HCS300
The crypt key, serial number and configuration data are
stored in an EEPROM array which is not accessible via
any external connection. The EEPROM data is pro-
grammable but read-protected. The data can be veri-
fied only after an automatic erase and programming
operation. This protects against attempts to gain
access to keys or manipulate synchronization values.
The HCS300 provides an easy-to-use serial interface
for programming the necessary keys, system parame-
ters and configuration data.
•
Learn
– Learning involves the receiver calculating
the transmitter’s appropriate crypt key, decrypting
the received hopping code and storing the serial
number, synchronization counter value and crypt
key in EEPROM. The K
EE
L
OQ
product family facil-
itates several learning strategies to be imple-
mented on the decoder. The following are
examples of what can be done.
-
Simple Learning
The receiver uses a fixed crypt key, common
to all components of all systems by the same
manufacturer, to decrypt the received code
word’s encrypted portion.
-
Normal Learning
The receiver uses information transmitted
during normal operation to derive the crypt
key and decrypt the received code word’s
encrypted portion.
-
Secure Learn
The transmitter is activated through a special
button combination to transmit a stored 60-bit
seed value used to generate the transmitter’s
crypt key. The receiver uses this seed value
to derive the same crypt key and decrypt the
received code word’s encrypted portion.
•
Manufacturer’s code
– A unique and secret 64-
bit number used to generate unique encoder crypt
keys. Each encoder is programmed with a crypt
key that is a function of the manufacturer’s code.
Each decoder is programmed with the manufac-
turer code itself.
The HCS300 code hopping encoder is designed specif-
ically for keyless entry systems; primarily vehicles and
home garage door openers. The encoder portion of a
keyless entry system is integrated into a transmitter,
carried by the user and operated to gain access to a
vehicle or restricted area. The HCS300 is meant to be
a cost-effective yet secure solution to such systems,
requiring very few external components (Figure 2-1).
Most low-end keyless entry transmitters are given a
fixed identification code that is transmitted every time a
button is pushed. The number of unique identification
codes in a low-end system is usually a relatively small
number. These shortcomings provide an opportunity
for a sophisticated thief to create a device that ‘grabs’
a transmission and retransmits it later, or a device that
quickly ‘scans’ all possible identification codes until the
correct one is found.
The HCS300 on the other hand, employs the K
EE
L
OQ
code hopping technology coupled with a transmission
length of 66 bits to virtually eliminate the use of code
‘grabbing’ or code ‘scanning’. The high security level of
the HCS300 is based on the patented K
EE
L
OQ
technol-
ogy. A block cipher based on a block length of 32 bits
and a key length of 64 bits is used. The algorithm
obscures the information in such a way that even if the
transmission information (before coding) differs by only
one bit from that of the previous transmission, the next
1.0
SYSTEM OVERVIEW
Key Terms
The following is a list of key terms used throughout this
data sheet. For additional information on K
EE
L
OQ
and
Code Hopping, refer to Technical Brief 3 (TB003).
•
RKE
- Remote Keyless Entry
•
Button Status
- Indicates what button input(s)
activated the transmission. Encompasses the 4
button status bits S3, S2, S1 and S0 (Figure 4-2).
•
Code Hopping
- A method by which a code,
viewed externally to the system, appears to
change unpredictably each time it is transmitted.
•
Code word
- A block of data that is repeatedly
transmitted upon button activation (Figure 4-1).
•
Transmission
- A data stream consisting of
repeating code words (Figure 8-1).
•
Crypt key
- A unique and secret 64-bit number
used to encrypt and decrypt data. In a symmetri-
cal block cipher such as the K
EE
L
OQ
algorithm,
the encryption and decryption keys are equal and
will therefore be referred to generally as the crypt
key.
•
Encoder
- A device that generates and encodes
data.
•
Encryption Algorithm
- A recipe whereby data is
scrambled using a crypt key. The data can only be
interpreted by the respective decryption algorithm
using the same crypt key.
•
Decoder
- A device that decodes data received
from an encoder.
•
Decryption algorithm
- A recipe whereby data
scrambled by an encryption algorithm can be
unscrambled using the same crypt key.
DS21137F-page 2
©
2001 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
