Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F21/00—Security arrangements for protecting computers, components thereof, programs or data against unauthorised activity
  • G06F21/70—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer
  • G06F21/71—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer to assure secure computing or processing of information
  • G06F21/72—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer to assure secure computing or processing of information in cryptographic circuits
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F21/00—Security arrangements for protecting computers, components thereof, programs or data against unauthorised activity
  • G06F21/70—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer
  • G06F21/71—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer to assure secure computing or processing of information
  • G06F21/75—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer to assure secure computing or processing of information by inhibiting the analysis of circuitry or operation
  • G06F21/755—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer to assure secure computing or processing of information by inhibiting the analysis of circuitry or operation with measures against power attack

Definitions

• FIGURE 1 is schematic illustrating a prior art simplified microcontroller.
• a microcontroller generally includes a microprocessor, memory, a peripheral module that provides communication, for example Universal Asynchronous Receiver/Transmitter (UART), SPI, and USB, and an interrupt controller.
• Microcontroller 100 includes microprocessor 102 coupled to memory 104.
• Address decoder 106 receives and decodes addresses from microprocessor 102 for memory 104 and peripherals 108.
• Address decoder 106 and peripherals 108 receive addresses on address bus 110 while address decoder 106 transmits select information on memory select 112 and peripheral select 114.
• Data is transmitted between microprocessor 102, memory 104, and peripherals 108 on data bus 116.
• a read or a write signal is transmitted between microprocessor 102 and memory 104 and peripherals 108 on read/write signal 117.
• Microcontroller 100 receives clock signal 118 and reset signal 120.
• Input 122 includes, for example, timer triggers and UART input data while output 124 includes, for example, UART transmitter output data.
• Interrupt controller 126 collects and processes interrupt signals from peripherals 108 along interrupt line 128.
• Peripherals 108 may be functional logic, for example UART, crypto-processing, digital signal processing (DSP), and digital filtering.
• FIGURE 2 illustrates one example of a peripheral, a crypto-processor.
• a crypto- processor With a crypto- processor, if a buffer of data must be ciphered or deciphered, software divides the data buffer, also called a message, into several parts. Each part represents data able to be processed during a processing time period. As soon as the part is input to the crypto- processor and/or a start signal is applied, the peripheral begins to process the part. After a period of clock cycles the processing period ends and the crypto-processor provides a ciphered/deciphered part that can be read back by the software.
• the non-processing time period begins and an interrupt signal may be asserted to inform the microprocessor that the part is ready for reading and crypto-processor is ready to cipher/decipher a new part.
• an interrupt signal may be asserted to inform the microprocessor that the part is ready for reading and crypto-processor is ready to cipher/decipher a new part.
• the non-processing time period ends and a new processing time period begins.
• the software continues reading and writing parts up to the end of the data buffer.
• the algorithm used by the crypto-processor is executed, current consumption due to digital cell switching increases when the processing starts and decreases when processing ends.
• the current increases due to operation of the combinatorial (for example AND, OR, INVERT, MUX, and XOR) and sequential (D flip flops, or DFFs) cells in the digital module that execute the algorithm.
• DFFs sequential flip flops, or DFFs
• User interface module 200 processes system data, for example address, data, read/write, and select signals, in order to generate commands and data for algorithm module 202.
• Algorithm module 202 performs cipher/decipher according to control command, data
• Peripheral 108 receives a start signal from user interface 200 and organizes the data path into algorithm module 202.
• Some crypto algorithms may be represented as a basic combinatorial function concatenated several times to obtain the result.
• a basic combinatorial function is implemented once and connected to storing means (DFFs or others).
• DFFs storing means
• a multiplexer is required to select the input of the algorithm function (data input or intermediate result) depending on a controller module n value (n being the number of iteration to perform to obtain the result, 16 for example in the Data Encryption Standard (DES)).
