MDEV-868-PRC datasheet(15/55 Pages) LINX

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The Join Process

The Join Process is a method of generating a random encryption key and

random network base address, then distributing the key and addresses to

associated modules through a series of button presses. This makes it very

simple to establish an encrypted network in the field or add new nodes to

an existing network without any additional equipment. It is also possible

to trigger the Join Process through commands on the Command Data

Interface.

All modules configured from the same administrator using the Join Process

can communicate with each other. Other modules are added to the

network one at a time.

The hardware required is a pushbutton that is connected to the PB

line. This takes the line to VCC when it is pressed and ground when it

is released. An LED connected to the MODE_IND line provides visual

indication of the module’s state.

A module is set as an administrator by pressing and holding the button for

30 seconds to start the Generate Key function. While the button is held,

the MODE_IND line is on. After 30s, the MODE_IND line repeats a double

blink, indicating that the function is selected. When the button is released

the key and address generation are performed and the module becomes

an administrator.

When Generate Key is performed, the unit is set as the network

administrator. It generates a random 128-bit AES encryption key based on

ambient RF noise and scrambled by an encryption operation. If UMASK

is the default value (0xFFFFFFFF), it is set to 0x000000FF, supporting

up to 254 nodes, and ADDMODE is set to Extended User Address

with encryption (0x27) (or without encryption (0x07) if flag PGKEY in

the SECOPT register was set to 0 by serial command). UMASK and

ADDMODE are not changed if UMASK is not 0xFFFFFFFF. A random

32-bit address is generated. By default, the lower 8 bits are 0, forming the

network base address. Other nodes are assigned sequential addresses,

starting with network base address +1. UDESTID is set to the bitwise OR

of USRCID and UMASK, which is the network broadcast address.

AES Encryption

HumPRCTM Series modules offer AES encryption. Encryption algorithms are

complex mathematical calculations that use a large number called a key

to scramble data before transmission. This is done so that unauthorized

persons who may intercept the signal cannot access the data. To decrypt

the data, the receiver must use the same key that was used to encrypt it.

It performs the same calculations as the transmitter and if the key is the

same, the data is recovered.

The HumPRCTM Series module has the option to use AES encryption,

arguably the most common encryption algorithm on the market. This is

implemented in a secure mode of operation to ensure the secrecy of the

transmitted data. It uses a 128-bit key to encrypt the transmitted data. The

source and destination addresses are sent in the clear.

There are two ways to enable encryption and set the key: sending serial

commands and using the Join Process.

Writing an encryption key to the module with the CDI

The module has no network key when shipped from the factory. An

encryption key can be written to the module using the CDI. The CMD

The same key must be written to all modules that are to be used together.

If they do not have the same key, then they will not communicate in

encrypted mode.

The JOIN Process

The Join Process can be used to generate and distribute the encryption

key and addresses through a series of button presses. The key is stored in

an Administrator device and the process uses a factory key to distribute the

key to node devices in a secure manner. See the Join Process section for

more information on this feature.

MDEV-868-PRC Datasheet(PDF) 15 Page - Linx Technologies

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