Abstract:
The invention relates to a device for interconnecting at least two data-communication networks, connecting a first network qualified as a high-security network and at least one second network qualified as a low-security network, the device including a one-way channel referred to as downlink channel between the high-security network and the low-security network, and a one-way channel referred to as uplink channel between the low-security network and the high-security network, the uplink channel being configured, in accordance with at least one predetermined data model from the low-security network or a dedicated loading channel, such as to transmit a return signal towards the high-security network whenever an uplink data stream sent from the low-security network to the high-security network includes all or part of the predetermined data model, the return signal being transmitted together with a transmission of the uplink data stream or at the end of a transmission of the uplink stream towards the high-security network.

Description:
GENERAL TECHNICAL FIELD 
       [0001]    The invention relates to a secure interconnection device enabling bidirectional communication between two communication networks; a first high-security network and a second network whereof the security is lower than that of the first network. Such a device can be used especially in an ETHERNET network, a network in which ETHERNET frames transit. 
       PRIOR ART 
       [0002]      FIG. 1  illustrates general architecture of a system comprising an interconnection device  10  for connecting a first network  11  to a second network  12 . The two networks  11 ,  12  have different levels of security. 
         [0003]    Network means an actual communication network and the set of connected devices which can communicate with each other. 
         [0004]    Level of security means a set of operating rules and constraints imposed on the network to ensure that only authorized data stream can transit over this network. 
         [0005]    When networks having different levels of security communicate with each other, it is necessary to ensure that the high-security network cannot be corrupted by attacks or erratic operations coming from the low-security network. 
         [0006]    In some contexts needing a high level of security, this guarantee must be very strong, or even absolute. 
         [0007]    This is particularly necessary in the context of avionics where the data network connecting the control units of the aircraft must absolutely offer a very high level of security especially during flight phases. 
         [0008]    It is however advantageous to connect this high-security network to a lower security network to, inter alia, recover data on the different parameters of flight during maintenance phases of the aircraft. 
         [0009]    It is also advantageous to be able to provide real-time information on and during the flight over a passenger network. 
         [0010]    It is known to construct one-way gateways between two networks having different levels of security. In this case, the gateway authorizes data transfers from the high-security network to the low-security network. The one-way aspect can even be guaranteed at the physical level of communication, for example by using a diode such as described in document EP 1 533 947 B1. 
         [0011]    This type of gateway ensures that it is impossible to let pass data coming from the low-security network and compromise the high-security network. 
         [0012]    However, to enable operation of some applications it can prove necessary to transmit information coming from the low-security network to the high-security network. These can sometimes be simple commands. 
         [0013]    It is also advantageous to have stream control mechanisms during data transfers from the high-security network to the low-security network. The stream control needs to be able to return information to the source of the transfer and therefore from the low-security network to the high-security network. 
         [0014]    However, it is preferable for the level of security to be maintained at a very high level. Control over information returning from the low-security network to the high-security network should therefore be retained. This control ensures security of a very high level. 
         [0015]    It is conventional to set up gateways using a firewall in this type of situation. These firewalls organize filtering of data circulating on the gateway. These instances of filtering are done as a function of the communication protocols used and addresses and port numbers involved in communication. 
         [0016]    But the level of security contributed by such a firewall is insufficient in some contexts where the need for security is particularly high. 
         [0017]    It is advantageous to be able to raise the level of security of such a gateway to ensure a level of security close to the level of security contributed by a one-way gateway. 
       PRESENTATION OF THE INVENTION 
       [0018]    The invention responds to this need and according to a first aspect proposes an interconnection device of at least two data communication networks, connecting a first network qualified as high-security network and at least one second network qualified as low-security network, the device comprising: 
         [0019]    a one-way channel known as downlink channel between the high-security network and the low-security network; 
         [0020]    a one-way channel known as uplink channel between the low-security network and the high-security network, the uplink channel being configured, as a function of at least one data model predetermined in advance originating from the low-security network or a dedicated loading channel, to transmit a return signal to the high-security network when an uplink data stream originating from the low-security network to the high-security network comprises all or part of the predetermined data model, the return signal being transmitted jointly to transmission of the uplink data stream or on completion of transmission of the uplink stream to the high-security network. 
         [0021]    The invention is advantageously completed by the following characteristics, taken singly or in any of their technically possible combinations. 
         [0022]    The data stream comprising a succession of data packets, each packet comprising several data fields, the uplink channel is configured to perform a detection step of a set of data in conformity with a reference data model in the uplink data stream originating from the low-security network. 
         [0023]    The uplink channel is further configured to perform a triggering step of transmission of a return signal to the high-security network when an uplink data stream originating from the low-security network to the high-security network comprises all or part of the predetermined data model. 
