precomp[0][1][1],
&precomp[0][2][0], &precomp[0][2][1],
&precomp[0][3][0], &precomp[0][3][1], group));
for (i = 1; i < 4; i++) {
MP_CHECKOK(group->
point_add(&precomp[0][3][0], &precomp[0][3][1],
&precomp[i][0][0], &precomp[i][0][1],
&precomp[i][3][0], &precomp[i][3][1], group));
}
d = (mpl_significant_bits(a) + 1) / 2;
/* R = inf */
MP_CHECKOK(mp_init(&rz));
MP_CHECKOK(ec_GFp_pt_set_inf_jac(rx, ry, &rz));
for (i = d; i-- > 0;) {
ai = MP_GET_BIT(a, 2 * i + 1);
ai <<= 1;
ai |= MP_GET_BIT(a, 2 * i);
bi = MP_GET_BIT(b, 2 * i + 1);
bi <<= 1;
bi |= MP_GET_BIT(b, 2 * i);
/* R = 2^2 * R */
MP_CHECKOK(ec_GFp_pt_dbl_jac(rx, ry, &rz, rx, ry, &rz, group));
MP_CHECKOK(ec_GFp_pt_dbl_jac(rx, ry, &rz, rx, ry, &rz, group));
/* R = R + (ai * A + bi * B) */
MP_CHECKOK(ec_GFp_pt_add_jac_aff
(rx, ry, &rz, &precomp[ai][bi][0], &precomp[ai][bi][1],
rx, ry, &rz, group));
}
MP_CHECKOK(ec_GFp_pt_jac2aff(rx, ry, &rz, rx, ry, group));
if (group->meth->field_dec) {
MP_CHECKOK(group->meth->field_dec(rx, rx, group->meth));
MP_CHECKOK(group->meth->field_dec(ry, ry, group->meth));
}
CLEANUP:
mp_clear(&rz);
for (i = 0; i < 4; i++) {
for (j = 0; j < 4; j++) {
mp_clear(&precomp[i][j][0]);
mp_clear(&precomp[i][j][1]);
}
}
return res;
}
/* Computes R = nP where R is (rx, ry) and P is (px, py). The parameters
* a, b and p are the elliptic curve coefficients and the prime that
* determines the field GFp. Elliptic curve points P and R can be
* identical. Uses mixed Jacobian-affine coordinates. Assumes input is
* already field-encoded using field_enc, and returns output that is still
* field-encoded. Uses 4-bit window method. */
mp_err
ec_GFp_pt_mul_jac(const mp_int *n, const mp_int *px, const mp_int *py,
mp_int *rx, mp_int *ry, const ECGroup *group)
{
mp_err res = MP_OKAY;
mp_int precomp[16][2], rz;
int i, ni, d;
MP_DIGITS(&rz) = 0;
for (i = 0; i < 16; i++) {
MP_DIGITS(&precomp[i][0]) = 0;
MP_DIGITS(&precomp[i][1]) = 0;
}
ARGCHK(group != NULL, MP_BADARG);
ARGCHK((n != NULL) && (px != NULL) && (py != NULL), MP_BADARG);
/* initialize precomputation table */
for (i = 0; i < 16; i++) {
MP_CHECKOK(mp_init(&precomp[i][0]));
MP_CHECKOK(mp_init(&precomp[i][1]));
}
/* fill precomputation table */
mp_zero(&precomp[0][0]);
mp_zero(&precomp[0][1]);
MP_CHECKOK(mp_copy(px, &precomp[1][0]));
MP_CHECKOK(mp_copy(py, &precomp[1][1]));
for (i = 2; i < 16; i++) {
MP_CHECKOK(group->
point_add(&precomp[1][0], &precomp[1][1],
&precomp[i - 1][0], &precomp[i - 1][1],
&precomp[i][0], &precomp[i][1], group));
}
d = (mpl_significant_bits(n) + 3) / 4;
/* R = inf */
MP_CHECKOK(mp_init(&rz));
MP_CHECKOK(ec_GFp_pt_set_inf_jac(rx, ry, &rz));
for (i = d - 1; i >= 0; i--) {
/* compute window ni */
ni = MP_GET_BIT(n, 4 * i + 3);
ni <<= 1;
ni |= MP_GET_BIT(n, 4 * i + 2);
ni <<= 1;
ni |= MP_GET_BIT(n, 4 * i + 1);
ni <<= 1;
ni |= MP_GET_BIT(n, 4 * i);
/* R = 2^4 * R */
MP_CHECKOK(ec_GFp_pt_dbl_jac(rx, ry, &rz, rx, ry, &rz, group));
MP_CHECKOK(ec_GFp_pt_dbl_jac(rx, ry, &rz, rx, ry, &rz, group));
MP_CHECKOK(ec_GFp_pt_dbl_jac(rx, ry, &rz, rx, ry, &rz, group));
MP_CHECKOK(ec_GFp_pt_dbl_jac(rx, ry, &rz, rx, ry, &rz, group));
/* R = R + (ni * P) */
MP_CHECKOK(ec_GFp_pt_add_jac_aff
(rx, ry, &rz, &precomp[ni][0], &precomp[ni][1], rx, ry,
&rz, group));
}
/* convert result S to affine coordinates */
MP_CHECKOK(ec_GFp_pt_jac2aff(rx, ry, &rz, rx, ry, group));
CLEANUP:
mp_clear(&rz);
for (i = 0; i < 16; i++) {
mp_clear(&precomp[i][0]);
mp_clear(&precomp[i][1]);
}
return res;
}
/* Uses mixed Jacobian-affine coordinates to perform a point
* multiplication: R = n * P, n scalar. Uses mixed Jacobian-affine
* coordinates (Jacobian coordinates for doubles and affine coordinates
* for additions; based on recommendation from Brown et al.). Not very
* time efficient but quite space efficient, no precomputation needed.
