MCS3142-ISLASHST datasheet(4/37 Pages) MICROCHIP

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MCS3142

DS40001747A-page 4

 2014 Microchip Technology Inc.

1.0

GENERAL DESCRIPTION

MCS3142 is a dual encoder, designed for secure

Remote Keyless Entry (RKE) and secure remote

control systems. MCS3142 utilizes both the Classic

KEELOQ code hopping technology and the new

Ultimate KEELOQ technology time-stamping solution.

Both of these encoders incorporate high security, a

small package outline and low cost to make this device

a perfect solution for unidirectional authentication

systems and access control systems.

Classic KEELOQ technology combines a hopping code

generated by a nonlinear encryption algorithm, a serial

number and Status bits to create a secure transmission

code. The length of the transmission eliminates the

threat of code scanning and code grabbing access

techniques.

Ultimate KEELOQ technology is generated using the

industry standard AES-128 encryption algorithm, a

serial number and a timer-driven message counter

which continuously increments, independent of events,

to provide a better, more secure solution. The

timekeeping

functionality

protects

against

jam-and-replay attack techniques.

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

programmable but read-protected. The data can be

verified only after an automatic erase and programming

operation. This protects against attempts to gain

access to keys or manipulate synchronization values.

In addition, MCS3142 provides an easy to use serial

interface for programming the necessary keys, system

parameters and configuration data.

1.1

Key Terms

The following is a list of key terms used throughout this

data sheet. For additional information on KEELOQ tech-

nology and code hopping, refer to “An Introduction to

KEELOQ® Code Hopping” Technical Brief (DS91002).

• RKE: Remote Keyless Entry

• Function Code: It indicates what button input(s)

activated the transmission. It encompasses the

function code bits.

• 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

• Transmission: A data stream consisting of

repeating code words

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

for Classic KEELOQ technology, 128-bit for

Ultimate KEELOQ technology) used to encrypt and

decrypt data. In a symmetrical block cipher such

as those used on MCS3142, the encryption and

decryption keys are equal and, therefore, will

generally be referred to as the crypt key.

• Encoder: A device that generates and encodes

data

• Encryption Algorithm: A method 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

• Decryption Algorithm: A recipe whereby data,

scrambled by an encryption algorithm, can be

unscrambled using the same crypt key

• Time-Stamp: The time-derived value recorded

with a message

• Learn: Learning involves the receiver calculating

the transmitter’s appropriate crypt key, decrypting

the received hopping code and storing the serial

number, synchronization counter or timer value,

and crypt key in EEPROM. The KEELOQ technol-

ogy product family facilitates several learning

strategies to be implemented 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

number (64-bit for Classic KEELOQ technology,

128-bit for Ultimate KEELOQ technology) used to

derive crypt keys. Each encoder is programmed

with a crypt key that is a function of the

manufacturer’s

code.

Each

decoder

programmed with the manufacturer’s code itself.

The MCS3142 code hopping encoder is designed

specifically for keyless entry systems. Typical

applications include vehicles and home garage door

openers. The encoder portion of a keyless entry system

is integrated into a transmitter carried by the user. The

transmitter is operated to gain access to a vehicle or a

restricted area. MCS3142 is meant to be a cost-

effective, yet secure solution to such systems, requiring

very few external components (see Figure 2-1).

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