• DES Data Encryption Standard
• TDES Triple Data Encryption Standard
• Controller 204 receives a start signal on start line 206.
• the start signal triggers a first-cycle signal from controller 204 to multiplexer 208 in algorithm module 202.
• Multiplexer 208 receives first-cycle signal and selects input from in-data line 210.
• Input data then goes to combinatorial circuit 212, which, in combination with a key and a cipher, manipulates the input data.
• Combinatorial circuit 212 begins processing upon receipt of the first-cycle signal and the input data, thus beginning the processing period.
• Combinatorial circuit 212 transmits the manipulated input data to multiplexer 213.
• multiplexer 213 receives processing period signal from controller 204 and therefore selects data from combinatorial circuit 212.
• Multiplexer 213 transmits the manipulated input data to DFF 214, which then sends the manipulated data to output 216, multiplexers 208 and 213. For subsequent iterations, no first-cycle signal is transmitted to multiplexer 208, so multiplexer 208 selects the manipulated input data from DFFs 214 and sends it to combinatorial circuit 214, which again manipulates the input data. Controller 204 keeps track of each iteration and counts down until the last iteration. At the last iteration, controller 204 sends a last-cycle signal to combinatorial circuit 212, indicating the end of the processing time period. The processing period signal from controller 204 triggers multiplexer 213 to select input from DFF 214 rather than combinatorial circuit 212.
• DFF 214 receives recycled data, which at this point in the cycle is desired output data.
• An interrupt signal is sent from controller 204 indicating that data available at output 216 is a desired output, so user interface module 200 retrieves the output data from output 216 after an interrupt is asserted.
• controller 204 is reset and waits for a new sequence to be started.
• FIGURE 3 is a graph illustrating a timing diagram and a current waveform representing activation of combinatorial circuit 212 during the processing period. When a buffer of data is processed, current consumption can be seen as a series of pulses. The low level period of this waveform represents the current consumption of the clock tree and the clock pin of the DFFs of the peripheral module. The high level period represents combinatorial circuit 212 switching current.
• FIGURE 3 illustrates clock signal 300 and input data 305.
• Input data 305 is available on input data line 210 (FIGURE 2) and represents part of the divided buffer of input data.
• Start signal 310 is transmitted along start line 206 and triggers the beginning of processing time period 315.
• Controller 204 counts down, in this case from 15 to zero for DES, with interval value 320.
• First-cycle signal 325 transmits from controller 204 in conjunction with the first count on interval controller 320.
• Last-cycle signal 330 transmits from controller 204 in conjunction with the last count on interval controller 320, and signals the end of processing time period 315 and the beginning of non-processing time period 335.
• Combinatorial circuit 212 is driven with switching data during processing time period 315, drawing more current than during non-processing time period 335. If a stable clock period is used to schedule the different steps of data processing, processing time period 315 may be detected or observed by non-intrusive methods like current consumption shape analysis.
• First waveform 340 is compared to second waveform 345.
• step 2 of 16 for DES may undergo differential power analysis by comparing the current levels in the two waveforms. Consequently, it is possible to determine data processed inside an integrated circuit. What is needed is a system and method of making the analysis of current consumption more difficult.
• the invention consists of altering, randomly or pseudo-randomly, the number of clock cycles over which an algorithm is performed.
• the invention may be used in any circuit where digital logic modules are embodied.
• the invention takes place in the digital part of an integrated circuit.
• combinatorial logic operates and causes an increase in power consumption.
• the increase in current is primarily due to cell switching, considering only the digital logic.
• the total cell leakage current is low compared to this switching current.
• the system and method reshapes current consumption in order to make current analysis more difficult. Current reshaping is performed during processing time period by an additional combinatorial circuit.
• the invention completes the DES algorithm over 16 or fewer clock cycles. This increases the difficulty of extracting values from the algorithm because each processing period may have a different number of clock cycles during which the algorithm was performed. Step 2 of 16, for example, will be at two different positions on two different waveforms and superimposing the waveforms will not yield as much useful information as in FIGURE 3.
