HCS301 KEELOQ Code Hopping Encoder Data Sheet

1 HCS301 . KEELOQ code Hopping Encoder FEATURES DESCRIPTION. Security The HCS301 from Microchip Technology Inc. is a code Hopping Encoder designed for secure Remote Keyless Programmable 28-bit serial number Entry (RKE) systems. The HCS301 utilizes the KEELOQ . Programmable 64-bit encryption key code Hopping technology, which incorporates high Each transmission is unique security, a small package outline and low cost, to make this device a perfect solution for unidirectional remote 66-bit transmission code length keyless entry systems and access control systems.

2 32-bit Hopping code 34-bit fixed code (28-bit serial number, PACKAGE TYPES. 4-bit button code , 2-bit status) PDIP, SOIC. Encryption keys are read protected Operating S0 1 8 VDD. HCS301 . - operation S1 2 7 LED. Four button inputs S2 3 6 PWM. No additional circuitry required 15 functions available S3 4 5 VSS. Selectable baud rate Automatic code word completion Battery low signal transmitted to receiver HCS301 BLOCK DIAGRAM. Battery low indication on LED Oscillator Power latching Non-volatile synchronization data Controller and RESET circuit switching LED.

3 Other LED driver Functionally identical to HCS300. Easy-to-use programming interface EEPROM Encoder On-chip EEPROM. On-chip oscillator and timing components PWM. Button inputs have internal pull-down resistors 32-bit shift register Current limiting on LED output Low external component cost VSS. Button input port Typical Applications VDD. The HCS301 is ideal for Remote Keyless Entry (RKE). applications. These applications include: S3 S2 S1 S0. Automotive RKE systems Automotive alarm systems The HCS301 combines a 32-bit Hopping code , generated by a nonlinear encryption algorithm, with a Automotive immobilizers 28-bit serial number and 6 information bits to create a Gate and garage door openers 66-bit code word.

4 The code word length eliminates the Identity tokens threat of code scanning and the code Hopping mecha- Burglar alarm systems nism makes each transmission unique, thus rendering code capture and resend schemes useless. 2001 Microchip Technology Inc. DS21143B-page 1. HCS301 . The crypt key, serial number and configuration data are Learn Learning involves the receiver calculating stored in an EEPROM array which is not accessible via the transmitter's appropriate crypt key, decrypting any external connection. The EEPROM data is pro- the received Hopping code and storing the serial grammable but read-protected.

5 The data can be veri- number, synchronization counter value and crypt fied only after an automatic erase and programming key in EEPROM. The KEELOQ product family facil- operation. This protects against attempts to gain itates several learning strategies to be imple- access to keys or manipulate synchronization values. mented on the decoder. The following are The HCS301 provides an easy-to-use serial interface examples of what can be done. for programming the necessary keys, system parame- - Simple Learning ters and configuration data . The receiver uses a fixed crypt key, common to all components of all systems by the same SYSTEM OVERVIEW manufacturer, to decrypt the received code word's encrypted portion.

6 Key Terms - Normal Learning The following is a list of key terms used throughout this The receiver uses information transmitted data Sheet . For additional information on KEELOQ and during normal operation to derive the crypt code Hopping , refer to Technical Brief 3 (TB003). key and decrypt the received code word's encrypted portion. RKE - Remote Keyless Entry - Secure Learn Button Status - Indicates what button input(s). The transmitter is activated through a special activated the transmission. Encompasses the 4. button combination to transmit a stored 60-bit button status bits S3, S2, S1 and S0 (Figure 4-2).

7 Seed value used to generate the transmitter's code Hopping - A method by which a code , crypt key. The receiver uses this seed value viewed externally to the system, appears to to derive the same crypt key and decrypt the change unpredictably each time it is transmitted. received code word's encrypted portion. code word - A block of data that is repeatedly Manufacturer's code A unique and secret 64- transmitted upon button activation (Figure 4-1). bit number used to generate unique Encoder crypt Transmission - A data stream consisting of keys.

8 Each Encoder is programmed with a crypt repeating code words (Figure 8-2). key that is a function of the manufacturer's code . Crypt key - A unique and secret 64-bit number Each decoder is programmed with the manufac- used to encrypt and decrypt data . In a symmetri- turer code itself. cal block cipher such as the KEELOQ algorithm, The HCS301 code Hopping Encoder is designed specif- the encryption and decryption keys are equal and ically for keyless entry systems; primarily vehicles and will therefore be referred to generally as the crypt home garage door openers.

9 The Encoder portion of a key. keyless entry system is integrated into a transmitter, Encoder - A device that generates and encodes carried by the user and operated to gain access to a data . vehicle or restricted area. The HCS301 is meant to be Encryption Algorithm - A recipe whereby data is a cost-effective yet secure solution to such systems, scrambled using a crypt key. The data can only be requiring very few external components (Figure 2-1). interpreted by the respective decryption algorithm Most low-end keyless entry transmitters are given a using the same crypt key.

10 Fixed identification code that is transmitted every time a Decoder - A device that decodes data received button is pushed. The number of unique identification from an Encoder . codes in a low-end system is usually a relatively small Decryption algorithm - A recipe whereby data number. These shortcomings provide an opportunity scrambled by an encryption algorithm can be for a sophisticated thief to create a device that grabs'. unscrambled using the same crypt key. a transmission and retransmits it later, or a device that quickly scans' all possible identification codes until the correct one is found.