Abstract:
This invention relates to a secure integrated electronic device comprising  
     a processing unit ( 10 ) containing a logical processor and a non-volatile memory,  
     an energy source ( 11 ),  
     at least one sensor ( 12, 13, 14 ) capable of measuring a determined physical magnitude and supplying a value representative of this magnitude,  
     means ( 15, 16, 17 ) of comparison of each value with at least one predefined threshold (ref 1 , ref 2,  ref 3 ) giving result signals,  
     a device ( 20 ) for protection of the processing unit,  
     a logical device ( 21 ) for making decisions capable of activating the protection device after seeing the result signals.

Description:
TECHNICAL DOMAIN  
         [0001]    This invention relates to a secure integrated electronic device, for example a smart card.  
         STATE OF PRIOR ART  
         [0002]    The power supply to smart cards according to prior art is applied when the card is inserted in a reader. This is the only time at which an active protection can be provided. There is no way that these cards can detect an invasive attack when there is no power supply applied to the circuit. Therefore a reverse engineering attack made by a dishonest person to retrieve confidential information memorised on this card, for example encryption keys and the personal identification code, would has a good chance of succeeding.  
           [0003]    A smart card circuit can be surrounded by a mesh of conductors according to the known method described in document reference [ 1 ] at the end of the description, in order to detect any prejudicial or even criminal intrusion in a smart card circuit. But this detection is only possible if a power supply is applied to the circuit.  
           [0004]    Therefore, the purpose of the invention is to solve this detection problem to enable protection of sensitive information recorded in a secure integrated electronic device such as smart card; this protection may be destruction or erasure of this information, regardless of whether or not the device is inserted in a reader.  
         PRESENTATION OF THE INVENTION  
         [0005]    This invention relates to a secure integrated electronic device, for example a smart card comprising a processing unit containing a logical processor and a non-volatile memory, characterized in that it comprises:  
           [0006]    an energy source,  
           [0007]    at least one sensor capable of measuring a given physical magnitude and outputting a value representative of this magnitude,  
           [0008]    means of comparison of each value with at least one predefined threshold giving result signals,  
           [0009]    a device for protection of the processing unit,  
           [0010]    a logical decision making device capable of activating the protection device after seeing the signals resulting from the comparison.  
           [0011]    The energy source may be integrated into the processor. It may also be a battery.  
           [0012]    Each sensor may be capable of measuring a physical magnitude characterizing the processor or the processor environment, or a sensor capable of measuring a physical magnitude characterizing communication coming into or out of the said device.  
           [0013]    Active monitoring is possible with this device, in other words permanent measures can be made of physical parameters characterizing normal operation, and then information can be protected by the protection device whenever necessary.  
           [0014]    In one particular embodiment, the device according to the invention comprises a sensor capable of detecting when the power supply circuit from the energy source to the logical processor source is broken, a contact free energy transfer device from the energy source to the processor and a device that triggers this transfer. This sensor is able to measure a physical magnitude characterizing the electrical connection between the logical processor and the energy source. The contact free energy transfer device may comprise two coils placed on each side of the electrical connection between the logical processor and the energy source. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 illustrates the device according to the invention.  
         [0016]    [0016]FIG. 2 illustrates a particular embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0017]    As illustrated in FIG. 1, the device according to the invention comprises:  
         [0018]    an energy source  11 ,  
         [0019]    an integrated circuit  10 , or a processing unit, particularly containing a logical processor and a nonvolatile memory,  
         [0020]    at least one sensor capable of measuring a given physical magnitude and outputting a value representative of this magnitude, there being three of these sensors,  12 ,  13 ,  14 ,  
         [0021]    means of comparing each measured value with a predetermined threshold, in this case made by three comparators  15 ,  16 ,  17  receiving signals ref 1 , ref 2 , ref 3  respectively on one of their inputs and the output from the corresponding sensor  12 ,  13  or  14  on the other input,  
         [0022]    a device  20  for protection of the processing unit  10 , the output of which is connected to an Act (action) input on the device.  
         [0023]    a logical decision making device  21  capable of activating the protection device  20  receiving output signals from comparators  15 ,  16  and  17 .  
         [0024]    Therefore this secure integrated electronic device according to the invention uses two active functions:  
         [0025]    an intrusion detection function,  
         [0026]    a safeguard function at all times, in other words regardless of whether or not it is inserted in a reader.  