• FIGURE 1 is a prior art schematic illustrating a simplified microcontroller.
• FIGURE 2 is a prior art schematic illustrating one example of a peripheral.
• FIGURE 3 is a prior art timing diagram illustrating two superimposed current waveforms for a peripheral from FIGURE 2.
• FIGURE 4 is a schematic illustrating one embodiment of the invention in a microcontroller.
• FIGURE 5 is a schematic illustrating one embodiment of the invention from FIGURE 4.
• FIGURE 6-1 is a timing diagram illustrating the operation of the invention from
• FIGURE 5 is a timing diagram illustrating the operation of the invention from FIGURE 5.
• FIGURE 7 is a timing diagram illustrating two superimposed current waveforms.
• FIGURE 8 is a flow diagram illustrating a method for a variable processing period in a digital logic module.
• FIGURE 9 is a flow diagram illustrating a method for a variable processing period in a digital logic module.
• FIGURE 4 is a schematic illustrating one embodiment of the invention in a digital logic module, or a peripheral of a microcontroller.
• Processing circuit 400 receives input from user interface 402 along input line 404.
• Controller 406 receives a start signal along start line 408 from user interface 402.
• Controller 406 transmits a first-cycle signal to processing circuit 400, which begins a processing time period.
• processing circuit 400 is manipulating the input in order to produce a desired output, for example an encrypted or decrypted version of the input. Due to the manipulation, for example logic cell switching, processing circuit 400 draws an active range of current during the processing time period and a corresponding waveform of the current over the period may be mapped.
• Processing is typically sixteen clock cycles for a DES algorithm.
• the invention is a method and system of varying the actual number of clock cycles over which the data part of a buffer is manipulated.
• controller 406 transmits a last-cycle signal to processing circuit 400 and the manipulated input is ready at output port 410 as output.
• processing circuit 400 includes combinatorial circuits 412 connected to multiplexer 414. Multiplexer 414 receives input from input line 404. If multiplexer 414 also receives a first-cycle signal from controller 406, then multiplexer 414 selects the input from input line 404 and sends it to combinatorial circuit 412-1.
• Combinatorial circuit 412-1 manipulates the input and delivers the manipulated input to combinatorial circuit 412-2 and multiplexer 416.
• Combinatorial circuit 412-2 receives the manipulated input from combinatorial circuit 412-1, manipulates it and also sends it to multiplexer 416.
• multiplexer 416 receives input reflective of the first and second steps of, for example, the DES algorithm.
• Each manipulation may derive from combinatorial circuit 412-1, while each consecutive manipulation following a first manipulation may derive from combinatorial circuit 412-2, depending on random number input received by controller 406.
• the second step, or each consecutive step of the DES algorithm derives from combinatorial circuit 412-2.
• combinatorial circuit 412-1 receives a first-cycle signal and a last-cycle signal.
• combinatorial circuit 412-2 performs the same function as combinatorial circuit 412-1.
• a select circuit, or multiplexer 416 receives manipulated input from combinatorial circuits 412.
• Multiplexer 416 receives a select signal from controller 406 indicating which of the two signals multiplexer 416 directs to its output.
• Controller 406 tracks the already processed manipulations and generated select signals. Controller 406 further generates select signals based on the remaining required manipulations and a random number input.
• the select signal to multiplexer 416 selects the manipulated input from combinatorial circuit 412-2 and the manipulation process for given data is complete.
• the end of manipulation for given data may occur at the eighth clock cycle in the sixteen round processing algorithm, the ninth, the tenth, and so on, all the way to the sixteenth.
• controller 406 may send a last cycle signal to either combinatorial circuit 412, for special processing required by the DES algorithm.