         [0024]    The reference data model belongs to a set of at least one reference data model, each reference data model of the set corresponding to a return stream associated with the detected reference data model. 
         [0025]    The reference data model is of a size greater than or equal to the return stream. 
         [0026]    The uplink channel is further configured to perform a construction step of a return stream from the data stream originating from the low-security network, the construction consisting of extracting some of the data from the uplink data stream, the return stream being the signal constructed as a result. 
         [0027]    The uplink channel is configured to perform a construction step of a reference data model from a data stream originating from the high-security network. 
         [0028]    The uplink channel is configured to perform verification of integrity of the uplink data stream. 
         [0029]    Verification of the data stream integrity is made during transmission of said uplink stream. 
         [0030]    The uplink channel is configured, if the uplink stream is not correct, while part of said uplink stream is transmitted to the high-security network, for inserting an indication in a frame of the uplink stream indicating that the uplink stream is not correct. 
         [0031]    If the uplink stream does not include automatic insertion of a CRC, the low-security network is configured to formulate a CRC such that the uplink stream intended for the secure network is correct. 
         [0032]    The downlink comprises a module qualified to guarantee a one-way character of said downlink said module preferably being a diode. 
         [0033]    The construction step of a reference data model from a data stream originating from the high-security network is performed after the following steps: 
         [0034]    detection in the data stream originating from the high-security network of a set of data in conformity with an initialization data stream; 
         [0035]    verification of integrity of the data stream detected in this way originating from the high-security network; and 
         [0036]    construction of the reference data model from the data stream originating from the high-security network or from the dedicated loading channel. 
         [0037]    The invention also relates to an assembly comprising a plurality of devices according to the invention, comprising one and the same dedicated channel for guiding the reference data model to each uplink channel of each device. 
         [0038]    The invention also relates to an assembly comprising a plurality of devices according to the invention, arranged head to tail and having dedicated configuration links independent of the uplink and downlink streams. 
         [0039]    According to a second aspect, the invention relates to an assembly comprising a plurality of devices according to the first aspect of the invention, comprising one and the same dedicated channel for guiding the reference data model to each uplink channel of each device. 
         [0040]    According to a third aspect, the invention relates to an assembly comprising a plurality of devices according to the first aspect of the invention, placed head to tail and having dedicated configuration links independent of the uplink and downlink streams. 
         [0041]    The invention can be implemented by hardware only, that is, without a processor, with security increasing since no software is required. Implementation is controlled end to end. 
         [0042]    The invention is especially based on transmission of a return signal preceded by a construction step of a return signal consecutively to recognition of a reference model expected at the start of each packet of the uplink data stream. 
         [0043]    In particular, construction of the return signal is dynamic. The return signal can consist of static data and/or data coming directly from the uplink data stream transmitted by the low-security network, the proportion of these data being flexible to ensure passage of a plurality of protocols or adapting to different levels of security. 
         [0044]    As a consequence, compared to the techniques of the prior art especially those described in document FR 2 992 705, there is no passage of data via a dedicated low-rate internal channel. 
     
    
     
       PRESENTATION OF THE FIGURES 
         [0045]    Other characteristics, aims and advantages of the invention will emerge from the following description which is purely illustrative and non-limiting and which must be considered with respect to the appended drawings in which, apart from the  FIG. 1  already discussed: 
           [0046]      FIG. 2  schematically illustrates an interconnection device according to a first aspect of the invention; 
           [0047]      FIG. 3  schematically illustrates a first embodiment of a method for controlling a transmission of a data stream in an interconnection device according to the invention; 
           [0048]      FIG. 4  schematically illustrates a second embodiment of a method for controlling a transmission of a data stream in an interconnection device according to the invention; 
           [0049]      FIG. 5  schematically illustrates a third embodiment of a method for controlling a transmission of a data stream in an interconnection device according to the invention; 
           [0050]      FIG. 6  schematically illustrates a fourth embodiment of a method for controlling a transmission of a data stream in an interconnection device according to the invention; 
           [0051]      FIG. 7  schematically illustrates an assembly according to a second aspect of the invention; 
           [0052]      FIG. 8  schematically illustrates an assembly according to a third aspect of the invention. 
       
    
    
       [0053]    In all figures similar elements bear identical reference numerals. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0054]      FIG. 2  illustrates an interconnection device  20  of at least two data communication networks, connecting a first network  11  qualified as high-security network and at least one second network  12  qualified as low-security network. 
         [0055]    Such a device further comprises a first communication interface  21  with the low-security network  11  and a second communication interface  22  with the high-security network  12 . 
         [0056]    The interconnection device also comprises a downlink  201  by which a downlink data stream F-DES originating from the high-security network  11  intended for the low-security network  12  transits. 
