[0001] The invention concerns a metastability based random number generator intended especially for generating truly random numbers and series.

[0002] From the publication of the Polish patent PL 225188 Bl, there is known in the art a metastability based random number generator comprising a multivibrator, which output is connected to an input of a time measurement circuit. To the time measurement circuit are connected both an input of a memory and a first input of a comparator circuit, which second input is connected to an output of the memory. Outputs of the comparator circuit are outputs of the metastability based random number generator.

[0003] From the same patent publication there is known a metastability based random number generator, having the output of the time measurement circuit connected to the first input of the comparator circuit through a second memory.

[0004] The aim of the invention is to simplify the implementation of the metastability based random number generator and to provide the possibility of implementing the invention in programmable devices.

[0005] In the metastability based random number generator comprising multivibrator, having output connected to an input of time measurement circuit, having output connected to both an input of a first memory and a first input of a comparator circuit, having a second input connected to an output of the first memory, according to the invention the multivibrator is an oscillatory response multivibrator. The effect of using such a circuit is that the multivibrator itself provides the time base for measuring the duration of its own response, which significantly simplifies the time measurement circuit construction. Moreover, it enables implementation in purely digital programmable devices, which means it can be produced in modern digital technological lines.

[ 0006] First input of the comparator circuit advantageously is connected to the output of the time measurement circuit through a second memory. Such a solution allows a comparison of stored values in order to provide a random response, while the multivibrator can generate another value.

[ 0007 ] Time measurement circuit advantageously is a counter. The counter allows to measure time in a simple way, i.e. by counting oscillations of the oscillatory response multivibrator. It is a indirect measurement of time and it depends on the multivibrator working conditions, but it is sufficient enough considering the goal, which is to obtain a random value.

[ 0008 ] Advantageously the oscillatory response multivibrator is an adjustable speed oscillatory response multivibrator. Such a solution makes it possible to adapt the generation conditions to the changing ambient conditions or attacks on the system, in which the metastability based random number generator according to the invention is used.

[ 0009] Advantageously a speed control input of the adjustable speed oscillatory response multivibrator is connected to a speed control output of a speed control system. The speed control system allows to determine the changing conditions and to detect attacks on a system in which the metastability based random number generator according to the invention is used. [0010] Advantageously the speed control system has at least one input connected to at least one output of the metastability based random number generator. Such a construction allows to perform a quality control of generated numbers by speed control system.

[0011] The adjustable speed oscillatory response multivibrator advantageously comprises at least one voltage-mode multivibrator, having a supply voltage connected to a speed control input of the multivibrator. Such a construction allows to regulate the speed by the value of the supply voltage of the voltage-mode gates.

[0012] Advantageously the adjustable speed oscillatory response multivibrator comprises at least one current- mode multivibrator, having regulated current source connected to a speed control input of the multivibrator. Such a construction allows to regulate the speed by the value of the supply current of the current-mode gates.

[0013] The invention enables the implementation of the circuit without the use of complicated time measurement circuits or circuits detecting the end of autonomous phase, the implementation in simple programmable devices and the speed control of the oscillatory response multivibrator .

[0014] The invention has been described below in detail, with reference to the attached figures. Fig.l presents a block diagram of metastability based random number generator comprising single memory, fig.2 presents a block diagram of metastability based random number generator comprising two memories, fig.3 presents a block diagram of metastability based random number generator comprising single memory and speed control system, fig.4 presents a block diagram of metastability based random number generator comprising two memories and speed control system, fig.5 presents a block diagram of metastability based random number generator comprising single memory and speed control system connected to outputs of the generator, fig.6 presents a block diagram of metastability based random number generator comprising two memories and speed control system connected to outputs of the generator, fig.7 presents a block diagram of voltage-mode adjustable speed oscillatory response multivibrator, and fig.8 presents a block diagram of current-mode adjustable speed oscillatory response multivibrator.

