diff options
Diffstat (limited to '2005/rfid-lk2005/rfid.xml')
| -rw-r--r-- | 2005/rfid-lk2005/rfid.xml | 504 |
1 files changed, 504 insertions, 0 deletions
diff --git a/2005/rfid-lk2005/rfid.xml b/2005/rfid-lk2005/rfid.xml new file mode 100644 index 0000000..84b384d --- /dev/null +++ b/2005/rfid-lk2005/rfid.xml @@ -0,0 +1,504 @@ + + + +<section> +<title>Introduction into RFID</title> +<para> +During the last couple of years, various different sectors of industry and +event government organizations started to advertise and deploy RFID technology. +</para> +<para> +The RFID industry makes huge promises, according to which RFID will penetrate +our everyday life in the very close future. As an example, RFID is used in the +ICAO-compliant electronic passports, for electronic ticketing in the public +transport sector and for tickets to events such as the soccer world +championships in 2006. Studies have been performed on the feasability of putting +RFID circuitry into every Euro bill. +</para> +<para> +Contrary to those industry promises, there is a growing opposition among civil +liberties groups and the data protection community. The fear of abuse of this +technology to invade privacy even further is big. +</para> +<para> +The public debate on RFID is mostly on a very high and therefore abstract +level. Even within the technical community, there's a severe lack of knowledge +when it comes to really understanding RFID. +</para> +<para> +This article tries to give a technical introduction into RFID, +summarizing what the author has learned throughout the last year during his +research and development. +</para> + + +<section> +<title>What is RFID?</title> +<para> +A lot of the ambuguity related to RFID comes from the unclear terminology. +Strictly speaking, "RFID" means "Radio Frequency IDentification" and therefore +refers to any technology facilitating identification of items using radio +frequency. +</para> +<para> +However, in reality the term "RFID" is used for meny different technologies and +concepts. +</para> +<para> +Another frequent misconception is that most RFID systems in use today are based +on standards. To the opposite: In fact they're mostly proprietary systems +produced by specific vendors, who obviously all proclaim to have invented an +'industry standard". Even those few RFID protocols that have been standardized +by international standardization bodies such as ISO/IEC reflect the usual +"either it's done way A, if not it's done way B" paradigm that seems to +dominate the whole smart card industry. But that's enough of a rant for now. +</para> +</section> + +<section> +<title>Components of an RFID system</title> +<para> +A RFID system is usually composed of a reader device (which is always called +reader, even if it can write) and some (RF)ID tag, sometimes referred to as +transponder. +</para> + +<section> +<title>Tag (or Transponder)</title> + +<section> +<title>1-bit Tags</title> +<para> +1-bit tags don't really provide any form of identification. A 1-bit RFID +system can only tell whether (at least) one tag is within reach of the reader. +While this is quite limited, it still has one very popular application: +Preventing theft of items from a store. +</para> +</section> + +<section> +<title>Serial Number Tags</title> +<para> +The most simplistic RFID systems come with read-only "serial number" tags. +This basically means that the tag has a vendor-defined serial number (much like +a barcode on product packaging), that can only be read. Such systems generally +don't employ any form of authentication. +</para> +</section> + +<section> +<title>WORM Tags</title> +<para> +Instead of vendor-programmed serial numbers, WORM(write once read many) tags +can be written once (usually at the customer site) and read many times. +</para> +</section> + +<section> +<title>Read/Write Tags</title> +<para> +Read/Write tags can be read and written a large number of times. r/w tags can be +seen analogous to synchronous memory chip cards in the contact-based world. +</para> +</section> + +<section> +<title>Read/Write with "passive" security</title> +<para> +This variant of tags employ read/writable memory plus some state machines that +allow for (mutual) authentication of reader and tag, and/or encryption of the +transferred data. +</para> +</section> + +<section> +<title>Cryptographic Smartcards with RF Interface</title> +<para> +The lateset generation of "tags" are not really tags anymore, but rather +cryptographic smart cards with an RF interface. This means that you have a +whole computer (sometimes called RFIC), including CPU, RAM, ROM, EEPROM, +hardware