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

[0002] There are known in the art designs of random number generators, which use pairs of ring oscillators and bistables, such as a phase detector or a metastability circuit.

[0003] In the state of the art, from the article by Piotr Z. Wieczorek, "Secure TRNG with Random Phase Stimulation", XL-th IEEE-SPIE Joint Symposium on Photonics, Web Engineering, Electronics for Astronomy and High Energy Physics Experiments, Wilga 2017, SPIE volume 10445, ISBN: 9781510613546, Electronic ISBN: 9781510613553, there is known a random number generator, which comprises two ring oscillators and a metastability circuit. Outputs of the ring oscillators are connected to inputs of the metastability circuit, whereas an output of the metastability circuit is an output of the random number generator. A ring oscillator comprise a delay line closed in a loop, where an input and an output are connected with each other and connected to an output of the ring oscillator. The delay line comprise delays connected in series and connected between the input and the output of the delay line. The disadvantage of such a random number generator is its low speed resulting from rare occurrences of events that are able to initiate a metastable work of the metastability circuit, which results from slow-moving random walk in phase.

[0004] From the publication of the US patent application US2011169580 , there is known in the art a random number generator comprising two ring oscillators a phase detector. Outputs of two ring oscillators are connected to inputs of the phase detector, whereas an output of the phase detector is connected to an output of the random number generator through a von Neumann corrector. A ring oscillator comprise a delay line closed in a loop, where an input and an output are connected with each other and connected to an output of the ring oscillator. The delay line comprise delays connected in series and connected between the input and the output of the delay line.

[0005] The aim of the invention is to provide nondeterministic phases of signals at the inputs of phase detectors as well as nondeterministic initialization of multiple metastability processes .

[0006] Random number generator comprising a first bistable, having an output connected to a first output of the random number generator and comprising two ring oscillators, having outputs connected to inputs of the bistable, whereas the ring oscillators comprise delay lines closed in a loops, and the delay lines comprise delays connected in series between inputs and outputs of the delay lines, according to the invention comprises at least one additional bistable, having output connected to an additional output of the random number generator, whereas the additional bistable has a first input connected to the delay line of one of the ring oscillators and a second input connected to the delay line of another of the ring oscillators. The effect of such a construction allows to obtain at least one additional, substantially independent random process on the additional output of the random number generator.

[0007] Random number generator according to the invention advantageously comprises at least one more ring oscillator. The effect is that the bistables connected to different ring oscillators are stimulated with less correlated signals than the bistables connected to the same ring oscillators.

[0008] Random number generator according to the invention advantageously comprises at least two bistables connected to the delay lines so, that the inputs of the bistables are separated in the delay lines with at least one delay. Such a solution assures that the delays are driven by bistables in the minimal manner.

[0009] Random number generator according to the invention advantageously comprises at least two bistables, having at least one of the inputs connected to different delay lines of different ring oscillators. Such a solution assures that the bistables are stimulated with different pair of ring oscillators, and thus with different processes resulting in phase shifts.

[0010] Advantageously at least one of the additional bistables is connected with the first input to a series of delays of a delay line of one of the ring oscillators after a delay having the first number in this series counting from the beginning of the delay line. Further the second input is connected to a series of delays of a delay line of another ring oscillator after a delay having the second number in this series counting from the beginning of the delay line. Further the first number is different from the second number. Such a solution causes that the bistable is triggered by the input signal with a different phase than the phase that is currently present in the ring oscillators.

[0011] At least two bistables advantageously are connected with at least one input each in the same place of at least one delay line. Having different bistables connected in the same places causes that the bistables are triggered with exactly the same signal .

[0012] At least one of the bistables advantageously is a phase detector. Phase detector provides a precise detection of the edge priority of input waveforms, which is used for phase correction.

[0013] At least one phase detector advantageously consists of a flip-flop with two inputs being the inputs of the phase detector and an output being the output of the phase detector.

[0014] Alternatively at least one phase detector comprises two flip-flops each having two inputs and two outputs, wherein the inputs of the flip-flops are connected to inputs of the phase detector, and outputs of the flip-flops are connected to outputs of the phase detector. Further the first input of the phase detector is connected to both the first input of the first flip- flop and the second input of the second flip-flop. Further the second input of the phase detector is connected to both the second input of the first flip-flop and the first input of the second flip-flop. Further the output of the phase detector is connected to chosen outputs of the flip-flops through a logic circuit. [0015] At least one of the bistables advantageously is a metastability circuit. Such a solution provides a random response of the circuit in the case of proximity of the edges of the input waveforms. More specifically, for phase shifts that do not fit in the metastability window, the metastability circuit provides a phase detection and is used to correct the phase of the ring oscillators connected to its inputs. However, for phase shifts located in the metastability window, the metastability circuit provides a random value on its output and consequently induces a random phase change, which differs the this circuit from the phase detector .

