HCS370 datasheet(2/42 Pages) MICROCHIP

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HCS370

DS41111E-page 2

2011 Microchip Technology Inc.

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.

In addition, the HCS370 supports a dual encoder. This

allows two manufacturers to use the same device with-

out having to use the same manufacturer’s code in

each of the encoders. The HCS370 provides an easy

to use serial interface for programming the necessary

keys, system parameters, and configuration data.

1.0

SYSTEM OVERVIEW

Key Terms

The following is a list of key terms used throughout this

data sheet. For additional information on KEELOQ and

code hopping, refer to Technical Brief (TB003).

• RKE - Remote Keyless Entry

• Button Status - Indicates what button input(s)

activated the transmission. Encompasses the 6

button status bits S5, S4, S3, S2, S1 and S0

(Figure 3-2).

• Code Hopping - A method by which a code,

viewed externally to the system, appears to

change unpredictably each time it is transmitted.

• Code Word - A block of data that is repeatedly

transmitted upon button activation (Figure 3-2).

• Transmission - A data stream consisting of

repeating code words (Figure 4-1).

• Crypt Key - A unique and secret 64-bit number

used to encrypt and decrypt data. In a symmetri-

cal block cipher such as the KEELOQ algorithm,

the encryption and decryption keys are equal and

will therefore be referred to generally as the crypt

key.

• Encoder - A device that generates and encodes

data.

• Encryption Algorithm - A recipe whereby data is

scrambled using a crypt key. The data can only be

interpreted by the respective decryption algorithm

using the same crypt key.

• Decoder - A device that decodes data received

from an encoder (i.e., HCS5XX).

• Decryption Algorithm - A recipe whereby data

scrambled by an encryption algorithm can be

unscrambled using the same crypt key.

• Learn – Learning involves the receiver calculating

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 KEELOQ product family facil-

itates several learning strategies to be imple-

mented on the decoder. The following are

examples of what can be done.

- Simple Learning

The receiver uses a fixed crypt key. The crypt

key is common to every component used by

the same manufacturer.

- Normal Learning

The receiver derives a crypt key from the

encoder serial number. Every transmitter has

a unique crypt key.

- Secure Learning

The receiver derives a crypt key from the

encoder seed value. Every encoder has a

unique seed value that is only transmitted by

a special button combination.

• Manufacturer’s Code – A unique and secret 64-

bit number used to derive 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 manufacturer

code itself.

The HCS370 code hopping encoder is designed specif-

ically for keyless entry systems. In particular, typical

applications include vehicles and home garage door

openers. The encoder portion of a keyless entry sys-

tem is integrated into a transmitter carried by the user.

The transmitter is operated to gain access to a vehicle

or restricted area. The HCS370 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 HCS370, on the other hand, employs the KEELOQ

code hopping technology coupled with a transmission

length of 67 bits to virtually eliminate the use of code

‘grabbing’ or code ‘scanning’. The high security level of

the HCS370 is based on the patented KEELOQ technol-

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 if a single

hopping code data bit changes (before encryption), sta-

tistically more than 50% of the encrypted data bits will

change.

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