Method for digital signing of a message

ES 2 173 652 T5

DESCRIPTION

Procedure for the digital signature of a message.

The present invention refers to a method for digitally signing a message, as well as the devices necessary to carry out the method.

Digital signatures, also known as electronic signatures, are usually made with the help of so-called Public-Key procedures. To do this, the signer is assigned a pair of keys, one of which is a secret key and the other a public key. Using the secret key, a signature is generated using a mathematical procedure, while said signature can be verified with the corresponding public key. The secret key is exclusively under the control of the signer, so that no one can sign on behalf of the signer. On the contrary, the public key can be known, so that anyone can verify the signature. Normally, the secret key is protected by a personal identification name (PIN), so that to make a signature it is necessary to know the personal identification name and have the secret key.

Digital signatures can be generated on a computer, for example a PC, with the help of software programs. Generally, for this, the corresponding secret key is stored on a hard disk or floppy disk, and to carry out the signature it is loaded into main memory. In general, the secret key is saved by itself in encrypted form and is protected by an identifying name, which must be provided by the owner through the software at the time of signing. This ensures that only the owner of the secret key can use it when signing. Since no additional hardware is required, this procedure is inexpensive. However, there is a drawback that the user must trust the integrity of the signing software, and this is often not considered secure enough.

As an alternative to generating digital signatures on a computer, hardware-based procedures can be used. They use special devices for signing, where the rendering components and the keyboard are hardware-coupled with the signature components, so the connection cannot be influenced at all. In general, such devices are connected to the computer through a galvanic connection, for example a cable to the serial ports. These devices provide a representation component, which shows the message to be signed, and through its own keyboard, the so-called PINPad, through which the identification name that releases the key is entered. Normally, the secret key is not stored in the signing apparatus, but on a chip card, which can be inserted into the apparatus. The signature itself can be generated on the chip card (on chip cards provided with the cryptographic processor) or on the device. The hardware-based method forms a closed signature system, made up of display components, keyboard, reader device 2 and chip card.

Unlike software-based procedures, hardware-based procedures are considerably more secure, thus their costs are also higher. Therefore, the so-called mixed procedures are used as an alternative. In them, the secret key is usually stored on a chip card and is made available through a reader device. The rest of the tasks such as representation, introduction of the identification name and generation of the signature, are carried out totally or partially on the computer. To this end, it can be envisaged that the signing device, that is, the reader and the chip card, is used as a pure means of storing the secret key, while the representation, the introduction of the identification name and the generation of the signature, are obtained completely on the computer.

As an alternative, it can be envisaged that the representation and the introduction of the identification name are carried out through the computer, the signing apparatus being additionally used to save the secret key and also to generate the signature. Finally there is the variant that only the representation takes place on the computer. In this variant, the signing device has its own keyboard or is connected directly to the computer keyboard, through the software of said computer. The signature is generated in the signature apparatus. The more tasks that are avoided by the computer software, and the less the signing apparatus has to work, the more economical the procedure is.

Patent WO-96/32700 publishes a method by which a message generated on a mobile phone can be digitally signed and transmitted. Patent EP-0,689,316-A1 publishes a procedure and a system for identifying and verifying data in a communication network.

However, in all these embodiments there is fundamentally the problem that exactly the data that the user wants to sign must be signed. It is also necessary to exclude the possibility that, for example a virus alters the data while the rendering components are transmitted, for example to the screen, in the signing component, for example in the encryption processor. Likewise, you must be sure that a secret number (for example PIN), necessary to issue the signature, cannot be read from the keyboard by other programs and can reach third parties.

Furthermore, the maximum universal use of the possibility for the digital signature is comparatively limited by the little diffusion of the signing devices. In potential application fields of digital signatures, such as Internet banking, it is necessary to create an expensive infrastructure to spread the signing devices. In such a case, the installation of signing devices on the computer is also problematic. On the one hand, the devices must be physically connected to the computer, with which the serial ports of a PC are often already occupied. Alternative procedures for connecting signature devices to computers are also problematic, since at least the installation of software triggers and sometimes additional hardware is required. Also, often for all signing appliances software components must be installed that allow the application program to communicate with the signing appliance.

Another problem with the usual procedures for digitized signature resides in the fact that they depend on each location. Certain fields of application for the use of digital signatures, for example in Internet banking, do not

ES 2 173 652 T5 are location dependent due to public Internet terminals that exist everywhere. If these Internet banking applications were combined with the well-known site-dependent procedures, the site-independence of this field of application would be lost.

The fundamental technical problem with which the present invention is faced, has for its object to prepare a workable and place-independent procedure for the digital signature of messages, as well as the appropriate devices for it.

This technical problem is solved by the teachings contained in the main claim.

