Method for digital signing of a message

p0001The present invention relates to a method for digitally signing a message as well as the devices required for carrying out this method.

p0002Digital signatures, ie electronic signatures, are usually implemented using so-called public-key methods. A key pair, which comprises a secret key and a public key, is assigned to a signer. Using the secret key, a signature is generated by a mathematical method, while this signature can be checked with the associated public key. The secret key is exclusively under the control of the signer, so no one can sign in the name of the signer. The public key, on the other hand, can be published so that anyone can check the signature. As a rule, the secret key is protected by a password (PIN) so that the knowledge about the password and the possession of the secret key is necessary to perform a signature.

p0003Digital signatures can be generated in a computer, for example in a PC, by means of software programs. The associated secret key is usually stored on a hard disk or a floppy disk and loaded into the main memory for generating the signature. Usually, the secret key itself is stored again in encrypted form and protected by a password, which the owner must specify when signing the software. This is to ensure that only the owner of the secret key can use it for signing. Since no additional hardware is required, this method is inexpensive. A disadvantage is that the user has to rely on the integrity of the signature software and is generally regarded as not sufficiently secure.

p0004As a further alternative to the generation of digital signatures in a computer, hardware-based methods are used. These use specialized devices for signing, in which the display component and the keyboard are coupled to the signing component by means of hardware such that no influence can be exerted on the connection. These devices are usually connected to the computer via a galvanic connection, for example a cable to the serial interface. These devices have their own display components, which display the message to be signed, and the PIN pad, which is used to enter the password for unlocking the key. Typically, the secret key is not stored in the signer, but on a chip card that can be inserted into the device. The actual signature can be generated on the chip card (with chip cards with its own cryptoprocessor) or in the device. The described hardware-based method represents a completed signing system comprising display component, keyboard, reader and chip card.

p0005Unlike the software-based techniques, hardware-based methods are much safer, but their cost is higher. Accordingly, so-called mixed methods are currently used. The secret keys are usually stored on a chip card and made available via a reader. The rest of the tasks, such as the representation, the input of the password and the generation of the signature, are carried out in the computer in whole or in part. It can be provided that the signing device, ie the reader and the chip card, is used as a pure storage medium for the secret key, while the representation, the input of the password and the generation of the signature are generated completely in the computer.

p0006Alternatively, provision can be made for the representation and the input of the password to be carried out via the computer, wherein the signing device is additionally used for storing the secret key also for generating the signature. Finally the variant exists, that only the representation in the computer takes place. In this variant, the signing device has its own keyboard or is connected directly to the computer keyboard, bypassing the computer software. The signature is generated in the signing device. The more tasks are taken over by the computer software and the less the marking device has to perform, the more cost-effectively the process is.

p0007The <patcit id="pcit0001" dnum="WO9632700A"><text>WO 96/32700</text></patcit> Discloses a method according to which a message generated in a mobile radio telephone is digitally signed and forwarded. The<patcit id="pcit0002" dnum="EP0689316A2"><text>EP 0 689 316 A2</text></patcit> Discloses a method and apparatus for identifying and verifying data in a communications network.

p0008However, in all of these embodiments, there is a fundamental problem that exactly the data which the user wishes to sign should be signed. It must therefore be excluded that a virus, for example, changes the data during the transmission from the display component, for example the display, to the signing component, for example the cryptoprocessor. It must also be ensured that a secret number (for example, PIN), which is necessary for triggering the signatures, can not be read by other programs from the keyboard and become known to third parties.

p0009Moreover, the use of the possibility of digital signatures, which is as wide as possible, is limited by the comparatively small distribution of signing devices. In potential fields of application of digital signatures, such as, for example, Internet banking, a cost-intensive infrastructure for distributing the signing devices would have to be created. The installation of signing devices on the computer is also problematic. On the one hand, the devices must be physically connected to the computer, whereby the serial interfaces of a PC are frequently already occupied. Alternative methods for connecting the signing devices to computers are also problematic, since at least the installation of software drivers and sometimes also of additional hardware is necessary. In addition, special software components, which allow the application program to communicate with the signing device, must frequently be installed for all signing devices.

p0010A further problem of the conventional methods for digital signature is that they are location-dependent. Certain areas of application for the use of digital signatures, such as Internet banking, are dependent on the availability of public Internet terminals. If these Internet banking applications were now combined with the known location-dependent methods for digital signatures, the location dependency of these application areas would be lost.

p0011The technical problem underlying the present invention is thus to provide a cost-effective, easy-to-implement and location-dependent method for the digital signing of messages as well as suitable devices for this purpose.

p0012This technical problem is solved by the teaching according to the main claim.

p0013In the context of the present invention, a digital signing of a message is understood to mean an operation in which the intention to dispense and the content of a message is confirmed electronically. This is done by partial or complete encryption of the message to be signed or by encryption of a cryptographic checksum of this message into a signed message by means of a secret key using a mathematical method. In the context of the present invention, a signed message is either the signed message as a whole or the signature itself. The signing is used to be able to authenticate the user later. In the context of the present invention, a signed message is also understood to mean only the electronically generated signature of the message. In the context of the present invention, a message is understood to be any type of information reproducible in electronic form, for example numbers, letters, combinations of numbers, letter combinations, graphics, tables, etc. In the context of the present invention, a signing device is understood to mean a unit which can perform a signing of a message, ie a secret key, a mathematical encryption method, dialog possibilities with the signer or user, possibly necessary interfaces, and a transmitting and receiving device. This unit may be composed of various elements, for example, a chip card and a reader or a chip card and a mobile radiotelephone. In the context of the present invention, a signing device is a component of the signing device which has the secret key and / or the encryption method and / or an interface to both or one of the aforementioned components.

