frost/secp256k1-zkp
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ct: Be cautious and use volatile trick in more "conditional" paths

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- secp256k1_scalar_cadd_bit
 - secp256k1_modinvXX_normalize_YY
 - secp256k1_modinvXX_divsteps_ZZ
 - ECMULT_CONST_TABLE_GET_GE

Even though those code loations are not problematic right now
(with current compilers).
This commit is contained in:
Tim Ruffing
2023-05-10 16:25:37 +02:00
parent 5fb336f9ce
commit 17fa21733a
5 changed files with 40 additions and 32 deletions
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3
src/scalar_8x32_impl.h
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@@ -142,8 +142,9 @@ static int secp256k1_scalar_add(secp256k1_scalar *r, const secp256k1_scalar *a,
static void secp256k1_scalar_cadd_bit(secp256k1_scalar *r, unsigned int bit, int flag) {
uint64_t t;
volatile int vflag = flag;
VERIFY_CHECK(bit < 256);
bit += ((uint32_t) flag - 1) & 0x100; /* forcing (bit >> 5) > 7 makes this a noop */
bit += ((uint32_t) vflag - 1) & 0x100; /* forcing (bit >> 5) > 7 makes this a noop */
t = (uint64_t)r->d[0] + (((uint32_t)((bit >> 5) == 0)) << (bit & 0x1F));
r->d[0] = t & 0xFFFFFFFFULL; t >>= 32;
t += (uint64_t)r->d[1] + (((uint32_t)((bit >> 5) == 1)) << (bit & 0x1F));