Relay attack: Initiating connections to both devices, and then relaying communication between them.
Relay Attacks are more of a application-level issue, as there is no way to verify at the hardware level that the device you are communicating with is who it says it is without an authentication procedure, which can be relayed. Reading: http://www.nedapsecurity.com/sites/default/files/whitepaper-relayattack-online.pdf
It seems that protecting the user-side with a faraday cage, implementing a simple timing to prevent extraneous timing being used in access (typical speeds will increase for relay attacks), and a proximity check to prevent card access outside the allowed boundaries of usage.
By Relay attacks in BLE side, I assume you were talking about the Man in the middle attack which can happen which reults in hacking the over the air data communicating over BLE. If then CyBLE supports the security modes of Unauthenticated / Authenticated Pairing and encryption. And you can whitelist that no other BLE devices should be able to connect. The link will be encrypted and no third person can't interpret the data as well.
Please go through the BLE security modes in the BLE spec for better understanding.
Hi colleagues, Thanks for the answers. They really help me. Best, Peter