[0015] Metastability based random number generator presented in fig.l comprises an oscillatory response multivibrator MOO with an output Q connected to an input TQ of a counter LCZ . An output T of the counter LCZ is connected to both an input Tl of a memory UP and a first input Kl of a comparator circuit UK. An output TIP of the memory UP is connected to a second input K2 of the comparator circuit UK, whereas outputs K and P of the comparator circuit UK are outputs LL and PLL of the metastability based random number generator.

[0016] The construction of the oscillatory response multivibrator MOO causes that, if it operates in the neighborhood of the metastable point - specifically, properly near the point of metastability in order to generate different time responses - there are diminishing oscillations at the output of the multivibrator, whereas the number of the oscillations can be counted by a simple counter LCZ, that needs to be fast enough, which replaces the need of time measurement. The memory UP saves the number counted by the counter LCZ, whereas the comparator circuit UK compares a previously stored value in the memory UP with a current value derived from counter LCZ. Depending on which number of oscillations is greater, at the output K of the comparator circuit UK appears a logical value "zero" or "one", and at the output PLL an information that the comparison was successful. If the compared numbers have the same value or are outside the counter range, an information about a wrong result will appear at the PLL output. The use of the same multivibrator to generate subsequent metastability time responses eliminates the problem of technological dispersion in electronic circuits, the problem that exists when multiple non- identical multivibrators are used to generate multiple time responses.

[0017] Metastability based random number generator presented in fig.2 comprises an oscillatory response multivibrator MOO with an output Q connected to an input TQ of a counter LCZ. An output T of the counter LCZ is connected to both an input Tl of the first memory UP and an input T2 of the second memory UP2. Outputs TIP and T2P of the memories UP and UP2 are connected to inputs K2 and Kl of a comparator circuit UK, whereas outputs K and P of the comparator circuit UK are outputs LL and PLL of the metastability based random number generator.

[0018] The construction of the oscillatory response multivibrator MOO causes that, if it operates in the neighborhood of the metastable point - specifically, properly near the point of metastability in order to generate different time responses - there are diminishing oscillations at the output of the multivibrator, whereas the number of the oscillations can be counted by a simple counter LCZ, that needs to be fast enough, which replaces the need of time measurement. The memories UP and UP2 save the numbers counted by the counter LCZ, whereas the comparator circuit UK compares the stored values in memories UP and UP2. Depending on which number of oscillations is greater, at the output K of the comparator circuit UK appears a logical value "zero" or "one", and at the output PLL an information that the comparison was successful. If the compared numbers have the same value or are outside the counter range, an information about a wrong result will appear at the PLL output. The use of the same multivibrator to generate subsequent metastability time responses eliminates the problem of technological dispersion in electronic circuits, the problem that exists when multiple non-identical multivibrators are used to generate multiple time responses.

[0019] Metastability based random number generator presented in fig.3 comprises an adjustable speed oscillatory response multivibrator MOORS with an output Q connected to an input TQ of a counter LCZ. An output T of the counter LCZ is connected to both an input Tl of a memory UP and a first input Kl of a comparator circuit UK. An output TIP of the memory UP is connected to a second input K2 of the comparator circuit UK, whereas outputs K and P of the comparator circuit UK are outputs LL and PLL of the metastability based random number generator. The adjustable speed oscillatory response multivibrator MOORS has a speed control input RS, which is connected to a speed control output SS of a speed control system USS.

[0020] The speed control of the multivibrator MOORS allows to minimize the harmful effects of various factors - for example, environmental factors, such as temperature or power supply voltage, or active side- channel attacks, aimed at disturbing the proper operation of the circuit. The speed control system USS analyzes the environmental measurements, on the basis of which it adjusts the speed in order to obtain the best properties of the circuit in terms of speed and randomness quality of generated numbers and series.