* group contains the elliptic curve coefficients and the prime that
* determines the field GFp. Elliptic curve points P and R can be
* identical. Performs calculations in floating point number format, since
* this is faster than the integer operations on the ULTRASPARC III.
* Uses left-to-right binary method (double & add) (algorithm 9) for
* scalar-point multiplication from Brown, Hankerson, Lopez, Menezes.
* Software Implementation of the NIST Elliptic Curves Over Prime Fields. */
mp_err
ec_GFp_pt_mul_jac_fp(const mp_int *n, const mp_int *px, const mp_int *py,
mp_int *rx, mp_int *ry, const ECGroup *ecgroup)
{
mp_err res;
mp_int sx, sy, sz;
ecfp_aff_pt p;
ecfp_jac_pt r;
EC_group_fp *group = (EC_group_fp *) ecgroup->extra1;
int i, l;
MP_DIGITS(&sx) = 0;
MP_DIGITS(&sy) = 0;
MP_DIGITS(&sz) = 0;
MP_CHECKOK(mp_init(&sx));
MP_CHECKOK(mp_init(&sy));
MP_CHECKOK(mp_init(&sz));
/* if n = 0 then r = inf */
if (mp_cmp_z(n) == 0) {
mp_zero(rx);
mp_zero(ry);
res = MP_OKAY;
goto CLEANUP;
/* if n < 0 then out of range error */
} else if (mp_cmp_z(n) < 0) {
res = MP_RANGE;
goto CLEANUP;
}
/* Convert from integer to floating point */
ecfp_i2fp(p.x, px, ecgroup);
ecfp_i2fp(p.y, py, ecgroup);
ecfp_i2fp(group->curvea, &(ecgroup->curvea), ecgroup);
/* Init r to point at infinity */
for (i = 0; i < group->numDoubles; i++) {
r.z[i] = 0;
}
/* double and add method */
l = mpl_significant_bits(n) - 1;
for (i = l; i >= 0; i--) {
/* R = 2R */
group->pt_dbl_jac(&r, &r, group);
/* if n_i = 1, then R = R + Q */
if (MP_GET_BIT(n, i) != 0) {
group->pt_add_jac_aff(&r, &p, &r, group);
}
}
/* Convert from floating point to integer */
ecfp_fp2i(&sx, r.x, ecgroup);
ecfp_fp2i(&sy, r.y, ecgroup);
ecfp_fp2i(&sz, r.z, ecgroup);
/* convert result R to affine coordinates */
MP_CHECKOK(ec_GFp_pt_jac2aff(&sx, &sy, &sz, rx, ry, ecgroup));
CLEANUP:
mp_clear(&sx);
mp_clear(&sy);
mp_clear(&sz);
return res;
}
/* Computes R = nP based on IEEE P1363 A.10.3. Elliptic curve points P and
* R can be identical. Uses affine coordinates. Assumes input is already
* field-encoded using field_enc, and returns output that is still
* field-encoded. */
mp_err
ec_GFp_pt_mul_aff(const mp_int *n, const mp_int *px, const mp_int *py,
mp_int *rx, mp_int *ry, const ECGroup *group)
{
mp_err res = MP_OKAY;
mp_int k, k3, qx, qy, sx, sy;
int b1, b3, i, l;
MP_DIGITS(&k) = 0;
MP_DIGITS(&k3) = 0;
MP_DIGITS(&qx) = 0;
MP_DIGITS(&qy) = 0;
MP_DIGITS(&sx) = 0;
MP_DIGITS(&sy) = 0;
MP_CHECKOK(mp_init(&k));
MP_CHECKOK(mp_init(&k3));
MP_CHECKOK(mp_init(&qx));
MP_CHECKOK(mp_init(&qy));
MP_CHECKOK(mp_init(&sx));
MP_CHECKOK(mp_init(&sy));
/* if n = 0 then r = inf */
if (mp_cmp_z(n) == 0) {
mp_zero(rx);
mp_zero(ry);
res = MP_OKAY;
goto CLEANUP;
}
/* Q = P, k = n */
MP_CHECKOK(mp_copy(px, &qx));
MP_CHECKOK(mp_copy(py, &qy));
MP_CHECKOK(mp_copy(n, &k));
/* if n < 0 then Q = -Q, k = -k */
if (mp_cmp_z(n) < 0) {
MP_CHECKOK(group->meth->field_neg(&qy, &qy, group->meth));
MP_CHECKOK(mp_neg(&k, &k));
}
#ifdef ECL_DEBUG /* basic double and add method */
l = mpl_significant_bits(&k) - 1;
