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Part: HCS300-I/SN
Category:
Others
-> Security Device->KEELOQ->->Encoders
Description: The HCS300 is a Code Hopping Encoder Designed For Secure Remote Keyless Entry (RKE) Systems
Company: Microchip Technology, Inc.
Datasheet: Download HCS300-I/SN datasheet File size : 154 kB
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Datasheet text preview:
HCS300
KEELOQ® Code Hopping Encoder
FEATURES
Security
· · · · · · · Programmable 28-bit serial number Programmable 64-bit encryption key Each transmission is unique 66-bit transmission code length 32-bit hopping code 28-bit serial number, 4-bit button code, 2-bit status Crypt keys are read protected
DESCRIPTION
The HCS300 from Microchip Technology Inc. is a code hopping encoder designed for secure Remote Keyless Entry (RKE) systems. The HCS300 utilizes the KEELOQ code hopping technology, incorporating high security, a small package outline and low cost. The HCS300 is a perfect solution for unidirectional remote keyless entry systems and access control systems.
PACKAGE TYPES
PDIP, SOIC S0 S1 S2 S3 1 HCS300 2 3 4 8 7 6 5
VDD
Operating
· · · · · · · · 2.0V - 6.3V operation Four button inputs No additional circuitry required 15 functions available Selectable baud rate Automatic code word completion Low battery signal transmitted to receiver Non-volatile synchronization data
LED PWM VSS
HCS300 BLOCK DIAGRAM
Oscillator RESET circuit Controller Power latching and switching
Other
· · · · · · Easy-to-use programming interface On-chip EEPROM On-chip oscillator and timing components Button inputs have internal pull-down resistors Current limiting on LED output Low external component cost
LED LED driver
EEPROM
Encoder
PWM 32-bit shift register
Typical Applications
The HCS300 is ideal for Remote Keyless Entry (RKE) applications. These applications include: · · · · · · Automotive RKE systems Automotive alarm systems Automotive immobilizers Gate and garage door openers Identity tokens Burglar alarm systems
VSS VD D
Button input port
S3 S2 S1 S0
The HCS300 combines a 32-bit hopping code, generated by a nonlinear encryption algorithm, with a 28-bit serial number and 6 information bits to create a 66-bit code word. The code word length eliminates the threat of code scanning and the code hopping mechanism makes each transmission unique, thus rendering code capture and resend schemes useless.
© 2001 Microchip Technology Inc.
DS21137F-page 1
HCS300
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. The HCS300 provides an easy-to-use serial interface for programming the necessary keys, system parameters and configuration data. · 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 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, common to all components of all systems by the same manufacturer, to decrypt the received code word's encrypted portion. - Normal Learning The receiver uses information transmitted during normal operation to derive the crypt key and decrypt the received code word's encrypted portion. - Secure Learn The transmitter is activated through a special button combination to transmit a stored 60-bit seed value used to generate the transmitter's crypt key. The receiver uses this seed value to derive the same crypt key and decrypt the received code word's encrypted portion. · Manufacturer 's code A unique and secret 64bit number used to generate unique encoder 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 HCS300 code hopping encoder is designed specifically for keyless entry systems; primarily vehicles and home garage door openers. The encoder portion of a keyless entry system is integrated into a transmitter, carried by the user and operated to gain access to a vehicle or restricted area. The HCS300 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 HCS300 on the other hand, employs the KEELOQ code hopping technology coupled with a transmission length of 66 bits to virtually eliminate the use of code `grabbing' or code `scanning'. The high security level of the HCS300 is based on the patented KEELOQ technology. 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 even if the transmission information (before coding) differs by only one bit from that of the previous transmission, the next
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 3 (TB003). · RKE - Remote Keyless Entry · Button Status - Indicates what button input(s) activated the transmission. Encompasses the 4 button status bits S3, S2, S1 and S0 (Figure 4-2). · 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 4-1). · Transmission - A data stream consisting of repeating code words (Figure 8-1). · Crypt key - A unique and secret 64-bit number used to encrypt and decrypt data. In a symmetrical 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. · Decryption algorithm - A recipe whereby data scrambled by an encryption algorithm can be unscrambled using the same crypt key.
DS21137F-page 2
© 2001 Microchip Technology Inc.
HCS300
coded transmission will be completely different. Statistically, if only one bit in the 32-bit string of information changes, greater than 50 percent of the coded transmission bits will change. As indicated in the block diagram on page one, the HCS300 has a small EEPROM array which must be loaded with several parameters before use; most often programmed by the manufacturer at the time of production. The most important of these are: · A 28-bit serial number, typically unique for every encoder · A crypt key · An initial 16-bit synchronization value · A 16-bit configuration value The crypt key generation typically inputs the transmitter serial number and 64-bit manufacturer's code into the key generation algorithm (Figure 1-1). The manufacturer 's code is chosen by the system manufacturer and must be carefully controlled as it is a pivotal part of the overall system security.
FIGURE 1-1:
Production Programmer
CREATION AND STORAGE OF CRYPT KEY DURING PRODUCTION
HCS300 EEPROM Array
Serial Number Crypt Key Sync Counter
Transmitter Serial Number
Manufacturer's Code
Key Generation Algorithm
Crypt Key
. . .
The 16-bit synchronization counter is the basis behind the transmitted code word changing for each transmission; it increments each time a button is pressed. Due to the code hopping algorithm's complexity, each increment of the synchronization value results in greater than 50% of the bits changing in the transmitted code word. Figure 1-2 shows how the key values in EEPROM are used in the encoder. Once the encoder detects a button press, it reads the button inputs and updates the synchronization counter. The synchronization counter and crypt key are input to the encryption algorithm and the output is 32 bits of encrypted information. This data will change with every button press, its value appearing externally to `randomly hop around', hence it is referred to as the hopping portion of the code word. The 32-bit hopping code is combined with the button information and serial number to form the code word transmitted to the receiver. The code word format is explained in greater detail in Section 4.0. A receiver may use any type of controller as a decoder, but it is typically a microcontroller with compatible firmware that allows the decoder to operate in conjunction with an HCS300 based transmitter. Section 7.0 provides detail on integrating the HCS300 into a system.
A transmitter must first be `learned' by the receiver before its use is allowed in the system. Learning includes 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. In normal operation, each received message of valid format is evaluated. The serial number is used to determine if it is from a learned transmitter. If from a learned transmitter, the message is decrypted and the synchronization counter is verified. Finally, the button status is checked to see what operation is requested. Figure 1-3 shows the relationship between some of the values stored by the receiver and the values received from the transmitter.
© 2001 Microchip Technology Inc.
DS21137F-page 3
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