WO2006082298A1

WO2006082298A1 - Implementing a remote cryptographic operation of a public key infrastructure (pki)

Info

Publication number: WO2006082298A1
Application number: PCT/FR2006/000191
Authority: WO
Inventors: Loïc HOUSSIER; Laurent Frisch; Julie Loc'h
Original assignee: France Telecom
Priority date: 2005-02-03
Filing date: 2006-01-27
Publication date: 2006-08-10
Also published as: FR2881591A1

Abstract

The invention concerns a cryptographic method including the following steps: a private key (12) of a certification authority (6) of a public key infrastructure managing public keys (3) is associated with a physical person (14) stored on a portable digital device; the physical person (14) moves to a user with his portable digital device; a cryptographic operation is performed on data supplied by the user to the portable digital device; data associated with the performed cryptographic operation are written into at least one database (7, 8, 13) connected to said infrastructure. The invention allows in particular a user unconnected to a public key infrastructure (3) to obtain the performance of a cryptographic operation with the private key of a certification authority of said infrastructure.

Description

Implementation of a remote cryptographic operation of a PKI

The invention relates to public key management infrastructures and in particular the implementation of public key cryptography operations, such as the signing of a digital certificate.

A digital certificate is notably intended to guarantee to a user that a public key which has been transmitted to him does not come from an impostor. A digital certificate standard for use on the Internet is defined in the X.509v3 standard. This certificate includes the certified public key, its validity period, the identity of its owner, a list of attributes defining its rights of use (message signature key, secure web server key ...) and a signature cryptographic of this data by the private key of the certification authority.

Figure 1 illustrates an example of public key infrastructure. A user 1 has a private key 9 and a public key 10 and wishes to obtain a digital certificate in order to guarantee to a user 2 that he is indeed the owner of the key 10.

A public key management infrastructure 3 manages the creation of certificates as well as their life (revocation, renewal, etc.). From an organizational point of view, a public key management infrastructure comprises three logical entities: a registration authority 4, a certification operator 5 and a certification authority 6. A key management infrastructure can interact in particular with a publication directory 7 or a certificate database 8.

The functions of these entities are as follows:

the local registration authority 4 collects requests from users wishing to obtain a certificate. Authority 4 formally checks the validity of these requests;

the certification operator 5 processes the certification request and issues certificates by applying the procedures defined by the certification authority 6. The operator 5 generally publishes the certificates in the directory 7 or makes these certificates available in the database 8; the certification authority 6 is a moral authority in the name of which the certificates are issued. Authority 6 establishes and verifies the application of certificate generation procedures. Authority 6 is generally located on a server accessible by a computer network.

User 1 obtains a certificate according to the following process: -user 1 transmits a request to the registration authority 4. This request contains his public key 10 and other information concerning him (name, email address, etc.);

-the registration authority 4 collects the request and formally checks its validity. The registration authority 4 records the information on the identity of the user 1 in the database 8;

the certification operator 5 recovers the private key of the certification authority 6, the public key 10 and the information provided by the user 1. The certification operator 5 then creates the certificate by signing the data provided by the user 1 with the private key of the certification authority 6. The certification operator 5 then transmits the certificate to user 1 or to the database 8, and optionally publishes it on the directory 7.

Increasingly, requests from a user to obtain a certificate are made online, the user and the various entities of the infrastructure communicating via a computer network. With the multiplication of disruptions' of computer networks (computer virus, failure of an operating system, lack of bandwidth, physical cut in the communication medium ...) the user may find himself unable to obtain a key management infrastructure certificate. This problem is all the more acute as the different entities are most often formed of independent modules put in communication by a computer network.

In addition, there are machines voluntarily not connected in reception to the key management infrastructure for security reasons. The user of the machine is then unable to generate a certificate.

In addition, different certification authorities can be managed by different natural persons.

