Understanding and using cyclic redundancy checks with Maxim 1-wire and iButton products, application note here (PDF!) from Maxim:
All 1-Wire® devices, including iButton® devices, contain an 8-byte unique registration number in read-only memory (ROM). This registration number is used as a unique network address on a 1-Wire bus. To ensure data communication integrity, one byte of each registration number is a 1-Wire CRC byte. This application note explains how to calculate this 8-bit 1-Wire CRC. It also goes on to explain the 16-bit CRC that is used to verify records saved in the memory of the devices. Both the 1-Wire CRC and the CRC-16 are generated in hardware of select 1-Wire devices to validate data.