[0016] At least one metastability circuit advantageously consists of a flip-flop with two inputs being the inputs of the metastability circuit and an output being the output of the metastability circuit.

[0017] Alternatively at least one metastability circuit comprises a metastable circuit with an oscillatory response with two inputs being the inputs of the metastability circuit and an output being the output of the metastability circuit.

[0018] The output of the metastable circuit with an oscillatory response advantageously is connected to the output of the metastability circuit through an adder and advantageously the metastability circuit comprises counter, having outputs connected to consecutive inputs of the adder, and having an input connected to the output of the metastable circuit with an oscillatory response .

[0019] Alternatively at least one metastability circuit comprises a metastable generator of time intervals, having inputs connected to the inputs of the metastability circuit and outputs connected to inputs of an arbiter circuit, having outputs connected to the outputs of the metastability circuit through a logic circuit.

[0020] Advantageously the metastable generator of time intervals comprises two flip-flops having two inputs and single outputs, wherein the inputs of the flip-flops of the metastable generator of time intervals are connected to the inputs of the metastability circuit and wherein, the first input of the metastability circuit is connected to both the first input of the first flip-flop and the first input of the second flip-flop, the second input of the metastability circuit is connected to both the second input of the first flip-flop and the second input of the second flip-flop. Further the arbiter circuit comprises two flip-flops having two inputs and two outputs each, wherein the outputs of the flip-flops of the metastable generator of time intervals are connected to the inputs of the flip-flops of the arbiter circuit and wherein, the output of the first flip-flop of the metastable generator of time intervals is connected to both the first input of the first flip- flop of the arbiter circuit and the second input of the second flip-flop of the arbiter circuit, the output of the second flip- flop of the metastable generator of time intervals is connected to both the second input of the first flip-flop of the arbiter circuit and the first input of the second flip-flop of the arbiter circuit. Further the logic circuit consists of a conjunction gate, through which selected outputs of the flip-flops of the arbiter circuit are connected to the outputs of the metastability circuit.

[0021] The invention has been described below in detail, with reference to the attached figures. Fig.l presents a block diagram of random number generator with two ring oscillators, fig.2 presents a block diagram of random number generator with three ring oscillators, fig.3 phase detector that consists of one flip- flop, fig.4 presents a block diagram of phase detector comprising two flip-flops, fig.5 presents a block diagram of metastability circuit that consists of flip-flop, fig.6 presents a block diagram of metastability circuit comprising metastable circuit with an oscillatory response, fig.7 presents a block diagram of metastability circuit comprising metastable circuit with an oscillatory response and adder, fig.8 presents a block diagram of metastability circuit comprising metastable circuit with an oscillatory response, adder and counter, and fig.9 presents a block diagram of metastability circuit comprising metastable generator of time intervals and arbiter circuit. [0022] Random number generator presented in fig.l comprises two ring oscillators GP1 and GP2 and seven bistables UB1, UB2, UB3, UB4, UB5, UB6 and UB7. The ring oscillators GP1 and GP2 comprise delay lines LOl and L02 closed in loops so, that an output o-LOl and o-L02 of a delay line LOl and L02 is connected to an input i- L01 and i-L02 of this delay line and also the outputs of the delay lines LOl and L02 are connected to outputs of the ring oscillators GP1 and GP2. The delay lines LOl and L02 comprise delays EO connected in series between the inputs i-LOl and i-L02 and the outputs o-LOl and o-L02 of these delay lines. Outputs o-UBl, o- UB2, o-UB3, o-UB4, o-UB5, o-UB6 and o-UB7 of the bistables UB1, UB2, UB3, UB4, UB5, UB6 and UB7 are connected to outputs ol-GL, o2-GL, o3-GL, o4-GL, o5-GL, 06-GL and o7-GL of the random number generator GL . First input il-UBl of the first bistable UB1 is connected to the delay line LOl of the first ring oscillator GP1 to an output of the last delay EO counting from the beginning of this delay line. Second input i2-UBl of the first bistable UB1 is connected to the delay line L02 of the second ring oscillator GP2 to an output of the last delay EO counting from the beginning of this delay line. First input H-UB2 of the second bistable UB2 is connected to the delay line LOl of the first ring oscillator GP1 to an output of the first delay EO counting from the beginning of this delay line. Second input i2-UB2 of the second bistable UB2 is connected to the delay line L02 of the second ring oscillator GP2 to an output of the first delay EO counting from the beginning of this delay line. First input H-UB3 of the third bistable UB3 is connected to the delay line LOl of the first ring oscillator GP1 to an output of the second delay EO counting from the beginning of this delay line. Second input i2-UB3 of the third bistable UB3 is connected to the delay line L02 of the second ring oscillator GP2 to an output of the second delay EO counting from the beginning of this delay line. First input H-UB4 of the fourth bistable UB4 is connected to the delay line LOl of the first ring oscillator GP1 to an output of the fourth delay EO counting from the beginning of this delay line. Second input i2-UB4 of the fourth bistable UB4 is connected to the delay line L02 of the second ring oscillator GP2 to an output of the fifth delay EO counting from the beginning of this delay line. First input il-UB5 of the fifth bistable UB5 is connected to the delay line LOl of the first ring oscillator GP1 to an output of the fifth delay EO counting from the beginning of this delay line. Second input i2-UB5 of the fifth bistable UB5 is connected to the delay line L02 of the second ring oscillator GP2 to an output of the seventh delay EO counting from the beginning of this delay line. First input il-UB6 of the sixth bistable UB6 is connected to the delay line LOl of the first ring oscillator GP1 to an output of the eighth delay EO counting from the beginning of this delay line. Second input i2-UB6 of the sixth bistable UB6 is connected to the delay line L02 of the second ring oscillator GP2 to an output of the eighth delay EO counting from the beginning of this delay line. First input il-UB7 of the seventh bistable UB7 is connected to the delay line LOl of the first ring oscillator GP1 to an output of the eighth delay EO counting from the beginning of this delay line. Second input i2-UB7 of the seventh bistable UB7 is connected to the delay line L02 of the second ring oscillator GP2 to an output of the eighth delay EO counting from the beginning of this delay line.