random number generator, hardware crypto, etc. inside the "tag". +Since such devices originate from the contact-based smart card world, they +sometimes even are available as "dual interface smart cards", i.e. employ both +contact-based and contactless (RFID) interface. +</para> +</section> + +</section> + + +<section> +<title>Reader</title> +<para> +Readers (sometimes called proximity coupling devices, PCDs) are usually +connected to some computer or network, using standard interfaces such as RS232 +ports, serial interfaces, USB, or Ethernet. Unfortuantely, there is no +standard either on hardware nor on software level. This means that most RFID +applications will be written against specific vendor-rprovided driver or +library API's. +</para> +<para> +There's one notable exception: Reader systems employing cryptographic +smartcards with RF interface often emulate API's from the contact-based smart +card world such as PC/SC or CT-API. +</para> +</section> + + +<section> +<title>RF Interface</title> +<para> +Between reader and tag there is some form of an RF interface. The RF interface +differs from system to system in many parameters, such as frequency, +modulation and operational principle. +</para> + +<section> +<title>Magnetic Coupling</title> +<para> +Most of todays RFID systems use a magnetic coupling principle. In such a +system, the reader provides a strong magnetic field (H-field). This field is +picked up by the antenna of a tag, and used to power the tag. Common +frequencies for such magnetically coupled RFID systems are 125kHz and 13.56MHz. +Magnetic systems often employ amplitude shift keying for the reader to tag +communications channel, and load modulation from tag to the reader. +</para> +<para> +The strong magnetic field only exists in the proximity of the readers' antenna. +Thus, magnetically coupled RFID systems are sometimes referred to as "proximity +or vicinity RFID", often with operational ranges less than 10cm. +</para> +<para> +The remaining article will focus on magnetic coupling RFID systems only, since +backscatter systems are not widely deployed yet, and therefore of little +practical relevance. +</para> +</section> + +<section> +<title>Backscatter</title> +<para> +A lot of RFID systems under current developemnt operate in the UHF frequency +range (868 to 956 MHz, depending on the regulatory domain). They use the +electric field of the reader, and employ backscatter modulation from tag to +reader. The electrical field extends over longer distance than the magnetic +field. Therefore, the operational range of backscatter systems are within tens +of metres. +</para> +</section> + +<section> +<title>Surface Accoustic Wave</title> +<para> +SAW tags use low-power microwave radio signals. The tag converts them to +ultrasonic accoustic signals using a piezoelectric crystalline material. +Variations of the reflected signal can be used to provide a unique identity +such as a serial number. +</para> +</section> + +</section> <!-- rf interface --> + +</section> <!-- overview --> + + +<section> +<title>Protocols and Standards</title> +<para> +For the commonly-used 13.56MHz based systems, there are two major protocols in +use, ISO 14443 and ISO 15693. ISO 15693 seems only be used for "dumb" tag +applications, whereas ISO 14443 is used frequently with RF interfaced processor +smart cards. +</para> + +<para> +Besides the "physical layer" issues such as modulation, coding, bit timing, +and frequency, there are some other important tasks of an RFID protocol. +</para> + +<para> +One of the funamental effects of RFID is the possibility of multiple tags +within the operating range of a reader, just like in any other shared medium +communication channel. +</para> + +<para> +In order to cope with multiple tags, an anticollision procedure has to be +specifieid. Some sophisticated protocols (as 14443-4 )even allow a reader to +assign logical addresses to individual tags in order to communitace with +multiple tags. +</para> + +<section> +<title>ISO 11784 / 11785</title> +<para> +The ISO 11784 / 11785 series of standards are used for identification of animals. +This family of standards operates at 134,2 kHz and uses the magnetic coupling +operational principle. It uses load modulation with no subcarrier and employs +a bi-phase-code for transmission of 64bit transponder data at 4194 bits/sec. +</para> +</section> + +<section> +<title>ISO 14223</title> +<para> +ISO 14223 is an extension of 11784/11785 and allows for more data stored on the +tag/transponder. +</para> +</section> + +<section> +<title>ISO 10536</title> +<para> +ISO 10536 describes "close coupling" smart cards, with an operational range of +up to 1cm. It employs inductive or capacitive coupling at 4.9152 MHz. Due to +this low operational range, they never appeared in widespread use on the market. +</para> +</section> + +<section> +<title>ISO 14443</title> +<para> +ISO 14443 describes "proximity coupling identification cards". As opposed to +ISO 10536, this standard has an operational range of up to 10cm. +</para> + +<para> +ISO 14443 has two variants: ISO 14443-A and ISO 14443-B. They both operate +on the same frequency, but with different parameters. +</para> + + +<informaltable border="1" width="90%"> + <tgroup cols="3"> + <thead> + <row> + <entry>Parameter</entry> + <entry>ISO 14443-A</entry> + <entry>ISO 14443-B</entry> + </row> + </thead> + <tbody> +<row><entry>Modulation Reader->Tag</entry><entry>100% ASK</entry><entry>10% ASK</entry></row> +<row><entry>Modulation Tag->Reader</entry><entry>load modulation at 847kHz subcarrier, ASK</entry><entry>load modulation at 847kHz subcarrier, BPSK</entry></row> +<row><entry>Code Reader->Tag</entry><entry>Modified Miller</entry><entry>NRZ</entry></row> +<row><entry>Code Tag->Reader</entry><entry>Manchester</entry><entry>NRZ</entry></row> +<row><entry>Anticollision</entry><entry>Binary Search</entry><entry>Slotted ALOHA</entry></row> + </tbody> + </tgroup> +</informaltable> + +<para> +ISO 14443-4 specifies an (optional) transport level protocol on top of the lower +three layers of the ISO 14443 protocol. This transport protocol is sometimes +referred to as "T=CL" (transport=contactless). This designation bears its +origin in the smart card world, where other protocols such as "T=0" and "T=1" +are in widespread use for decades. +</para> +<para> +The remaining paper will mostly look at ISO 14443, since it is in widespread use +today and also used by the electronic Passport system specified by ICAO. +</para> +</section> + +<section> +<title>ISO 15693</title> +<para> +ISO 15693 describes "vicinity coupling" RFID, with an operational range of up +to 1m. Like ISO 14443, it operates on 13.56 MHz and employs magnetic near-field +inductive coupling. +</para> +<para> +This standard again supports various modes, such as 10% or 100% ASK, 1.65kb/s +or 26.48kb/s data rate, ASK or FSK based load modulation. +</para> +<para> +Given the big distance between reader and tag, it is very unlikely that high +power consumption processor smart cards will be developed for this standard. +</para> +</section> + +<section> +<title>ISO 18000 series</title> +<para> +This ISO series is under current development. It intends to specify unique +world wide standards for item management. Specifications include operation +on 13.56MHz, 2.45GHz, 5.8GHz and the 868 to 956 MHz UHF band. +</para> +</section> + +</section> + + + + +<section> +<title>A closer look on Readers</title> +<para> +There's a variety of readers for the 13.56MHz world, ranging from embedded +reader modules to PC-connected readers for USB and serial connections, +Ethernet-connected readers as well as readers for handheld devices with +CompactFlash interface. +</para> + +<para> +As opposed to the contact-based smartcard world where most readers now support +the USB CCID standard (to my surprise even non-usb devices!), there is no +standardization. Neither does any of the readers - to the best of the authors' +knowledge - have any publicly and/or freely available documentation. A similar +lack is observed for Linux drivers. If they are available, then often for an +extra charge, and in proprietary x86-only format. +</para> + +<para> +On the electrical level, a lot of readers are surprisingly equal. Almost all +of them seem to use readily available "reader ASICs" of vendors such as TI or +Philips. Those ASIC's usually integrate both the analogue RF part (including +modulation/demodulation) and the digitial part. They are interfaced by serial +(SPI) or parallel address/data bus. As you could have guessed by now, there's +again no publicly/freely available documentation on any of the chipsets. +</para> + +<para> +After doing some research and re-engineering on commonly-available existing +readers, there seems to be a two different basic architectures: +</para> + +<section> +<title>Active Readers</title> +<para> +Active readers do all the 14443/15693 processing within a microcontroller of +the reader. Advantages of an active design are low latency, high speed and +applicability in embedded or remotely connected environments where no host +computer could do protocol processing. +</para> +</section> + +<section> +<title>Passive Readers</title> +<para> +Passive