HCS512-SN datasheet(2/20 Pages) MICROCHIP

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HCS512

DS40151C-page 2

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).

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

mitter. The encoder key controls the decryption

algorithm and is stored in EEPROM on the

decoder device.

• Learn – The receiver uses information that is

transmitted to derive the transmitter’s secret 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 an encryption algorithm

to achieve a high level of security. Code hopping is a

method by which the code transmitted from the trans-

mitter 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:

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

unique for every encoder

• An encoder key that is generated at the time of

production

• A 16-bit synchronization value

The serial number for each encoder is programmed by

the manufacturer at the time of production. The

generation of the encoder key is done using a key gen-

eration algorithm (Figure 1-1). Typically, inputs to the

key generation algorithm are the serial number of the

encoder and a 64-bit manufacturer’s code. The manu-

facturer’s code is chosen by the system manufacturer

and must be carefully controlled. The manufacturer’s

code is a pivotal part of the overall system security.

FIGURE 1-1:

CREATION AND STORAGE OF ENCODER KEY DURING PRODUCTION

Transmitter

Manufacturer’s

Serial Number or

Code

Encoder

Key

Generation

Algorithm

Serial Number

Encoder Key

Sync Counter

HCSXXX EEPROM Array

Seed

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