[0023] The first three of the bistables UB1, UB2 and UB3 are connected to delay lines in the way that assures the delays EO are driven by bistables in the minimal manner and at the same time the bistables are stimulated by similar signals - that is, similar phase shifts of the signals of the ring oscillators GP1 and GP2. The third, the fourth and the fifth of the bistables UB3, UB4 and UB5 are also connected to delay lines in the way that assures the delays EO are driven by bistables in the minimal manner, however each of these bistables is stimulated by completely different phase shift of signals of the ring oscillators GP1 and GP2. The sixth bistable UB6 is stimulated by the same signals as the seventh bistable UB7. The identical structure of these two bistables UB6 and UB7 provides similar conditions for their stimulation, whereas their different structure - in particular symmetrical with respect to one another, but with asymmetrical operating characteristics - ensures the stimulation of these circuits at different phase shifts .

[0024] The number of delays and the delay caused by each delay EO determine the basic operating frequencies of the ring oscillators GP1 and GP2. The basic frequency has a random component, resulting from physical phenomena - typical for electronic circuits (noise, thermal phenomena, jitter, etc.) - and because of that the signal phase also manifests random changes.

[0025] The positive or negative phase offset of the input signals of a bistable being a phase detector provides random values at the output of the phase detector. The proximity of the oscillators' phases means time closeness of the edges of generated signals, which are used to stimulate bistables being metastability circuits, which produce random phenomena. The exceptions are the bistables connected to the delay lines with particular shifts, because the goal is to achieve a different phase stimulation - shifted by one or multiple propagation times of a delay EO.

