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/*
* spreadspace avr utils
*
*
* Copyright (C) 2013 Christian Pointner <equinox@spreadspace.org>
* Othmar Gsenger <otti@wirdorange.org>
*
* This file is part of spreadspace avr utils.
*
* spreadspace avr utils 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
* any later version.
*
* spreadspace avr utils 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 spreadspace avr utils. If not, see <http://www.gnu.org/licenses/>.
*/
#include "keystore.h"
#include <avr/eeprom.h>
#include <stdio.h>
#include <string.h>
#include "led.h"
#include "anyio.h"
#define EEPROM_SIZE 1024
typedef uint8_t keyslot_t[8];
keyslot_t EEMEM keystore[EEPROM_SIZE/sizeof(keyslot_t)];
void flash_keystore_from_stdio(void)
{
keyslot_t ks;
uint8_t byte_pos=0;
printf("Flashing keys:\n\r");
fflush(stdout);
for(uint8_t ks_pos=0;ks_pos<EEPROM_SIZE/sizeof(ks);) {
anyio_task();
int16_t bytes_received = anyio_bytes_received();
while(bytes_received > 0) {
ks[byte_pos++]=fgetc(stdin);
bytes_received--;
if (byte_pos == sizeof(ks)) {
byte_pos=0;
eeprom_update_block(&ks,&keystore[ks_pos],sizeof(ks));
ks_pos++;
fputc('.', stdout);
fflush(stdout);
led_toggle();
}
}
}
printf("\n");
fputc(0, stdout);
led_off();
}
void dump_keystore_to_stdio(void)
{
keyslot_t ks;
for(uint8_t ks_pos=0;ks_pos<EEPROM_SIZE/sizeof(ks);ks_pos++) {
eeprom_read_block(&ks,&keystore[ks_pos],sizeof(ks));
for (uint8_t i=0; i< sizeof(ks); i++)
printf("%02X",ks[i]);
printf("\n\r");
}
}
/* this generates a Fletcher8 checksum */
/* code from: http://stackoverflow.com/questions/13491700/8-bit-fletcher-checksum-of-16-byte-data */
uint8_t generate_csum(uint8_t* data)
{
uint16_t sum1 = 0xf, sum2 = 0xf, len = sizeof(keyslot_t) - 1;
do { sum2 += ( sum1 += *data++ ); } while (--len);
return sum2<<4 | sum1;
}
uint8_t compare_keyslots(const keyslot_t a, const keyslot_t b)
{
uint8_t tmp=0;
// constant time compare
for(uint8_t i=0; i<sizeof(keyslot_t); ++i)
tmp |= a[i] ^ b[i];
return tmp;
}
uint8_t keystore_check_card(const uint8_t * uid, uint8_t uid_len)
{
keyslot_t card, ks;
memset(card, 0, sizeof(card));
for (uint8_t pos=0; pos<uid_len; pos++)
card[pos]=uid[uid_len-pos-1];
card[sizeof(keyslot_t)-1]=generate_csum(card);
uint8_t valid=0;
for(uint8_t ks_pos=0;ks_pos<(EEPROM_SIZE/sizeof(ks));ks_pos++) {
eeprom_read_block(&ks,&keystore[ks_pos],sizeof(ks));
if(!compare_keyslots(card, ks)) {
valid=1;
// break; // this would break security (not constant time)
}
}
return valid;
}
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