WO2003044639A2

WO2003044639A2 - Method and device for processing digital signatures

Info

Publication number: WO2003044639A2
Application number: PCT/FR2002/003977
Authority: WO
Inventors: Daniel Bois; Laurent Gauteron; Jean-Luc Giraud
Original assignee: Gemplus
Priority date: 2001-11-20
Filing date: 2002-11-20
Publication date: 2003-05-30
Also published as: WO2003044639A3; FR2832522B1; AU2002356250A1; FR2832522A1

Abstract

The invention concerns a secure device for signature processing (10) interposed between a computerized device for storing documents (1), such as a computer, a PDA or a telephone for example, and a so-called peripheral device (5) such as a display screen, a printer, which is used to display to a user the content of the document whereof the digital signature is to be processed. In that configuration, the secure device (10) controls the peripheral in a signature processing mode, during which the non-secure storage device is not involved. Said device (10) further contains a digital port, a cryptographic unit, a video converter, an input and a display output.

Description

Method and device for processing digital signatures

The invention relates to a secure method and device for producing digital signatures and verifying digital signatures. It is particularly suitable for environments that are not secure by nature, including for example computers, Internet links, etc. In particular, the invention guarantees that a document viewed and read on a screen or presented to a user by any other device called " peripheral "such as a printer, a speaker, ..., corresponds well to the document which is or will be signed. We will then use the term “processing” of digital signatures to signify the creation or verification of such a signature and we will understand by document any data set in the broad sense: it can be a text, data sound or any other type of data that a user may have an interest in signing to signify his agreement.

With the development of electronic commerce and electronic exchanges in general, the development of the digital signature becomes necessary. A legal framework is already in place to recognize the digital signature as a means of proof. In these conditions, it is important to consider the technical means to generate reliable digital signatures. The prior art is based on cryptographic techniques to generate digital signatures. A prior art device, which uses an RSA algorithm in a personal computer environment, is shown in Figure 1. The computer personnel (PC) 1 contains software which manages the production of digital signatures as well as the public key necessary for the cryptographic algorithm. To ensure the security of the process, it is connected to a cryptographic signature unit 3, which mainly comprises a microcontroller, and which performs the signature: this unit in particular ensures that the private key used by the cryptographic signature algorithm remains inaccessible. With a view to signing a document, the PC management software sends the document to be signed to screen 5 to present it to view 6 of the user by a conventional VGA connection connecting the input 4 and output 4 connectors. '' of the screen and the PC respectively. Then the user after reading gives his agreement on the PC: the document is then reduced by a hashing algorithm executed on the PC. The result of this calculation is sent to the cryptographic unit 3 via a digital link between the digital ports 2 of the PC 1 and the cryptographic unit 3. The latter contains the private key and the signature algorithm. with which she transforms the hashed document into a signed hash. Generally, the cryptographic unit uses a smart card for security reasons. Another equivalent device is to provide a PC with an integrated card reader. Then, to check the validity of a signature, the signed hashed document, the hashed document, and the public key are sent to the cryptographic unit 3 which verifies by a new calculation using the public key that the signature is valid. We will not go into detail on the signature calculation or signature verification, which can be carried out by various signature algorithms (symmetric cryptography or asymmetrical for example) suitably. Our invention does not relate to this calculation as such.

The disadvantage of these solutions of the prior art comes from the fact that part of the method relies on a PC 1 or another computer document storage device, which is not by nature a secure device since it is open. to the outside world by various means of communication such as the Internet for example. In fact, attacks using Trojans that hide a malicious program on these devices are possible. Such a program can for example modify the data of the document that the user wishes to sign between the moment when he views them and the moment when the signature is generated. These solutions are therefore not reliable.

A first object of the present invention consists in defining a method and its associated device for carrying out the digital signature of documents in a reliable manner.

A second object of the present invention consists in proposing a relatively simple and inexpensive solution.

A third object of the present invention is to provide a solution compatible with existing computer devices, in particular PCs, screens, printers, means of communication ...