[0026] Random number generator presented in fig.2 comprises three ring oscillators GP1, GP2 and GP3 and seven bistables UB1, UB2, UB3, UB4 , UB5 , UB6 and UB7. The ring oscillators GP1, GP2 and GP3 comprise delay lines L01, L02 and L03 closed in loops so, that an output o-LOl, O-L02 and O-L03 of a delay line L01, L02 and L03 is connected to an input i-LOl, i-L02 and i-L03 of this delay line and also the outputs of the delay lines o-LOl, o-L02 and o-L03 are connected to outputs of the ring oscillators o-GPl, o-GP2 and o- GP3. The delay lines L01, L02 and L03 comprise delays EO connected in series between the inputs i-LOl, i-L02 and i-L03 and the outputs o-LOl, o-L02 and O-L03 of these delay lines. Outputs o-UBl, o-UB2, o-UB3, o-UB4, o-UB5, o-UB6 and o-UB7 of the bistables UB1, UB2, UB3, UB4, UB5, UB6 and UB7 are connected to outputs ol-GL, o2-GL, o3-GL, o4-GL, o5-GL, 06-GL and o7-GL of the random number generator GL . First input il-UBl of the first bistable UB1 is connected to the delay line L01 of the first ring oscillator GP1 to an output of the last delay EO counting from the beginning of this delay line. Second input i2-UBl of the first bistable UB1 is connected to the delay line L02 of the second ring oscillator GP2 to an output of the last delay EO counting from the beginning of this delay line. First input il-UB2 of the second bistable UB2 is connected to the delay line LOl of the first ring oscillator GP1 to an output of the first delay EO counting from the beginning of this delay line. Second input i2-UB2 of the second bistable UB2 is connected to the delay line L03 of the third ring oscillator GP3 to an output of the first delay EO counting from the beginning of this delay line. First input il-UB3 of the third bistable UB3 is connected to the delay line L02 of the second ring oscillator GP2 to an output of the second delay EO counting from the beginning of this delay line. Second input i2-UB3 of the third bistable UB3 is connected to the delay line L03 of the third ring oscillator GP3 to an output of the second delay EO counting from the beginning of this delay line. First input il-UB4 of the fourth bistable UB4 is connected to the delay line LOl of the first ring oscillator GP1 to an output of the fourth delay EO counting from the beginning of this delay line. Second input i2-UB4 of the fourth bistable UB4 is connected to the delay line L02 of the second ring oscillator GP2 to an output of the fifth delay EO counting from the beginning of this delay line. First input il-UB5 of the fifth bistable UB5 is connected to the delay line LOl of the first ring oscillator GP1 to an output of the fifth delay EO counting from the beginning of this delay line. Second input i2-UB5 of the fifth bistable UB5 is connected to the delay line L02 of the second ring oscillator GP2 to an output of the seventh delay EO counting from the beginning of this delay line. First input il-UB6 of the sixth bistable UB6 is connected to the delay line LOl of the first ring oscillator GP1 to an output of the eighth delay EO counting from the beginning of this delay line. Second input i2-UB6 of the sixth bistable UB6 is connected to the delay line L03 of the third ring oscillator GP3 to an output of the eighth delay EO counting from the beginning of this delay line. First input il-UB7 of the seventh bistable UB7 is connected to the delay line LOl of the first ring oscillator GP1 to an output of the eighth delay EO counting from the beginning of this delay line. Second input i2-UB7 of the seventh bistable UB7 is connected to the delay line L03 of the third ring oscillator GP3 to an output of the eighth delay EO counting from the beginning of this delay line.

[0027] The first three of the bistables UB1, UB2 and UB3 are connected to delay lines in the way that assures the delays EO are driven by bistables in the minimal manner and at the same time the bistables are stimulated by similar signals - that is, similar phase shifts of the signals of the ring oscillators GP1 and GP2, GP1 and GP3, GP2 and GP3. In result the stimulations of bistables connected to different ring oscillators are uncorrelated or slightly correlated, which improves the randomness of numbers on the outputs of these circuits. The first, the fourth and the fifth of the bistables UB1, UB4 and UB5 are also connected to delay lines in the way that assures the delays EO are driven by bistables in the minimal manner, however each of these bistables is stimulated by completely different phase shift of signals of the ring oscillators GP1 and GP2. The sixth bistable UB6 is stimulated by the same signals as the seventh bistable UB7. The identical structure of these two bistables UB6 and UB7 provides similar conditions for their stimulation, whereas their different structure - in particular symmetrical with respect to one another, but with asymmetrical operating characteristics - ensures the stimulation of these circuits at different phase shifts.

[0028] Phase detector presented in fig.3 consists of a flip-flop P having two inputs D and C being the inputs il-DF and i2-DF of the phase detector DF, and an output Q being the output of the phase detector o-DF.

[0029] Depending on whether the rising edge on the D input of the flip-flop occurs before or after the rising edge on the C input of the flip-flop, the logic ^' 1' or logic ^' O' will appear on the output Q. The type of the flip-flop - e.g., D flip-flop, RS flip-flop, JK flip-flop etc. - is of secondary importance, as long as the flip- flop detects which of the input signals slopes came first. [0030] Phase detector presented in fig.4 comprises a logic circuit AND having two inputs and one output as well as two flip-flops PI and P2, having two inputs Dl, Cl and D2, C2 each as well as two outputs Ql, nQl and Q2, nQ2 each. The inputs of the flip-flops are connected to inputs of the phase detector DF, whereas the outputs of the flip-flops are connected to outputs of the phase detector through the logic circuit AND. The first input of the phase detector il-DF is connected to both the first input of the first flip-flop Dl and the second input of the second flip-flop C2. The second input of the phase detector i2-DF is connected to both the second input of the first flip-flop Cl and the first input of the second flip-flop D2. The inputs of the logic circuit AND are connected to the second output of the first flip-flop nQl and the first output of the second flip-flop Q2. The output of the logic circuit AND is connected to the output of the phase detector o- DF.

