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Fix overflowing mults in NTRUHRSS701

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This commit is contained in:
Thom Wiggers 2020-03-09 18:02:44 -04:00
parent 39fa1ccfc7
commit bc86182b93
No known key found for this signature in database
GPG Key ID: 001BB0A7CE26E363
1 changed files with 2 additions and 2 deletions
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crypto_kem/ntruhrss701/clean/sample.c
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@ -37,14 +37,14 @@ void PQCLEAN_NTRUHRSS701_CLEAN_sample_iid_plus(poly *r, const unsigned char unif
/* s = <x*r, r>. (r[n-1] = 0) */ /* s = <x*r, r>. (r[n-1] = 0) */
for (i = 0; i < NTRU_N - 1; i++) { for (i = 0; i < NTRU_N - 1; i++) {
s += r->coeffs[i + 1] * r->coeffs[i]; s += (uint16_t)((uint32_t)r->coeffs[i + 1] * (uint32_t)r->coeffs[i]);
} }
/* Extract sign of s (sign(0) = 1) */ /* Extract sign of s (sign(0) = 1) */
s = 1 | (-(s >> 15)); s = 1 | (-(s >> 15));
for (i = 0; i < NTRU_N; i += 2) { for (i = 0; i < NTRU_N; i += 2) {
r->coeffs[i] = s * r->coeffs[i]; r->coeffs[i] = (uint16_t)((uint32_t)s * (uint32_t)r->coeffs[i]);
} }
/* Map {0,1,2^16-1} -> {0, 1, 2} */ /* Map {0,1,2^16-1} -> {0, 1, 2} */