The checksum is calculated using Dallas APPLICATION NOTE 27 table method: Understanding and Using Cyclic Redundancy Checks with Dallas Semiconductor iButton Products. One can use the following algorithms to calculate the checksum with a polynom ^8 + a^5 + a^4 + 1 (C language):

Version 1:

1 U8 CRC8 (U8 b, U8 crc)
2 {
3   U8 i = 8;
4   do {
5    if ( (b ^ crc) & 0x01) {
6     crc = ( (crc ^ 0x18) >> 1 ) | 0x80;
7    } else {
8     crc >>= 1;
9    }
10   b >>= 1;
11  } while (--i);
12  return crc;
13 }

Version 2:

1 U8 CRC8(U8 data, U8 crc)
2 {
3   U8 i = data ^ crc;
4   crc = 0;
5   if(i & 0x01) crc ^= 0x5e;
6   if(i & 0x02) crc ^= 0xbc;
7   if(i & 0x04) crc ^= 0x61;
8   if(i & 0x08) crc ^= 0xc2;
9   if(i & 0x10) crc ^= 0x9d;
10  if(i & 0x20) crc ^= 0x23;
11  if(i & 0x40) crc ^= 0x46;
12  if(i & 0x80) crc ^= 0x8c;
13  return crc;
14 }