The invention is based on a secure digital signature processing device comprising a cryptographic unit for processing the digital signature of a document originating from a computer type computer device, characterized in that it comprises means for selecting an operating mode. and display means for presenting said document to a user on a device beyond the influence of the computing device in a signature processing mode.

The signature processing device may include means for enabling direct connection between a computing device and a peripheral in a transparent mode of operation. It may include an indicator so as to indicate to a user the current operating mode of said device.

It can have a digital port for exchanging a document whose signature is to be processed with a computer device. Advantageously, it is suitable for processing the signature of a document exchanged with a computer device in an interpreted format and contains an interpreter to allow the translation of the document before its display by a video converter. It may further comprise a user-friendly means for controlling the display of a document in a signature processing mode.

In one particular mode, it has a card reader of the smart card type, said card comprising an interpreter and / or a cryptographic unit. Provision may be made for a means such as a button for switching from transparent mode to signature processing mode as well as means for identifying the user. The invention is also based on a method of producing a digital signature characterized by the following steps:

- a document to be signed is sent from a computer device to a secure device for signature processing as presented above; the signature processing device switches from a transparent mode to a signature processing mode during which it presents the document to a user on a peripheral device outside the influence of the computing device; the user triggers the signature of the document which is carried out within the cryptographic unit of said signature processing device; It is possible to add the following step before the previous ones: - the computing device is connected to a peripheral by means of the signature processing device in a transparent mode; In addition, the method provides for the transmission of the document to the signature processing device in the form of a digital signal in an interpreted format and the transformation of the signal by an interpreter before being presented to the user on an output device. . Likewise, the invention is based on a digital signature verification method characterized in that it comprises the following steps:

- A document whose signature is to be verified as well as his signature are sent from a computer device to a secure signature processing device as described above; the signature processing device switches from a transparent mode to a signature processing mode during which it presents the document to a user on a peripheral device outside the influence of the computing device; the cryptographic unit of the signature processing device verifies the signature of the document. In this method, transmission of the document to the signature processing device can be in the form of a digital signal in an interpreted format and the signal can be transformed by an interpreter in order to be presented to the user.

Other characteristics and advantages of the present invention will appear on reading the following description of particular embodiments, given by way of illustration and not limitation, and of the appended drawings in which:

- Figure 1 shows an electronic signature device of the prior art;

- Figure 2 shows a first embodiment of an electronic signature device according to the present invention, -

- Figure 3 shows a second embodiment of an electronic signature device according to the present invention.

In these different figures, the same references are used to designate the same elements. Figure 1 has been described above. The principle of the invention, as we will see, consists in inserting a secure signature processing device 10 between a computer document storage device (1), such as a computer, a PDA or a telephone for example, and a so-called "peripheral" device such as a screen, printer, etc., the function of which is to present the content of documents to a user. In this configuration, the secure device 10 controls the peripheral in a signature processing mode, during which the non-secure storage device does not intervene.

FIG. 2 represents a first embodiment of the invention in which a device 10 is inserted between a PC 1 and a screen 5. A digital link between the device 10 and the PC 1 is established via their ports 2 respective: this link is for example of the USB or network type. The device 10 further comprises an input 4 and an output 4 'of analog type, for the purpose of exchanging analog signals, of VGA type. It also contains an analog / digital converter 11 and a video converter 12, the functions of which are described below. A cryptographic unit 3 similar to that of the prior art processes the digital signature. The microcontroller of this unit also manages the operation of the entire device and in particular, using a s itch 13 and a switch 16 establishes a means of selecting an operating mode from two modes. An indicator is provided (not shown), for example an LED, to indicate to the user the currently selected operating mode. In a first transparent mode, the secure signature device 10 is inactive. The input 4 and its output 4 'are connected directly to each other by means of the switch 13 in a first position and of the switch in the closed position. A conventional VGA link is thus established between the PC 1 and the screen 5. In a second mode, it makes it possible to process the document signature.

