User's Manual

USER MANUAL PREVIEW

PTM 535BZ – BLUETOOTH AND ZIGBEE GREEN POWER PUSHBUTTON TRANSMITTER

5.7.5.1 USER1_PIN_HASH and USER2_PIN_HASH

PTM 535BZ provides 16-bit hash representations of the 32-bit USER1_PIN (called

USER1_PIN_HASH) and the 32-bit USER2_PIN (called USER2_PIN_HASH). These hash values

allow NFC tools to verify if they possess the correct NFC pin code.

The length of the hash value has been chosen to minimize the likelihood of a false match

while on the other hand making it not feasible to derive the actual NFC pin code from it.

On one hand, the likelihood that an incorrect 32 bit NFC PIN would generate a matching 16-

bit hash is 1/(2^16) meaning 1 in 65536. If an NFC tool possesses an NFC pin code which

generates a matching hash, then the likelihood is 99,999% that this PIN code is correct.

On the other hand, each 16-bit hash corresponds to 2^16 different 32-bit NFC pin codes

meaning that 65536 NFC pin codes would have to be tried. Each try requires a sequence of

NFC write – ECO actuation – NFC read meaning that 65536 individual ECO actuations would

be required to determine the correct NFC pin.

The hash values are generated using a simple algorithm such that they are dependent on the

user (USER1_PIN will create a different has than USER2_PIN) and the individual PTM 535BZ

device (using the globally unique NFC ID of the NFC tag in PTM 535BZ). This prevents at-

tackers from determining if different devices use the same NFC pin code.

The implementation of the hash function is shown in Figure 51 below. Appendix F provides

step by step instructions for this process.

Figure 51 – USER1_PIN_HASH and USER2_PIN_HASH generation