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LICAL-DEC-HS001

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型号: LICAL-DEC-HS001
PDF文件:
  • LICAL-DEC-HS001 PDF文件
  • LICAL-DEC-HS001 PDF在线浏览
功能描述: HS SERIES ENCODER DATA GUIDE
PDF文件大小: 392.42 Kbytes
PDF页数: 共9页
制造商: ETC2[List of Unclassifed Manufacturers]
制造商LOGO: ETC2[List of Unclassifed Manufacturers] LOGO
制造商网址:
捡单宝
PDF页面索引
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Page 6 Page 7
REMOTE CONTROL OVERVIEW
Wireless remote control is growing in popularity and finding its way into more
unique applications. Remote Keyless Entry (RKE) systems for unlocking cars or
opening garage doors quickly come to mind, but how about a trash container that
signals the maintenance office when it needs to be emptied? The idea behind
remote control is simple: a button press or contact closure on one end causes
some action to be taken at the other. Implementation of the wireless RF stage
has traditionally been complicated, but with the advent of simpler discrete
solutions and modular products, such as those from Linx, implementation has
become significantly easier.
Encoder and decoder ICs are
generally employed to maintain the
security and uniqueness of a wireless
RF or IR link. These devices encode
the status of inputs, usually button or
contact closures, into a data stream
suitable for wireless transmission.
Upon successful recovery and
validation, the decoder’s outputs are
set to replicate the states of the
encoder’s inputs. These outputs can
then be used to control the circuitry
required by the application.
Prior to the arrival of the Linx HS Series, encoders and decoders typically fell into
one of two categories. First were older generation, low-security devices that
transmitted a fixed address code, usually set manually with a DIP switch. These
products were easy to use, but had significant security vulnerabilities. Since they
sent the same code in every transmission, they were subject to code grabbing.
This is where an attacker records the transmission from an authorized
transmitter and then replays the transmission to gain access to the system.
Since the same code is transmitted every time, the decoder has no way to
validate the transmission.
These concerns resulted in the development of a second type of encoder and
decoder that focused on security and utilized a changing code to guard against
code grabbing. Typically, the contents of each transmission changes based on
complex mathematical algorithms to prevent someone from reusing a
transmission. These devices gained rapid popularity due to their security and the
elimination of manual switches; however, they imposed some limitations of their
own. Such devices typically offer a limited number of inputs, the transmitter and
receiver can become desynchronized, and creating relationships and
associations among groups of transmitters and receivers is difficult.
The HS Series offers the best of all worlds. The HS Series uses an advanced
high security encryption algorithm called CipherLinx™ that will never become
desynchronized or send the same packet twice. It is easily configured without
production programming and allows for “button level” permissions and unique
encoder and decoder relationships. Eight inputs are available, allowing a large
number of buttons or contacts to be connected.
To learn more about different encoder and decoder methodologies, please refer
to Application Note AN-00310.
DEC
Rx
GND
HS
Series
ENC
VCC
Tx
HS
Series
LR
Series
LR
Series
Figure 5: Remote Control Block Diagram
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 2
80
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 encoder has not been
associated with a decoder, its commands will not be recognized.
The user or manufacturer may also set “button level” permissions. Permission
settings control how the decoder will respond to the reception of a valid
command, either allowing the activation of an individual data line or not. The
decoder is programmed with the permission settings during set-up, and those
permissions are retained in the decoder’s non-volatile memory.
The HS decoder has the ability to identify and output a decoder-assigned
identification number for a specific encoder. An encoder’s key, a 40-bit counter,
and permissions are stored in one of fifteen memory locations within the
decoder. The decoder is able to output an 8-bit binary number that corresponds
to the memory location of the encoder’s information. This provides the ability to
identify the specific encoder from which a signal originated. This identification
can be used in various ways, including systems that record access attempts or
in applications where the originating user needs to be known.
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