The DS2432 combines 1024 bits of EEPROM, a 64-bit secret, an 8-byte register/control page with up to 5 user read/write bytes, a 512-bit SHA-1 engine and a fully-featured 1-Wire interface in a single chip. Each DS2432 has its own 64-bit ROM registration number that is factory lasered into the chip to provide a guaranteed unique identity for absolute traceability. Data is transferred serially via the 1-Wire protocol, which requires only a single data lead and a ground return. The DS2432 has an additional memory area called the scratchpad that acts as a buffer when writing to the main memory, the register page or when installing a new secret. Data is first written to the scratchpad from where it can be read back. After the data has been verified, a copy scratchpad command will transfer the data to its final memory location, provided that the DS2432 receives a matching 160-Bit MAC. The computation of the MAC involves the secret and additional data stored in the DS2432 including the device's registration number. Only a new secret can be loaded without providing a MAC. The SHA-1 engine can also be activated to compute 1 of 30