KeeLoq® Technology FAQs

KeeLoq code hopping technology enables designers to develop highly secure authentication applications for automotive, residential, personal and commercial markets. Sample applications include:

• Garage door openers
• Tire pressure monitoring systems
• Automotive Remote Keyless Entry (RKE systems)
• Automotive alarm systems
• Remote key pads
• Security and safety sensors
• Wireless sensors
• Remote controls

The Ultimate KeeLoq protocol is a timer-based solution offering enhancements to the Classic KeeLoq protocol structure such as industry-standard AES-128 block cipher, programmable 32-bit serial number, programmable 128-bit encryption key and KEELOQ Secure Learn Mode (128-bit seed). It incorporates a timer-driven message counter which continuously increments, independent of events, to provide a better, more secure solution. The time-keeping functionality provides additional protection against capture and replay attack techniques.

Remote control via RF or IR is popular for many applications, including vehicle alarms and automatic garage doors. Conventional remote control systems are based on unidirectional transmission and have limited security. More sophisticated devices based on bidirectional transmission are also available but, because of their high cost and other disadvantages, they are not widely used in commercial remote control devices.

Popular unidirectional transmission systems currently have two very important security shortcomings: the codes they transmit are usually fixed and the number of possible code combinations is relatively small. Either of these shortcomings can lead to unauthorized access. Secure remote control systems can only be implemented if two conditions are met. The KeeLoq code hopping system meets both these conditions with ease.

• A large number of possible combinations must be available
• The system must never respond twice to the same transmitted code
  

The KeeLoq code hopping protocol meets both these conditions with ease. Its 64-bit transmission code with two to five bits of status information are used for a total of 66 to 69 bits to make scanning impossible. The 32-bit encrypted portion provides for more than 4 billion code combinations. A complete scan of these code combinations would take 17 years. The hopping code algorithm will never respond to the same code twice over several lifetimes of a typical system.

KeeLoq technology offers two basic types of transmission for authentication:

KeeLoq Unidirectional Transmission

KeeLoq Unidirectional Transmission, also called KeeLoq code hopping technology, is a worldwide standard that is used to defeat scanners and grabbers to provide a simple yet highly secure solution for authentication, RKE or Passive Keyless Entry (PKE) applications. Its features include:

• 66-bit transmission length (32-bit hop code, 34-bit fixed code)
• Two to five status bits
• Multiple functions per transmitter (up to 15)
• Low-voltage encoder operation
• Nonvolatile memory with error correction
• Minimal external components
• User unique 128-bit encryption key to configure algorithm
• Transparent synchronization

KeeLoq Bidirectional Transponder Transmission

• 32-bit data challenge and 32-bit data response system
• Encryption keys are read protected to prevent duplication
• Reprogrammable EEPROM
• Minimal external component count
• User unique 128-bit encryption key to configure algorithm
• User read/write capability (64-bit)
• Contactless/contact configuration
• Fully code-hopping compatible

Typically used in vehicle security systems, a remote control transmitter is a small radio transmitter that transmits a code number on a certain frequency. This code number is normally generated by an integrated circuit encoder. The transmit frequency is normally fixed by legislation within a particular country. Due to the simple transmission format, it is easy to build a simple receiver, which is called a code or key grabber, that can receive signals from these transmitters and record the transmissions for replaying at a later time.

Due to the limited number of combinations available in most remote control systems, all possible combinations can be transmitted in a relatively short time. A code scanner is a handheld microprocessor-based system that can be used to access the system and quickly scan these combinations.  

KeeLoq technology supports three levels of security:

• Simple method: Use of a fixed user encryption key
• Normal method: Use of serial number to generate user encryption key
  
• Secure method: Use of learn seed to generate user encryption key

Learning involves the receiver calculating the transmitter’s crypt key, decrypting the received hopping code and storing the serial number, synchronization counter value and crypt key in EEPROM. The different types of learning are:

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 Learning - 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.

We offer the following hardware components:

• General-purpose PIC® microcontrollers (MCUs)
• PIC MCUs with hardware KeeLoq technology engine (PIC12F635/636/639 family)
• KeeLoq encoders (HCS1xx/2xx/3xx family)
• KeeLoq decoders (HCS5xx family or any PIC MCU)
• KeeLoq transcoder/encoder (transponder and encoder combinations) (HCS4xx family)
• Battery authentication products (MCP73826/7/8, MCP73841/2/3/4, MCP73861/2)

All KeeLoq technology devices are programmed using a serial method, which uses CLK, DATA and MCLR for a few of the devices. This serial mode allows the devices to be programmed while in the system or programmer socket, which increases the flexibility of designing cryptographic encoders, decoders and transponders into electronic systems. The manufacturer’s code, crypt keys and synchronization information are stored in encrypted form in external/internal EEPROM as the devices are memory mapped. The programming voltage range for VDD is +5V ± 10% for all devices.

Read the HCSXXX Memory Programming Specification for more information about programming KeeLoq technology devices.

Note: Devices with on-chip EEPROM do not store encrypted keys; only devices with off-die EEPROM will encrypt information before storing it.

Yes, you need to be licensed by Microchip to use our KeeLoq encoder and decoder products. If you are using one of our HCSxxx devices that integrates the KeeLoq technology software, your license is part of your standard terms and conditions of sale.

If you would like to integrate the KeeLoq technology encoder or decoder software into a PIC MCU yourself, then you will need to agree to the click-through license agreement terms before you download the software:

• KeeLoq Technology Encoder Software
• KeeLoq Technology Decoder Software
  

Any installation, use, or copying of the KeeLoq technology encoder or decoder software or documentation shall also constitute acceptance of license agreement terms. Contacting your local Microchip sales representative for additional information.

RKE: Remote Keyless Entry

PKE: Passive Keyless Entry

LF: Low Frequency, refers to a typical 125 kHz frequency

Transcoder: Device combining unidirectional transmitter capabilities with bidirectional authentication capabilities

Anticollision: A scheme where the transponders in the same field can be addressed individually, preventing simultaneous response to a command

Code Hopping: A method by which a code, when viewed externally from the system, appears to change unpredictably each time it is transmitted

Code Word: A block of data that is repeatedly transmitted upon button/key activation

KeeLoq Transmission: A data stream consisting of repeating code words

Crypt Key: A unique and secret 64-bit number used to encrypt and decrypt data. In a symmetrical block cipher such as the KeeLoq technology 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

Device Identifier: 16-bit value used to uniquely select one of multiple transponders for communication

IFF: Identify Friend or Foe, a classic authentication method

Manufacturer’s Code: A unique and secret 64-bit number used to generate unique encoder crypto keys. Each encoder is programmed with a crypto key that is a function of the manufacturer’s code. Each decoder is programmed with the manufacturer code itself.

Proximity Activation: A method whereby an encoder automatically initiates a transmission in response to detecting an inductive field