hcs200 Microchip Technology Inc., hcs200 Datasheet - Page 2

• Manufacturer Part Number: hcs200
• Description: K L Code Hopping Encoder
• Manufacturer: Microchip Technology Inc.

HCS200
The HCS200 combines a 32-bit hopping code,
generated by a non-linear encryption algorithm, with a
28-bit serial number and 6 information bits to create a
66-bit code word. The code word length eliminates the
threat of code scanning and the code hopping mecha-
nism makes each transmission unique, thus rendering
code capture and resend schemes useless.
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 HCS200 provides an easy to use serial interface
for programming the necessary keys, system parame-
ters and configuration data.
1.0
Key Terms
The following is a list of key terms used throughout this
data sheet. For additional information on K
Code Hopping, refer to Technical Brief 3 (TB003).
• RKE - Remote Keyless Entry
• Button Status - Indicates what button input(s)
• Code Hopping - A method by which a code,
• Code word - A block of data that is repeatedly
• Transmission - A data stream consisting of
• Crypt key - A unique and secret 64-bit number
• Encoder - A device that generates and encodes
• Encryption Algorithm - A recipe whereby data is
• Decoder - A device that decodes data received
• Decryption algorithm - A recipe whereby data
DS40138C-page 2
activated the transmission. Encompasses the 4
button status bits S3, S2, S1 and S0 (Figure 4-2).
viewed externally to the system, appears to
change unpredictably each time it is transmitted.
transmitted upon button activation (Figure 4-1).
repeating code words (Figure 8-2).
used to encrypt and decrypt data. In a symmetri-
cal block cipher such as the K
the encryption and decryption keys are equal and
will therefore be referred to generally as the crypt
key.
data.
scrambled using a crypt key. The data can only be
interpreted by the respective decryption algorithm
using the same crypt key.
from an encoder.
scrambled by an encryption algorithm can be
unscrambled using the same crypt key.
SYSTEM OVERVIEW
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• Learn – Learning involves the receiver calculating
• Manufacturer’s code – A unique and secret 64-
The HCS200 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 HCS200 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 HCS200, on the other hand, employs the K
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 HCS200 is based on the patented K
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
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
itates several learning strategies to be imple-
mented on the decoder. The following are
examples of what can be done.
- Simple Learning
- Normal Learning
- Secure Learn
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 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.
The receiver uses information transmitted
during normal operation to derive the crypt
key and decrypt the received code word’s
encrypted portion.
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.
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