In relation to the present invention, the digital signature of a message is understood to be a process by which, through electronic routes, the will to send and the content of a message is confirmed. This happens by partially or totally encrypting the message to be signed or encrypting a cryptographic checksum of said message, in a message signed by means of a secret key using a mathematical procedure. In relation to the present invention, a signed message is understood to be both the message signed in its entirety or the signature itself. The signature is used to carry out a subsequent authentication of the user. In connection with the present invention, a signed message is also understood to be only the electronically generated signature of the message. In relation to the present invention, a message is understood to be any type of electronically reproducible information, such as, for example, numbers, letters, combinations of numbers, combinations of letters, graphs, tables, etc. In relation to the present invention, it is understood as an apparatus for signing a unit, by means of which a message can be signed, that is to say a secret key, a procedure to provide a mathematical key, possibilities of dialogue with the signer or user, and that in In certain cases, it presents the necessary interfaces and a transmission and reception device. Said unit can be composed of different elements, such as a chip card and a reader device or a chip card and a mobile phone. In relation to the present invention, a signing device is a component of the signing apparatus, which has the secret key and / or the method for forming the key and / or an interface for both or one of the aforementioned components.

Due to the particularly advantageous use of the invention in the telephone network for the transmission of the messages requiring signature to a signing apparatus, which in the preferred embodiment is in the form of a mobile telephone, it is possible from a conventional computer with connection to a respective message server, for example via e-Mail, transmitting messages to the signing device, without having to carry out installations or other changes on the computer.

In an advantageous embodiment, the invention provides a method of the aforementioned type, in which the message to be signed is transmitted from a sending device, also called a message source, for example a PC, to a receiving device, for example a server. of messages, to then send said message from the receiving device to a signing device arranged in the sending device, especially a mobile phone, then the message in question is signed on the mobile phone, and then it is returned to the receiving device as a signature, that is, as a signed message.

The invention also provides that an unsigned or signed message is sent from a message source to a receiving device, for example a message server. The receiving device then takes care of transferring the message to be signed to the signature apparatus, especially to the mobile telephone. This takes place either through existing documentation on the receiving device or through information, which is sent together with the message to be signed from the sending device to the receiving device. The translation from the signing apparatus, preferably from the mobile phone, to the message source need not be any broad translation, but a pure informational translation. The translation also consists of determining which signing device, and thus which user, must sign the received message in order to be signed. The mobile telephone used in the preferred embodiment of the invention is in an advantageous situation to present a message to be signed and, under the instructions of the user and preferably with the aid of a chip card, to sign it. The message signed in this way is transmitted to the receiving device and there, in certain cases, it is compared with the original and authenticated message. From the receiving device, the message is signed and, in certain cases, authenticated, is distributed to a recipient.

The invention also refers to a previously mentioned method in which, advantageously, it has been envisaged to use a Public-Key procedure for signing, in which the sending device works through a secret key transferred to it, while the receiving device it does so through public keys related to the secret key. This procedure has the advantage that the keys do not have to be transmitted.

In another advantageous embodiment, the invention refers to a previously mentioned method, in which the message to be signed or the message already signed, that is, for example, the signature between the receiving device and the signing device, are transmitted, especially by mobile phone, through the short message service SMS (Short Message Service). In a particularly advantageous embodiment, it can be provided that both the transmission of the message to be signed from the receiving device to the mobile phone, as well as the transmission of the signed message or the signature, are carried out from the mobile phone to the receiving device by means of the SMS. .

In another embodiment, the invention provides that the message to be signed is presented by means of an indicator system existing in a mobile telephone. This can take place on the screen normally found in mobile phones. In this way, simple texts can be presented without problems, such as bank transactions or even simple graphics.

Then, in this presentation provided in certain cases, the user gives, in a dialogue provided for this purpose, the respective instruction to perform the signature. In a particularly advantageous embodiment, the invention provides a method of the aforementioned type, in which the key necessary for signing is found on a smart card of the mobile phone, and said key is authorized by means of a secret number (hereinafter referred to as PIN). entered using a mobile phone keypad. Preferably with

ES 2 173 652 T5 the corresponding habitual programming of the mobile phone can be guaranteed that the PIN entered is only transferred to the chip card, without the possibility of being heard from outside.

In another alternative embodiment of the aforementioned method, according to the invention, it is foreseen that the secret key necessary for the signature is entered through a keyboard of the mobile telephone.

In another preferred embodiment of the invention, it is provided that in one of the aforementioned methods, the secret key is not only stored on the smart card of the mobile phone, but also where the message is signed. In this way it can be advantageously ensured that the secret key never leaves the smart card and can be used by unauthorized persons.

In another advantageous embodiment of the invention it is envisaged that the mobile telephone not only serves to sign the message, but also as a sender to transmit the signed message to the receiving device.

The invention also relates to devices for carrying out the aforementioned processes, in particular mobile telephones and smart cards.

In a particularly advantageous embodiment of the invention, a mobile telephone 4 is provided, comprising a keyboard, an indication system and a smart card device for reading and / or writing a smart card that can be inserted into the mobile phone, an apparatus being additionally provided to sign, suitable for example to communicate with a smart card according to the invention and / or to establish a signed message from a message to be signed. Preferably, the signing apparatus is linked to the keyboard for entering a secret key or a secret number.

