Real-Time Systems. Design Principles for Distributed Embedded Applications. Herman Kopetz. Second Edition (811374), страница 91
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It is thuspossible to track objects in real-time.Example: An electronic ski pass is an RFID tag that is queried by the reader that is builtinto the admission gate to a ski lift. Based on the object identifier, a picture of the personthat owns the ski pass is displayed to the operator and the gate is opened automatically if theoperator does not intervene.13.4.2 The Electronic Product CodeWhereas an optical barcode denotes a product class (all boxes of the same producthave the same barcode), the EPC of an RFID tag denotes an object instance (everybox has a unique identifier).
It is the intent of the EPC to assign a unique identifier(UID) to every identifiable thing on the globe, i.e., a unique name to each smartobject of the IoT.The EPC is managed by the international organization EPC global. In order tocope with the huge number of things the EPC must identify, the EPC contains anumber of fields. A small header field determines the structure of the remainingfields. A typical EPC has a length of 96 bits and contains the following fields:llllHeader (8 bits): defines the type and the length of all subsequent fields.EPC Manager (28 bits): specifies the entity (most often the manufacturer) thatassigns the object class and serial number in the remaining two fields.Object Class (24 bits): specifies a class of objects (similar to the optical barcode).Object Identification Number (36 bits): contains the serial number within theobject class.The EPC is unique product identification, but does not reveal anything about theproperties of the product.
Two things that have the same properties, but aredesigned by two different manufacturers, will have completely different EPCs.13.4 RFID Technology317Normally, the unique EPC is used as a key to find the product record in a productdatabase. The product record contains all required information about the attributesof the product.13.4.3 RFID TagsA RFID Tag contains as its most important data element the EPC of the associatedphysical thing. A number of different RFID tags have been developed and standardized.
Basically, they fall into two main categories: passive RFID tags and activeRFID tags.Passive RFID Tags. Passive tags do not have their own power supply. They get thepower needed for their operation from energy harvested out of the electric field thatis beamed on them by the RFID reader. The energy required to operate a passive tagof the latest generation is below 30 mW and the cost of such a tag is below 5 ¢.Passive tags contain in addition to a standardized EPC (Electronic Product Code) asa unique identification number selected other information items about productattributes.
Due to the low level of the available power and the cost pressure onthe production of RFID tags, the communication protocols of passive RFID tags donot conform to the standard Internet protocols. Specially designed communicationprotocols between the RFID tag and the RFID reader that consider the constraints ofpassive RFID tags have been standardized by the ISO (e.g., ISO 18000-6C alsoknown as the EPC global Gen 2) and are supported by a number of manufacturers.The parameters of a typical low-cost passive RFID tag are given in Table 13.1.Active RFID Tags. Active tags have their own on-board power supply, e.g., abattery that gives them the capability to support many more services than passivetags. The lifetime of an active tag is limited by the lifetime of the battery, typicallyin the order of a year.
Active tags can transmit and receive over a longer distancethan passive tags, typically in the order of hundreds of meters, can have sensors tomonitor their environment (e.g., temperature, pressure) and sometimes supportstandard Internet communication protocols. In some sense, an active RFID tagresembles a small embedded system. The ISO standard 18000-7 specifiesTable 13.1 Parameters of a typical low-cost passive RFID tag (Adaptedfrom [Jue05])Storage128–512 bits of read-only storageMemory32–128 bits of volatile read-write memoryGate count1,000–10,000 gatesOperating frequency868–956 MHz (UHF)Clock cycles per read10,000 clock cyclesScanning range3mPerformance100 read operations per secondTag power sourcePassively powered by reader via RF signalPower consumption10 mW31813 Internet of Thingsthe protocol and the parameters for the communication with an active tag in the433 MHz range.
The reduction of the power consumption of an active RFID Tagin the sleep mode is a topic of current research.13.4.4 RFID ReadersThe RFID reader is a gateway component between the world of RFID tags and theInternet. These two worlds are characterized by different architectural styles,naming conventions, and communication protocols.
On the Internet side, anRFID reader looks like a standard web server that adheres to all Internet standards.On the RFID side, the RFID reader respects the RFID communication protocolstandards. The RFID reader has to resolve all property mismatches.13.4.5 RFID SecurityWhenever we connect a computer to the Internet, sensitive security issues arise[Lan97] that must be addressed. Standard security techniques are based on thedeployment of cryptographic methods, like encryption, random number generation,and hashing as outlined in Sect.
