BACKGROUND 
     The invention relates to the field of personal identification, and in particular to the protection against skimming of identity documents provided with a machine readable electronic chip. 
     To improve the capacity of a controlling authority (like a law-enforcement or national security agency) to detect fake identity documents, a wide range of identity documents (such as passports, identity cards, driving licenses, resident cards or the like), are provided with a machine readable electronic chip. Such identity documents are intended to reduce fraud, ease identity checks and enhance security. 
     Moreover, according to given security check proposals, there are risks of data leakage that could lead to identity theft by passport skimming or risks of offending the bearer&#39;s privacy. Skimming basically consists in fraudulently reading the user data in the chip to replicate such data in the chip of another identity document (either on a completely fake passport or on a legally issued passport). 
     According to the designs, the chips can be accessed either through a contact interface or through a RFID interface. As its use is far more convenient, the RFID interface tends to generalize. Various risks shall be avoided with RFID interfaces. A first risk is to have a hidden fraudulent chip reader approach the identity document and capture its data. 
     For preventing such risks, ICAO recommends that e-Passports be designed with Basic Access Control (BAC) features and enhanced with a Password-based mechanism according TR-SAC (Supplemental Access Control). BAC recites two protections. A first protection is that the front and back cover of the e-passport be lined with aluminum to shield the chip. This means that the passport booklet must be opened in order to communicate with the RFID interface of the chip. The second protection is the implementation of a read key consisting of a Machine Readable Zone (MRZ) on the e-passport. The MRZ is commonly a string of alphanumeric characters. The Machine Readable Zone must be scanned and its fields that are protected by check-digits are used to derive Basic Access Keys serving for confidentiality and integrity of the exchanges with the chip. Thus, a fraudulent user is thereby prevented to access the chip as long as the MRZ remains hidden. 
     To carry out such transactions, the cryptographic configuration (defining the cryptographic security levels supported by the chip) are stored in a memory of the chip (files EF.CardAccess and EF.DG14). The security levels are declared by the chip to the checking terminal, the terminal selects an appropriate security level available and the transaction is then carried out. One possible fraud (particularly affecting the EF.CardAccess file) would be to modify the supported security levels declared in the chip to force the use of a degraded security level during the transaction. The fraudulent user could then more easily interfere during the transaction. 
     Many organizations are involved in the definition of the specifications of both the controlling process and the identity support security features. In the case of the e-passports, ICAO, ISO and various national agencies are notably involved. This leads to a tedious negotiation process, necessary to guarantee that different organizations throughout the world will select identical security specifications before further improvements are validated. This is particularly complicated for electronic passports that have to be controlled in a wide range of countries throughout the world, which involves setting identical specifications in the various countries. In practice, no satisfying solution to the above security issue was found, that would be both accepted by these authorities and comply with the specifications already in force. 
     SUMMARY 
     Thus, there is a need for a security identity document solving one of these drawbacks. The invention proposes a secured identity document, comprising:
         an externally readable chip storing a cryptographic configuration of the chip for establishing a secure communication with a controlling terminal, storing a private key of a cryptography key pair and adapted to cipher data based on the stored private key;   a support to which the chip is fastened, the support having a machine optically readable area, the data encoded in this area including:   said cryptographic configuration of the chip for establishing a secure communication with a controlling terminal in non ciphered form;   the cryptographic configuration of the chip ciphered based on said private key.       

     The externally readable chip may include a contactless communication interface. The chip may provide an access through the contactless communication interface to the stored cryptographic configuration without requesting the controlling terminal to authenticate. 
     The data encoded in the optically readable area include authentication capacities of the chip in non ciphered form and the authentication capacities of the chip ciphered based on said private key. 
     The chip may be adapted to:
         receive a message;   receive a request to sign said message;   sign said message using said private key;   send the signed message.       

     The support advantageously displays identification data of the owner. 
     The invention also relates to a system for securely controlling the identity of an identity document bearer, comprising:
         an identity document as recited above;   a controlling terminal comprising:   a device adapted to scan the machine optically readable area and to decode the data contained in the scanned area;   a storage area storing the public key of said cryptography key pair;   a processing device adapted to decipher a first part of the decoded data based on the stored public key and to compare the deciphered first part with a second part of the decoded data;   a communication interface configurable to establish a secure communication channel with the chip of the identity document, the security level of the secure communication being based on the decoded cryptography configuration.       

