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International JournalElectronics and Communication Engineering & Technology (IJECET),  International Journal of of Electro...
International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 09...
International Journal of Electronics and Communication Engineering & Technology (IJECET),  ISSN 0976 – 6464(Print), ISSN 0...
International Journal of Electronics and Communication Engineering & Technology (IJECET),    ISSN 0976 – 6464(Print), ISSN...
International Journal of Electronics and Communication Engineering & Technology (IJECET),  ISSN 0976 – 6464(Print), ISSN 0...
International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET),  ISSN 0976 – 6464(Print), ISSN 0...
International Journal of Electronics and Communication Engineering & Technology (IJECET),    ISSN 0976 – 6464(Print), ISSN...
International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 097...
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A random number generator for rfid tags

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Transcript of "A random number generator for rfid tags"

  1. 1. International JournalElectronics and Communication Engineering & Technology (IJECET), International Journal of of Electronics and CommunicationEngineering 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME ISSN 0976 – & Technology (IJECET) IJECETISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online)Volume 1, Number 1, Sep - Oct (2010), pp. 71-87 ©IAEME© IAEME, http://www.iaeme.com/ijecet.html A RANDOM NUMBER GENERATOR FOR RFID TAGS Mala Mitra Department of Electronics and Communication Engineering PES School of Engineering, Hosur Road, Electronic City Bangalore, Email: mala_2001_in@yahoo.com ABSTRACT In this paper, a true random number generator based on a simple circuit is proposed. The circuit consists of an operational amplifier with a positive feedback. It is a Schmitt trigger circuit without any applied input signal. A Schmitt trigger circuit gives a positive saturated output voltage +Vsat or negative saturated output voltage -Vsat depending on the differential input is negative or positive at the instant of power supply switch on. In the presence of any input signal the output state changes at the crossing of either the upper trigger point or the lower trigger point. In absence of any input signal the input shall be governed by resultant thermal noise voltage of the resistors present at the input. It shall be set at one level either +Vsat /bit 1 or -Vsat /bit 0 depending on the polarity of the differential input thermal noise. Instead of constant supply voltages to bias the operational amplifier clock pair may be used. The polarity of the thermal noise voltage of the resistors present at the input at the instant of rising/falling edge of the clock pair decides the polarity of the output pulses. Since polarity of thermal noise voltage is random the output bit-pattern of 1 and 0 is also random. The output bits are in polar RZ format with no dc component. Results show that, the output passes the NIST test directly. No further randomization of the output bits or input voltage control is required. The proposed random number generator is suitable for RFID tag security and privacy algorithms as the random number generator is very robust to noise, thermal and power attacks prevalent in RFID systems. The simple circuit proposed here can be implemented in existing popular embedded systems for RFID tags e.g. MSP430 microcontroller or WISP. 71
  2. 2. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEMEKeywords: Johnson noise, NIST test, Operational amplifier, Schmitt trigger, Securityand privacy of RFID systems.INTRODUCTION RFID is a low-cost solution for object identification. Some of the typicalapplications are supply chain management, access control, library management, smartappliances etc. [1, 2]. As technology advances, RFID is penetrating more and more in oureveryday life. For more widespread applications and to make these systems more popularthe security and privacy of the system must be enhanced [3, 4]. An RFID tag sends anElectronic Product Code or EPC for the object to which it is tagged. It gives informationabout the object class and a unique identification number to any interrogator. This maycreate a privacy problem. For instance, an RFID tag can be impregnated on little Alice. While Alice playsalone in her wonderland her parents can keep track of her using a RFID detector. Even ifAlice hides behind a bush the EPC code from the tag can be read by the detector as RFIDsystem does not need any Line of Sight (LOS) operation. But the problem is, the tag onAlice responds to any detector that conforms to the standard. An adversary can use herdetector and by reading the object class can find out all the kids with RFID tags in thevicinity. A kidnapper may track little Alice with the identity number available in the EPCcode. This may help to concoct a kidnap plan. Further after knowing the EPC code a tagcan be cloned with the same code. The cloned tag can be used for misguiding the parentsafter a kidnap. The transmission from the original impregnated tag on Alice can beprevented by a metal shield. Standard encryption algorithms e.g. RSA, ECC [5, 6] cannot protect againsttracking and cloning. After standard encryption a tag shall send the same encrypted EPCfor any interrogation by any detector. An adversary can track an object or a person by theencrypted EPC. No knowledge of the secret key is needed. With the encrypted EPC, tagsmay be cloned. In case of RFID tag, the encryption algorithm should give differentcipher-text or encrypted EPC for each enquiry. However, the authentic interrogatorshould have some secret information or a key to decrypt and get the unique EPC in everyinterrogation. Without this secret key the adversary shall not be able to track the tag as 72
