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Make it more constant-time.
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@dfaranha
dfaranha committed Dec 28, 2024
1 parent 8d9f71c commit c6cfc0f
Showing 1 changed file with 84 additions and 59 deletions.
143 changes: 84 additions & 59 deletions src/bn/relic_bn_rec.c
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Original file line number Diff line number Diff line change
Expand Up @@ -699,12 +699,9 @@ void bn_rec_rtnaf(int8_t *tnaf, size_t *len, const bn_t k, int8_t u, size_t m,

void bn_rec_reg(int8_t *naf, size_t *len, const bn_t k, size_t n, size_t w) {
int i, l;
bn_t t;
dig_t t0, mask;
dig_t mask, t[RLC_FP_DIGS + 1] = { 0 };
int8_t u_i;

bn_null(t);

mask = RLC_MASK(w);
l = RLC_CEIL(n, w - 1);

Expand All @@ -714,40 +711,28 @@ void bn_rec_reg(int8_t *naf, size_t *len, const bn_t k, size_t n, size_t w) {
return;
}

RLC_TRY {
bn_new(t);
bn_abs(t, k);

memset(naf, 0, *len);
memset(naf, 0, *len);
dv_copy(t, k->dp, k->used);

i = 0;
if (w == 2) {
for (i = 0; i < l; i++) {
u_i = (t->dp[0] & mask) - 2;
t->dp[0] -= u_i;
naf[i] = u_i;
bn_hlv(t, t);
}
bn_get_dig(&t0, t);
naf[i] = t0;
} else {
for (i = 0; i < l; i++) {
u_i = (t->dp[0] & mask) - (1 << (w - 1));
t->dp[0] -= u_i;
naf[i] = u_i;
bn_rsh(t, t, w - 1);
}
bn_get_dig(&t0, t);
naf[i] = t0;
i = 0;
if (w == 2) {
for (i = 0; i < l; i++) {
u_i = (t[0] & mask) - 2;
t[0] -= u_i;
naf[i] = u_i;
bn_rsh1_low(t, t, RLC_FP_DIGS + 1);
}
*len = l + 1;
}
RLC_CATCH_ANY {
RLC_THROW(ERR_CAUGHT);
}
RLC_FINALLY {
bn_free(t);
naf[i] = t[0];
} else {
for (i = 0; i < l; i++) {
u_i = (t[0] & mask) - (1 << (w - 1));
t[0] -= u_i;
naf[i] = u_i;
bn_rshb_low(t, t, RLC_FP_DIGS + 1, w - 1);
}
naf[i] = t[0];
}
*len = l + 1;
}

void bn_rec_jsf(int8_t *jsf, size_t *len, const bn_t k, const bn_t l) {
Expand Down Expand Up @@ -831,48 +816,88 @@ void bn_rec_jsf(int8_t *jsf, size_t *len, const bn_t k, const bn_t l) {

void bn_rec_glv(bn_t k0, bn_t k1, const bn_t k, const bn_t n, const bn_st *v1,
const bn_st *v2) {
bn_t t, b1, b2;
int r1, r2;
size_t bits;
bn_t t;
int r1, r2, s1, s2;
size_t bits = bn_bits(n), d = bits >> RLC_DIG_LOG, b = bits % RLC_DIG;
dig_t b1[2 * RLC_FP_DIGS] = { 0 }, b2[2 * RLC_FP_DIGS] = { 0 };
dig_t _k[2 * RLC_FP_DIGS] = { 0 }, _v[RLC_FP_DIGS] = { 0 };
dig_t _k0[2 * RLC_FP_DIGS] = { 0 }, _k1[2 * RLC_FP_DIGS] = { 0 };

bn_null(b1);
bn_null(b2);
bn_null(t);

