Preventing replay/relay attacks in keyless entry systems

A method for controlling access to a resource, the method performed by a system comprising a first component, a second component and a third component, wherein:

• the first component comprises a first cryptographic key;
• the second component comprises a second cryptographic key;
• and
• the method comprises:
• transmitting, by the third component, a signal;
• generating, by the first component, a first channel observation;
• generating, by the second component, a second channel observation;
• generating, by the second component, a first data value based on the second channel observation and the second cryptographic key;
• transmitting, by the second component, to the first component, the second channel observation and the first data value;
• verifying the second component, by the first component, based on the second channel observation, the first cryptographic key and the first data value;
• and
• allowing access to the resource in response to determining that the second component is:
• 1) permitted to gain access to the resource;
• and 2) located proximate to the first component.