  3. 3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME each time her detector receives an apparently random number. Many algorithms have been proposed in recent days to prevent tracking and cloning. Most of the advanced algorithms use random numbers to randomize the cipher-text [7, 8]. Many random number generators (RNGs) have been proposed in the past and in recent times [9 - 28]. Some of them are quite fit to serve a specific application e.g. genetic algorithm [21], cryptography [10], random frequency hopping in a spread spectrum communication system [22]. These technologies cannot be directly implemented for RFID tags as RNG of an RFID tag must have some special features. Some of the special requirements of the RNG for an RFID tag are listed below.I. Robust to Thermal Attacks: RFID tags and so the RNG must work for a varying working environment. Thermal attack where an adversary deliberately changes the tag temperature to get predictable data is quite possible. However, any RNG may fail beyond a certain range of temperature. It is to be noted that attack usually takes place when a human carries the tag. A human being feels uncomfortable when the temperature deviates abruptly by ± 15 0C from the normal. In such situation the tag can be made inoperable with a metal film cover. Within the comfortable temperature range the RNG should deliver unpredictable data. Tokunaga et al. and Bellido et al [11, 23] utilized thermal noise voltage as input to a meta-stable system. It was shown that at meta-stable point deterministic noise is less when the resolution time of the output bit is high and the output bits from the system can be considered as random. This meta-stable point is very sensitive to input bias, which in its turn changes with ambient temperature. A control system brings the system back to a meta-stable point if resolution time is below threshold. With a thermal attack before the control system works initial bits may get predictable. As a measure, bits are dropped when resolution time is low. But measured resolution time is an average for 128 bits. The attack may happen for less number of bits maintaining the average resolution time at a satisfactory level.II. Robust to Power Attacks: The random number generator should be robust against power attacks. Most of the RFID tags are passive or battery-less. Those utilize the detector power. An adversary 73
  4. 4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME may deliberately transmit less power from the detector. The tag RNG may generate same bit 0 or predictable bits when it is power hungry or supply voltage or current to the circuit is low. This attack has been demonstrated for Philips Mifare tags [29]. In many of the RNGs randomness is decided by the clock jitter or time difference between a clock pair. In a passive RFID tag instead of generation of clock pair the transmitted pulse train from the detector can be utilized. In that case, the time difference or clock jitter information is also available in the detector and the random number produced is known to adversary [15].III.Lightweight: RNG and the RFID tag containing it must be lightweight. In most of the cases the strategies used for RNGs give pseudo-random numbers. Additional circuits are used to further randomize it. This takes additional chip area and the RNG no longer remains lightweight. One of the strategies for RNG is to utilize thermal noise voltage as it is known as one of the best sources of random noise. Since amplitude of noise voltage is very low efforts were made to amplify it [20, 24]. In the process of amplification, the voltage gets corrupted by deterministic noise generated in the amplifier. Also the finite bandwidth of the amplifier makes the output colored though there is random or white noise at the input. Further randomization is done with additional hardware. This consumes additional Si area. For superconductive RNG in SFQ circuits [10] the circuit is very sensitive to low thermal noise voltage and further magnification is not required. However, maintenance of superconductive temperature is beyond the scope of a portable lightweight device e.g. RFID.IV.No Seed Value: RNGs that require seed values [15, 28, 30] are not suitable for RFIDs. In this automated system manual entry of seed value is not possible. If known parameters e.g. date or time is used to provide the seed value the unpredictability of the output pattern is lost. Most of the recent hardware RNGs do not need any seed value.V.Intermittent Operation: In some RNGs e.g. continuous chaotic oscillator [9, 25], meta-stable system [11] initial few bits depend on the initial condition and are predictable. It quickly transforms 74
