// convert byte-reversed 12 digit hex to unsigned long
unsigned long long hexreversetoulonglong(BYTE *hex)
{
unsigned long long ret= 0LL;
BYTE tmp[9];
// this may seem an odd way to do it, but weird compiler issues were
// breaking direct conversion!
tmp[8]= '\0';
memset(tmp + 4, '0', 4);
memcpy(tmp, hex + 8, 4);
ret= hexreversetoulong(tmp);
ret <<= 32;
memcpy(tmp, hex, 8);
ret += hexreversetoulong(tmp);
return ret;
}
// note that PRN is not created with security in mind - just using a simple seed
BOOL hitag2_crypto_auth(BYTE *response, BYTE *hexkey)
{
BYTE tmp[65], tmphex[9];
unsigned long long key;
unsigned long uid;
unsigned long initvec;
// use default transport key if none specified
if(strlen(hexkey) == 0)
hexkey= HITAG2_KEY_DEFAULT;
// get UID for initialisation
if(!hitag2_get_uid(tmp))
return FALSE;
// convert to numerics for crypto routines
uid= hexreversetoulong(tmp);
key= hexreversetoulonglong(hexkey);
// generate 32 bit PRN for challenge
srand(Led_Count);
initvec= rand();
initvec <<= 16;
initvec += rand();
// prepare to send IV in the clear to tag
ulongtobinstring(tmp, initvec, 32);
// convert IV to MSB for crypto routines
binstringtohex(tmphex, tmp);
initvec= hexreversetoulong(tmphex);
// initialise crypto
hitag2_init(&Hitag_Crypto_State, rev64(key), rev32(uid), rev32(initvec));
// send inverse of 1st 32bits of keystream to tag for authentication
ulongtobinstring(tmp + 32, hitag2_crypt(0xFFFFFFFF, 32), 32);
// restart the tag & auth process
if(!hitag2_get_uid(TmpBuff))
return FALSE;
// wait for RX->TX period, then send PRN+secret
if(!rwd_send(tmp, strlen(tmp), NO_RESET, BLOCK, RWD_STATE_WAKING, RFIDlerConfig.FrameClock, 0, RFIDlerConfig.RWD_Wait_Switch_RX_TX, RFIDlerConfig.RWD_Zero_Period, RFIDlerConfig.RWD_One_Period, RFIDlerConfig.RWD_Gap_Period, RFIDlerConfig.RWD_Wait_Switch_TX_RX))
return FALSE;
// skip 1/2 bit to synchronise manchester
HW_Skip_Bits= 1;
// get 37 bit response: sync + config byte + 24 bit TAG pwd
if(read_ask_data(RFIDlerConfig.FrameClock, RFIDlerConfig.DataRate, tmp, 37, RFIDlerConfig.Sync, RFIDlerConfig.SyncBits, RFIDlerConfig.Timeout, ONESHOT_READ, BINARY) == 37)
{
// check sync bits
if (memcmp(tmp, Hitag2Sync, 5) != 0)
return FALSE;
CryptoActive= TRUE;
// decrypt
binarraytohex(response, tmp + 5, 32);
return hitag2_hex_crypt(response, response);
}
return FALSE;
}
