Many tags include the name of manufacturer, the model and, sometimes, the RFID standard. With such data, it is usually easy to get more specific information on the way the tags behave and how to perform security tests.
Radio frequency detection. There are software and hardware mechanisms to determine which is the operating frequency, like using a spectrum analyzer, or disassembling the tag or the reader to observe the hardware components of the radio interface. Standard identification. Once obtained the three previous parameters frequency, modulation, and coding , it is straightforward to determine whether there exists an RFID standard compliant with such configuration.
If it is not the case, the research could become tricky, since it might involve a proprietary protocol. In the next subsections, the analysis is divided into LF and HF tags, since the way they work varies noticeably. As it will be detailed, it is possible to work at a physical level with LF tags, but that is not easy in the case of HF devices.
The first step of the methodology consists in obtaining the operation frequency. For such a purpose, one of the antennas LF or HF has to be placed far from any tag and the Proxmark command hw tune has to be executed. The command gives us the received voltage in the different supported frequencies. Then, the operation has to be performed next to the unknown tag: if one of the voltages has decreased remarkably for a specific frequency, it means that such a frequency is the operating frequency. When determining whether a tag follows an LF standard, the first step consists in figuring out the data modulation and coding.
For such a purpose, the following sequence of Proxmark commands has to be executed: LF read [ h ]: the tag is powered with the selected frequency KHz by default, or KHz using the parameter h. The command also records the signal transmitted by the tag. Data sample x : it downloads x of the previously recorded samples to the PC. Data plot : it allows the user to open a new window to plot the signal. It is useful for evaluating the signal visually.
Different instructions can be used to modify, amplify, decimate, or normalize signal values to ease signal identification. If the signal is clean enough, and its modulation has been recognized, the user can try to demodulate it. For instance, if the signal is modulated in amplitude-shift keying ASK , the command data askdemod can be executed.
In the case of frequency-shift keying FSK modulated signals, fskdemod is the right command. The next step consists in searching for a bit pattern, which might lead to determine the length of the identifier. Thus, the signal has to be observed during certain periods of time and look for similarities. In order to understand the transmitted data, it can be useful to find the standard that defines and structures them. At this point, the HID tag can be emulated with the Proxmark using the command lf hid sim ; and it can even be cloned with a rewritable tag like Atmel T HF tags behave in a slightly different way than the LF ones: their signal is so fast that it cannot be processed so easily at plain sight.
Moreover, in general, HF tags are smarter than LF tags, and they not only transmit an identifier repeatedly but also perform more complex communications with the reader. There exist many HF transmission modes and protocols. Furthermore, HF tags and readers can vary their modulation during the same transmission. The steps required to analyze HF tags are not as clear as in LF, so the study becomes more like a trial-and-error process. In order to validate the methodology proposed, three different commercial RFID systems were analyzed and tested.
The next subsections first introduce the tags audited and then give details on the analysis and the steps required testing their security. Please note that such aliases were given to avoid legal issues, since there are still several hundred thousand units of the cards still in use. In the case of the M card, it has been used in the last years by the city council of a relevant city in Spain for paying different services such as public transportation, museum access, or sport events. It is said that the council has sold more than , units of the card.
Regarding the T card, it is an RFID card developed by a Spanish regional government that provides public transportation payment to a population of 2. It was designed to be compatible with the M card; therefore, in the next subsection a joint analysis of both cards is performed. In plain sight, there are no signs or symbols that indicate the frequency band of the RFID cards. It can be assumed that by the reading range and the amount of information stored, they could be HF tags, but a deeper analysis should be performed to verify it accurately. Radio frequency. Although both cards seem to be HF, the steps described in Section 3.
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Such steps confirm that they are HF tags. Once the radio frequency is obtained, it has to be decided which of the possible standards the tags follow, and then, the modulation can be determined. It also defines two kinds of tags type A and type B , which differ in parts 2 and 3. The first step for the security analysis consisted in obtaining a good set of data samples of the communications carried out between each card and the reader. Note that data samples were taken during real trips in public transportation.
Once the radio signals were captured by the antenna, they were demodulated and decoded with the Proxmark. The main problem with this setup was electric noise: many samples were lost because they became corrupted. It is important to emphasize that the communications of the system analyzed were not encrypted.
Regarding the messages transmitted when the tag is in the active state, they can be of three types: i-block, s-block, and r-block. The first one is used for transmitting and asking for data from the application layer. The other ones are for protocol operations or are related to data from lower layers. The same happens with the byte INS, which identifies the type of command.
The third field on the header is bytes P1 and P2 that in general, refer to memory positions on the card, but they may actually be any parameter PARAM of the command. The most common answer during a correct sequence of commands is , but, sometimes, the execution of the sequence can be successful and return a different value. In the same way, a good trace should have alternating messages from the tag and the reader, instead of containing two consecutive messages from the same device except from the case when the reader is looking for tags.
As it can be observed, the sequence of messages is not correct: some are missing, and others have not been received in the correct order. First, at timestamp , the reader sends different REQB commands to wake up tags that are in its surroundings. The first byte of the command is always set to 05, while the second one is the AFI, that is, equal to 0 i.
The byte PARAM varies between both commands, being 00 in the first case and 08 in the second one they are aimed at waking up tags in different states. Finally, the last two bytes conform the CRC-B field, which checks the integrity of the message. The next four bytes are 08 10 2a 1d, which are the pseudo-unique PICC identifier PUPI, which is fixed for each tag of the system analyzed, but it might be random in other systems.
