Linx Technologies HUM-xxx-DT - Manual (Page 13)

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Encryption
The module implements AES encryption in ECB mode. The packet header
information is sent in the clear and the payload data is encrypted.
Encryption algorithms are complex mathematical equations that use a
number, called a key, to encrypt data before transmission. This is done
so that unauthorized persons who may intercept the transmission cannot
access the data. In order to decrypt the transmission, the receiver must
use the same key that was used to encrypt it. The receiver performs the
same calculations as the encoder and, if the key is the same, recovers the
data.
The AES encryption algorithm is widely used, from basic wireless data links
to Internet traffic to government communications. It is considered highly
secure and reliable. The AES algorithm supports key lengths of 128, 192
and 256 bits. The HumDT
TM module only supports 128 bits. The larger key
lengths are more subject to government import and export regulations,
though the user will need to confirm that 128 bits is allowable in their
industry.
The strength of the encryption algorithm and the length of the key are only
two factors in a secure system. The ultimate requirement is the secrecy
of the key. The HumDT
TM module only allows the key to be read out of
the Access Point. It can be written into an End Device, but is otherwise
inaccessible.
The AP should be kept in a secure location to prevent physical access by
unauthorized persons. If the key is stored outside the system, such as in a
database or list, then it should also be kept secure.
Restore Factory Defaults
The transceiver is reset to factory default with a serial command
through the Command Data Interface. This command restores all of the
configurations to factory default settings. These are shown in Figure 19.
The module address is not changed to the factory default. This value is
retained. This serial command requires knowing the current serial baud
rate. If that is not known then all 10 supported rates should be tried to find
out which is correct.
Factory Default Configurations
Parameter Default Value
Device Type ED
Module Address 0x00-0x00-0x00-0x00
Serial Baud Rate 9.6kbps
Channel Mapping Single Channel (911.5MHz)
TX Output Power 0dBm
Network ID 0x00-0x00-0x00-0x00
All GPIOs Digital Input with Pull-up
AES Key
0x2B, 0x7E, 0x15, 0x16, 0x28, 0xAE, 0xD2, 0xA6,
0xAB, 0xF7, 0x15, 0x88, 0x09, 0xCF, 0x4F, 0x3C
Figure 19: HumDT TM Factory Default Configurations