     The invention also relates to a Method for establishing a secure communication channel between a secured identity document and a controlling terminal, comprising the steps of:
         scanning a machine optically readable area of a support of the identity document and decoding the data contained in the scanned area;   deciphering in the terminal a first part of the decoded data based on a public key available to the terminal, this public key belonging to a cryptography key pair, the first part of the decoded data being ciphered based on the private key of the cryptography key pair;   comparing the matching between the deciphered first part with a second part of the decoded data;   establishing a secure communication channel between the chip and the terminal based on a cryptography configuration recited in the decoded data if the deciphered first part matches the second part of the decoded data.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantage of the present invention will become apparent from the following description of several embodiments with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic view of an identity card used in an embodiment of the invention; 
         FIG. 2  is a schematic view of the structure of a chip embedded in the identity card; 
         FIG. 3  is a schematic view of a terminal for carrying out a card validity check; 
         FIG. 4  is a flowchart illustrating an example of method for performing the invention; 
         FIG. 5  is a flowchart illustrating an alternate part of the method; 
         FIG. 6  is a flowchart illustrating another alternate part of the method. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic view of an identity document  1  according to an embodiment of the invention. The illustrated identity document  1  is a national identity card. The identity card comprises a support  7 . The support  7  can comprise fibrous layers and/or plastic layers and/or metallic layers or a combination of such layers. A picture  3  of the owner of the identity card is fastened or integrated in the support  7 . The support  7  also bears alphanumeric identification data  4  relating to the owner of the card  1 . The identification data  4  may comprise usual identification data known from someone ordinary skilled in the art, such as the first and last names, the date of birth, the place of birth or the like. The identification data may also comprise additional information like the number of the identity card  1  or the identification of the authority that issued the card  1 . 
     A RFID chip  2  is fastened to the support  7 . The chip  2  may be embedded between several layers of the support  7  according to techniques commonly known by someone skilled in the art. 
     As illustrated at  FIG. 2 , the chip  2  comprises a processor  21 . The processor  21  is connected to a RAM memory  22 , to a owner identification data storage area  23 , to a private key storage area  24 , to a cryptographic tools storage area  25  and to a cryptographic configuration storage area  26 . Storage areas  23  to  26  belong to one or more non volatile memories. The processor  21  is connected to a RFID communication interface  27 . 
     Storage area  23  is a container storing identification data relating to the card owner. This container may be a file or a data object protected against external reading by access rules such as recited in the ISO 7816-4 requirements. 
     The storage area  25  stores cryptographic tools. When executed by the processor  21 , these cryptographic tools are notably able to perform deciphering operations using the stored private key or comparison operations. 
     The storage area  26  is a container storing the cryptographic configuration of the chip  2 . The cryptographic configuration can comply with the EF.CardAccess requirements set in the ICAO specification named ‘Supplemental Access Control for Machine Readable Travel Documents’ EAC v1.11. This container is an always readable file protected against external writing by access rules such as recited in the ISO 7816-4 requirements. This cryptographic configuration is intended to be provided to a terminal in charge of checking the validity of the card  1 . A terminal retrieving the cryptographic configuration of the chip  2  can thereby determine the various security levels or variants (e.g. algorithm, key length, type of mapping, type of secure messaging for PACE protocol) that the chip  2  supports for performing a security transaction. The terminal can thereby set the security level of the security transaction with chip  2 . 
     The support  7  also comprises an optically accessible area  5  encoding data. Area  5  is machine readable. The area  5  of the example is a 2D barcode. The area  5  comprises: the cryptographic configuration of area  26  authentication capacities of chip  2  in non ciphered version, a ciphered version of the cryptographic configuration and of the authentication capacities of the chip  2 . The authentication capacities of the chip  2  relate to the capacity of the chip to perform a chipcard authentication and/or to perform a terminal authentication. The ciphering of these data is performed during the manufacturing process of the card  1  based on a ciphering key. The ciphering process may in practice be a digital signature of a hash of the cryptographic configuration and of the authentication capacities. The ciphering key is a private key stored in the storage area  24 . The private key is associated to a public key. The public key is provided to the control access authorities by the distributor of the card  1 . The public key may be distributed in a certificate signed by the distributor. 
     The machine readable optical area  5  may notably be based on a 2D-barcode or a guilloche network. Encoding specifications of 2D barcodes such as QR Code, Aztec Code, PDF417 or Datamatrix can notably be used. The 2D-barcode may notably comply with the requirements set in the ISO/IEC 15415 specification. This ciphered optical area  5  may be integrated in the support by printing or engraving, by various techniques known per se by someone skilled in the art. The ciphered optical area  5  may notably be based on microprinting, on optical variable ink, on UV printing, on rainbow printing, on a diffractive optical variable device, or on changeable multiple laser image; 
       FIG. 3  schematically illustrates an example of system  8  for checking the validity of the card  1 . The use of system  8  may for instance be performed in airport terminals or in border checkpoints. System  8  includes a terminal  81 . A scanner  82  is connected to the terminal  81 . The scanner  82  is controlled by an application executed on terminal  81 . This application is adapted to decode the optical area  5  into binary data. The scanner  82  and the associated application may conform to the 2D barcode ISO/IEC 15426-2 specifications. 
     A chip reader  83  is also connected to the terminal  81 . The chip reader  83  is advantageously a RFID reader suitable for communicating with chip  2  if chip  2  has no contact communication interface and is embedded inside card  1 . A display  84  is also connected to terminal  81  to display the result of the card validity check and/or display various identification data concerning the owner of the card  1 . 
     The validity check of card  1  may be performed as follows. 
     At step  100 , the card  1  is located close to the chip reader  83 . The RFID interface  26  is thus in the communication range of the chip reader  83 . The optical area  5  is scanned using the scanner  82 . 