Then, the command continues with another four bytes 53 4e 44 4b that indicate the applications of the tag. Next, three bytes 33 81 93 specify different aspects of the communications protocol. However, this trace is useful for illustrating the sequence of commands executed during the exchange. The command is composed by a first byte 1d that identifies the command, four bytes that indicate the PUPI from the previous command 08 10 2a 1d , three bytes that determine the communications protocol, a byte 00, the Card Identifier CID that selects a tag and two final bytes that contain the CRC-B.
Since this is just an example of what can be done with the methodology proposed, we will not deepen into the details, but it will be mentioned briefly the structure of the first two pairs of commands. The last two bytes of the message are the CRC-B, so the transmitted data are composed by five bytes 80 26 4f 11 0a. This first command is followed by the first response of the tag. Its structure is as follows:. For instance, bytes 2—3 indicate the total number of trips carried out with the card and bytes 12—13 contain the state of the execution of the command , successful execution.
The second request is also always the same: 03 80 32 00 00 18 ea Byte 1 03 : i-block 1. Since CLA is 80, the command is proprietary. The second answer is related to the use of special fares during a trip. The data are structured as follows: Byte 1 03 : i-block 1. For instance, bytes 12—13 and 14—15 indicate the activation and expiration dates of a special fare, and byte 11 the type of fare e.
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The rest of the pairs answer-response contain other interesting information such the balance of the card, the place where the card was recharged e. After all the analysis, it was not found a severe security threat in the system, but there are several issues regarding data privacy that developers should consider. The main problem is that the RFID communications are performed in plain text, without any kind of ciphering, what leads to the possibility of snooping and emulating them.
Thanks to that, an attacker can emulate an unauthorized reader and obtain private data such as the credit balance or the specific characteristics of the trips of a user. The complete disassembling of the protocol opens the possibility to perform MitM attacks, where a third device might alter the data on the RFID transactions in order to get certain benefits e.
We can only see the contacts of traditional smart card interfaces, so there are at least two interfaces: one wired and another wireless.
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Operating frequency. Like the previous cards, it is fair to assume that due to its use for public transportation, there is a high likelihood that it is an HF card. And this fact was confirmed by following the verification steps described in Section 3. These tags use a really simple application-specific integrated circuit ASIC that basically stores data. Their memory is divided into sectors and blocks that are protected with a simple access control system. Each sector is divided into four blocks: three of them contain data, while the other one stores the data access permissions and the access keys.
There is not a fixed data format, although there is a special format called value block with specific operations for incrementing and decrementing values. Sectors use two keys A and B. Each key allows for managing different permissions: a key could be valid only for reading data, while the other one could be dedicated to modify them.
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The first 16 bytes of the internal memory are read-only and contain the serial number and other data related to the model and the manufacturer. Data are coded in Crypto-1, an already-broken cryptographic protocol [ 26 — 28 ]. Its name derives from its byte internal storage, which is divided into 16 byte sectors. It stores bytes in 5 sectors the actual useful data space is bytes. As it was explained in the previous subsection, MIFARE Classic cards implement a security system that prevents reading or writing the internal data.
However, this system is outdated and has already been broken. To get the access keys to read and write the different internal blocks, the Proxmark official firmware offers several options. For instance, the command hf mf mifare executes the darkside attack [ 28 ] to obtain a valid key.
Such an attack usually takes from 30s to half an hour sometimes it has to be executed several times. Once all the keys have been obtained, a dump of the memory can be extracted.
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With the dump, it is possible to study the different parameters e. Pet identification has been carried out throughout Europe since the late s. RFID tags are generally implanted subcutaneously. In this case, a visual assessment to detect any sign of the underlying technology is not necessary, since these kinds of tags are regulated and specified by the different European regulations previously mentioned. It was verified with the Proxmark that a sample tag already implanted on a dog was LF, as it was expected from the information given in the previous section. In this case, it was not straightforward to recognize the modulation used, because the signals captured had a lot of noise the tag had been implanted on the dog a year before these tests were performed.
When these experiments were carried out, the official Proxmark firmware did not support FDX-B, so it was necessary to implement it. Such an implementation first filters and demodulates the signal, and then decodes it. The system works at In HDX mode, the tag is not able to send data and receive power at the same time. Thus, reading consists in powering the tag for a short interval and then waiting for the tag to transmit the data.
An additional chunk of 24 bits is also sent and includes information on the application. The tags that operate in FDX-B mode are able to transmit data and be powered at the same time. Data are sent in less-significant bit LSB order, so, when the reader receives the bits, it can reconstruct them just using simple binary shifts. By making use of the functions implemented, it was straightforward to read data from any FDX-B tag.
The software extracts the two main parameters: the country code and the national code the actual identifier. Security is almost nonexistent in this kind of tags: although writing is not allowed, the tag continuously sends the stored data without any authentication requirement. It may seem that the scenario is not susceptible for including high-security mechanisms, since the objective is to identify the clinical records and the owner of a dog, but in terms of privacy and uniqueness of the identifier, the current system is not effective.
Note that, using a device such as Proxmark, it is not only easy to read the data, but also to emulate tags and clone them. This security problem is even worse when tags are attached to animals aimed at producing human food e. Cloning or erasing the data breaks traceability, which is the way to determine where an epidemic outbreak was originated. The methodology proposed in this chapter for evaluating security in commercial RFID systems has allowed for detecting relevant flaws in real-world developments, including the following: Ability to clone animal identification information.
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