One of the simplest ways to attack an RFID system is to prevent the tag on an object from being detected and read by a reader. Since many metals can block radio frequency (RF) signals, all that is needed to defeat a given RFID system is to wrap the item in aluminum foil or place it in a metallic-coated Mylar bag. This technique works so well that New York now issues a metallic-coated Mylar bag with each E-ZPass.
From the standpoint of over-the-air attacks, the tags and readers are seen as one entity. Even though they perform opposite functions, they are essentially different faces of the same RF portion of the system.
An attack-over-the air-interface on tags and readers typically falls into one of four types of attacks: spoofing, insert, replay, and Denial of Service (DOS) attacks.
Spoofing attacks supply false information that looks valid and that the system accepts. Typically, spoofing attacks involve a fake domain name, Internet Protocol (IP) address, or Media Access Code (MAC). An example of spoofing in an RFID system is broadcasting an incorrect Electronic Product Code™ (EPC™) number over the air when a valid number was expected.
Insert attacks insert system commands where data is normally expected. These attacks work because it is assumed that the data is always entered in a particular area, and little to no validation takes place.
Insert attacks are common on Web sites, where malicious code is injected into a Web-based application. A typical use for this type of attack is to inject a Structured Query Language (SQL) command into a database. This same principle can be applied in an RFID situation, by having a tag carry a system command rather than valid data in its data storage area (e.g., the EPC number).
In a replay attack, a valid RFID signal is intercepted and its data is recorded; this data is later transmitted to a reader where it is "played back." Because the data appears valid, the system accepts it.
DOS attacks, also known as flood attacks, take place when a signal is flooded with more data than it can handle. They are well known because several large DOS attacks have impacted major corporations such as Microsoft and Yahoo. A variation on this is RF jamming, which is well known in the radio world, and occurs when the RF is filled with a noisy signal. In either case, the result is the same: the system is denied the ability to correctly deal with the incoming data. Either variation can be used to defeat RFID systems.