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/*
* Copyright (C) 2016 Andreas Steffen
* HSR Hochschule fuer Technik Rapperswil
*
* Based on public domain code by Erdem Alkim, Léo Ducas, Thomas Pöppelmann,
* and Peter Schwabe.
*
* 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 "newhope_reconciliation.h"
typedef struct private_newhope_reconciliation_t private_newhope_reconciliation_t;
/**
* Private data of an newhope_reconciliation_t object.
*/
struct private_newhope_reconciliation_t {
/**
* Public newhope_reconciliation_t interface.
*/
newhope_reconciliation_t public;
/**
* Array sizes
*/
int n, n4;
/**
* Multiples of modulus q
*/
int32_t q, q2, q4, q8, q16;
};
static inline int32_t rec_abs(int32_t v)
{
int32_t mask = v >> 31;
return (v ^ mask) - mask;
}
/**
* Auxiliary function used by help_reconcile() method
*/
static int32_t rec_f(private_newhope_reconciliation_t *this,
int32_t v, uint8_t r, int32_t *v0, int32_t *v1)
{
int32_t x, xit, t, b;
x = 8 * v + 2 * r;
/* compute t = x/q */
b = x * 2730;
t = b >> 25;
b = x - t * this->q;
b = this->q - 1 - b;
b >>= 31;
t -= b;
r = t & 0x01;
xit = (t >> 1);
*v0 = xit + r ; /* v0 = round(x/(2q)) */
t -= 1;
r = t & 0x01;
*v1 = ( t>> 1) + r;
return rec_abs(x - (*v0) * this->q2);
}
/**
* Auxiliary function used by reconcile() method
*/
static int32_t rec_g(private_newhope_reconciliation_t *this, int32_t x)
{
int32_t t, r, b;
/* t = x/(4*q) */
b = x * 2730;
t = b >> 27;
b = x - t * this->q4;
b = this->q4 - 1 - b;
b >>= 31;
t -= b;
r = t & 0x01;
t = (t >> 1) + r; /* t = round(x/(8q)) */
t *= this->q8;
return abs(t - x);
}
METHOD(newhope_reconciliation_t, help_reconcile, uint8_t*,
private_newhope_reconciliation_t *this, uint32_t *v, uint8_t *rbits)
{
int32_t v0[4], v1[4], v_tmp[4], k;
int i, i0, i1, i2, i3, j;
uint8_t *r, rbit;
/* allocate output vector */
r = (uint8_t*)malloc(this->n);
for (i = 0; i < this->n4/8; i++)
{
for (j = 0; j < 8; j++)
{
i0 = 8*i + j;
i1 = i0 + this->n4;
i2 = i1 + this->n4;
i3 = i2 + this->n4;
/* iterate through all 256 random bits */
rbit = (rbits[i] >> j) & 0x01;
k = rec_f(this, v[i0], rbit, &v0[0], &v1[0]);
k += rec_f(this, v[i1], rbit, &v0[1], &v1[1]);
k += rec_f(this, v[i2], rbit, &v0[2], &v1[2]);
k += rec_f(this, v[i3], rbit, &v0[3], &v1[3]);
k = (this->q2 - 1 - k) >> 31;
v_tmp[0] = ((~k) & v0[0]) ^ (k & v1[0]);
v_tmp[1] = ((~k) & v0[1]) ^ (k & v1[1]);
v_tmp[2] = ((~k) & v0[2]) ^ (k & v1[2]);
v_tmp[3] = ((~k) & v0[3]) ^ (k & v1[3]);
r[i0] = (v_tmp[0] - v_tmp[3]) & 0x03;
r[i1] = (v_tmp[1] - v_tmp[3]) & 0x03;
r[i2] = (v_tmp[2] - v_tmp[3]) & 0x03;
r[i3] = (v_tmp[3] - k + v_tmp[3]) & 0x03;
}
}
return r;
}
METHOD(newhope_reconciliation_t, reconcile, chunk_t,
private_newhope_reconciliation_t *this, uint32_t *v, uint8_t *r)
{
size_t key_len;
uint8_t *key;
int32_t tmp[4], t;
int i, i0, i1, i2, i3, j;
key_len = this->n4 / 8;
key = (uint8_t*)malloc(key_len);
memset(key, 0x00, key_len);
for (i = 0; i < key_len; i++)
{
for (j = 0; j < 8; j++)
{
i0 = 8*i + j;
i1 = i0 + this->n4;
i2 = i1 + this->n4;
i3 = i2 + this->n4;
tmp[0] = this->q16 + 8 * (int32_t)v[i0] -
this->q * (2*r[i0] + r[i3]);
tmp[1] = this->q16 + 8 * (int32_t)v[i1] -
this->q * (2*r[i1] + r[i3]);
tmp[2] = this->q16 + 8 * (int32_t)v[i2] -
this->q * (2*r[i2] + r[i3]);
tmp[3] = this->q16 + 8 * (int32_t)v[i3] -
this->q * ( r[i3]);
t = rec_g(this, tmp[0]) + rec_g(this, tmp[1]) +
rec_g(this, tmp[2]) + rec_g(this, tmp[3]) - this->q8;
key[i] |= ((t >> 31) & 0x01) << j;
}
}
return chunk_create(key, key_len);
}
METHOD(newhope_reconciliation_t, destroy, void,
private_newhope_reconciliation_t *this)
{
free(this);
}
/*
* Described in header.
*/
newhope_reconciliation_t *newhope_reconciliation_create(int n, int32_t q)
{
private_newhope_reconciliation_t *this;
INIT(this,
.public = {
.help_reconcile = _help_reconcile,
.reconcile = _reconcile,
.destroy = _destroy,
},
.n = n,
.n4 = n / 4,
.q = q,
.q2 = 2 * q,
.q4 = 4 * q,
.q8 = 8 * q,
.q16 = 16 * q,
);
return &this->public;
}
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