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/*
* Copyright (C) 2014 Andreas Steffen
* HSR Hochschule fuer Technik Rapperswil
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version. See <http://www.fsf.org/copyleft/gpl.txt>.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*/
#include "bliss_utils.h"
#include <asn1/asn1.h>
#include <crypto/hashers/hasher.h>
#include <utils/debug.h>
/**
* See header.
*/
int32_t bliss_utils_scalar_product(int32_t *x, int32_t *y, int n)
{
int32_t product = 0;
int i;
for (i = 0; i < n; i++)
{
product += x[i] * y[i];
}
return product;
}
/**
* See header.
*/
void bliss_utils_round_and_drop(bliss_param_set_t *set, int32_t *x, int16_t *xd)
{
int32_t factor;
int i;
factor = 1 << set->d;
for (i = 0; i < set->n; i++)
{
xd[i] = ((x[i] + (factor >> 1)) / factor) % set->p;
}
}
/**
* See header.
*/
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;
uint64_t extra_bits;
uint16_t index, rounds = 0;
uint8_t hash[HASH_SIZE_SHA512], un16_buf[2];
chunk_t un16 = { un16_buf, 2 };
bool index_taken[n];
while (TRUE)
{
if (!hasher->get_hash(hasher, data_hash, NULL))
{
return FALSE;
}
for (i = 0; i < n; i++)
{
htoun16(un16_buf, ud[i]);
if (!hasher->get_hash(hasher, un16, NULL))
{
return FALSE;
}
index_taken[i] = FALSE;
}
htoun16(un16_buf, rounds++);
if (!hasher->get_hash(hasher, un16, hash))
{
return FALSE;
}
extra_bits = untoh64(hash + sizeof(hash) - sizeof(uint64_t));
for (i = 0, j = 0; j < sizeof(hash); j++)
{
index = 2 * (uint16_t)hash[i] + (extra_bits & 1);
if (!index_taken[index])
{
c_indices[i++] = index;
index_taken[index] = TRUE;
}
if (i == kappa)
{
return TRUE;
}
}
}
}
/**
* See header.
*/
bool bliss_utils_check_norms(bliss_param_set_t *set, int32_t *z1, int16_t *z2d)
{
int32_t z2ds[set->n];
int32_t z1_min, z1_max, norm;
int16_t z2d_min, z2d_max;
int i;
/* some statistics on the values of z1 and z2d */
z1_min = z1_max = z1[0];
z2d_min = z2d_max = z2d[0];
for (i = 1; i < set->n; i++)
{
if (z1[i] < z1_min)
{
z1_min = z1[i];
}
else if (z1[i] > z1_max)
{
z1_max = z1[i];
}
if (z2d[i] < z2d_min)
{
z2d_min = z2d[i];
}
else if (z2d[i] > z2d_max)
{
z2d_max = z2d[i];
}
}
DBG2(DBG_LIB, "z1 = %d..%d, z2d = %d..%d", z1_min, z1_max, z2d_min, z2d_max);
/* Restriction on infinite norm */
for (i = 0; i < set->n; i++)
{
z2ds[i] = (1 << set->d) * z2d[i];
if (z1[i] >= set->B_inf || z2ds[i] >= set->B_inf ||
z1[i] <= -set->B_inf || z2ds[i] <= -set->B_inf)
{
DBG2(DBG_LIB, "signature rejected due to excessive infinite norm");
return FALSE;
}
}
/* Restriction on l2-norm */
norm = bliss_utils_scalar_product(z1, z1, set->n) +
bliss_utils_scalar_product(z2ds, z2ds, set->n);
if (norm >= set->B_l2)
{
DBG2(DBG_LIB, "signature rejected due to excessive l2-norm");
return FALSE;
}
return TRUE;
}
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