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Reduce the amount of generated random bytes

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This commit optimized the generation of key shares by letting
the SKAHE256 PRF only generate the exact amount of random bytes
that is needed.
This commit is contained in:
Daan Sprenkels
2017-04-25 17:54:40 +02:00
parent c32c015050
commit 23f96d00e1
1 changed files with 4 additions and 4 deletions
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8
hazmat.c
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@@ -59,7 +59,7 @@ static uint8_t gf256_inv(uint8_t a)
static int create_byte_shares(ByteShare *out,
uint8_t secret,
uint8_t n, uint8_t k,
uint8_t random_bytes[256])
uint8_t *random_bytes)
{
uint8_t poly[256] = { 0 }, x, y, xpow;
size_t point_idx, coeff_idx;
@@ -70,7 +70,7 @@ static int create_byte_shares(ByteShare *out,
if (k > n) return -1;
/* Create a random polynomial of order k */
memcpy(&poly[255 - k], &random_bytes[255 - k], k);
memcpy(&poly[255 - k], random_bytes, k);
/* Set the secret value in the polynomial */
poly[255] = secret;
@@ -129,7 +129,7 @@ static uint8_t combine_byte_shares(const ByteShare *shares, const uint8_t k)
size_t byte_idx, share_idx;
uint8_t x;
ByteShare byte_shares[n * sizeof(ByteShare)];
uint8_t random_bytes[256*256];
uint8_t random_bytes[k * 256];
/* Generate a lot of random bytes */
FIPS202_SHAKE256(key, 32, random_bytes, sizeof(random_bytes));
@@ -141,7 +141,7 @@ static uint8_t combine_byte_shares(const ByteShare *shares, const uint8_t k)
for (byte_idx = 0; byte_idx < 32; byte_idx++) {
create_byte_shares(byte_shares, key[byte_idx], n, k,
&random_bytes[byte_idx*256]);
&random_bytes[byte_idx * k]);
for (share_idx = 0; share_idx < n; share_idx++) {
assert(out[share_idx].x == byte_shares[share_idx].x);
out[share_idx].y[byte_idx] = byte_shares[share_idx].y;