To describe the first case of making a signature, we consider a small document, which can be viewed as a whole at the same time on screen 5. After viewing the document in the first transparent mode described below above, a user 6 will indicate his wish to sign the document by pressing the key 14 of the device 10. The device 10 then stores the corresponding signal then opens the switch 16 to cut the device 10 of the PC 1. The device continues to display the corresponding image by its video converter 12, which in particular comprises a processor and a digital / analog converter so as to manage a display. After re-reading the document, the user will sign the document by pressing the button 15. Before this signature, we can ask him to identify himself by any known means (not shown) such as entering a PIN code , biometric data capture ... The document, transformed from its analog form into a digital signal, in bitmap format, by the converter 11 before being communicated to the cryptographic unit 3, is signed in a manner similar to art prior. The signed document and the bitmap used are then returned to PC 1. In the second case of signature verification, we consider the same previous document, signed, for which the user wishes to verify the validity of the signature. The PC contains the bitmap document as well as its signature, a term improperly used to designate the hashed and signed document according to the method described above. The user will indicate his wish to verify the signature of the document by pressing the 1 key. the signature and the bitmap document are transmitted to the cryptographic unit 3 by the digital link (via port 2). The signature is verified according to the method of the prior art. In parallel, the document is displayed on the screen 5 via the video converter 12 and then its 4 'output, the switch 13 being in the second position. The user can therefore view the document which is signed on the screen, while being sure that what he reads corresponds to what is signed.

FIG. 3 represents a second embodiment of the invention. This embodiment is more particularly suitable for signing large documents. The processing of these documents poses a first problem of transfer time to the security device 10 since the data corresponding to images can be very large. Then, a second problem arises when signing these documents by the fact that only a small part can be viewed at a given instant on the screen 5. The previous embodiment is suitable for processing these documents by a "screen by screen" processing: the signals corresponding to a screen are sent to the device 10, presented on the screen 5, signed and then returned to the PC before then allowing similar signature of the following data corresponding to a new screen. The second embodiment seeks to improve the user-friendliness of this treatment. For this, the device 10 includes some differences compared to the device of the previous embodiment. Mainly, it has only one way to allow data entry from the outside to its cryptographic unit 3 through its port 2. It also includes an interpreter 17 whose function is to transform digital data from the 'cryptographic unit 3 in a bitmap format capable of being displayed on the screen 5 by the video converter 12. In the first transparent operating mode, the switch 13 is in a first position which directly connects the connectors 4 and 4' of the device 10. A conventional VGA link between the personal computer 1 and the screen 5 is then produced. We add that to manage the signature processing, a new driver is planned within the PC which offers the menus of "signature" and "signature verification" to the user. The processing of the signature is thus managed on the PC in a similar way to the processing of a print for example.

The method of processing the signature embodiment of the device 10 will now be described.

In the first case of signing a document, the user 6 wishing to sign a document chooses a "signature" option on his PC. The signature driver will then transform the document into a predetermined digital format, chosen for its universal character as well as for the small space memory it uses: for example, postscript, PCL, Windows Meta File (WMF), PDF formats may be suitable, bitmap format is not suitable because it requires too much memory space. The term "interpreted format" will be used to determine this set of possible formats having the qualities described above. Then, this transformed document is sent to the cryptographic unit 3. By this digital transmission, the entire document is transmitted to the device 10. Thanks to the interpreted format, this transmission is rapid. Then the switch 13 then switches to its second position and the device 10 takes control of the screen 5. It is then in its second operating mode called "signature processing mode". The display of the entire document on the screen 5 is then managed by the device 10 via the interpreter 17 and the video converter 12. Means are provided within the device 10 (not shown) to allow the user of user-friendly display commands such as scrolling through the document to facilitate re-reading, for example. This embodiment offers this possibility in particular by the fact that the device 10 has the entire document. The user will then trigger the signature by pressing the key 15. The realization of the signature then proceeds as before. This embodiment is suitable for signing the document as a whole as for signing the document in pieces, page by page for example.