         [0057]    The interconnection device also comprises an uplink channel  202  by which an uplink data stream F-ASC transits which can trigger sending a return signal SIG-RET to the low-security network  11 . This triggering can be initiated as a function of at least one datum of the uplink data stream. 
         [0058]    The downlink, uplink data streams and the return signal SIG-RET preferably consist of data organized according to packets in ETHERNET format, which implies that a CRC is automatically inserted into the frames composing the different streams. 
         [0059]    In this way, the downlink  201  is configured to let pass all the data stream of the High-security network  11  to the low-security network  12 . 
         [0060]    In particular, the downlink comprises a module qualified to guarantee a one-way character of the downlink. Such a module is preferably similar to a function of diode type. 
         [0061]    Furthermore, as a function of at least one data model F-REF predetermined in advance (hereinbelow reference data model F-REF) originating from the high-security network  11  or a dedicated independent loading channel  30 , the uplink channel  202  is configured to transmit a return signal SIG-RET to the high-security network  11  when an uplink data stream F-ASC originating from the low-security network  12  to the high-security network  11  comprises all or part of the predetermined data model F-REF. The return signal SIG-RET can be transmitted at the same time as the uplink stream F-ASC or else on completion of the complete transmission of the uplink stream F-ASC. 
         [0062]    It is under some particular conditions that transmission of a return signal SIG RET to the low-security network  12  will be initiated, conditions which will be described hereinbelow in the embodiments of a method for controlling a transmission of a data stream executed by the uplink channel  202  configured to perform the steps described hereinbelow in relation to each of the embodiments. 
         [0063]      FIG. 3  illustrates a first embodiment of a method for controlling a transmission of a data stream executed by the uplink channel  202  of the interconnection device of  FIG. 2 . 
         [0064]    According to this first embodiment, in a first step DET-F-REF a set of data in conformity with a reference data model F-REF is detected in the uplink data stream F-ASC originating from the low-security network  12  intended for the high-security network  11 . The reference data model F-REF can come either from the high-security network or from a dedicated channel  30 . 
         [0065]    Next, in a second step VER-CRC, integrity of the uplink data stream F-ASC is verified as is standard to avoid spreading content the integrity of which would not be correct. 
         [0066]    Next, if a set of data in conformity with a reference model F-REF is detected and if the uplink data stream F-ASC is correct, in a third step DEC-EMI transmission of a return signal SIG-RET to the high-security network  11  is triggered, the return signal SIG-RET being a predetermined return data stream FRET. 
         [0067]    The return signal in this first embodiment is independent of the downlink stream F-DES and of the uplink stream F-ASC. 
         [0068]    Also, this return data stream F-RET is predetermined in that it is in conformity with a set of data pre-loaded in a memory (not shown) of the interconnection device. 
         [0069]    The return signal SIG-RET in this first embodiment is transmitted on completion of transmission of the uplink stream F-ASC. 
         [0070]      FIG. 4  illustrates a second embodiment, according to which, in addition to the characteristics of the first embodiment the reference data model F-REF belongs to a set of reference data models F-REF 1 , F-REF 2 , F-REF 3 , F-REF 4  such that a reference data model from these reference data models is detected DET-F-REFi with i=1, 2, 3, 4 or more generally i=1, . . . , N, with N the number of reference data models, and it is integrity of the detected reference data model F-REFi which is verified, with detection and verification triggering transmission DEC-EMI of a return signal SIG-RET which is a predetermined data stream F-RETi corresponding to the detected reference data model. The reference data models F-REFi can come either from the high-security network or a dedicated channel  30 . 
         [0071]    According to this embodiment, for each stored reference stream, a predetermined return stream FRET is stored. 
         [0072]    For each of the first and second embodiments described hereinabove the reference model is of a size greater than or equal to the return stream FRET this which intrinsically causes a rate reduction along the uplink channel. 
         [0073]    Also, the uplink channel  202  can comprise a rate reducer (not shown) which limits the number of packets transmitted per time unit on the uplink channel and especially those of the return signal SIG-RET. Such rate reduction can be carried out by means of a monostable device, a decimation device or else a sliding window. 
         [0074]    The advantage of the resulting rate limitation is that the first high-security network  11  will not be stressed beyond a predetermined load. 
         [0075]    In this second embodiment, the return signal SIG-RET is transmitted on completion of the transmission of the uplink stream F-ASC. 
         [0076]      FIG. 5  illustrates a third embodiment comprising a construction step CONS-F-RET of the return stream F-RET from the uplink data stream originating from the Low-security network  12 , the construction consisting of extracting some of the data from the uplink data stream, the return signal SIG-RET being the signal constructed as a result. 
