HS Series Overview
The HS Series encoder encrypts the status of up to eight buttons
or contacts into highly secure encrypted serial data stream intended
for wireless transmission via an RF or infrared link. The series uses
CipherLinx? technology, which is based on the Skipjack algorithm
developed by the United States National Security Agency (NSA). The
CipherLinx? protocol in the HS Series has been independently evaluated
by Independent Security Evaluators (ISE). A full evaluation white paper is
available at www.linxtechnologies.com/cipherlinx.
The encoder combines eight bits representing the state of the eight data
lines with counter bits and integrity bits to form a 128-bit message. To
prevent unauthorized access, this message is encrypted with CipherLinx?
in a mode of operation that provides data integrity as well as secrecy.
CipherLinx? never sends or accepts the same data twice, never loses
sync, and changes codes with every packet, not just every button press.
Decoding of the received data signal is accomplished by a corresponding
Linx HS Series decoder. When the decoder receives a valid command
from an encoder, it will activate its logic-level outputs, which can be used
to control external circuitry. The encoder will send data continuously as
long as the SEND line is held high. Each time the algorithm is executed,
the counter is decremented, causing the code to be changed with the
transmission of each packet. This, combined with the large counter
value and the timing associated with the protocol, ensures that the same
transmission is never sent twice.
An 80-bit key used to encrypt the data is created in the decoder by the
user. The decoder is placed into Create Key Mode, and a line is toggled 10
times, usually by a button. This is required to gather entropy to ensure that
the key is random and chosen from all 280 possible keys. A high-speed
timer is triggered by each rise and fall of voltage, recording the time that
the line is high and low. The 80-bit key is generated by combining the
low-order bits of the twenty timer values. To create an association, the key,
a 40-bit counter, and a decoder-generated ID are sent to the encoder via a
wire, contacts, IR, or other secure serial connection.
The HS Series allows the end user or manufacturer to create associations
between the encoder and decoder. If the encoder and decoder have been
associated through a successful key exchange, then the decoder will
respond to the encoder’s commands based on its permissions. If an
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