         [0027]    We will now consider each of these elements of the device according to the invention.  
         [0028]    The processing unit  10  that contains a processor and a non-volatile memory is the unit that is conventionally found in the smart cards. It contains the following functions:  
         [0029]    a Central Processing Unit (CPU),  
         [0030]    a read only memory (ROM),  
         [0031]    a volatile work memory (RAM),  
         [0032]    a non-volatile storage memory (EEPROM),  
         [0033]    a communication interface, with contact or contact free, that supplies:  
         [0034]    the circuit power supply (external),  
         [0035]    a two directional communication channel,  
         [0036]    possibly a clock,  
         [0037]    and possibly a reset processor signal.  
         [0038]    It may also contain other functions, for example sensor, comparator and logic functions.  
         [0039]    The energy source  11  may be a micro-battery such as a button battery, ultra-flat battery, integrated battery, etc. It must be capable of supplying power to the device according to the invention to implement the active intrusion detection function and the protection activation function.  
         [0040]    This energy source  11  may also be made using processes derived from microelectronics, for example by adding three technological levels or more above the levels typically dedicated to production of the integrated circuit  10 : these three levels being used to collectively produce the energy source  11 , connections and the solid state electrolyte.  
         [0041]    The energy source  11  may also be external to the integrated circuit  10 .  
         [0042]    Sensors may be:  
         [0043]    environment monitoring sensors; these sensors must verify if the nominal conditions of use (circuit powered through the communication channel) and rest conditions for the circuit are actually satisfied. Any detected difference from a reference value means that an intrusion attempt is being made. In particular, these sensors may be:  
         [0044]    a temperature sensor to protect the energy source  11 ,  
         [0045]    an ultraviolet rays sensor, for example to detect aggression on the EEPROM memory,  
         [0046]    an X-rays sensor, to detect a radiography type aggression on the integrated circuit  10 ,  
         [0047]    a protection mesh to detect an attempt at reverse engineering,  
         [0048]    an electric or magnetic field sensor (antenna, etc.),  
         [0049]    sensors monitoring the communication link. This type of sensor electronically monitors what is happening on the communication line. For example:  
         [0050]    monitoring the power supply voltage,  
         [0051]    monitoring the clock signal.  
         [0052]    Other functions are also possible for:  
         [0053]    recharging the energy source  11 , if it is a battery, through the communication line. A battery recharge function can be included inside the device according to the invention, regardless of whether the communication is made with contact or if it is contact free.  
         [0054]    activating/deactivating the device according to the invention. In some applications, it may useful to control use of the energy source. A start/stop remote control is then possible through the communication channel.  
         [0055]    Thus, as shown in FIG. 1, the first and second sensors  12 ,  13  may for example be ultra-violet and X-ray sensors, and the third sensor  14  may be a sensor to detect the impedance measurement of the galvanic connection  25  between the source  11  and the processing unit  10 .  
         [0056]    The purpose of the comparison means is to regularly inspect the various parameters output from the sensors  12 ,  13 ,  14  and to compare them with the different reference values ref 1 , ref 2  and ref 3 .  
         [0057]    For example, comparators  15 ,  16  and  17  may be operational amplifiers; the reference values ref 1 , ref 2  and ref 3  are either internal or are imposed from outside or by the microprocessor.  
         [0058]    These comparison means may also detect:  
         [0059]    firstly, a low energy level (first threshold) to give an alarm that a maintenance operation is necessary. If the energy source is a rechargeable battery, the objective is to detect the load level below which a warning recharge request signal should be output,  
         [0060]    secondly, a critical energy level (second threshold) to produce an alert and to implement the protection. Since the energy remaining below this second threshold is only just sufficient to activate protection, it is triggered to guarantee security.  
         [0061]    The protection device  20  protects confidential information. This protection may consist of:  
         [0062]    resetting all memories,  
         [0063]    physical destruction of vital connections,  
         [0064]    start-up of a contact free connection  26  between the energy source  11  and the processing unit  10 .  
         [0065]    The main objective for electronic circuits in smart cards is to erase the contents of the memories in which encryption and identification keys are stored.  