  5. 5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME to a state where generated data is unpredictable. For a continuously functioning generator the first few predictable bits can be discarded. A passive RFID tag goes for a deep sleep in absence of a detector and the available power. Generator should work satisfactorily as soon as it wakes up. VI.Qualify NIST Test Suite: The output should not follow any definite pattern. The adversary should not be able to predict the output by applying her knowledge. NIST test [31] has been accepted as the standard for unpredictability. The output should pass the NIST test. Apart from these essential features there are some desired features for RFID tags. These are listed below:VII.Part of an Embedded System: There is an urgent need of secured RFID system. It is desirable that the RNG can be implemented on an embedded system that is already in use for tags e.g. MSP430 / WISP [32]. In that case, no extra component is needed for the development of tags to provide security or privacy. Si Chip Implementation: If embedded implementation is not feasible a fully tested light-weight IC that can be readily incorporated in the system is desirable.VIII.Pulsating Voltage: It is desirable that the system consumes low power. As mentioned earlier, a passive tag utilizes detector power. Detector transmits power in the form of a pulse train. Rectifier and regulator circuits are required to convert this pulsating voltage to a stable dc supply. A part of this power is consumed in these circuits. It is desirable that an RNG can function with the pulsating voltage instead of stable dc supplies to minimize wastage of power. Table I and II show the suitability of recently proposed RNGs for RFID tags. 75
  6. 6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME Table 1 suitability of proposed random number generators for rfid tagsRefere Basic Principle Any particular Robust Lightweight Intermitt NIST Test nce drawback to ent Results Thermal Operatio (T), and n Power (P) Attacks Chaotic oscillator, time Implementation No No difference between clock of off-chip pairs and further oscillator (T) Not randomization inductance along- 17 out of [9] known with tag antenna 17 (P) No inductance without mutual coupling [10] Thermal noise detection Maintenance of No No Not 1 out of 17 in Superconductive superconductive known Single Flux Quantum temperature 4.2 Circuit K [11] Meta-stability based -- No No No 7 out of quality control 17* [12] Chaos based generator -- Yes No No No result [13] Meta-stability based Too many No No No 15 out of output control reference 17 voltages to be converted from pulsating voltage in a passive RFID tag [14] Clock jitter and further -- Not Yes Yes 13 out of chaos known 17 [15] Rising edge time (i) Generation of No Yes Yes Not done difference between two a pair of independent clocks independent clocks in a passive RFID tag. (ii) Further processing is affected by clock period variation. A time attack is possible. [16] Chaos due to Bernoulli Difficult to (T) Yes Yes Yes 9 out of 17 shift and further implement on Si (P) No randomization due to process variation [17] Random jitter in a Nearby ring Not No Yes Not shown 76
  7. 7. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME number of ring oscillators oscillators get known and further randomization phase locked and randomness is less than expected[19] Random fluctuation of Soft breakdown No Yes No Not shown current in a MOS voltage is capacitor after soft extremely breakdown and further sensitive to randomization fabrication process and operating temperature. Any fluctuation in the operating point may lead to no breakdown or hard breakdown.[20] Amplification of thermal Amplifier (T) Not No Yes Not noise voltage of a resistor degrades the known done and further randomization randomness of (P) No the thermal noise voltageThis Saturation of thermal Yes Yes Yes 11 out ofwork noise voltage 17 Table 2 suitability of proposed random number generators for rfid tags (continued) Implemental in embedded processors Implemented PulsatingReference on Si Power [9] Not fully No No [10] No Partly No [11] No Partly No [12] Yes, PSOC No need Partly [13] No Partly No [14] Yes, Xilinx Vertex II No need Yes [15] Yes, MSP430 No need No [16] No No No [17] Yes, any FPGA. But consumes huge amount No No of hardware [19] No No No [20] No Partly No This Yes, MSP430, PSOC No need Yes workIn the next section the proposed circuit of this paper is discussed. 77
  8. 8. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEMEPROPOSED CIRCUIT The proposed circuit configuration is based on a Schmitt Trigger circuit [33] asshown in Fig. 1. Schmitt trigger is a special configuration of operational amplifier wherepositive feedback is used. When the input signal applied at negative input exceeds any ofthe voltage limits namely upper trigger point or the lower trigger point, the output getssaturated to negative or the positive saturation voltage respectively. Question that remains is: what will be the state of the output in absence of inputsignal i.e. when the input voltage does not exceed any of the trigger points? Suppose thesupply voltage of the operational amplifier is switched on. The output will saturate toeither the positive or the negative value depending on the polarity of the differencevoltage at the inputs at the time of supply switch on. It will remain to this saturated valueas the input voltage does not exceed the trigger point. Instead of constant supply we canapply clock and inverted clock at the positive and negative supply terminals of theoperational amplifier respectively as shown in Figure 1. The polarity of the output will bedecided by the polarity of the differential input voltage at the beginning of each pulsepair. This input voltage can be given as:Vin = Vtp − Vtn …………………………………………………… (1) Where, Vtp and Vtn are the random thermal noise voltage of the resistor or Johnsonnoise at the non-inverting (marked as + in Figure 1) and inverting node (marked as – in 78
