HCS512 Datasheet, PDF (2/20 Pages) Microchip Technology – KEELOQ CODE HOPPING DECODER

HCS512
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
Serial Number or
Seed
Manufacturer’s
Code
Key
Generation
Algorithm
Encoder
Key
HCSXXX EEPROM Array
Serial Number
Encoder Key
Sync Counter
.
.
.
DS40151C-page 2
© 1997 Microchip Technology Inc.