6.2. The execution of cryptographic methodsrequires energy and silicon real estate, which are not sufficiently available in allsmart objects, such as low-cost RFID tags. The often-heard argument that computationally constrained RFID tagged objects will disappear in the near future asthe microelectronic devices become cheaper overlooks the price pressure onsimple RFID tags. If low-cost RFID tags are placed on billions of retail products,even a 1-¢ increase in the cost of a tag for the provision of cryptographic capabilities will be shunned.The information security threats in the IoT can be classified into three groups:(1) the threats that compromise the authenticity of information, (2) the threats toprivacy caused by a pervasive deployment of IoT products, and (3) denial of servicethreats.
We assume that the vast majority of IoT devices are connected to thecyberspace by a wireless connection. A wireless connection always presents aserious vulnerability since it opens the door to an unnoticed observation of thetraffic by an adversary.Authentication. It is a basic assumption in the IoT that the electronic device, e.g., aRFID tag, represents a unique physical thing in cyberspace and that this linkbetween the electronic device and the physical thing which has been establishedby a trusted authority can be relied upon. This belief in tag authenticity can beshaken easily.
Scanning and replicating an unprotected tag is relatively easy, since atag is nothing else than a string of bits that can be copied without difficulty.13.4 RFID Technology319Attaching another physical thing – e.g., a faked product – to an authentic tag canbreak the link between the physical thing and the tag – the representative of thephysical thing in cyberspace. This kind of attack has to be addressed in the levelof physical design of a smart object and cannot be dealt with by cyberspacesecurity methods.The known techniques to ensure the authenticity of the thing behind a low costRFID tag are quite limited.
A tag is a bit-string that can be read by any commodityreader and can be copied to produce a cloned tag. Even a digital signature could notprevent cloning of tags. Men in the middle attacks, where an attacker mimics a correcttag, might break the established link between the reader and the tag. Accessing theproduct database can detect the existence of cloned tags by discovering that theuniqueness property of the EPC has been violated, but it cannot eliminate cloning.Example: Accessing the product database can identify a counterfeit piece of art thatcarries a cloned tag and finding out that the genuine object is at a location that is differentfrom the tag reader.Tamper-proof tags that physically break when they are detached from the thing theyhave been attached to by the trusted authority are one solution to the problem ofphysical tag stealing.
In order to be able to ascertain the authenticity of valuablethings physical one-way functions (POWF) have been proposed [Pap02]. An example for a POWF is a transparent optical device with a random three-dimensionalmicrostructure that is attached to the thing in a tamper-proof manner. Since therandomness of the structure cannot be controlled during the manufacturing process,it is impossible to produce two POWF that are alike. When read by a laser under aspecific angle, a POWF response is a bit stream that is characteristic for this uniquePOWF. Depending on the reading angle, different characteristic bit streams can beretrieved.
These bit streams can be stored in the product database. It is difficult foran adversary to clone a POWF, because it is a thing with random characteristicphysical properties that cannot be represented by a mathematical function.A POWF is not a construct of cyberspace that can be copied or reconstructed.Privacy. The main privacy concern in the RFID world is the clandestine reading ofa tag by an unauthorized reader. Since low-cost RFID tags are unprotected and canbe read by commodity readers, clandestine tag tracking by unauthorized readersdiscloses valuable information to an adversary.
If the adversary uses a sensitivereader with a high-power antenna output (rogue reading), he can significantlyextend the nominal read range. The information about EPC codes and otherattributes that are contained in the tag can be linked with the identity of the personcarrying the tag in order to construct a personal profile. Since a low-cost tag doesnot have the cryptographic capability to authenticate the reader, it will disclose itsinformation whenever it is queried. Clandestine tag reading can be prevented bypermanently killing the tag as soon as the tag enters the consumer domain, i.e., atthe point-of-sale. Tag killing enforces consumer privacy effectively.
However, iftags support the functionality of tag killing, a vulnerability with respect to availability is established.32013 Internet of ThingsExample: By analyzing the tagged medication a person is carrying, an adversary couldinfer information about the health condition of the person.Example: If – as has been proposed – money bills contain an RFID tag, an adversary witha hidden reader could determine unnoticeably the amount of money a person is carrying inher/his briefcase.Example: In a commercial setting, an adversary with a hidden reader could periodicallymonitor the inventory of goods in a competing supermarket.Another privacy enforcement technique does not prevent, but detects clandestinereading.
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