From RFID Wiki

[edit] Filter chain for the RFID channel

An RFID communication port comes with a filter chain. The application can register filters with the filter chain. The application can choose the moment in time at which a filter is invoked: immediately after reception; after all immediate filters have run, but before the response is sent ('second chance filter'); in the case that reading and parsing of the frame meets an error; or after the response has been sent, or would have been sent.

A filter can determine what happens to the response after it has run. It can fill in a response frame, and indicate the action to take by the filter chain: CONTINUE lets filter processing continue; RESPOND breaks from the filter chain and causes the response to be sent. Typically, a spoof filter would fill in the response frame and indicate RESPOND. An ACL filter would check whether the response should be jammed, and if so, fill the response with jamming data and indicate RESPOND.

The filter chain that is invoked after any response is designed with logging in mind.

The filter chain that is invoked on error can e.g. be used to implement request-interference Guardian protection.

Depends on:

RFID protocol stacks

RFID communication ports

Applications

User Interface Implementation: ACL

The ACL module of the User Interface Implementation uses a filter to obtain the queries for inspection, and to pass its decision for execution

Guardian SSL

The Guardian SSL module has a filter that watches for Guardian discovery. When that is noticed, it enters an SSL handshake with the external reader. If the handshake is successful, the SSL filter intercepts all read/write multiple data requests to use as its data channel.

Logging

A log filter can be registered to be activated after response time.

Fuzzing

The fuzzing module also uses a filter, so it can modify well-formed response messages at will. This is typically invoked in the second-chance time slot.