Abstract:
The method for archiving a document includes a step of encryption of the document with a symmetric key, a step of transmission of said encrypted document to an archiving operator, and a step of transmission of the symmetric encryption key of said document to an escrow operator distinct from the archiving operator. The method may also include a step of encrypting of the symmetric key with a key consisting of a dual key comprising asymmetric keys. Depending on whether it is applied to personal archiving or to document transmission, during the step of encryption with the asymmetric key, the asymmetric key is that of the user having transmitted said document or that of the recipient of the document.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national phase application under §371 of PCT/EP2010/053953, filed Mar. 25, 2010, which claims priority to French Patent Application No. 0901441, filed Mar. 26, 2009 and French Patent Application No. 0901442, filed Mar. 26, 2009 all of which are incorporated herein in their entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    Various embodiments of the present invention relate to a method and a device for encrypting a document, and in particular to the confidential or secret archiving of documents for subsequent retrieval by their legitimate owner and to the confidential transmission of documents to a recipient. 
         [0004]    2. Description of the Related Art 
         [0005]    Numerous encryption methods are known, based on symmetric keys or asymmetric dual keys (for example conforming to the public key infrastructure PKI). However, these encryption methods are not suitable for providing both a high level of security of the documents and a possibility of retrieval of the documents if the keys are lost (for example, in the case of decease of their owner or of a legal decision aimed at retrieving them). 
       BRIEF SUMMARY 
       [0006]    Various embodiments of the present invention aim to remedy these drawbacks. 
         [0007]    To this end, embodiments of the present invention disclose a method for archiving a document by a user comprising a step of encryption of the document with a symmetric key and a step of transmission of said encrypted document to an archiving operator; a step of transmission of the symmetric encryption key of said document to an escrow operator distinct from the archiving operator; and a step of encryption of the symmetric key with a key having a dual key comprising asymmetric keys. 
         [0008]    Advantageously, an embodiment method comprises a step of generation of said symmetric key for each document to be encrypted. 
         [0009]    Advantageously, said symmetric key can be different for each document to be encrypted. 
         [0010]    Advantageously, during the step of encryption with the asymmetric key, said asymmetric key can be the public key of the user having transmitted said document. 
         [0011]    Advantageously, during the step of encryption with the asymmetric key, said asymmetric key can be the public key of a user receiving the document. 
         [0012]    Advantageously, embodiment methods also comprise a step of deletion of the encrypted document and of retention of the symmetric key by the computer system performing the encryption steps. 
         [0013]    Advantageously, an embodiment method also comprises a step of transmission by the archiving operator to the user of the encrypted document, a step of transmission by the escrow operator to said user of the symmetric encryption key of the encrypted document and a step of decryption by said user of said encrypted document with said symmetric key. 
         [0014]    Advantageously, an embodiment method also comprises a step of transmission by the archiving operator to an authorized third party of the encrypted document, a step of transmission by the escrow operator to said authorized third party of the symmetric encryption key of the encrypted document and a step of decryption by said authorized third party of said encrypted document with said symmetric key. 
         [0015]    Embodiments of the invention also disclose a device for archiving a document by a user comprising a module configured to encrypt said document with a symmetric key, a module configured to transmit said encrypted document to an archiving operator, a module for transmitting the symmetric encryption key of said document to an escrow operator separate from the archiving operator, and a module for encrypting the symmetric key with a key having a dual key comprising asymmetric keys. 
         [0016]    Advantageously, an embodiment device further comprises a means for generating said symmetric key for each document to be encrypted. 
         [0017]    Advantageously, said symmetric key can be different for each document to be encrypted. 
         [0018]    Advantageously, an embodiment device further comprises a module configured to handle the transmission by the archiving operator to the user of the encrypted document, a module configured to handle the transmission by the escrow operator to said user of the symmetric encryption key of the encrypted document and a module configured to handle the decryption by said user of said encrypted document with said symmetric key. 
