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Generalize c_indices generation using SHA-512 random oracle. 

This generalization allows the ring dimension n to be different
from the current n = 512 and allows kappa to be > 56. Also the
hash octets are consumed in a more consistent manner.
This commit is contained in:
Markku-Juhani Olavi Saarinen 2015-06-18 12:46:16 +02:00 committed by Andreas Steffen
parent 68d8a16830
commit 7b7c510eec
1 changed files with 25 additions and 19 deletions
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44
src/libstrongswan/plugins/bliss/bliss_utils.c
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@ -57,23 +57,27 @@ void bliss_utils_round_and_drop(bliss_param_set_t *set, int32_t *x, int16_t *xd)
bool bliss_utils_generate_c(hasher_t *hasher, chunk_t data_hash, uint16_t *ud,
int n, uint16_t kappa, uint16_t *c_indices)
{
int i, j, j_max;
uint64_t extra_bits;
uint16_t index, rounds = 0;
int i, index_found, rounds;
uint16_t index;
uint8_t hash[HASH_SIZE_SHA512], un16_buf[2];
chunk_t un16 = { un16_buf, 2 };
bool index_taken[n];
/* number of indices that can be derived in a single random oracle round */
j_max = sizeof(hash) - sizeof(extra_bits);
while (TRUE)
for (i = 0; i < n; i++)
{
index_taken[i] = FALSE;
}
index_found = 0;
for (rounds = 0; rounds < 0x10000; rounds++)
{
/* hash data */
if (!hasher->get_hash(hasher, data_hash, NULL))
{
return FALSE;
}
/* followed by the ud vector */
for (i = 0; i < n; i++)
{
htoun16(un16_buf, ud[i]);
@ -81,32 +85,34 @@ bool bliss_utils_generate_c(hasher_t *hasher, chunk_t data_hash, uint16_t *ud,
{
return FALSE;
}
index_taken[i] = FALSE;
}
htoun16(un16_buf, rounds++);
/* hash the round iteration */
htoun16(un16_buf, rounds);
if (!hasher->get_hash(hasher, un16, hash))
{
return FALSE;
}
extra_bits = untoh64(hash + j_max);
for (i = 0, j = 0; j < j_max; j++)
for (i = 0; i < HASH_SIZE_SHA512; i += 2)
{
index = 2 * (uint16_t)hash[j] + (extra_bits & 1);
index = untoh16(&hash[i]) % n;
if (!index_taken[index])
{
c_indices[i++] = index;
c_indices[index_found++] = index;
index_taken[index] = TRUE;
if (index_found == kappa)
{
return TRUE;
}
}
if (i == kappa)
{
return TRUE;
}
extra_bits >>= 1;
}
}
DBG1(DBG_LIB, "aborted c_indices generation after 2^16 rounds");
return FALSE;
}
/**