In the second signature verification case, the document is sent to the device 10 by the signature driver in the same way as for the signature. Of moreover, the corresponding signature (the signed hashed document) is also transmitted to the device 10. The latter performs, on the one hand, the usual calculations for verifying the signature and, on the other hand, displays the content of the signed document for verification by the user. . The result of the verification can be displayed on screen 5 or be indicated to the user by means of a red / green indicator.

This second embodiment therefore offers a user-friendly solution adapted to the processing of the signature of large documents since it allows on the one hand a user-friendly visualization of the document and on the other hand rapid data exchanges between the PC and the device. It can therefore be seen that the invention provides a reliable solution for processing the signature, which guarantees the user the accuracy of the content of the document which he is handling and which is signed. This content is presented via a peripheral such as a screen 5, a printer 20 for a paper output or a loudspeaker (not shown) for the sound data. It is noted that the transparent mode described in the modes of embodiment consists in interposing the device between a computer and a screen, so that the connectors 4 and 4 ′ are connectors for “screen” signals. The same inventive concept can be reproduced with any other combination of computing device and output device.

The solution requires little or no change to PCs and peripherals, and is based on a simple and inexpensive device.

Finally, this solution easily adapts to any computer / screen assembly of the prior art, or to any other similar device. The document to be processed can pass through a PDA, a telephone, etc.

Several sub-variant embodiments may be of interest: the use of a smart card within the device 10 to fulfill certain functions requiring great security such as the storage of the private key and / or the execution of the algorithm signing and / or checking the display, including for example the interpreter, can bring great benefits, not only in terms of security but also in terms of flexibility of use; indeed, by a simple change of card, the device can allow several users to sign one or more documents (each inserts their personal card), the device can become compatible with several PCs which would not have opted for the same driver signature (insert the card containing the correct interpreter) ... -The device 10 can be provided with a device test program, which sends specific data to the latter, to verify that it does not have a abnormal behavior.

The same device can be easily adapted to digital screens by a person skilled in the art: in fact, in this context, the device 10 is simplified since there is in particular no longer any need to provide analog / digital converters. The connectors 4 and 4 'are in this case digital ports for "digital screen".

-We can provide that the user gives the green light for a signature after identifying himself by entering a PIN code or biometric data, either by a sensor on the device 10 or by a sensor located directly on a smart card.

-Wired links have been used in the preferred embodiments but one can imagine the use of contactless cards and / or devices communicating by contactless means, of the radio frequency type for example (bluetooth, 802.11 ...).

Claims

1. A method of producing a digital signature characterized in that it comprises the following steps: a document to be signed is sent from a computer device (1) to a secure signature processing device (10); - the signature processing device (10) switches from a transparent mode to a signature processing mode during which it presents the document to a user on a peripheral (5, 20) without any influence from the computing device (1 ); the user triggers the signature of the document which is carried out within the cryptographic unit (3) of the signature processing device (10);

2. Method according to claim 1 characterized in that the first step is preceded by the following step: the computer device (1) is connected to a peripheral (5) via the signature processing device (10) in a transparent mode;

3. Method according to one of claims 1 or 2 characterized in that the transmission of the document to the signature processing device (10) takes place in the form of a digital signal in an interpreted format and in that the signal is transformed by an interpreter before being presented to the user.

4. A digital signature verification method characterized in that it comprises the following steps: a document whose signature is to be verified as well as its signature are sent from a computer device (1) to a secure signature processing device ( 10); - the signature processing device (10) switches from a transparent mode to a signature processing mode during which it presents the document to a user on a peripheral (5, 20) without any influence from the computing device (1 ); the cryptographic unit (3) of the signature processing device (10) verifies the signature of the document;

5. Method according to claim 4 characterized in that the transmission of the document to the signature processing device (10) takes place in the form of a digital signal in an interpreted format and in that the signal is transformed by an interpreter into to be presented to the user.