KeeLoq^® Technology FAQs

• Why do you need our KeeLoq^® technology?
• What types of transmissions are available with KeeLoq technology?
• What is a code grabber?
• What is a code scanner?
• What security levels are available with KeeLoq technology?
• What is "learning" in KeeLoq technology?
• How are KeeLoq technology devices programmed?
• Do you need a license to work on KeeLoq technology products?
• Glossary

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 are not widely used because of their high cost and other disadvantages.

Popular unidirectional transmission systems currently have two crucial 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. Two conditions are required to implement secure remote-control systems:

• Many possible combinations must be available
• The system must never respond twice to the same transmitted code

The KeeLoq protocol's code-hopping system easily meets both conditions. Its 64-bit transmission code with two to five bits of status information uses a total of 66 to 69 bits to make scanning impossible. The 32-bit encrypted portion provides 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: unidirectional and bidirectional transponder.

A remote-control transmitter is a small radio transmitter typically used in vehicle security systems that transmits a code number on a particular frequency. An integrated circuit encoder normally generates this code number, and the transmit frequency is set by the country in which the code is being used. Due to the simple transmission format, it is easy to build a simple receiver, called a code or key grabber, that can receive signals from these transmitters and record the transmissions for replaying later.

Due to the limited number of combinations available in most remote-control systems, they can quickly transmit all possible combinations. A code scanner is a handheld microprocessor-based system that accesses the system and quickly scans these combinations. 

KeeLoq technology supports three levels of security:

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

Learning involves the receiver calculating the transmitter’s crypt key, decrypting the received hopping code, storing the serial number and synchronizing the 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 the 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 using a button combination to transmit a stored 60-bit seed value that generates the transmitter’s crypt key, and the receiver uses this seed value to derive the same crypt key and decrypt the received code word’s encrypted portion

All KeeLoq technology devices are programmed using a serial method, which uses CLK, DATA and MCLR for a few devices. This serial mode allows the devices to be programmed in the system or programmer socket, which increases the flexibility of designing cryptographic encoders, decoders and transponders into electronic systems.

The manufacturer’s code, encryption keys and synchronization information are encrypted in the external or internal EEPROM as the devices are memory mapped. The programming voltage range for V_DD is +5V ± 10% for all devices.

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

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

If you want to integrate the KeeLoq technology encoder or decoder software into another product, 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, decoder software or documentation shall also constitute acceptance of license agreement terms. Contact your local Microchip sales representative for additional information.

• Anti-Collision: A scheme where the transponders in the same field are addressed individually, preventing simultaneous responses 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
• Crypt Key: A unique and secret 64-bit number used to encrypt and decrypt data
• 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: A 16-bit value used to select one of the multiple transponders for communication uniquely
• Encoder: A device that generates and encodes data
• Encryption Algorithm: An algorithm where data is scrambled using a crypt key and can only be interpreted by a decryption algorithm using the same crypt key
• IFF: Identify Friend or Foe (IFF), a classic authentication method
• KeeLoq Transmission: A data stream consisting of repeating code words
• LF: Low Frequency (LF), refers to a typical 125 kHz frequency
• Manufacturer’s Code: A unique and secret 64-bit number that generates unique encoder crypto keys; encoders are programmed with a crypto key that is a function of the manufacturer’s code, and decoders are programmed with the actual manufacturer code
• PKE: Passive Keyless Entry
• Proximity Activation: A method whereby an encoder automatically initiates a transmission in response to detecting an inductive field
• RKE: Remote Keyless Entry
• Transcoder: A device that combines unidirectional transmitter capabilities with bidirectional authentication capabilities