KeeloQ
Summary
This article provides an overview of KeeloQ and the hopping code and friend or foe algortihms, which are used in KeeloQ.
Requirements
- Basic knwoledge of blockcipher
Description
KeeloQ
KeeloQ is used for access authorization in electronic remote keys. Every new sender e.g. remote key must be registrated on the reciever system. The new remote keys are registrated with their serial number.
KeeloQ is an blockcipher that uses 64 bit keys. Every command for an action has an unique code. This code is always the same for every transmission, therefore hopping code and friend or foe algortihms are used.
Hopping code
Without hopping code the transmitted code for an unique action would be every time the same. This would cause that someone who monitored the message would be able to perform the action. In hopping code a counter is used. This counter is incremented every time an action is sent. The counter value is also transmited. If the counter value if the reciever is approximately the same as the recieved the action is performed.
Friend or foe
This is an challlenge response protokoll. The reciever sends an message to the sender e.g. remote key. The sender encrypts this message and sends it back to the reciever. If the messages can be decrypted successfully, further masseges from the sender will be accepted.