In a particularly advantageous embodiment of the mobile telephone, it is provided that the signing device has a different software component compared to the software component of a conventional mobile telephone. This different software component, in an advantageous embodiment of the invention, serves to sign the message after dialoguing with the user. In another embodiment, the different software component of the signing apparatus, provided according to the invention, is preferably able to communicate with the smart card according to the invention to carry out the signature according to the invention. In a particularly advantageous embodiment of the invention, it is provided that the device of the signing apparatus can process algorithms that make it possible to display the message to be signed in the indication area of ​​the mobile telephone.

In a particularly advantageous mode, the present invention also presents an implementation system, according to which only the software components are modified with respect to the software components used in the conventional mode. No need to change hardware.

In another embodiment of the invention, it also refers to smart cards for mobile phones, especially for the aforementioned mobile phones, in which the smart card comprises a signature device, being able to store the user's secret key. Preferably, the chip card signing device has conditions to generate a signed message from a message received on the mobile phone, that is, from a message to be signed. In relation to the present invention, it is understood as a device for signing a chip card, that is, a device that stores the user's secret key, and, in an advantageous embodiment, also carries out the signature. However, the signature must not take place immediately on the chip card, but can also be done by means of a software and / or hardware component in the mobile phone.

Other preferred embodiments of the invention are indicated in the accompanying claims.

The invention is explained in more detail with the aid of the figures as well as the corresponding exemplary embodiments.

Figures show:

Figure 1 shows the process of the method according to the invention;

Figure 2 shows, schematically, the construction of a mobile telephone according to the invention; Y

Figure 3 is a schematic representation of a smart card according to the invention.

Figure 1 presents the sending device 1, which can be in the form of a PC, provided with a text editor or a home banking program, a message to be signed 3, a receiving device 5, in the form of a message server , a mobile phone 7, a message to be signed 9 and a recipient 11.

By means of a home banking program, contained in the sending device 1, a message to be signed 3 is sent, for example by e-Mail, to the receiving device 5. The receiving device 5 converts the received message to be signed 3 into a message, which can be sent to the mobile telephone 7, by means of the advantageous form of SMS, in particular via a mobile telephone network. The receiving device 5 provides the message to be signed 3 to the mobile phone 7, for example by means of information existing in the receiving device 5. It can also be envisaged that the association takes place by means of information that is transmitted by the sending device 1 together with the message. to sign 3. This information is usually the mobile phone number.

In the mobile phone 7 the received message 3 is presented in an indicator system 13. The exact way to proceed is explained in more detail in the description of figure 2. Once the message to be signed 3 has been shown in the indicator system 13, said The message to be signed 3 is signed by the user, and the signed message 9 is relayed to the receiving device 5 or also to another recipient. The transmission of the signed message 9 from the mobile phone 7 to the receiving device 5 is also done via SMS. The receiving device 5 can compare the signed message 9 with the original message to be signed 3 and then transmit it to a recipient 11. Transmission to the recipient 11 can be carried out by any desired means.

Figure 2 represents a mobile phone 7. The mobile phone comprises an indicating system 13, a sending and receiving device 15, a smart card device 17, a keyboard 19 and a signing apparatus 21.

The message to be signed 3, sent from the receiving device 5, is received by the sending and receiving device 15 of the mobile phone 7, and in certain cases it is redirected to the signing device 21 for processing. The signing device 21 takes care of manage the signing process. The signing apparatus 21 contains software components to control the pointer system 13 so that it can display

ES 2 173 652 T5 is the message to be signed 3. Furthermore, the message to be signed 3 is signed within the signing device 21. In order to carry out the signing process, the signing device 21 must communicate with the card device chip 17. Furthermore, it is necessary for the signing apparatus 21 to come into contact via the keyboard 19 either directly with the secret key or to communicate with the PIN. If the PIN is entered by the user through the keyboard 19, which is normally shorter, and therefore occupies less space than the secret key, then the PIN can almost release, by means of a smart card 25 operating system, the secret key inaccessible for the signing process. Through a bidirectional connection line 23, the signing apparatus 21 can communicate with the chip card 25. The chip card device 27 ensures that the orders or commands of the signing device are executed and that the signed message 9 is retransmitted, through the signing device 21, to the sending and receiving device 15. That is, the device of Smart card 27 represents an interface between the signing apparatus 21 and the smart card 25.

Figure 3 shows a highly simplified schematic representation of a chip card 25 according to the invention. Essentially, it comprises a contact pin 31 as well as a storage unit 27 and a cryptographic module 29. In the storage unit 27 there is the secret key necessary to execute the signed message.

9. The cryptographic module 29 serves to encrypt the message to be signed 3, for example by means of an RSA method. Through the contact pin 31, the storage unit 27 or the cryptographic module 29, it can be communicated with the chip card device 27. For reasons of clarity, other elements necessary for the operation of the device have not been represented in Figure 3. chip card 25, such as a controller.