         [0019]    Advantageously, an embodiment device also comprises a module configured to handle the transmission by the archiving operator to an authorized third party of the encrypted document, a module configured to handle the transmission by the escrow operator to said authorized third party of the symmetric encryption key of the encrypted document and a module configured to handle the decryption by said authorized third party of said encrypted document with said symmetric key. 
         [0020]    The particular advantages, aims and features of this device can be similar to those of an embodiment method, as briefly explained hereinabove, so they will not be reviewed here. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Other advantages, aims and features of the present invention will become apparent from the following description, given as a non-limiting explanatory example, in light of the appended drawings in which: 
           [0022]      FIG. 1  schematically represents a first particular embodiment device suited to the case in which the sender is also the recipient of the processed document, 
           [0023]      FIG. 2  represents, in the form of a flow diagram, a first particular embodiment method for transmission of a document suited to the case in which the sender is also the recipient of the processed document and does not have a personal dual key, 
           [0024]      FIG. 3  schematically represents a second particular embodiment device suited to the case in which the sender and the recipient of the processed document are separate, 
           [0025]      FIG. 4  represents, in the form of a flow diagram, a third particular embodiment method for personal archiving of a document suited to the case in which neither the sender nor the recipient has a personal dual key, 
           [0026]      FIG. 5  represents, in the form of a flow diagram, a fourth embodiment method for transmission of a document suited to the case in which the sender is also the recipient and has a personal dual key, and 
           [0027]      FIG. 6  represents, in the form of a flow diagram, a fifth particular embodiment method for personal archiving of a document suited to the case in which the sender and the recipient have a personal dual key. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  shows a scheduling and certification agency/authority  105 , an escrow operator  110 , a transmission operator  120  and an archiving operator  145 . A first user, also hereinafter called a “sending” user, sets up a terminal  125  to interact with the agency  105 . 
         [0029]    The scheduling and certification agency/authority  105 , the escrow operator  110 , the transmission operator  120  and the archiving operator  145  generally set up servers (not represented) which communicate, with one another, via computer networks (not represented), for example the Internet. 
         [0030]    For each document archival or transmission, the use is made, in accordance with an embodiment of the present invention, of a symmetric key. This symmetric key is preferably assigned to the sending user for each document that he archives or transmits. 
         [0031]    As can be seen in  FIG. 2 , to perform an encrypted archiving of a document when the sender does not have a dual key, the terminal  125  transmits this document unencrypted, to the scheduling and certification agency  105 , during a step  205 . 
         [0032]    During a step  210 , the agency  105  generates a symmetric encryption key. As a variant, it is the terminal  125  of the sending user which supplies this symmetric encryption key to the agency  105 . 
         [0033]    Then, during a step  215 , the agency  105  transmits the document and the symmetric key to the escrow operator  110 . During a step  220 , the agency  105  transmits this symmetric key to the private management office (BPG) of the sending user. The private management office is a space made available to a user by a community application provider, in this case combined with the agency  105 , and protected at least by a user name and a password known only to this user. 
         [0034]    During a step  225 , the escrow operator  110  performs the encryption of the document with the symmetric key received during the step  215 . During a step  230 , the escrow operator  110  retains the symmetric key and transmits the document, encrypted with the symmetric key, to the archiving operator who performs a second encryption, with his/her own private key, of the document already encrypted with the symmetric key and retains the doubly-encrypted document. 
         [0035]    During a step  235 , the escrow operator returns to the agency  105  the encrypted document with the symmetric key and a summary list encryption justification, which justifies the carrying out of all the steps provided to handle the encryptions. 
         [0036]    During a step  240 , the agency  105  checks the encryption justification, destroys the unencrypted document and the symmetric key and has the unencrypted document retained by the receiving third party  110  destroyed. 
         [0037]    During a step  245 , the agency  105  performs a time-stamping of the encrypted document and of the encryption justification. 
         [0038]    During a step  250 , the agency  105  sends an acknowledgement of receipt and of time-stamped encryption certification to the escrow operator  110  and the escrow operator  110  retains this acknowledgement of receipt and of certification as well as the symmetric key of the sending user but destroys the encrypted document. 