     At step  102 , the application run in the terminal  81  and associated to the scanner decodes the scanned optical area  5  into a binary data string. 
     At step  104 , the application run in the terminal  81  retrieves the non ciphered cryptographic configuration and the non ciphered authentication capacities of the chip  2  from the binary data string. 
     At step  106 , the application run in the terminal  81  deciphers the ciphered part of the binary data string, using the public key of the key pair shared with the chip  2 . 
     At step  108 , the application run in the terminal  81  checks that the deciphered data match the non ciphered cryptographic configuration and authentication capacities. The authenticity of the cryptographic configuration provided in area  5  is thus checked. The terminal  81  has thereby also authenticated the authentication capacities of chip  2 . 
     At step  110 , the terminal  81  establishes a secure communication channel with chip  2 , based on the cryptographic configuration. Thus, even if the cryptographic configuration is freely readable by external devices, its reading cannot be used to fraudulently trigger a reduced security for the secure communication channel. The terminal  81  selects for instance the cryptographic configuration available for chip  2  that provides the highest security for the secure communication channel. The secure communication channel may be established for instance according to the BAC or PACE mechanisms recited in the EAC v1.11 and TR-SAC specifications released by the ICAO. 
     At step  112 , the terminal  81  uses the retrieved authentication capacities to perform an active authentication of chip  2 . The terminal  81  can thereby determine that chip  2  really contains the private key originally used to cipher part of area  5 , which confirms that the secure communication channel was established based on the real available cryptographic configuration of chip  2 . 
     At step  114 , the terminal can request the chip  2  to compare the retrieved cryptographic configuration with the cryptographic configuration stored in area  26 . The terminal  81  can thereby confirm that neither the chip  2  nor the area  5  were fraudulently altered. 
     At step  116 , in the context of the EAC v1.11 specification, a passive authentication of the Security Object file can be carried out. This passive authentication can guarantee the integrity of the various data groups (DG) stored in chip  2 . 
     At step  118 , the chip  2  can perform a terminal authentication. 
     At step  120 , the chip  2  has authenticated terminal  81 . It thus allows the access by terminal  81  to biometric data stored in area  23 . 
     At step  122 , the biometric data retrieved by terminal  81  can be used to perform an additional security check on the card bearer. 
     In practice, a fraudulent user cannot successfully provide the terminal  81  with a fake cryptography configuration on area  5 , since he will not be able to provide the terminal  81  with the encrypted form of this cryptography configuration. 
     Even if the fraudulent user provides a fake cryptography configuration on a communication channel of the terminal  81  or by altering the storage area  26 , the fraud will be detected by comparing the fake cryptography configuration with the cryptography configuration retrieved from the area  5 . 
     Various alternate methods can be designed. For instance, steps  112  to  122  can be replaced by the following steps: 
     At step  200 , a chip authentication is carried out based on ephemeral-static Diffie-Hellman key agreement protocol (DH or ECDH) that provides secure communication and implicit unilateral authentication of the chip. 
     At step  202 , in the context of the EAC v1.11 specification, a passive authentication of the Security Object file can be carried out. 
     At step  204 , the chip  2  allows the access by terminal  81  to its various data groups. 
     Steps  112  to  122  can also be replaced by the following steps: 
     At step  300 , a chip authentication is carried out based on ephemeral-static Diffie-Hellman key agreement protocol (DH or ECDH). 
     At step  302 , in the context of the EAC v1.11 specification, a passive authentication of the Security Object file can be carried out. 
     At step  304 , chip  2  can performs a terminal authentication. 
     At step  306 , the chip  2  has authenticated terminal  81 . It thus allows the access by terminal  81  to biometric data stored in area  23 . 
     At step  308 , the biometric data retrieved by terminal  81  can be used to perform an additional security check on the card bearer. 
     Such a method is particularly suitable to enhance the ICAO EAC v1.11 specification relating to authenticity checking of electronic passports. Indeed, the authenticity of the cryptographic configuration of chip  2  can be checked at a very early stage. Thus, the secure communication channel is established based on a reliable cryptographic configuration. Moreover, this method is not in contravention with the requirements recited in this specification. For instance, chip authentication steps can take place before terminal authentication steps. 
     Such a method notably allows avoiding carrying out a terminal authentication before the authenticity of the chip cryptography configuration is checked. Such a terminal authentication has been proposed for standardization to guarantee the confidentiality of the chip  2 . However, such a method had the major drawback of being incompatible with the requirements of the ICAO EAC v1.11 specification. 
     This method can be applied to other identity documents for which the inclusion of a RFID chip is foreseen, like driving licenses, resident permits or national insurance cards.
The invention relates to a secured identity document having an externally readable chip storing a cryptographic configuration of the chip, defining the cryptographic security levels supported by the chip, for establishing a secure communication with a controlling terminal, storing a private key of a cryptography key pair and adapted to cipher data based on the stored private key; a support to which the chip is fastened, the support having a machine optically readable area, the data encoded in this area including the cryptographic configuration of the chip for establishing a secure communication with a controlling terminal in non ciphered form and the cryptographic configuration of the chip ciphered based on said private key.