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115 lines
4.7 KiB
C
115 lines
4.7 KiB
C
/**
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*
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* <bf_decoding.c>
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*
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* @version 2.0 (March 2019)
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*
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* Reference ISO-C11 Implementation of the LEDAcrypt KEM-LT cipher using GCC built-ins.
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*
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* In alphabetical order:
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*
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* @author Marco Baldi <m.baldi@univpm.it>
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* @author Alessandro Barenghi <alessandro.barenghi@polimi.it>
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* @author Franco Chiaraluce <f.chiaraluce@univpm.it>
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* @author Gerardo Pelosi <gerardo.pelosi@polimi.it>
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* @author Paolo Santini <p.santini@pm.univpm.it>
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*
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* This code is hereby placed in the public domain.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHORS ''AS IS'' AND ANY EXPRESS
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* OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
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* OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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**/
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#include "bf_decoding.h"
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#include "gf2x_arith_mod_xPplusOne.h"
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#include <string.h>
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#include <assert.h>
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#define ROTBYTE(a) ( (a << 8) | (a >> (DIGIT_SIZE_b - 8)) )
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#define ROTUPC(a) ( (a >> 8) | (a << (DIGIT_SIZE_b - 8)) )
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int thresholds[2] = {B0, (DV * M) / 2 + 1};
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int bf_decoding(DIGIT out[], // N0 polynomials
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const POSITION_T HtrPosOnes[N0][DV],
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const POSITION_T QtrPosOnes[N0][M],
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DIGIT privateSyndrome[] // 1 polynomial
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) {
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#if P < 64
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#error The circulant block size should exceed 64
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#endif
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uint8_t unsatParityChecks[N0 * P];
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POSITION_T currQBlkPos[M], currQBitPos[M];
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DIGIT currSyndrome[NUM_DIGITS_GF2X_ELEMENT];
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int check;
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int iteration = 0;
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do {
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gf2x_copy(currSyndrome, privateSyndrome);
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memset(unsatParityChecks, 0x00, N0 * P * sizeof(uint8_t));
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for (int i = 0; i < N0; i++) {
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for (int valueIdx = 0; valueIdx < P; valueIdx++) {
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for (int HtrOneIdx = 0; HtrOneIdx < DV; HtrOneIdx++) {
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POSITION_T tmp = (HtrPosOnes[i][HtrOneIdx] + valueIdx) >= P ? (HtrPosOnes[i][HtrOneIdx] + valueIdx) - P : (HtrPosOnes[i][HtrOneIdx] + valueIdx);
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if (gf2x_get_coeff(currSyndrome, tmp)) {
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unsatParityChecks[i * P + valueIdx]++;
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}
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}
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}
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}
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/* iteration based threshold determination*/
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int corrt_syndrome_based = thresholds[iteration];
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//Computation of correlation with a full Q matrix
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for (int i = 0; i < N0; i++) {
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for (int j = 0; j < P; j++) {
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int currQoneIdx = 0; // position in the column of QtrPosOnes[][...]
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int endQblockIdx = 0;
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int correlation = 0;
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for (int blockIdx = 0; blockIdx < N0; blockIdx++) {
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endQblockIdx += qBlockWeights[blockIdx][i];
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int currblockoffset = blockIdx * P;
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for (; currQoneIdx < endQblockIdx; currQoneIdx++) {
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int tmp = QtrPosOnes[i][currQoneIdx] + j;
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tmp = tmp >= P ? tmp - P : tmp;
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currQBitPos[currQoneIdx] = tmp;
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currQBlkPos[currQoneIdx] = blockIdx;
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correlation += unsatParityChecks[tmp + currblockoffset];
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}
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}
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/* Correlation based flipping */
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if (correlation >= corrt_syndrome_based) {
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gf2x_toggle_coeff(out + NUM_DIGITS_GF2X_ELEMENT * i, j);
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for (int v = 0; v < M; v++) {
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unsigned syndromePosToFlip;
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for (int HtrOneIdx = 0; HtrOneIdx < DV; HtrOneIdx++) {
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syndromePosToFlip = (HtrPosOnes[currQBlkPos[v]][HtrOneIdx] + currQBitPos[v] );
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syndromePosToFlip = syndromePosToFlip >= P ? syndromePosToFlip - P : syndromePosToFlip;
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gf2x_toggle_coeff(privateSyndrome, syndromePosToFlip);
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}
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} // end for v
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} // end if
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} // end for j
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} // end for i
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iteration = iteration + 1;
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check = 0;
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while (check < NUM_DIGITS_GF2X_ELEMENT && privateSyndrome[check++] == 0);
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} while (iteration < ITERATIONS_MAX && check < NUM_DIGITS_GF2X_ELEMENT);
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return (check == NUM_DIGITS_GF2X_ELEMENT);
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} // end QdecodeSyndromeThresh_bitFlip_sparse
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