  9. 9. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME Figure 1) respectively. Since the polarity of the output is dependent only on the difference of two thermal noise voltages or Johnson noise voltages it is truly random. To satisfy this condition the output voltage Vout should become zero at the end of the off- state of the clock cycle. In the beginning of the on-state of the clock cycle there should not be any residual voltage Vor from the previous on-state of the clock cycle. If there is any Vor then its polarity will decide the polarity of Vin as well as Vout. In this case, the output will be of same signal level a string of all 1s or all 0s. For a fast clock there will be Vor. For a fast decay of the output at the off-state of the clock many circuit enhancement has been thought of. One of them is connection of an nmos / nFET with slightly negative threshold voltage e.g. -0.1 volt in between output and ground. The gate of the nFET should be connected to clk . In the off-state of the clock, gate voltage is 0 and the nFET should conduct. In the on-state, the gate voltage is negative and below threshold of the nFET so the nFET remains off. The simple circuit proposed here fulfils the requirement of an RNG for an RFID tag. These requirements are listed in Table I and discussed in Introduction section. The following gives the properties of the Proposed Circuit (PC) those make it suitable for an RFID tag. I. Robust to Thermal Attacks: Output bit in the PC depends upon the polarity of the input thermal voltage. Since variation in temperature does not change the polarity of the input the RNG is robust to thermal attacks. PC uses only an op-amp and resistors. These components work for a wide temperature range. For example, LM741, the op-amp used here, has an operating temperature range of -55 0C to 125 0C. If implemented on MSP430 microcontroller, during thermal attacks if the temperature goes beyond this range the in-built temperature sensor can be used to switch it off.II. Robust to Power Attacks: PC uses a clock pair instead of constant supplies. If the clock pair amplitude is reduced the circuit will still remain functional.III. Lightweight: PC output gives random bits that pass the NIST test. No further randomization is 79
  10. 10. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME necessary. The simple circuit is very lightweight consisting of only one operational amplifier. IV. No Seed Value: PC is a true random number generator and does not need any seed value. V. Intermittent Operation: PC does not need any resolution time to get unpredictable data. Whenever clock pair is applied at the supply terminals of the operational amplifier random bits are produced. VI. Qualify NIST Test Suite: The tests suitable for small volume of data are done. All the tests are passed. From NIST test qualification point of view it can be said that, the RNG is unpredictable for this small volume of data.VII. Part of an Embedded System: Since PC consists of only one operational amplifier it can be implemented easily in MSP430 from Texas Instruments or PSOC from Cypress Semiconductors.VIII. Pulsating Voltage: PC does not need any constant power supply instead it functions with a clock pair as shown in Figure 1. RESULTS To study the behavior of the operational amplifier IC741 with a clock pair applied at the supply terminals simulation is done. The output voltage as given in Fig. 2 is simulated in TINA TI, a tool developed and supported by Texas Instruments. The clocks given as clk and clk are applied at negative and positive supply terminal of the operational amplifier respectively. In this simulator thermal noise voltage could not be applied at input. Instead a faster clock is applied at the inverting node marked as - in Fig. 1. It can be observed that, the output voltage assumes -3 volts (or +3 volts) if input clock is +200 mV (or -200 mV) at the beginning of the on-state of the clocks. The output bit- stream is in polar RZ format with the advantage of no dc component [34]. 80
  11. 11. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME The circuit given in Figure 1 has been implemented on a bread-board. 289 bitshave been collected. Some of the tests in NIST require 106 bits. Automatic dataacquisition set-up is not ready at this moment. So such an amount of data could not beproduced. Only those tests with recommended data size less than 289 are carried out.Lempel Ziv test has not been done as it was deleted from the test suite in the latestversion 800-22b. The programs necessary for all the tests were written in MATLAB. Theprograms were tested with standard data that give predictable p-values. The results for thestandard data are listed in Table IV. Table III shows the results for measured data. The p-values show that all the tests were passed. So the proposed RNG is definitelyunpredictable for 289 data. For higher volume of data it is quite likely that it shall remainunpredictable. 81
