padding.c

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/*
This file is part of BitPunch
Copyright (C) 2013-2015 Frantisek Uhrecky <frantisek.uhrecky[what here]gmail.com>
Copyright (C) 2013-2014 Andrej Gulyas <andrej.guly[what here]gmail.com>
Copyright (C) 2013-2014 Marek Klein  <kleinmrk[what here]gmail.com>
Copyright (C) 2013-2014 Filip Machovec  <filipmachovec[what here]yahoo.com>
Copyright (C) 2013-2014 Jozef Kudlac <jozef[what here]kudlac.sk>

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 3 of the License, or
(at your option) any later version.

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.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
#include "padding.h"

#include <bitpunch/debugio.h>
#include <bitpunch/math/gf2.h>

int BPU_padAdd(BPU_T_GF2_Vector *padded_message, const BPU_T_GF2_Vector *message, const uint16_t padding_len) {
        int i;

        if (message->len + padding_len != padded_message->len) {
                BPU_printError("Wrong message len");
                return -1;
        }
        // copy message into padded message
        for (i = 0; i < message->elements_in_row; i++){
                padded_message->elements[i] = message->elements[i];
        }
        // add padding - first padded bit set to 1, rest keep 0
        BPU_gf2VecSetBit(padded_message, message->len, 1);

        return 0;
}

int BPU_padDel(BPU_T_GF2_Vector *message, const BPU_T_GF2_Vector *padded_message) {
        int i, message_size = 0;

        // count the message size
        for (i = padded_message->len-1; i >= 0; i--) {
                // nula - padding
                if (BPU_gf2VecGetBit(padded_message, i) == 1) {

                        // ci bola aspon jedna 0 pred 1
                        //if (i <= padded_message->len-3) {
                                message_size = i;
                                break;
                        //}
                        // inak zly padding
                        /*else {
                                BPU_printError("del_padding: message padding is incorrect");
                                return -1;
                        }*/
                }
        }
        if (message->len < message_size) {
                BPU_printError("Wrong message size.");
                return -1;
        }
        message->len = message_size;

        // copy n-1 elements of padded message into message
        for (i = 0; i < padded_message->elements_in_row - 1; i++){
                message->elements[i] = padded_message->elements[i];
        }
        // copy the rest of message
        for (i = (padded_message->elements_in_row - 1) * padded_message->element_bit_size; i < message->len; i++){
                BPU_gf2VecSetBit(message, i, BPU_gf2VecGetBit(padded_message, i));
        }
        return 0;
}