Alessandro Trifiletti

A high-speed oscillator-based truly random number source for cryptographic applications on a smart card IC

The design of a high-speed IC random number source macro-cell, suitable for integration in a smart card microcontroller, is presented. The oscillator sampling technique is exploited and a jittered oscillator which features an amplified thermal noise source has been designed in order to increase the output throughput and the statistical quality of the generated bit sequences. The oscillator feedback loop acts as an offset compensation for the noise amplifier, thus solving one of the major issues in this kind of circuit. A numerical model for the proposed system has been developed which allows us to carry out an analytical expression for the transition probability between successive bits in the output stream. A prototype chip has been fabricated in a standard digital 0.18 /spl mu/m n-well CMOS process which features a 10 Mbps throughput and fulfills the NIST FIPS and correlation-based tests for randomness. The macro-cell area, excluding pads, is 0.0016 mm/sup 2/ (184 /spl mu/m /spl times/ 86 /spl mu/m) and a 2.3 mW power consumption has been measured.

Three-phase dual-rail pre-charge logic

This paper investigates the design of a dual-rail pre-charge logic family whose power consumption is insensitive to unbalanced load conditions thus allowing adopting a semi-custom design flow (automatic place & route) without any constraint on the routing of the complementary wires. The proposed logic is based on a three phase operation where, in order to obtain a constant energy consumption over the operating cycle, an additional discharge phase is performed after pre-charge and evaluation. In this work, the proposed concept has been implemented as an enhancement of the SABL logic with a limited increase in circuit complexity. Implementation details and simulation results are reported which show a power consumption independent of the sequence of processed data and load capacitances. An improvement in the energy consumption balancing up to 100 times with respect to SABL has been obtained.

Leakage Power Analysis Attacks: A Novel Class of Attacks to Nanometer Cryptographic Circuits

In this paper, a novel class of power analysis attacks to cryptographic circuits is presented. These attacks aim at recovering the secret key of a cryptographic core from measurements of its static (leakage) power. These attacks exploit the dependence of the leakage current of CMOS integrated circuits on their inputs (including the secret key of the cryptographic algorithm that they implement), as opposite to traditional power analysis attacks that are focused on the dynamic power. For this reason, this novel class of attacks is named ¿leakage power analysis¿ (LPA). Since the leakage power increases much faster than the dynamic power at each new technology generation, LPA attacks are a serious threat to the information security of cryptographic circuits in sub-100-nm technologies. For the first time in the literature, a well-defined procedure to perform LPA attacks that is based on a solid theoretical background is presented. Advantages and measurement issues are also analyzed in comparison with traditional power analysis attacks based on dynamic power measurements. Examples are provided for various circuits, and an experimental attack to a register is performed for the first time. An analytical model of the LPA attack result is also provided to better understand the effectiveness of this technique. The impact of technology scaling is explicitly addressed by means of a simple analytical model and Monte Carlo simulations. Simulations on a 65- and 90-nm technology and experimental results are presented to justify the assumptions and validate the leakage power models that are adopted.

A countermeasure against differential power analysis based on random delay insertion

Differential power analysis is widely recognized as an extremely powerful and low-cost technique to extract secret information from cryptographic devices. As a consequence, DPA-countermeasures have been proposed in the technical literature ranging over every abstraction level in an embedded system, from software to transistor-level techniques. In this paper, a novel gate-level countermeasure is proposed which, exploiting the insertion of random delays in the datapath of a cryptographic processor, allows us to randomize not just the instantaneous current consumption profile but also the total charge quantity transferred from the power supply during a clock cycle.

A high-speed IC random-number source for SmartCard microcontrollers

The design of a high-speed integrated circuit random number source macro-cell, suitable to be integrated in a SmartCard microcontroller, is presented. The direct amplification of a thermal-noise source is exploited and an accurate and low-area offset zeroing system has been developed in order to increase the statistical quality of the output bit sequences. Moreover, an analytical model has been developed, allowing the estimation of the output bit correlation as a function of the main circuit parameters. Using a standard 0.18-/spl mu/m n-well CMOS process, a prototype has been fabricated and measured, obtaining a random behavior for an output data rate up to 40 Mb/s. The macro-cell area, excluding pads, is 0.025 mm/sup 2/ (220 /spl mu/m/spl times/116 /spl mu/m) and its power consumption is about 3.6 mW when clocked at 10 MHz.