• Storage circuit 420 is connected to and receives input from multiplexer 416. Storage circuit 420 directs the input from multiplexer 416 to multiplexer 414 and output port 410 until manipulation of part of the data buffer is complete. Storage circuit 420 receives a select signal from controller 406, indicating that manipulation is complete and storage circuit 420 should store the recently received data from multiplexer 416. Storage circuit 420 maintains the data through the non-processing time period, and transmits it to output port 410 and multiplexer 414. At the beginning of the next processing time period, processing signal may indicate that storage circuit 420 should stop storing and revert to transmitting whatever input it receives.
• Storage circuit 420 provides the manipulated part of the data buffer to output port 410 until the next processing time period and receipt by processing circuit 400 of a new part of the data buffer.
• storage circuit 420 includes multiplexer 422 and DFF 424. Multiplexer 422 receives input from DFFs 424 and multiplexer 416. Once multiplexer 422 receives an active high signal from controller 406, multiplexer 422 selects input from multiplexer 416 and send it to DFFs 424. DFFs 424 make the input from multiplexer 422 available to output port 410 and multiplexer 414. Until multiplexer 422 receives a processing signal, the same data cycles between multiplexer 422 and DFFs 424.
• FIGURE 5 is a schematic illustrating a more detailed embodiment of the invention from FIGURE 4.
• controller 406 is controller 500.
• Controller 500 is one example of a circuit configured to track processing, as well as the number of steps in manipulating each data buffer.
• One skilled in the art will recognize that different circuits and logic may replace controller 500 and perform a similar function.
• Controller 500 provides a control signal to processing circuit 410 indicating whether one or two steps of manipulation in a given clock cycle will be completed. Controller 500 receives a reset signal and resets its count, in one example the count is 16 for DES, so controller 500 counts down from 15 to zero. Controller 500 includes multiplexer 505 that receives the start signal, so upon receiving the reset and start signal, controller 500 transmits a first-cycle signal and resets its DFFs. The start signal causes multiplexer 505 to select the input with a value of 15, in the case of DES. The value of 15 is transmitted to DFFs 510, which then hold and transmit the value to subtractors 515 and counter 527. Furthermore, the start signal causes DFF 520 to be set and sets a value of 15 on the counter.
• DFF 520 When DFF 520 is set, the processing signal indicates that storage circuit 420 (see FIGURE 4) should transmit data it receives, rather than stored data.
• Subtractor 515-1 subtracts one from the input, so when receiving a value of 15, subtractor 515-1 outputs a value of 14.
• Subtractor 515-2 subtracts two from the input, so when receiving a value of 15, subtractor 515-2 outputs a value of 13.
• Decoder 525 receives input from DFFs 510 (through counter 527) and decoding circuit 530. Decoder 525 receives a signal from decoding circuit 530, which decoder 525 decodes and indicates whether to process two steps or one step of manipulation in a given clock cycle.
• Decoding circuit 530 receives a random number from a random number generator and sends, in one embodiment, a one-bit signal to decoder 525. Decoder 525 receives the count and transmits the first-cycle signal with a count of 15, for example. Decoder 525 receives the count through decoding circuit 530. Based on the signal from decoding circuit 530, decoding circuit sends a select signal to multiplexer 535 and processing circuit 400. The select signal will determine whether multiplexer 535 selects the input from subtractor 515-1 or subtractor 515-2. Similarly, the select signal will cause multiplexer 416 to select between input from combinatorial circuits 412.
• Selection of subtractor 515-1 corresponds to selection of combinatorial circuit 412-1
• selection of subtractor 515-2 corresponds to selection of combinatorial circuit 412-2.
• the count in controller 500 will decrement by one with the selection of subtractor 515-1 and combinatorial circuit 412-1, signifying that one step was performed within one clock cycle.
• the count in controller 500 will decrement by two with the selection of subtractor 515-2 and combinatorial circuit 412-2, signifying that two steps were performed within one clock cycle.