readers simply include the most basic logic to interface the reader +ASIC with the external interface. Therefore all protocol processing has to be +done on the host system. +</para> +<para> +For obvious reasons, the passive architecture allows for cheaper development +and total product cost. The author anticipates that all PC-based readers will +eventually become passive. A commonly-available passive reader (Omnikey +CardMan 5121) was chosen for the development of librfid. +</para> +</section> + + +<section> +<title>Omnikey CardMan 5121</title> + +<para> +On the first glance, the cm5121 is a USB CCID contact based smartcard reader. +It can be used with vendor-supplied proprietary drievers, or with various +freely available CCID reader drivers, such as the OpenCT project. +</para> +<para> +However, the RFID part is simply a Philips CL RC632 reader asic that can be +accessed transparently by issuing read/write_byte and read/write_fifo commands +via CCID PC_to_RDR_Escape usb messages. +</para> +<para> +The author further obtained a (publicly available, but encrypted) detailed data +sheet of the Philips CL RC632 reader asic, which magically decrypted itself by +using a couple of days worth of CPU power. +</para> +<para> +The CL RC632 is a multi-protocol reader asic, supporting 14443-A, 14443-B, +15693 as well as the proprietary 14443A-based Mifare system. +</para> +<para> +Using the data sheet, a free and GPL licensed RFID stack could be implemented +from scratch. +</para> +</section> + +</section> <!-- closer look on readers --> + + +<section> +<title>Security Issues</title> + +<section> +<title>Eavesdropping</title> +<para> +Like any RF interface, the magnetic RFID interface can be passively sniffed. +Due to the use of the H-field in 125kHz and 13.56MHz systems, the possible +surveillance range is very slow. Also, given the enormous power constraints +within the tag, the power put into the tag->reader channel is very low. +Furthermore, the main carrier and the subcarrier are very close in the radio +spectrum - while their signal strength differs some 60 to 80 dB. +</para> + +<para> +Measurements conducted by the author do not suggest that passive surveilance of +ISO 14443 compliant systems is not possible outside a range of 4-5 metres - at +least not with DIY equipment. +</para> +</section> + +<section> +<title>Denial of Service</title> +<para> +ISO 14443-A and -B anticollision systems are subject to denial of service +attacks. +</para> +<para> +For 14443-A, such an attack could simply cause one collision for every bit in +the address, thus preventing the reader to complete its binary search algoritm +and fully select one of the available tags. +</para> +<para> +There have already been public demonstrations of "blocker tags" which employ +such a technique to prevent other tags in the vicinity of the blocker tag from +being read. +</para> +</section> + +<section> +<title>Authenticity/Confidentiality</title> +<para> +ISO 14443-A doesn't provide any form of security. Any kind of authentication +and/or encryption has to be employed at a higher level, such as ISO 7816 secure +messaging. Compare the system with a TCP/IP stack (level 1..4) with SSL/TLS on +top. +</para> +</section> + +<section> +<title>Proprietary Security</title> +<para> +The security of vendor-speciifc proprietary systems such as Mifare are based on +security by obscurity. The encryption alogorithm is not publicly documented, +and only implemented in vendor-supplied hardware, usually the reader ASIC and +inside the tag itself. Keys are stored on the tag and in the reader ASIC. +</para> +<para> +Security by obscurity within the software industry generally doesn't work. +However, in the hardware world vendors still seems to assume it as a valid +paradigm. +</para> +<para> +The key lengths used in many proprietary systems seem extermely small (40bit, +sometimes even only 24 bit). Should the algorithm ever be uncovered, it is +expected to compromise the security of the whole system. The arithmetic +complexity of the algorithm can only be low, given it's implementation in +lowest-cost state-machine-only tags. Therefore it is expected that once +somebody has performed the difficult task of re-engineering a reader ASIC, the +system security will be compromised. +</para> +<para> +Brute-force attacks on tags themselves seem very unlikely, due to the extremely +slow hardware. However, after a successful (legitimate) conversation between +reader and tag has been sniffed, brute forcing can be done on fast computers. +</para> +</section> + +</section> <!-- security --> + +</section> <!-- rfid --> |