The invention aims to solve one or more of these drawbacks. The invention thus relates to a method for implementing a crypto graphic operation, comprising the following steps: ^" " - a private key of a certification authority of a public key management infrastructure is associated with a natural person, the private key being stored on a portable digital device;

the natural person moves with a user with his portable digital device disconnected from said infrastructure;

a cryptographic operation is carried out on data supplied by the user and includes cryptographic calculations carried out with the portable digital device memorizing the private key;

information associated with the cryptographic operation carried out is recorded in at least one database connected to said infrastructure.

A cryptographic operation can thus be performed on data supplied by a user not connected to the infrastructure, while keeping the database connected to the infrastructure up to date.

According to a variant, the natural person has a machine disconnected from the infrastructure and able to memorize said information associated with the cryptographic operation carried out and intended to be recorded in a database, and said information is transmitted by the machine to the infrastructure when reconnecting the machine to the infrastructure.

The user thus does not have to make a connection with the infrastructure for the updating of the infrastructure database to be carried out.

According to yet another variant, the infrastructure has a machine intended to remain disconnected upon reception of the infrastructure and having a local registration authority 25, and the natural person connects the portable digital device to the machine before the carrying out the cryptographic operation.

Thus, the crypto graphic operation can be carried out on a machine in a secure environment and the natural person provided with the portable digital device needs only a minimum of equipment. 0.

According to another variant, the information associated with the cryptographic operation is stored in the portable digital device and then recorded in the infrastructure database. Thus, the updating of the infrastructure database can be carried out by the natural person simply provided with the portable digital device.

The invention also relates to a device for transferring a public key management infrastructure to a database, comprising:

a module for generating a report containing the information associated with a cryptographic operation carried out with a private key of a certification authority of a public key infrastructure, the private key being associated with a natural person; - a connection module to the public key infrastructure; and

- a module for transmitting the report to the public key infrastructure. This device makes it possible to update the infrastructure database following a cryptographic operation carried out with a machine disconnected from this infrastructure.

The invention also relates to a system intended to carry out a cryptographic operation, comprising:

-a portable digital device including:

a memory storing said private key; -a data reception interface on which cryptographic calculations must be carried out;

a calculation module capable of performing cryptographic calculations with said private key on the data supplied; a transfer device as described above, capable of communicating with the calculation module of the portable digital device.

The system makes it possible to perform the cryptographic operation on data supplied by a user not connected to the infrastructure, while keeping the database connected to the infrastructure up to date.

According to a variant, the transfer device is included in a machine capable of being connected to the portable digital device, the machine further including a module for shaping the cryptographic calculations performed by the portable digital device. Such a system allows to realize: ⁵ the cryptographic operation, to format the result of the calculation and update the database.

According to another variant, the portable digital device stores several private keys associated with separate respective certification authorities.

The same natural person may thus participate in the performance of cryptographic operations for several separate certification authorities. It is therefore not necessary to contact a different person for each different certification authority.

The invention also relates to an infrastructure for managing public key keys, comprising at least one database of information associated with cryptographic operations, and an update module, capable of receiving an operation report. cryptographic and update the database from a report received.

The cryptographic information database can thus be updated even when the infrastructure has not performed an associated cryptographic operation. The flexibility of performing crypto graphic operations does not therefore affect the updating of the database.

Other characteristics and advantages of the invention will emerge clearly from the description which is given below, for information and in no way limitative, with reference to the appended drawings, in which:

FIG. 1 illustrates the structure of an example of certification infrastructure; FIG. 2 illustrates a certification process according to the invention;

FIG. 3 illustrates a method carrying out cryptographic operations during a failure of a key management infrastructure.

The invention proposes to associate the private key of a certification authority of a public key infrastructure with a natural person provided with a portable digital device. The natural person makes himself available to a user who does not have a connection to the T key management infrastructure (IGC) network. A cryptographic operation is carried out with the private key stored in the digital device. ITGC databases are updated retrospectively with information concerning the cryptographic operation.