         [0039]    During a step  255 , the agency  105  transmits the encrypted document to the transmission operator  120 . During a step  260 , the transmission operator  120  places the encrypted document in the correspondence current account of the sender. During a step  265 , the transmission operator  120  returns to the agency  105 , via the trusted third party  115 , a summary list justification of the placement of the encrypted document in the correspondence current account of the sender. This justification represents the correct completion of all the steps linked to the placement of the encrypted document in the correspondence current account of the sending user. 
         [0040]    During a step  270 , the agency  105  transmits to the transmission operator  120  a time-stamped transmission certificate. 
         [0041]    To reread the document, during a step  275 , the sender accesses the symmetric key and, during a step  280 , the sender decrypts the encrypted document. The steps  275  and  280  are possibly handled via the receiving third party with time-stamping and transmission at the agency  105  of a summary list decryption justification. 
         [0042]    If necessary, for example for legal instruction operations and/or on a rogatory commission, during a step  285 , the symmetric key retained by the escrow operator and the encrypted document retained by the archiving operator are transmitted to a third party who decrypts the encrypted document with this symmetric key. 
         [0043]    Thus, in the case of the personal archiving (the sender and the recipient of the document are the same) in which the sender does not have a dual key, the document is encrypted with a symmetric key assigned exclusively to this document. The symmetric key used to encrypt the document remains with the receiving third party and it is retained by the sender of the document in his/her private management office. 
         [0044]    The document encrypted by the symmetric key with the receiving third party is sent to the archiving third party (for example a trusted third party operator) who performs a second encryption with his/her private key for legal archiving. 
         [0045]    If the sender wants to decrypt and consult his/her document in clear, he can do so in his/her private management office, which is secured. Either he/she has retained, in this private management office, the symmetric key received during the step  220  and the encrypted document available in his/her correspondence current account and the decryption is done simply in his/her private management office, based on these two items. 
         [0046]    Or, the archiving third party sends the decrypted document with his/her public key but still encrypted with the symmetric key, to the community application provider which manages the private management office of the sender. Thus, the sender can decrypt the document, by performing a decryption with the symmetric key associated with this document, in his/her private management office. 
         [0047]    As a variant, the archiving third party sends the doubly-encrypted document to the community application provider. Thus, the sender can decrypt the document, by first performing a decryption with the public key of the trusted third party operator then with the symmetric key held in his/her office for this document decrypt the document. 
         [0048]    In case of a rogatory commission or a notarial procedure (decease, guardianship, etc.), it is always possible to ask the receiving third party to decrypt the document without the intervention of the sender of the document. In fact, as has been seen, the receiving third party has a symmetric key dedicated to the document which is sufficient to decrypt it. 
         [0049]      FIG. 3  shows a scheduling and certification agency/authority  105 , a escrow operator  110 , a transmission operator  120 , and an archiving operator  145 . A first user, also hereinafter called “sending” user, sets up a terminal  125  to interact with the agency  105 . A second user, also hereinafter called “recipient” user, sets up a terminal  130  to interact with the transmission operator  120 . 
         [0050]    It should be noted that, in  FIGS. 4 and 6 , it has been assumed that the sender and the recipient were linked to the same transmission operator and to the same agency. Should they be linked to different operators and agencies, the steps concerning the encrypted documents mentioned in these figures, for the transmission operator and for the agency, would be performed, in parallel and separately, by the two operators and two agencies concerned. 
         [0051]    As can be seen in  FIG. 4 , to perform an encrypted transmission of a document from a sender to a recipient, the terminal  125  transmits this document unencrypted, to the scheduling and certification agency  105 , during a step  305 . 
         [0052]    During a step  310 , the agency  105  generates two different symmetric encryption keys intended, respectively, for the sender and for the recipient. 