RLC_TRY {
bn_new(b1);
bn_new(b2);
bn_new(t);

bn_abs(t, k);
bits = bn_bits(n);

bn_mul(b1, t, &(v1[0]));
r1 = bn_get_bit(b1, bits);
bn_rsh(b1, b1, bits + 1);
bn_add_dig(b1, b1, r1);
dv_copy(_k, k->dp, k->used);
dv_copy(_v, v1[0].dp, v1[0].used);
bn_muln_low(b1, _k, _v, RLC_FP_DIGS);
r1 = (b1[d] >> b) & (dig_t)1;
dv_rshd(b1, b1, 2 * RLC_FP_DIGS, d);
bn_rshb_low(b1, b1, 2 * RLC_FP_DIGS, b);
bn_rsh1_low(b1, b1, 2 * RLC_FP_DIGS);
bn_add1_low(b1, b1, r1, 2 * RLC_FP_DIGS);
s1 = t->sign ^ v1[0].sign;

dv_zero(_v, RLC_FP_DIGS);
dv_copy(_v, v2[0].dp, v2[0].used);
bn_muln_low(b2, _k, _v, RLC_FP_DIGS);
r2 = (b2[d] >> b) & (dig_t)1;
dv_rshd(b2, b2, 2 * RLC_FP_DIGS, d);
bn_rshb_low(b2, b2, 2 * RLC_FP_DIGS, b);
bn_rsh1_low(b2, b2, 2 * RLC_FP_DIGS);
bn_add1_low(b2, b2, r2, 2 * RLC_FP_DIGS);
s2 = t->sign ^ v1[0].sign;

dv_zero(_v, RLC_FP_DIGS);
dv_copy(_v, v1[1].dp, v1[1].used);
bn_muln_low(_k0, b1, _v, RLC_FP_DIGS);
k0->used = 2 * RLC_FP_DIGS;
k0->sign = s1 ^ v1[1].sign;
dv_copy(k0->dp, _k0, k0->used);
bn_trim(k0);

dv_zero(_v, RLC_FP_DIGS);
dv_copy(_v, v2[1].dp, v2[1].used);
bn_muln_low(_k1, b2, _v, RLC_FP_DIGS);
k1->used = 2 * RLC_FP_DIGS;
k1->sign = s2 ^ v2[1].sign;
dv_copy(k1->dp, _k1, k1->used);
bn_trim(k1);

if (k0->sign != k1->sign) {
bn_negs_low(_k1, _k1, k1->sign, 2 * RLC_FP_DIGS);
}
k0->sign = bn_addn_low(_k0, _k0, _k1, 2 * RLC_FP_DIGS);
k0->used = 2 * RLC_FP_DIGS;
dv_copy(k0->dp, _k0, k0->used);
bn_trim(k0);

bn_sub(k0, t, k0);

bn_mul(b2, t, &(v2[0]));
r2 = bn_get_bit(b2, bits);
bn_rsh(b2, b2, bits + 1);
bn_add_dig(b2, b2, r2);
dv_zero(_v, 2 * RLC_FP_DIGS + 1);
dv_copy(_v, v1[2].dp, v1[2].used);
bn_muln_low(k1->dp, b1, _v, RLC_FP_DIGS);
k1->used = 2 * RLC_FP_DIGS;
k1->sign = s1 ^ v1[2].sign;
bn_trim(k1);

bn_mul(k0, b1, &(v1[1]));
bn_mul(k1, b2, &(v2[1]));
bn_add(k0, k0, k1);
bn_sub(k0, t, k0);
dv_zero(_v, 2 * RLC_FP_DIGS + 1);
dv_copy(_v, v2[2].dp, v2[2].used);
bn_muln_low(t->dp, b2, _v, RLC_FP_DIGS);
t->used = 2 * RLC_FP_DIGS;
t->sign = s2 ^ v2[2].sign;
bn_trim(t);

bn_mul(k1, b1, &(v1[2]));
bn_mul(t, b2, &(v2[2]));
bn_add(k1, k1, t);
bn_neg(k1, k1);
k1->sign ^= 1;
}
RLC_CATCH_ANY {
RLC_THROW(ERR_CAUGHT);
}
RLC_FINALLY {
bn_free(b1);
bn_free(b2);
bn_free(t);
}
}
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