         [0066]    These different elements may form a “protected” area which is supposed to be composed of a circuit considered to be unbreakable. The links between the different functions (chip, energy source, sensors) are then valid at all times and cannot be attacked or modified. But it is also possible to:  
         [0067]    either detect that a sensor  12 ,  13  and  14  is disconnected by checking that the direct measurement is incorrect, or by making calibration means,  
         [0068]    or get around disconnection of the energy source  11  by transmitting energy in other ways, at least temporarily.  
       SPECIAL CASE OF DISCONNECTION OF THE ENERGY SOURCE  11   
       [0069]    In this particular embodiment, the device according to the invention is used to associate the logical processor and the memory with a sensor  14  capable of detecting if the power supply circuit is interrupted, a contact free energy transfer device  26  transferring energy from the energy source  11  to the processor, and a device to trigger this transfer.  
         [0070]    For example, the contact free energy transfer device  26  comprises two coils  28  and  29  placed on each side of the electrical connection between the processor and the energy source that makes an inductive connection capable of transferring energy from one to the other. These coils are not necessarily immediately adjacent to each other, they may be at some distance from each other and form an inductive link.  
         [0071]    As illustrated in FIG. 2, a bar made of a ferrite type material  27  may connect two coils  28  and  29  for correct magnetic coupling. It is always possible to detect either a break in the galvanic link by an impedance measurement, or withdrawal of the ferrite bar  27  (or a modification of the coupling) by a variation of the inductance of one of the coils  28  or  29 .  
         [0072]    The power supply to the electronic device  10  (or more precisely the active monitoring circuit) is normally made through the galvanic link  25 . If this galvanic link is broken, the device instantaneously redirects the energy transfer through the inductive link  26 . If the contact free link is defective, all that is transferred through the galvanic link  25  is an alarm signal to decide upon protection of the device.  
         [0073]    As shown in FIG. 2, the galvanic link  25  comprises pads  30 . It performs the following functions:  
         [0074]    power supply (+pole and −pole),  
         [0075]    two-directional transmission of information by carrier current (modulation/demodulation),  
         [0076]    detection of load presence, otherwise in the case of an open circuit, tear off detection alarm.  
         [0077]    Additional pads could be used if the information transmission disturbs the power supply in some applications.  
         [0078]    The protection of the galvanic link can be improved by surrounding the device with a galvanic contact “ring”. Thus, it will be possible to detect an attack from any direction intended to separate the energy source  11  from the processor.  
         [0079]    The inductive link  26  comprises two coils  28  and  29 , and performs the following functions:  
         [0080]    remote power supply by carrier current at a suitable frequency,  
         [0081]    two-directional transmission of information by modulation/demodulation of the carrier,  
         [0082]    detection of load presence, otherwise in the case of an open circuit, tear off detection alarm.  
         [0083]    Detection of separation of the energy source  11  circuit from the device  10  is based on a sudden change in the power supply load. As soon as a contact break is detected, the device reconfigures itself to send a maximum amount of energy through the inductive link  26 . This supplies power to the device for a brief moment, but sufficient to provide the protection.  
         [0084]    There are also several different possible variants in this embodiment:  
         [0085]    when a battery is used for the power supply source  11 , a battery recharge module can draw its power supply source either through the power supply of the electronic circuit when it is in a reader (it would be possible to add specific pads) or by remote power supply through inductive coupling using the coil that is already present.  
         [0086]    a remote control to switch the energy source  11  on and off may be available through the communication channel. This may be provided either by galvanic coupling or by a contact free inductive coupling.  
         [0087]    a temperature sensor may check if nominal usage conditions (device powered through the communication channel) and rest conditions for the device are actually satisfied. A detected difference then means either a potential intrusion attempt or an environment change that could be fatal for the energy source  11 ,  
         [0088]    the storage memory may be located close to the energy source  11 . If there is a sudden change in the connection between the power supply and the electronic device, the power supply will not have any difficulty in transmitting the energy to erase sensitive data. Transmission channels are used to exchange data with the device according to the invention during its use. Inductive coupling is no longer compulsory.  
         [0089]    The energy source  11  can use the inductive link  26  to transmit an alarm message to the device according to the invention. This message is transmitted in the form of a signal modulating the carrier, and is decoded by the device that reacts accordingly.  
       REFERENCES  
       [0090]    [ 1 ] Design principles for tamper-resistant smart card processors” by Oliver Kömmerling and Mazkus G. Kuhn (Proceedings of the USENIX Workshop on smart card technology, Chicago, Ill., USA, May 10-11, 1999).