MP_CHECKOK(mp_copy(&qx, &sx));
MP_CHECKOK(mp_copy(&qy, &sy));
for (i = l - 1; i >= 0; i--) {
/* S = 2S */
MP_CHECKOK(group->point_dbl(&sx, &sy, &sx, &sy, group));
/* if k_i = 1, then S = S + Q */
if (mpl_get_bit(&k, i) != 0) {
MP_CHECKOK(group->point_add(&sx, &sy, &qx, &qy, &sx, &sy, group));
}
}
#else /* double and add/subtract method from \
* standard */
/* k3 = 3 * k */
MP_CHECKOK(mp_set_int(&k3, 3));
MP_CHECKOK(mp_mul(&k, &k3, &k3));
/* S = Q */
MP_CHECKOK(mp_copy(&qx, &sx));
MP_CHECKOK(mp_copy(&qy, &sy));
/* l = index of high order bit in binary representation of 3*k */
l = mpl_significant_bits(&k3) - 1;
/* for i = l-1 downto 1 */
for (i = l - 1; i >= 1; i--) {
/* S = 2S */
MP_CHECKOK(group->point_dbl(&sx, &sy, &sx, &sy, group));
b3 = MP_GET_BIT(&k3, i);
b1 = MP_GET_BIT(&k, i);
/* if k3_i = 1 and k_i = 0, then S = S + Q */
if ((b3 == 1) && (b1 == 0)) {
MP_CHECKOK(group->point_add(&sx, &sy, &qx, &qy, &sx, &sy, group));
/* if k3_i = 0 and k_i = 1, then S = S - Q */
} else if ((b3 == 0) && (b1 == 1)) {
MP_CHECKOK(group->point_sub(&sx, &sy, &qx, &qy, &sx, &sy, group));
}
}
#endif
/* output S */
MP_CHECKOK(mp_copy(&sx, rx));
MP_CHECKOK(mp_copy(&sy, ry));
CLEANUP:
mp_clear(&k);
mp_clear(&k3);
mp_clear(&qx);
mp_clear(&qy);
mp_clear(&sx);
mp_clear(&sy);
return res;
}
/* Computes R = nP where R is (rx, ry) and P is (px, py). The parameters
* a, b and p are the elliptic curve coefficients and the prime that
* determines the field GFp. Elliptic curve points P and R can be
* identical. Uses Jacobian coordinates. Uses 4-bit window method. */
mp_err
ec_GFp_point_mul_jac_4w_fp(const mp_int *n, const mp_int *px,
const mp_int *py, mp_int *rx, mp_int *ry,
const ECGroup *ecgroup)
{
mp_err res = MP_OKAY;
ecfp_jac_pt precomp[16], r;
ecfp_aff_pt p;
EC_group_fp *group;
mp_int rz;
int i, ni, d;
ARGCHK(ecgroup != NULL, MP_BADARG);
ARGCHK((n != NULL) && (px != NULL) && (py != NULL), MP_BADARG);
group = (EC_group_fp *) ecgroup->extra1;
MP_DIGITS(&rz) = 0;
MP_CHECKOK(mp_init(&rz));
/* init p, da */
ecfp_i2fp(p.x, px, ecgroup);
ecfp_i2fp(p.y, py, ecgroup);
ecfp_i2fp(group->curvea, &ecgroup->curvea, ecgroup);
/* Do precomputation */
group->precompute_jac(precomp, &p, group);
/* Do main body of calculations */
d = (mpl_significant_bits(n) + 3) / 4;
/* R = inf */
for (i = 0; i < group->numDoubles; i++) {
r.z[i] = 0;
}
for (i = d - 1; i >= 0; i--) {
/* compute window ni */
ni = MP_GET_BIT(n, 4 * i + 3);
ni <<= 1;
ni |= MP_GET_BIT(n, 4 * i + 2);
ni <<= 1;
ni |= MP_GET_BIT(n, 4 * i + 1);
ni <<= 1;
ni |= MP_GET_BIT(n, 4 * i);
/* R = 2^4 * R */
group->pt_dbl_jac(&r, &r, group);
group->pt_dbl_jac(&r, &r, group);
group->pt_dbl_jac(&r, &r, group);
group->pt_dbl_jac(&r, &r, group);
/* R = R + (ni * P) */
group->pt_add_jac(&r, &precomp[ni], &r, group);
}
/* Convert back to integer */
ecfp_fp2i(rx, r.x, ecgroup);
ecfp_fp2i(ry, r.y, ecgroup);
ecfp_fp2i(&rz, r.z, ecgroup);
/* convert result S to affine coordinates */
MP_CHECKOK(ec_GFp_pt_jac2aff(rx, ry, &rz, rx, ry, ecgroup));
CLEANUP:
mp_clear(&rz);
return res;
}