FIG. 2 illustrates a method of generating certificates on a machine 18 deliberately not having a reception connection with a key management infrastructure. A natural person 14 is associated with a certification authority 6 of an unrepresented key management infrastructure. The natural person 14 has a portable digital device capable of being connected to the machine 18.

The private key 12 of the authority 6 is stored on the portable digital device. The portable digital device stores and is capable of executing a cryptographic application using the key 12.

The machine 18 has cryptographic tools intended to format the certificate to be issued. The machine has a local registration authority. These various functionalities are for example produced by applications installed on the machine 18. The machine 18 therefore has a cryptographic module which makes it possible to generate certificates which can be signed by the key 12.

The machine 18 transmits a request to the natural person 14, so that this natural person makes available his portable digital device.

The portable digital device is for example a portable computer or a removable digital medium such as a USB key or a smart card. The natural person 14 then moves to connect his portable digital device to the machine 18. The machine 18 then has the private key of the certification authority 12. The machine 18 and the digital device then generate the digital certificates C1 to Cn signed with the private key 12. An infrastructure database 3 is then updated by any appropriate means. The information associated with the generation of certificates can thus be stored on the portable digital device before being transferred to the databases of infrastructure 3. This information can be transferred to the databases of infrastructure 3 by a connection (which can be limited to transmission) from the machine 18.

FIG. 3 illustrates a cryptographic operation of a certification authority 6 and the updating of the databases of its key management infrastructure 3. The natural person associated with the authority ⁷ I certification 6 has a portable digital device (for example a removable digital medium such as a USB key). This portable digital device contains at least the private key 12 of the certification authority 6 (but may also contain the certificate for example), and may contain a calculation module capable of performing cryptographic calculations using the key 12.

The portable digital device is connected to a machine 21 having a module for implementing cryptographic operations 15 and a module 16 for transferring information to the databases associated with the cryptographic operations. This machine 21 is for example a laptop computer of the natural person 14. A machine of a user 1 cannot connect to the infrastructure for managing keys 3 due to network problems leading to the unavailability of the link 22. The user therefore cannot request a cryptographic operation (such as a certificate request) from the key management infrastructure.

During step 31, the natural person 14 moves with the user 1 and takes his portable digital device. After the connection of the portable digital device to the machine 21, the module 15 processes a request for carrying out a cryptographic operation. The data entry on which the cryptographic operation must be carried out can be carried out by a local machine registration authority 21. The registration can be supervised by the natural person 14 by verifying the data supplied by the user 1 or be performed independently by user 1.

During step 32, in the case of the issue of a certificate; the module 15 generates a pair of keys (if this has not been done before), builds the corresponding certificate (with the recipient's data). This certificate is then signed with the private key 12. The module 15 also generates a set of information associated with the cryptographic operation carried out. This information is intended to be stored in the databases of the key management infrastructure 3 and may in particular include the type of cryptographic operation carried out, the serial number of a digital certificate, the beneficiary of a digital certificate. , the digital certificate signed, the certification authority whose private key was used, notifications or archiving of requests or a revocation date for a digital certificate. The crypto graphic result (in this case a certificate and its private key) is supplied to user 1. This mechanism remains valid for any other cryptographic operation requiring the signing of a CA, for example the signing of a CRL (Acronym for the English word Certificate Revocation List) and its publication.

Steps 31 and 32 can be implemented to process batches of requests. A batch of requests can in particular be in the form of a file containing several requests to be processed sequentially.

During step 33, the private key 12 can be made available to the key management infrastructure 3 if it had been extracted from the IGC (we can imagine the most probable cases where only a copy of the key is located on the portable device). This provision is made for example by connecting a host laptop computer or the portable digital device to the key management infrastructure 3. When machines can again connect to infrastructure 3, this infrastructure is again available to perform cryptographic operations. The natural person 14 can then no longer carry out cryptographic operations locally with the private key 12 of the authority 6, the portable digital device memorizing this key 12 being used by the infrastructure 3.