A Power Consumption Randomization Countermeasure for DPA-Resistant Cryptographic Processors

Attacks based on a differential power analysis (DPA) are a main threat when designing cryptographic processors. In this paper, a countermeasure against DPA is presented and evaluated on a case study simulation. It can be implemented, using a standard digital technology, by applying a straightforward transformation to the original design, without an actual redesign. A methodology to perform a DPA in simulation is presented which can be exploited to test the resistance of a cryptographic processor during its design flow. By using the above methodology, the proposed countermeasure shows a 30dB attenuation of the signals exploited by the DPA.

Effectiveness of Leakage Power Analysis Attacks on DPA-Resistant Logic Styles Under Process Variations

This paper extends the analysis of the effectiveness of Leakage Power Analysis (LPA) attacks to cryptographic VLSI circuits on which circuit level countermeasures against Differential Power Analysis (DPA) are adopted. Security metrics used for assessing the DPA-resistance of crypto core implementations, such as the minimum number to disclosure (MTD) and the asymptotic correlation coefficient, have been extended to the case of LPA. The LPA-resistance has been evaluated in terms of MTD as a function of the on chip noise. Noise variances up to 10000 times greater than the signal variance have been taken into account and LPA attacks have been successfully executed for all the logic styles under analysis using less than 100000 measurements. Moreover the role of process variations has been investigated through extensive Monte Carlo simulations in order to evaluate their impact on the leakage model for the logic styles under analysis. Results show that LPA attacks can be successfully carried out on the different anti-DPA logic styles even in presence of process variations. To the best of our knowledge, this work proves for the first time the effectiveness of LPA attacks in a real scenario where on chip noise and process variations are taken into account.

A novel yield optimization technique for digital CMOS circuits design by means of process parameters run-time estimation and body bias active control

This work presents a novel approach to optimize digital integrated circuits yield referring to speed, dynamic power and leakage power constraints. The method is based on process parameter estimation circuits and active control of body bias performed by an on-chip digital controller. The associated design flow allows us to quantitatively predict the impact of the method on the expected yield in a specific design. We present the architecture scheme, the theoretical foundation, the estimation circuits used, and two application case studies, referring to an industrial 0.13-/spl mu/m CMOS process data. The approach results to be remarkably effective at high operating temperature. In the presented case study, initial yields below 14% are improved to 86% by using a single controller and a single set of estimation circuits per die.

Linearization Technique for Source-Degenerated CMOS Differential Transconductors

A supplementary linearization technique for CMOS differential pairs with resistive source degeneration is proposed. The approach exploits an auxiliary (degenerated) differential pair to drive the bulk terminals of the main pair. Transistor-level simulations on a design using a 0.25-mum process and powered with 2.5 V and 1 mA, show that total harmonic distortion (THD) in the voltage-to-current conversion is decreased by 10 dB (for an input differential signal with a peak amplitude of 0.5 V and for frequencies up to 100 MHz) compared to the traditional source-degenerated transconductor. This THD improvement is achieved with a negligible increase in power consumption.

Efficient Digital Background Calibration of Time-Interleaved Pipeline Analog-to-Digital Converters

A novel technique for the digital background calibration of time-interleaved analog-to-digital converters is proposed. The technique corrects at the same time for both errors due to gain, offset and timing mismatches among the time-interleaved channels and errors due to nonlinearities in the channels, for instance due to capacitor mismatches in switched capacitor implementations. This feature, together with the use of the recursive least mean squares algorithm, makes the technique particularly fast (12 bits of accuracy can be achieved after about 4000 samples for a two-channel converter). The proposed calibration technique employs wideband differentiators, thus enabling digital background calibration of timing skews even with wideband input signals. Besides, undersampled differentiator filters are proposed, and it is shown that the technique is capable of calibrating undersampling converters by estimating the derivative of wideband input signals even outside the first Nyquist band.