[0021] Metastability based random number generator presented in fig.4 comprises an adjustable speed oscillatory response multivibrator MOORS with an output Q connected to an input TQ of a counter LCZ . An output T of the counter LCZ is connected to both an input Tl of the first memory UP and an input T2 of the second memory UP2. Outputs TIP and T2P of the memories UP and UP2 are connected to inputs K2 and Kl of a comparator circuit UK, whereas outputs K and P of the comparator circuit UK are outputs LL and PLL of the metastability based random number generator. The adjustable speed oscillatory response multivibrator MOORS has a speed control input RS, which is connected to a speed control output SS of a speed control system USS.

[0022] The speed control of the multivibrator MOORS allows to minimize the harmful effects of various factors - for example, environmental factors, such as temperature or power supply voltage, or active side- channel attacks, aimed at disturbing the proper operation of the circuit. The speed control system USS analyzes the environmental measurements, on the basis of which it adjusts the speed in order to obtain the best properties of the circuit in terms of speed and randomness quality of generated numbers and series.

[0023] Metastability based random number generator presented in fig.5 has the same construction as the one presented in fig.3, in which additionally the outputs LL and PLL of the metastability based random number generator are connected to inputs WLL and WPLL of the speed control system USS.

[ 0024 ] The connection of the outputs of the metastability based random number generator to the inputs of the speed control system USS allows the system furthermore to analyze statistics of the generated random numbers and series, and based on these statistics it can adjust the speed in order to obtain the best properties of the circuit in terms of speed and randomness quality of generated numbers and series.

[ 0025 ] Metastability based random number generator presented in fig.6 has the same construction as the one presented in fig.5, in which additionally the outputs LL and PLL of the metastability based random number generator are connected to inputs WLL and WPLL of the speed control system USS.

[ 0026] The connection of the outputs of the metastability based random number generator to the inputs of the speed control system USS allows the system furthermore to analyze statistics of the generated random numbers and series, and based on these statistics it can adjust the speed in order to obtain the best properties of the circuit in terms of speed and randomness quality of generated numbers and series.

[ 0027 ] Voltage-mode adjustable speed oscillatory response multivibrator presented in fig.7, included in a metastability based random number generator, comprise a voltage-mode multivibrator NM with two inputs D' and C connected to inputs D and C of the adjustable speed oscillatory response multivibrator MOORS and an output Q' connected to an output Q of the adjustable speed oscillatory response multivibrator MOORS. An input of the positive supply voltage VDD of the voltage-mode multivibrator NM is connected to a speed control input RS of the adjustable speed oscillatory response multivibrator MOORS, whereas an input of the negative supply voltage VSS of the voltage-mode multivibrator NM is connected to general ground of the circuit GND .

[0028] The voltage-mode multivibrator NM in the form of "D" flip-flop, based on standard logical gates or CMOS technology, can be regulated in terms of speed by changing the power supply voltage of the flip-flop. Lower voltage means slower operation, whereas higher voltage means faster operation. The power supply voltage can be reduced even to the subthreshold voltage of the transistors. The maximum voltage is determined by the boundary parameters of the circuit operation.

[0029] Current-mode adjustable speed oscillatory response multivibrator presented in fig.8, included in a metastability based random number generator, comprise a regulated current source ISS and connected to it a logical block of the multivibrator LM with two inputs D' and C connected to inputs D and C of the adjustable speed oscillatory response multivibrator MOORS and an output Q' connected to an output Q of the adjustable speed oscillatory response multivibrator MOORS. A speed control input RS of the adjustable speed oscillatory response multivibrator MOORS is connected to the regulated current source ISS. The source of the positive supply voltage is connected to the logical block of the multivibrator LM, and the general ground of the circuit is connected to the regulated current source ISS.

[0030] The multivibrator MOORS made of current-mode gates can be regulated in terms of speed by changing the current value of these gates. Lower current means slower operation, whereas higher current means faster operation. Current sources in the form of current mirrors allow to easy and simultaneous control of multiple current sources.

[0031] The invention can be applied and used in generating truly random numbers and series in circuits resistant to side-channel attacks and changing ambient conditions .