  12. 12. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME Table 3 NIST 800-22b test results for measured dataTest Input size Recommended p value* Input SizeFrequency Sample size, n=289 n>=100 0.3776(Monobit) Test Sample size n=122 1.0000Frequency within a The length of each M>20, M>0.01n,block block, M=96 . N<100, n≥100 0.4821 The no. of blocks, N =3. Total sample size, n= MN= 288.Run Sample size, n=289 n≥100 0.401573Longest Run Sample size, n=128. n M Set I 0.6889 Block length, M=8 128 8 Set II 6272 128 0.9732 750000 100000Binary Matrix Rank No. of rows in each 0.162297 matrix, M=2 N>= 38 No. of columns in each matrix, Q=2 No. of matrices, N=n/{MQ}=72 Total sample size, n= 288Non-Overlapping No. of blocks, N=2, N≤100 All p_values≥Template Matching No. of data in each 0.148207 block, M=144, Template length, m=6Serial (m=2) Sample size, n=289 m<log2n - 2 p value 1 = 0.888179, Template size, m=2 p value 2 =0.842701.Serial (m=3) Sample size, n=289 m<log2n - 2 p value 1 = 0.162805, Template size, m=3 p value 2 = 0.084058.Approximate Sample size, n=289 m<log2n - 2 p value= 0.453542Entropy Template size, m=3Cusum forward Sample size, n=289 n≥100 p value=1.000Cusum reverse Sample size, n=289 n≥100 p value=1.000 82
  13. 13. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME Table 4 NIST 800-22b test results for standard data Test p value for data pattern All 0 All 1 1010-- Frequency 8.2120e-65 8.2120e-65 0.9531 Monobit Frequency 0.0000 0.0000 1.0000within a block Run No need of run test as No need of run test as 8.15516e-65 monobit freq test fails monobit freq test fails |pai-0.5|=0.500000 >= |pai-0.5|=0.500000 >= tau=0.117647 tau=0.117647 Longest Run Set I: Set I: Set I: 1.5129X10-32 4.85445X10-41 1.5129X10-32 Set II: Set II: Set II: 1.5129X10-32 4.85445X10-41 1.5129X10-32Binary Matrix 0.0000 3.2371X10-28 3.2371X10-28 Rank Non- p value=0.000 for p value = 0.000 for p value = Overlapping template template 0.000 for Template 000000000 111111111 templates: Matching p value = 0.145254 p value = 0.145254 010101010 for other templates fot other templates 101010101 p value = 0.145254 for other templates Serial (m=2) p value 1 = 0,000, p value p value 1 = 0.000, p value p value 1 = 2 = 0.000 2 = 0.000 0.000, p value 2 = 0.000 Serial (m =3) p value 1 = 0,000, p value p value 1 = 0,000, p value p value 1 = 2 = 0.000 2 = 0.000 0,000, p value 2 = 0.000 Approximate 0.000 0.000 0.000 EntropyCusum forward -1.000 -1.000 1.000Cusum reverse -1.000 -1.000 1.000CONCLUSION A random number generator suitable for RFID tags is proposed. The simplecircuit consists of an op-amp in the Schmitt trigger configuration. In-place of stablepower supplies to the op-amp terminals, clk and clk are applied. No signal is applied at 83
  14. 14. International Journal of Electronics and Communication Engineering & Technology (IJECET),ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEMEthe input instead the thermal noise voltage of the resistors at the input is allowed tosaturate and give the output as positive or negative saturation voltage. The circuit outputis simulated with the help of TINA TI. The circuit with a 741 op-amp is developed on abread-board. Measured output passes the NIST test. The simple circuit can be implemented on popular embedded processors for RFIDtags e.g. MSP430 or WISP. Design effort can be made to achieve a low power high speedop-amp suitable for this purpose.REFERENCES1. A. Agarwal and M. Mitra (2006), RFID: Promises and Problems, Techonline. Available: http://www.techonline.com, Accessed on 12th Nov., 2009.2. R. Das (2007), RFID Forecasts, Players & Opportunities 2007-2017, ED Online and IDTechEx.Available http://www.elecdesign.com/Articles/Index.cfm?ArticleID=14840&pg=3 and http://www.idtechex.com/research/articles/rfid_forecasts_players_and_opportunities_ 2007_2017_00000521.asp, Accessed on 12th Nov., 2009.3. A. Juels (2006), RFID Security and Privacy: A Research Survey, An invited paper, IEEE Journal on Selected Areas in Communications, vol. 24 no. 2, pp. 381-394.4. S. Garfinkel, A. Juels, and R. Pappu (2005), RFID Privacy: An Overview of Problems and Proposed solutions, IEEE Security and Privacy, vol. 3 no. 3, pp. 34-43.5. W. Stallings (2003), “Cryptography and Network Security: Principles and Practices”, Pearson Education, India.6. D. R. Stinson (2002), “Cryptography Theory and Practice”, K. H. Rosen, Ed. CRC, New York,.7. S. Yeo and J. Kwak (2007), Privacy Enhanced Authentication Protocol for RFID Tag System Security, IJCSNS, International Journal of Computer Science and Network Security, vol. 7 no. 9, pp. 1-6.8. M. Mitra (2008), Privacy for RFID Systems to Prevent Tracking and Cloning, IJCSNS, International Journal of Computer Science and Network Security, IJCSNS, vol. 8 no.1, pp. 1 – 5. Digital Object Identifier 10.1109/MPOT.2007.913680. 84
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