         [0077]    Furthermore, as in the first and second embodiments, the method comprises a step DET-F-REF according to which a set of data in conformity with a reference data model F-REF is detected in the uplink data stream F-ASC originating from the low-security network  12  intended for the high-security network  11 . The reference data model F-REF can come either from the high-security network or from a dedicated channel  30 . 
         [0078]    And if a set of data in conformity with a reference model is detected, transmission of the return signal SIG-RET to the high-security network  11  is triggered. 
         [0079]    The return stream FRET, and therefore the return signal SIG-RET, comprises data coming from the uplink stream and data F-INIT predetermined in advance. As a consequence, the return stream comprises both static and dynamic data (since they depend on data from the uplink stream which can be different from one stream to the other). 
         [0080]    According to this embodiment, the return signal SIG-RET can be transmitted after complete receipt of the uplink stream F-ASC or else jointly on transmission of the uplink stream. 
         [0081]    More precisely the reference data model F-REF includes a set of information defining byte by byte the way of working out on the fly (such as a partition) the return stream FRET from the uplink stream F-ASC. It indicates placing on the return stream FRET:
       either a static datum F-INIT which is a subset of the reference data model F-REF;   or a datum coming from the uplink stream F-ASC, which is further maskable bit by bit to finely select the extent of what will be authorized to return from the non-secure network  12  to the secure network  11 ;   or automatic insertion, or not, of an integrity check word CRC at the end of the frame relating to the stream now formulated on the fly.       
 
         [0085]    According to this embodiment and in the case of joint transmission of the uplink stream F-ASC and of the return signal VER-CRC-RET, the CRC is calculated during transmission of the uplink stream F-ASC and verification VER-CRC of integrity of the stream is done on the fly. If the verified stream is not correct, while part is received, a CRC indicating non-integrity of the stream will be inserted in the frame during transmission of the uplink stream to indicate to the high-security network that the received stream is not correct. 
         [0086]    Advantageously, if addition of the automatic CRC is deactivated and the corresponding placement is attributed to the uplink stream F-ASC, the non-secure network  12  will be responsible for working out a correct value for CRC relating for the entire return stream FRET formulated dynamically. To this end, the non-secure network  12  has to have complete knowledge of the return signal FRET and the corresponding static data F-INIT. In the absence of this information it will be impossible for the non-secure network  12  to submit an uplink stream F-ASC valid for the secure network  11 . 
         [0087]    In addition, as in the second embodiment illustrated in  FIG. 4 , the reference data model F-REF can belong to a set of reference data models F-REF 1 , F-REF 2 , F-REF 3 , F-REF 4  (not shown), the return streams F-RETi further comprise data F-INITi predetermined in advance, a reference data model F-REF of the set of reference data models. 
         [0088]      FIG. 6  illustrates a fourth embodiment in conformity with the third embodiment but in which the uplink channel  202  is further configured to perform a construction step CONS-F-REF of a reference data model in this case from the data stream originating from the high-security network  11 . 
         [0089]    Advantageously and in addition, the construction step CONS-F-REF of the reference stream from a data stream originating from the high-security network  11  is performed after the following steps: 
         [0090]    detection in the data stream originating from high-security network of a set of data in conformity with an initial reference data stream F-REF 0 ; 
         [0091]    verification, of known type, VER-CRC 0  of integrity of the initial reference data stream detected in this way originating from the high-security network. 
         [0092]    As is evident from  FIG. 6 , the construction step CONS-F-REF of the reference stream is performed if and only if the reference data stream F-REF 0  is correct, i.e, with a correct CRC. 
         [0093]    In addition, it is possible in conformity with this fourth embodiment to construct several reference streams, and as for the first embodiment the return stream belongs to a set of several return streams, a return stream corresponding to a reference stream. 
         [0094]    The reference data model F-REFi can originate either from the high-security network or from a dedicated channel  30 . 
         [0095]    According to a second aspect,  FIG. 7  illustrates a set of interconnection devices in conformity with the first aspect of the invention and operating according to the first, second or even third embodiments aggregated such that one and the same dedicated channel  30  feeds each interconnection arrangement  20   1 ,  20   2 ,  20   N  with reference data models F-REFi,n with n=1, N and i the index of the reference data model. 
         [0096]    According to a third embodiment,  FIG. 8  illustrates a set of two interconnection devices  20 # 1 ,  20 # 2  in conformity with the first aspect of the invention operating according to a method in conformity with the first, second or even third embodiments arranged relative to each other head to tail. According to this embodiment, access both to the high-security network  11  and also the low-security network  12  is controlled by uplink and downlink channels described earlier. Each device  20 # 1 ,  20 # 2  further comprises a dedicated channel  30  for guiding reference data models F-REFi# 1 , F-REFi# 2 . Such a configuration produces an assembly offering controlled security independently in each direction.