HCS500 Datasheet, PDF (2/24 Pages) Microchip Technology – KEELOQ CODE HOPPING ENCODER

HCS500
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.
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.
FIGURE 1-1: CREATION AND STORAGE OF ENCRYPTION KEY DURING PRODUCTION
Transmitter
Serial Number or
Seed
Manufacturer’s
Code
Key
Generation
Algorithm
Encryption
Key
HCS500 EEPROM Array
Serial Number
Encryption Key
Sync Counter
.
.
.
DS40153B-page 2
Preliminary
© 1997 Microchip Technology Inc.