[0031] The phase detector composed of two flip-flops provides symmetrical detection of negative and positive phase shifts.

[0032] Metastability circuit presented in fig.5 consists of a flip- flop Pa having two inputs Da and Ca being the inputs il-UM and i2- UM of the metastability circuit UM, and an output Qa being the output of the metastability circuit o-UM.

[0033] The flip-flop Pa is characterized by the fact that the proximity of the edges of signals on the inputs of the flip-flop Da and Ca causes a metastable range of operation resulting in a random logic state on the output Qa. The type of the flip-flop - e.g., D flip-flop, RS flip-flop, JK flip-flop etc. - is of secondary importance, as long as the flip-flop provides a random response at the output in case of appropriate proximity of the edges of the input signals.

[0034] Metastability circuit presented in fig.6 comprise a metastable circuit with an oscillatory response UMOO having two inputs R and S being the inputs il-UM and i2-UM of the metastability circuit UM, and an output wOO being the output of the metastability circuit o-UM. [0035] The flip-flop UMOO is characterized by the fact that the proximity of the edges of signals on the inputs of the flip-flop R and S causes a metastable range of operation resulting in oscillatory response of the flip-flop with a variable number of oscillations as well as in a random response at the output wOO .

[0036] Metastability circuit presented in fig.7 has the same construction as the one presented in fig.6, wherein the output wOO of the metastable circuit with an oscillatory response UMOO is connected to the output of the metastability circuit o-UM through an adder SUM.

[0037] The adder SUM is used for adding up a variable number of oscillations at the output wOO .

[0038] Metastability circuit presented in fig.8 has the same construction as the one presented in fig.7, wherein it additionally comprises a counter LCZ, having outputs connected to consecutive inputs of the adder SUM and having an input i-LCZ connected to the output of the metastable circuit with an oscillatory response wOO .

[0039] The counter LCZ is used for counting a variable number of oscillations at the output wOO, which then adds the adder SUM. Moreover, the logical state at the output wOO is also taken into account in this circuit.

[0040] Metastability circuit presented in fig.9 comprises a metastable generator of time intervals GMIC, an arbiter circuit ARB and a logic circuit AND. The metastable generator of time intervals GMIC comprises two flip-flops Pb and Pc, having two inputs Db and Cb as well as Dc and Cc each, and having single outputs Qb and Qc each. The arbiter circuit ARB comprises two flip- flops Pd and Pe, having two inputs Dd and Cd as well as De and Ce each, and having two outputs Qd and nQd as well as Qe and nQe each. The logic circuit AND has two inputs and one output. The inputs of the flip-flops of the metastable generator of time intervals GMIC are connected to the inputs of the metastability circuit UM so, that the first input of the metastability circuit il-UM is connected to both the first input of the first flip-flop Db and the first input of the second flip-flop Dc, whereas the second input of the metastability circuit i2-UM is connected to both the second input of the first flip-flop Cb and the second input of the second flip-flop Cc. The outputs of the flip-flops Qb and Qc are connected to the inputs of the flip-flops of the arbiter circuit ARB so, that the output of the first flip-flop Qb is connected to both the first input of the first flip-flop of the arbiter circuit Dd and the second input of the second flip-flop of the arbiter circuit Ce, whereas the output of the second flip-flop Qc is connected to both the second input of the first flip-flop of the arbiter circuit Cd and the first input of the second flip-flop of the arbiter circuit De . The output of the metastability circuit o- UM is connected to the outputs of the flip-flops of the arbiter circuit nQd and Qe through the logic circuit AND. The inputs of the logic circuit AND are connected to the second output of the first flip-flop of the arbiter circuit nQd and the first output of the second flip-flop of the arbiter circuit Qe . The output of the logic circuit AND is connected to the output of the metastability circuit o-UM.

[0041] Providing to the flip-flops Pb and Pc of the metastable generator of time intervals GMIC digital signals with relatively close proximity of the edges of the signals at the inputs of the flip-flops, causes metastable states in them, which result in logical values at the outputs Qb and Qc in various moments. Both the logical values and the time intervals are sources of randomness with specific properties of these randomities. The arbiter circuit compares the response times of the flip-flops Pb and Pc, and the result of this comparison - which is a random value - is interpreted by the logic circuit AND as logical zero or logical one .

[0042] The invention can be applied and used in generating truly random numbers and series.