• the decremented count from multiplexer 535 is transmitted to multiplexer 505, which selects the decremented count in the next clock cycle, as the start signal is no longer indicating the start of a processing time period.
• decoder 527 may indicate a count of one (meaning two manipulations of the data remain).
• decoder 525 receives a random number indicating two manipulations are to be performed during the clock cycle, then decoder 525 sends a last-cycle signal to combinatorial circuit 412-2 and clears DFF 520.
• DFF 520 sends a processing signal to processing circuit 400 indicating that processing is finished and the data to be received should be saved.
• decoder 525 receives a random number indicating one manipulation is to be performed during the clock cycle.
• FIGURE 6-1 a timing diagram illustrating the operation of the invention from FIGURES 4 and 5. For example, in the beginning of a sixteen-clock cycle processing period 600 for the DES algorithm, multiplexer 414 receives input data 605.
• Multiplexer 505 receives start signal 610 and selects an input of value of fifteen.
• Processing signal 615 indicates to processing circuit 400 that while processing is ongoing, storage should not occur.
• decoded random input 617 is asserted, indicating 2 iterations, or manipulations, within one clock cycle.
• Decoder 525 receives decoded random input 617, indicating that two steps should occur in one clock cycle 615, and therefore transmits select signal 620, triggering a decrement of two steps in one clock cycle.
• Controller 500 decrements the count from 15 to 13, at counter 635, while multiplexer 416 selects the output from combinatorial circuit 412-2. Controller 500 also transmits first cycle signal 620 to processing circuit 400.
• FIGURE 6-2 a timing diagram illustrating the operation of the invention from FIGURES 4 and 5. The differences between FIGURE 6-1 and 6-2 will be discussed.
• decoder 525 When counter 650 is at one, decoder 525 receives decoded random input 655, indicating 1 iteration or manipulation in a clock cycle. On the next clock cycle, decoder 525 receives decoded random input 660, indicating two iterations in a clock cycle. However, because counter 650 indicates zero (one iteration remaining), the two iterations are ignored by decoder 525 and the last cycle performs one iteration. Last cycle signal 665 is asserted to combinatorial circuit 412-1.
• FIGURE 7 is a timing diagram illustrating two superimposed current waveforms.
• Waveform 700-1 formed over processing time period 710, taking, for example, a full sixteen clock cycles.
• Waveform 700-2 formed over some number of clock cycles less than sixteen. Comparing the waveforms 700 at any point, for example point 720, does not yield as much useful information as in the prior art.
• Waveform 700-1 may be in step six of the DES cycle while waveform 700-2 may be in step thirteen of the DES cycle, for example. Little useful information may be gained by comparing the waveforms in this manner because they are in different steps of the DES cycle and a point-to-point comparison of the waveforms does not correlate.
• Non-processing time period 730 follows processing time period 710.
• FIGURE 8 is a flow diagram illustrating a method for a variable processing period in a digital logic module.
• block 800 receive an input.
• block 810 manipulate the input in the processing circuit during N clock cycles, N being an integer defining each of a plurality of processing time periods.
• block 820 assign a value of L to a count, L being an integer corresponding to the number of times the input is manipulated in order to create the output.
• block 830 decrement the count by a value of one or more over a single clock cycle.
• block 840 complete L manipulations of the input over N clock cycles, N being an integer and equal to or less than L, wherein N varies randomly over each of the plurality of processing time periods.
• block 850 track the value of count initialized L, where L is an integer, and N with a controller, the controller coupled to the processing circuit.
• FIGURE 9 is a flow diagram illustrating a method for a variable processing period in a digital logic module.
• receive a first input In block 910, track a first processing time period.
• manipulate the first input during the first processing time period In block 930, complete manipulation of the first input.
• receive a second input In block 940, receive a second input.
• track a second processing time period wherein the second processing time period has a different duration from the first processing time period.

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• 2004
  • 2004-10-15 EP EP04795572A patent/EP1676192A4/de not_active Withdrawn
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