In step 34, the information associated with the cryptographic operation carried out is transmitted by the module 15 to the transfer module 16. The transfer module 16 consists for example of an application stored in the machine 21. It is also possible to envisage that the module 16 is placed on an apparatus independent of the machine 21. The natural person 14 then puts the module 16 into communication with an update module 17 of the databases connected to the infrastructure 3. The module 17 registers the information communicated by module 16 in the infrastructure databases 3. The generated certificates are for example published in the publication directory 7 and stored in the certificate database 8. Thus, the databases of the infrastructure 3 have all the data associated with the cryptography operation, as if the cryptography operations had been carried out by infrastructure 3. In order to improve the level of security registration of information, registration of information in the database may be subject to entry of a personal identification code by the associated natural person.

The module 17 can also carry out a verification of the information to be entered. The module 17 can for example verify the signature of the certificate with the key public of the AC 6. The inscriptions deformations in the infrastructure are thus better secured.

The natural person 14 is responsible for the portable digital device. This person is therefore responsible for the cryptographic operations carried out with the private key 12 of this certification authority 6. In order to increase the level of security, a personal identification code may be required from the holder of the portable digital device during connection. from the digital device to the machine 18 or 21.

We can also consider associating a certification authority and its private key with several individuals each having a copy. The defection of a natural person is then not detrimental to the performance of cryptographic operations.

In order to guarantee a high level of security without requiring the presence of all natural persons, it is also possible to provide a private key shared between a number n of natural persons and reconstitutable only in the presence of at least p natural persons among the N.

Claims

REVEio DICATIONS

1. Method for implementing a cryptographic operation, characterized in that it comprises the following steps: a private key (12) of a certification authority (6) of a key-to-key management infrastructure public (3) is associated with a natural person (14), the private key being stored on a portable digital device; the natural person (14) moves with a user with his portable digital device disconnected from said infrastructure; a cryptographic operation is carried out on data supplied by the user and includes cryptographic calculations carried out with the portable digital device memorizing the private key;

information associated with the crypto graphic operation carried out is entered in at least one database (7, 8, 13) connected to said infrastructure.

2. Method according to claim 1, in which:

the natural person (14) has a machine (21) disconnected from the infrastructure (3) and able to memorize said information associated with the crypto graphic operation carried out and intended to be recorded in a database;

said information is transmitted by the machine (21) to the infrastructure (3) upon reconnection of the machine to the infrastructure.

3. Method according to claim 1, in which: the infrastructure has a machine (18) intended to remain disconnected when receiving the infrastructure (3) and having a local registration authority;

the natural person (14) connects the portable digital device to the machine (18) before carrying out the cryptographic operation.

4. The method of claim 3, wherein the information associated with the cryptographic operation is stored in the portable digital device and then entered in the database (7, 8, 13) of the infrastructure.

5. Device for transferring to a database (7, 8 and 13) a public key management infrastructure, characterized in that it comprises:

a module (15) for generating a report containing the information associated with a cryptographic operation carried out with a private key (12) of a certification authority of a public key infrastructure (3), the private key being associated with a natural person; a module (16) for connection to the public key infrastructure; and a module (16) for transmitting the report to the public key infrastructure.

6. System intended to carry out a cryptographic operation, characterized in that it comprises:

a portable digital device comprising: a memory storing said private key (12);

-a data reception interface on which cryptographic calculations must be carried out;

a calculation module capable of performing cryptographic calculations with said private key on the data supplied; a transfer device according to claim 5, capable of communicating with the calculation module of the portable digital device.

7. The system of claim 6, wherein the transfer device is included in a machine (21) capable of being connected to the portable digital device, the machine further including a formatting module (15) of the cryptographic calculations performed. by the portable digital device.

8. System according to claim 6 or 7, characterized in that the portable digital device stores several private keys associated with respective respective certification authorities.

9. Public key management infrastructure (3), characterized in that it comprises: at least one database of information associated with cryptographic operations (7, 8, 13);

an update module (17) capable of receiving a cryptographic operation report and of updating the database from a report received.