MCS3122 datasheet(3/26 Pages) MICROCHIP

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 2014 Microchip Technology Inc.

DS40001762A-page 3

MCS3122

1.0

GENERAL DESCRIPTION

MCS3122 is a KEELOQ encoder, designed for secure

Remote Keyless Entry (RKE) and secure remote

control systems. MCS3122 utilizes the Advanced

KEELOQ code hopping technology. The encoder

incorporates a high- security, low-cost small package

outline to make this device the perfect solution for

unidirectional

authentication

systems and access

control systems.

The Advanced KEELOQ technology uses the industry

standard AES-128 encryption algorithm, a

serial

number and a message counter which continuously

increments with each button press.

The crypt key, serial number and configuration data are

stored in a Flash array which is not accessible via any

external connection. The Flash 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.

addition,

MCS3122 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

technology 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 (128-bit

for Advanced KEELOQ technology) used to

encrypt and decrypt data. In a symmetrical block

cipher such as those used on MCS3122, 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.

• 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

technology 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

(128-bit

for

Advanced

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 is programmed with the manufacturer’s

code itself.

The MCS3122 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. MCS3122 is meant to be a cost-

effective, yet secure solution to such systems, requiring

very few external components (see 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.

Advanced KEELOQ technology uses the industry

standard AES-128 encryption algorithm to obscure

data using 128 bits for both its block and key length. In

addition to the security of Advanced KEELOQ

technology,

the

encoder

sends

message

authorization block which is used to separate the

message encryption from the message authentication.

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