         [0053]    Then, during a step  315 , the agency  105  transmits the document and the symmetric keys to the escrow operator  110 . During a step  320 , the agency  105  transmits the symmetric key of the sender to the private management office “BPG” of the sending user and the symmetric key of the recipient sender to the private management office of the recipient. 
         [0054]    During a step  325 , the escrow operator  110  performs the encryptions of the document with each of the symmetric keys received during the step  315 . During a step  330 , the escrow operator  110  retains the symmetric keys and transmits the documents, encrypted with the symmetric keys, to the archiving operator who performs a second encryption, with his/her own private key, of the documents already encrypted with the symmetric keys and retains the doubly-encrypted documents. 
         [0055]    During a step  335 , the escrow operator returns to the agency  105  the documents encrypted with the symmetric keys and a summary list encryption justification, which justifies the carrying out of all of the steps provided to perform the encryptions. 
         [0056]    During a step  340 , the agency  105  checks the encryption justification, destroys the unencrypted document and the symmetric keys and has the unencrypted document retained by the receiving third party  110  destroyed. 
         [0057]    During a step  345 , the agency  105  performs a time-stamping of the encrypted document and of the encryption justification. 
         [0058]    During a step  350 , the agency  105  sends an acknowledgement of receipt and of time-stamped encryption certification to the escrow operator  110  and the escrow operator  110  retains this acknowledgement of receipt and of certification as well as the symmetric keys but destroys the encrypted documents. 
         [0059]    During a step  355 , the agency  105  transmits the encrypted documents to the transmission operator  120 . During a step  360 , the transmission operator  120  places the document encrypted with the symmetric key of the sender in the correspondence current account of the sender. During the step  360 , the transmission operator  120  also places the document encrypted with the symmetric key of the recipient in the correspondence current account of the recipient. During a step  365 , the transmission operator  120  returns to the agency  105 , via the trusted third party  115 , a summary list justification of the placement of the encrypted documents in correspondence current accounts. This justification represents the correct completion of all the steps linked to the placement of the encrypted documents in the correspondence current accounts. 
         [0060]    During a step  370 , the agency  105  transmits to the transmission operator  120  a time-stamped transmission certificate. 
         [0061]    To reread the document, during a step  375 , the sender accesses his/her symmetric key and decrypts the encrypted document. The step  375  is possibly carried out via the receiving third party with time-stamping and transmission to the agency  105  of a summary list decryption justification. 
         [0062]    To read the document, during a step  380 , the recipient accesses his/her symmetric key, via the receiving third party, and the encrypted document, and decrypts the encrypted document. At the end of this operation, a time-stamping and a transmission to the agency  105  of a summary list decryption justification are performed. 
         [0063]    If necessary, for example for legal instruction operations and/or on rogatory commission, during a step  385 , one of the symmetric keys retained by the escrow operator and the corresponding encrypted document retained by the archiving operator are transmitted to a third party who decrypts the encrypted document with the symmetric key. 
         [0064]    In a variant of the embodiment illustrated in  FIG. 4 , the two symmetric keys are identical. 
         [0065]    As can be seen in  FIG. 5 , to perform an encrypted archiving of a document when the sender has a dual key, the terminal  125  transmits this document unencrypted, to the scheduling and certification agency  105 , during a step  405 . 
         [0066]    During a step  410 , the agency  105  generates a symmetric encryption key. As a variant, it is the terminal  125  of the sending user which supplies this symmetric encryption key to the agency  105 . 
         [0067]    Then, during a step  415 , the agency  105  transmits the document, the symmetric key and the public key of the sender to the escrow operator  110 . During a step  420 , the agency  105  transmits this symmetric key to the private management office “BPG” of the sending user. 
         [0068]    During a step  425 , the escrow operator  110  performs the encryption of the document with the symmetric key received during the step  415  and the encryption of the symmetric key with the public key of the sender. During a step  430 , the escrow operator  110  retains the symmetric key and transmits the document, encrypted with the symmetric key and the symmetric key encrypted with the public key of the sender, to the archiving operator who performs a third encryption, with his/her own private key, of the document already encrypted with the symmetric key and of the symmetric key encrypted with the public key of the sender and retains the doubly-encrypted document and the doubly-encrypted key. 
