HCS500 datasheet(2/24 Pages) MICROCHIP

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HCS500

DS40153B-page 2

Preliminary

1.0

KEELOQ SYSTEM OVERVIEW

1.1

Key Terms

• Manufacturer’s Code – A 64-bit word, unique to

each manufacturer, used to produce a unique

encoder key in each transmitter.

• Encoder Key – A 64-bit key, unique for each trans-

mitter. The encoder key controls the KeeLoq

decryption algorithm and is stored in EEPROM on

the decoder device.

• Learn – The receiver uses information that is

transmitted to derive the transmitter’s encoder key,

decrypt the discrimination value, and the synchro-

nization counter in learning mode. The encoder

key is a function of the manufacturer’s code and

the device serial number and/or seed value.

The HCS encoders and decoders employ the KeeLoq

code hopping technology and a KeeLoq encryption

algorithm to achieve a high level of security. Code

hopping is a method by which the code transmitted

from the transmitter to the receiver is different every

time a button is pushed. This method, coupled with a

transmission length of 66 bits, virtually eliminates the

use of code ‘grabbing’ or code ‘scanning’.

1.2

HCS Encoder Overview

The HCS encoders have a small EEPROM array which

must be loaded with several parameters before use.

The most important of these values are:

• An encoder key that is generated at the time of

production

• A 16-bit synchronization counter value

• A 28-bit serial number which is meant to be

unique for every encoder

The manufacturer programs the serial number for each

encoder at the time of production, while the ‘Key Gen-

eration Algorithm’ generates the encoder key (Figure 1-

1). Inputs to the key generation algorithm typically con-

sist of the encoder’s serial number and a 64-bit manu-

facturer’s code, which the manufacturer creates.

FIGURE 1-1:

CREATION AND STORAGE OF ENCRYPTION KEY DURING PRODUCTION

Note:

The manufacturer code is a pivotal part of

the

system’s

overall

security. Conse-

quently, all possible precautions must be

taken and maintained for this code.

Transmitter

Manufacturer’s

Serial Number or

Code

Encryption

Key

Generation

Algorithm

Serial Number

Encryption Key

Sync Counter

HCS500 EEPROM Array

Seed

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