I am doing thesis on "NFC relay attack" in my BSc last year. I have studied 10-15 papers and learned the basics of NFC and relay attack. Still I am no where near to understand how relay attack is performed on NFC and how the protocols work in NFC. What should I learn to know how the Relay attack is performed and how the NFC protocols are related to the attack?
I would stop focusing on 'relay' and do more research into MITM or man in the middle attacks. A relay is essentially just a MITM. Also initially I may even back off of NFC and just study MITM attacks on something that is more thoroughly documented, such as regular MITM over tcp.
When ever I am having trouble wrapping my head around a particular topic I try and create a lab to accomplish this. Research how to implement MITM attacks, specifically with NFC. As you work through that problem you will become intimately familiar with the concepts of the attacks as well as the protocols involved in NFC
Security is an essential aspect of the success of NFC technology. The high interoperability of the popular collection of standards must be integrated with appropriate mechanisms to protect data.
Implementation of security mechanisms to a tag requires analysis of costs versus benefits. There are various solutions that imply different economic and computational costs, therefore it is crucial to understand exactly what information has to be protected and which are the main threats.
Newer tags have security functionality built into the chip but are not a part of the NFC tag specification; the principal objectives to pursue for data protection are:
Principal menaces are represented by an attacker’s ability to intercept and manipulate the data without detection. In both cases, the above principles are violated.
you should definitely read this. it might clear stuff on NFC- http://resources.infosecinstitute.com/near-field-communication-nfc-technology-vulnerabilities-and-principal-attack-schema/#gref