         [0069]    During a step  435 , the escrow operator returns to the agency  105  the document encrypted with the symmetric key, the symmetric key encrypted with the public key of the sender and a summary list encryption justification which justifies the carrying out of all of the steps provided to perform the encryptions. 
         [0070]    During a step  440 , the agency  105  checks the encryption justification, destroys the unencrypted document and the symmetric key and has the unencrypted document retained by the receiving third party  110  destroyed. 
         [0071]    During a step  445 , the agency  105  performs a time-stamping of the encrypted document and of the encryption justification. 
         [0072]    During a step  450 , the agency  105  sends an acknowledgement of receipt and of time-stamped encryption certification to the escrow operator  110  and the escrow operator  110  retains this acknowledgement of receipt and of certification as well as the encrypted symmetric key of the sending user, but destroys the encrypted document and the unencrypted symmetric key. 
         [0073]    During a step  455 , the agency  105  transmits the encrypted document and the encrypted symmetric key to the transmission operator  120 . During a step  460 , the transmission operator  120  places the encrypted document and the encrypted symmetric key in the correspondence current account of the sender. During a step  465 , the transmission operator  120  returns to the agency  105 , via the trusted third party  115 , a summary list justification of the placement of the encrypted document and of the encrypted symmetric key in the correspondence current account of the sender. This justification represents the correct completion of all the steps linked to the placement of the encrypted document and of the encrypted symmetric key in the correspondence current account of the sending user. 
         [0074]    During a step  470 , the agency  105  transmits to the transmission operator  120  a time-stamped transmission certificate. 
         [0075]    To reread the document, during a step  475 , the sender accesses the encrypted symmetric key, decrypts it with his/her private key and, during a step  480 , the sender decrypts the encrypted document. The steps  475  and  480  are possibly carried out via the receiving third party with time-stamping and transmission to the agency  105  of a summary list decryption justification. 
         [0076]    If necessary, for example for legal instruction operations and/or on rogatory commission, during a step  485 , the encrypted symmetric key retained by the escrow operator, the encrypted document retained by the archiving operator and the private key retained by a trusted third party (not represented) are transmitted to a third party which decrypts the encrypted document with this symmetric key after having decrypted the symmetric key with the private key of the sender. 
         [0077]    In a variant, during the step  450 , the unencrypted symmetric key is retained by the escrow operator and, during the step  485 , the escrow operator transmits this unencrypted symmetric key to the third party responsible for the decryption. 
         [0078]    It will be noted that the sender can consult the document in two ways. 
         [0079]    Either he/she asks the archiving third party to upload to his/her private management office only the document encrypted with the symmetric key of which he/she holds the double in this same office. With the second symmetric key, he/she can read the encrypted document in his/her private management office. 
         [0080]    The sender can also ask the archiving third party to transfer to his/her workstation all of the document encrypted by the symmetric key, and the symmetric key encrypted by his/her public key. On receiving the batch of these two encrypted items, he/she begins by decrypting the symmetric key with his/her personal private key. Then, he/she uses the decrypted symmetric key to decrypt the encrypted document. 
         [0081]    There is also, for the Citizen Strong Box, another possibility which is to have the symmetric key retained by the escrow operator and not by the private management office of the sender. However, in this case, the sender cannot use his/her private management office to decrypt the document since he/she does not have the necessary symmetric key. However, he/she can ask for the encrypted document and the encrypted symmetric key to be transferred to his/her workstation to decrypt everything by first using his/her private key to decrypt the symmetric key used to decrypt the document. 
         [0082]    This option is preferably retained under the assumption that the member has a digital national identity card working with an electronic citizen strong box. 
         [0083]    As can be seen in  FIG. 6 , to perform an encrypted transmission of a document to a recipient, when the sender and the recipients have dual keys, the terminal  125  transmits the document unencrypted, to the scheduling and certification agency  105 , during a step  505 . 
