An often overlooked, yet critical application area for edge security involves radio-frequency identification (RFID) devices. RFID, first used during World War II to differentiate British from German bombers in England, has gradually entered more areas of our daily lives. Today RFID is used to pay for subways, start vehicles, collect tolls, track goods and products as well as identify people. Each system is very simple in its basic architecture: RFID readers and antenna communicate wirelessly to RFID tags, receive stored information and pass it on to backend systems. Within this framework security can play a vital role. As long as RFID tags only store a simple identifier, usually an abstract number, security concerns are low. However, when the tags hold vital information, then the economic incentives and thus target attractiveness can increase dramatically.
When we look at RFID system security, we differentiate between three main areas of focus:
1) Privacy – protecting the identity of persons, objects or object owners either due to legal mandates or de-facto requirements such as a strong regional culture around privacy protection.
2) Data – protection of information on tags that should not be shared, used and available for abuse. This is true for high-memory tags as much as for license plates on which altered data can cause disruptions.
3) Process – insiders or outsiders should not be able to interfere with business processes that have been automated through RFID technology. This is particularly important when human control has been reduced substantially in those processes.
We strongly believe that all three areas will gain relevance over the next six to twelve months. The ability of manufacturers and users alike to apply viable security solutions will mature accordingly. It is a matter of time before attacks on RFID systems go beyond initial hacks of the NXP MiFare Classic microchip for example.
This is a very instructive case in that it illustrates how easy it is to reverse-engineer a well-known and widely used microchip that already had security implemented.[1],[2] The same type of attack can happen to virtually any RFID microchip. It brings up an interesting point about how hackers operate. Oftentimes, system operators do not wish to deal with a large number of secret keys. Hence, they will put the same key on lots of RFID tags in order not to manage the key populations. What happens when a hacker breaks a tag and steals a global key? He has gained access to the entire system or a large part of it. Conversely, what happens when each RFID tag has its own unique secret key? Then only a single tag is compromised, but the system continues to operate normally.
The economic motivation of hackers becomes apparent in this scenario. A hacker will attack systems where the attack leads to the greatest economic advantage e.g. where the largest number of tags can be eliminated or where the attack leads to the biggest damage. In either scenario global keys, meaning the use of a single key for many tags, make it very easy to attack an entire system. Hence, the consequence is that implementers and end-users should leverage so called symmetric keys (both sides of the communication use one shared key). In symmetric key systems, each RFID tag can receive its own unique key thus minimizing the economic incentive of the attacker. There are other, efficiency and power-management related reasons for using symmetric keys that will not be discussed here. Suffice it to say that the alternative, asymmetric keys, most often implemented for public key infrastructure (PKI), is not suited for passive RFID systems today. To secure RFID systems it is pivotal that communications between tags and readers are not easy to intercept and, likewise, that each reader communicating with an RFID tag is authenticated as a viable device.
Figure 1: Secure RFID System Architecture
Obviously, the ability to secure communications between readers and tags is not the only requirement. RFID systems, especially when they need to operate very fast, can make the best use of a local crypto server, which manages secure symmetric keys and becomes the counter-party to an information exchange between tag and reader under certain circumstances. In this case the reader becomes a pass-through. This may not speedup a transaction, but it greatly increases the overall level of security in a RFID system. There are other scenarios, when the reader needs to be the counter-party to the tag so that the fastest possible transaction speed is achieved. This is particularly interesting when the administration and handling of secret keys is not complex. In this case, the reader and crypto server also need to establish a trusted, secure communication using Hummingbird HB-2. Obviously, it would be of little help to secure the front-end of a transaction while leaving later system components unprotected. An attacker would simply wait for the data stream after it has passed through the reader. A secure RFID system also needs to protect the communication between crypto server and backend system.
Figure 2: Secure Crypto Server Managing Secret Keys
One of the biggest challenges in information security is the handling of shared secrets. As mentioned, a cipher uses a key as its shared secret to encrypt and decrypt information. Once an attacker has access to the key, the system is no longer secure. Distributing and then finding symmetric keys are two of the requirements that secure RFID solutions must address very reliably. RFID systems are logically and often geographically distributed and can include hundreds or even thousands of antenna and readers. Think of automotive tolling systems that cover entire cities or the RFID system that Wal-Mart is deploying across thousands of stores. Also, there often isn’t just one domain that controls access to all of these RFID devices e.g. supply chain solutions that leverage RFID tags from manufacturer to distributor and retailer. The management of keys from insertion of the first key to reliable revocation of keys can be an enormous undertaking. Well-designed edge security enables the exchange of keys in regular intervals and timely revocation of keys. It is yet another pivotal requirement to establish the security of the entire system. This functionality usually resides on the secure crypto server (shown above), which connects to high-level key servers.
[1] Nohl, K.; Ploetz, H.: “Little Security, Despite Obscurity”, Chaos Communication Congress, 2007, URL: http://events.ccc.de/congress/2007/Fahrplan/events/2378.en.html
[2] Dayal, G.: “How they hacked it: The MiFare RFID crack explained”, Computerworld, 2008, URL: http://www.computerworld.com/s/article/9069558/How_they_hacked_it_The_MiFare_RFID_crack_explained?pageNumber=1
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