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ec_mult.h: add minimal countermeasure against power-monitoring attack. #192

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ec_mult.h: add minimal countermeasure against power-monitoring attack. #192

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df779fb
vect.h: add vec_czero.
dot-asm Sep 20, 2023
a09f934
ec_mult.h: add minimal countermeasure against power-monitoring attack.
dot-asm Sep 20, 2023
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58 changes: 42 additions & 16 deletions src/ec_mult.h
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Original file line number Diff line number Diff line change
Expand Up @@ -66,20 +66,22 @@ static limb_t booth_encode(limb_t wval, size_t sz)
* infinity "naturally," since resulting Z is product of original Z.]
*/
#define POINT_MULT_SCALAR_WX_IMPL(ptype, SZ) \
static void ptype##_gather_booth_w##SZ(ptype *restrict p, \
const ptype table[1<<(SZ-1)], \
limb_t booth_idx) \
static bool_t ptype##_gather_booth_w##SZ(ptype *restrict p, \
const ptype table[1<<(SZ-1)], \
limb_t booth_idx) \
{ \
size_t i; \
bool_t booth_sign = (booth_idx >> SZ) & 1; \
\
booth_idx &= (1<<SZ) - 1; \
vec_zero(p, sizeof(ptype)); /* implicit infinity at table[-1] */\
vec_copy(p, table, sizeof(ptype)); \
/* ~6% with -Os, ~2% with -O3 ... */\
for (i = 1; i <= 1<<(SZ-1); i++) \
for (i = 2; i <= 1<<(SZ-1); i++) \
ptype##_ccopy(p, table + i - 1, byte_is_zero((byte)(i ^ booth_idx))); \
\
ptype##_cneg(p, booth_sign); \
\
return byte_is_zero((byte)booth_idx); \
} \
\
static void ptype##_precompute_w##SZ(ptype row[], const ptype *point) \
Expand All @@ -101,7 +103,8 @@ static void ptype##s_mult_w##SZ(ptype *ret, \
limb_t wmask, wval; \
size_t i, j, window, nbytes; \
const byte *scalar, **scalar_s = scalars; \
ptype temp[1]; \
ptype sum[1], row[1]; \
bool_t sum_is_inf, row_is_inf, ret_is_inf; \
\
if (table == NULL) \
table = (ptype (*)[1<<(SZ-1)])alloca((1<<(SZ-1)) * sizeof(ptype) * \
Expand All @@ -128,16 +131,22 @@ static void ptype##s_mult_w##SZ(ptype *ret, \
wval = (scalar[0] << 1) & wmask; \
\
wval = booth_encode(wval, SZ); \
ptype##_gather_booth_w##SZ(ret, table[0], wval); \
ret_is_inf = ptype##_gather_booth_w##SZ(ret, table[0], wval); \
\
i = 1; \
while (bits > 0) { \
for (; i < npoints; i++) { \
scalar = *scalar_s ? *scalar_s++ : scalar+nbytes; \
wval = get_wval(scalar, bits - 1, window + 1) & wmask; \
wval = booth_encode(wval, SZ); \
ptype##_gather_booth_w##SZ(temp, table[i], wval); \
ptype##_dadd(ret, ret, temp, NULL); \
row_is_inf = ptype##_gather_booth_w##SZ(row, table[i], wval); \
ptype##_dadd(sum, ret, row, NULL); \
ptype##_ccopy(ret, sum, (ret_is_inf | row_is_inf) ^ 1); \
sum_is_inf = vec_is_zero(ret->Z, sizeof(ret->Z)); \
ret_is_inf |= sum_is_inf; \
row_is_inf |= sum_is_inf; \
ptype##_ccopy(ret, row, ret_is_inf); \
ret_is_inf &= row_is_inf; \
} \
\
for (j = 0; j < SZ; j++) \
Expand All @@ -153,17 +162,26 @@ static void ptype##s_mult_w##SZ(ptype *ret, \
scalar = *scalar_s ? *scalar_s++ : scalar+nbytes; \
wval = (scalar[0] << 1) & wmask; \
wval = booth_encode(wval, SZ); \
ptype##_gather_booth_w##SZ(temp, table[i], wval); \
ptype##_dadd(ret, ret, temp, NULL); \
row_is_inf = ptype##_gather_booth_w##SZ(row, table[i], wval); \
ptype##_dadd(sum, ret, row, NULL); \
ptype##_ccopy(ret, sum, (ret_is_inf | row_is_inf) ^ 1); \
sum_is_inf = vec_is_zero(ret->Z, sizeof(ret->Z)); \
ret_is_inf |= sum_is_inf; \
row_is_inf |= sum_is_inf; \
ptype##_ccopy(ret, row, ret_is_inf); \
ret_is_inf &= row_is_inf; \
} \
\
vec_czero(ret->Z, sizeof(ret->Z), ret_is_inf); \
} \
\
static void ptype##_mult_w##SZ(ptype *ret, const ptype *point, \
const byte *scalar, size_t bits) \
{ \
limb_t wmask, wval; \
size_t j, window; \
ptype temp[1]; \
ptype sum[1], row[1]; \
bool_t sum_is_inf, row_is_inf, ret_is_inf; \
ptype table[1<<(SZ-1)]; \
\
ptype##_precompute_w##SZ(table, point); \
Expand All @@ -177,7 +195,7 @@ static void ptype##_mult_w##SZ(ptype *ret, const ptype *point, \
: (limb_t)scalar[0] << 1; \
wval &= wmask; \
wval = booth_encode(wval, SZ); \
ptype##_gather_booth_w##SZ(ret, table, wval); \
ret_is_inf = ptype##_gather_booth_w##SZ(ret, table, wval); \
\
while (bits > 0) { \
for (j = 0; j < SZ; j++) \
Expand All @@ -191,10 +209,18 @@ static void ptype##_mult_w##SZ(ptype *ret, const ptype *point, \
: (limb_t)scalar[0] << 1; \
wval &= wmask; \
wval = booth_encode(wval, SZ); \
ptype##_gather_booth_w##SZ(temp, table, wval); \
if (bits > 0) ptype##_add(ret, ret, temp); \
else ptype##_dadd(ret, ret, temp, NULL); \
row_is_inf = ptype##_gather_booth_w##SZ(row, table, wval); \
if (bits > 0) ptype##_add(sum, ret, row); \
else ptype##_dadd(sum, ret, row, NULL); \
ptype##_ccopy(ret, sum, (ret_is_inf | row_is_inf) ^ 1); \
sum_is_inf = vec_is_zero(ret->Z, sizeof(ret->Z)); \
ret_is_inf |= sum_is_inf; \
row_is_inf |= sum_is_inf; \
ptype##_ccopy(ret, row, ret_is_inf); \
ret_is_inf &= row_is_inf; \
} \
\
vec_czero(ret->Z, sizeof(ret->Z), ret_is_inf); \
}

#if 0
Expand Down
15 changes: 15 additions & 0 deletions src/vect.h
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Original file line number Diff line number Diff line change
Expand Up @@ -381,6 +381,21 @@ static inline void vec_zero(void *ret, size_t num)
#endif
}

static inline void vec_czero(void *ret, size_t num, bool_t cbit)
{
limb_t *rp = (limb_t *)ret;
size_t i;
limb_t mask;

launder(cbit);
mask = (limb_t)0 - (cbit^1);

num /= sizeof(limb_t);

for (i = 0; i < num; i++)
rp[i] &= mask;
}

/*
* Some compilers get arguably overzealous(*) when passing pointer to
* multi-dimensional array [such as vec384x] as 'const' argument.
Expand Down