         [0084]    During a step  510 , the agency  105  generates two symmetric encryption keys intended, respectively, for the sender and for the recipient. In a variant, it is the terminal  125  of the sending user which supplies these symmetric encryption keys to the agency  105 . 
         [0085]    Then, during a step  515 , the agency  105  transmits the document, the symmetric keys and the public keys of the sender and of the recipient to the escrow operator  110 . During a step  520 , the agency  105  transmits these symmetric keys to the private management offices “BPG”, respectively of the sender and of the recipient. 
         [0086]    During a step  525 , the escrow operator  110  performs the encryption of the document with each symmetric key received during the step  515  and the encryption of the symmetric keys with the public keys respectively of the sender and of the recipient. During a step  530 , the escrow operator  110  retains the symmetric keys and transmits the documents encrypted with the symmetric keys and the symmetric keys encrypted with the public keys of the sender and of the recipient, to the archiving operator who performs a third encryption, with his/her own private key, of the documents already encrypted with the symmetric keys and of the symmetric keys encrypted with the public keys and retains the doubly-encrypted documents and the doubly-encrypted keys. 
         [0087]    During a step  535 , the escrow operator returns to the agency  105  the documents encrypted with the symmetric keys, the symmetric keys encrypted with the public keys of the users and a summary list encryption justification which justifies the carrying out of all of the steps provided to perform the encryptions. 
         [0088]    During a step  540 , the agency  105  checks the encryption justification, destroys the unencrypted document and the symmetric keys. 
         [0089]    During a step  545 , the agency  105  performs a time-stamping of the encrypted documents and of the encryption justification. 
         [0090]    During a step  550 , the agency  105  sends a time-stamped acknowledgement of receipt and of encryption certification to the escrow operator  110  and the escrow operator  110  retains this acknowledgement of receipt and of certification but destroys the encrypted documents and the unencrypted symmetric keys. 
         [0091]    During a step  555 , the agency  105  transmits the encrypted documents and the encrypted symmetric keys to the transmission operator  120 . During a step  560 , the transmission operator  120  places the encrypted documents and the encrypted symmetric keys in the correspondence current accounts respectively of the sender and of the recipient. During a step  565 , the transmission operator  120  returns to the agency  105 , via the trusted third party  115 , a summary list justification of the placement of the encrypted documents and the encrypted symmetric keys in correspondence current accounts. 
         [0092]    During a step  570 , the agency  105  transmits to the transmission operator  120  a time-stamped transmission certificate. 
         [0093]    To reread the document, during a step  575 , the sender accesses his/her encrypted symmetric key, decrypts it with his/her private key and decrypts the encrypted document available in his/her correspondence account. The step  575  is possibly carried out via the receiving third party with time-stamping and transmission to the agency  105  of a summary list decryption justification. 
         [0094]    To read the document, during a step  580 , the sender accesses his/her encrypted symmetric key, decrypts it with his/her private key and decrypts the encrypted document available in his/her correspondence account. The step  580  is possibly carried out via the receiving third party with time-stamping and transmission to the agency  105  of a summary list decryption justification. 
         [0095]    If necessary, for example for legal instruction operations and/or on rogatory commission, during a step  585 , an encrypted symmetric key retained by the escrow operator, the corresponding encrypted document, retained by the archiving operator and the corresponding private key, retained by a trusted third party (not represented) are transmitted to a third party which decrypts the document encrypted with this symmetric key after having decrypted the symmetric key with the private key of one of the users. 
         [0096]    In a variant, during the step  550 , the unencrypted symmetric keys are retained by the escrow operator and, during the step  485 , the escrow operator transmits one of these unencrypted symmetric keys to the third party responsible for the decryption. 
         [0097]    It can be seen that embodiments of the present invention make it possible to create a personal document strong box for which the private key can be retained in an electronic identity card. The user can thus save copies of his/her identity papers, his/her diplomas, his/her insurance certificates, his/her payslips, his/her tax and social declarations, for example.