p0014Due to the particularly preferred use of the radiotelephone network for transmitting the messages to be signed to a signing device, which in an advantageous embodiment is designed as a mobile radio telephone, it is possible to use a commercially available computer with a connection to a corresponding message server, for example via e-mail , To transmit messages to the signing device without having to make any installation or other changes to the computer itself.

p0015In a particularly preferred embodiment, the invention provides a method of the aforementioned type wherein the message to be signed is transmitted by a transmitting device, for example a PC, which is also to be designated as a message source, to a receiving device, for example a message server Receiving device is transmitted to a signing device, in particular mobile telephone, which is assigned to the transmitting device, then this message is signed in the mobile radio telephone, and is then retransmitted to the receiving device as a signature, that is, as a signed message.

p0016The invention thus provides that an unsigned or to be signed message is transmitted from a message source to a receiving device, for example a message server. The receiving device then carries out an assignment of the message to be signed to the signing device, in particular the mobile telephone. This is done either by means of a documentation stored in the receiving device or by information which has been transmitted by the transmitting device together with the message to be signed to the receiving device. The allocation of the signing device, advantageously of the mobile radio telephone, to the message source does not need to be a spatial assignment, but is a purely informative assignment. The assignment thus consists in determining which signing device and thus which user is to sign the received, to be signed message. The mobile radio telephone used in the preferred embodiment of the invention is advantageously able to display a message to be signed and to sign it on the instructions of the user and with the aid of the advantageously used chip card. The message thus signed is transmitted to the receiving device and, where appropriate, is compared with the original message and authenticated there. From the receiving device, the signed and possibly authenticated message is then relayed to an addressee.

p0017The invention also relates to a method according to the invention, wherein it is advantageous to use a public-key method for signing, in which the transmitting device has a secret key assigned to it and the receiving device has the corresponding public key assigned to the secret key. This approach offers the advantage that the keys do not have to be transmitted.

p0018In a further advantageous embodiment, the invention relates to a method according to the invention, wherein the message to be signed or the already signed message, that is to say, for example, the signature between the receiving device and the signing device, in particular the mobile radiotelephone, are transmitted by means of the short message service (SMS). In a particularly preferred embodiment it can be provided that both the transmission of the message to be signed from the receiving device to the mobile radio telephone as well as the transmission of the signed message or the signature from the mobile radiotelephone to the receiving device is carried out by means of the SMS.

p0019The invention provides in a further embodiment that the message to be signed is displayed by means of a display device provided in the mobile radio telephone. This can be done on the display of commercially available mobile radiotelephones. In this way, simple texts such as banktransactions or even simple graphics can easily be displayed.

p0020Following this presentation, the user provides a corresponding instruction for activating the signing in a dialog provided for this purpose. In a particularly preferred embodiment, the invention provides a method of the aforementioned type wherein the secret key necessary for signing is stored in a chip card of the mobile radio telephone and this key is released by means of a secret number (hereinafter referred to as PIN) which can be entered via a keyboard of the mobile radio telephone . Advantageously, by means of a corresponding usual programming of the mobile radio telephone, it can be ensured that the entered PIN is only transmitted to the chip card and can not be intercepted from the outside.

p0021In a further alternative embodiment of the aforementioned methods according to the invention, it is provided that the secret key necessary for signing is entered via a keyboard of the mobile radio telephone.

p0022In a further preferred embodiment of the invention it is provided that, in one of the aforementioned methods, the secret key is not only stored on the chip card of the mobile radio telephone, but also the signing of the message is performed there. This advantageously ensures that the secret key never leaves the chip card and can thus be used by unauthorized persons.

p0023In a further advantageous embodiment of the invention it is provided that the mobile radio telephone is used not only for signing the message, but additionally also as transmitter for transmitting the signed message to the receiving device.

p0024The invention also relates to devices for carrying out the above-mentioned methods, in particular mobile radiotelephones and chip cards.

p0025In a particularly preferred embodiment of the invention, a mobile radio telephone is provided which comprises a keyboard, a display device and a chip card device for reading and / or writing a chip card pluggable into the mobile radio telephone, wherein additionally a signing device is provided, For communication with a chip card according to the invention and / or for producing a signed message from a report to be signed. Advantageously, the signing device is connected to the keyboard for the input of a secret key or a secret number.

p0026In a particularly advantageous embodiment of the above-mentioned mobile radio telephone, it is provided that the signing device represents a software component which is changed in contrast to the conventional software component of a mobile radio telephone. In a preferred embodiment of the invention, this modified software component is suitable for performing the signing of the message after dialogue with the user. In a further embodiment, the modified software component of the signing device provided according to the invention is advantageously capable of communicating with the chip card according to the invention for carrying out the signing according to the invention. In a particularly advantageous embodiment of the invention it is provided that the signing device of the signing device can additionally process algorithms which enable the display of the message to be signed in the display field of the mobile radio telephone.

p0027In a particularly advantageous manner, the present invention thus provides a system according to which only software components are to be modified in a conventional manner compared to software components. It is not necessary to change the hardware.

p0028In a further embodiment of the invention, the invention also relates to chip cards for mobile radiotelephones, in particular to the aforementioned mobile radiotelephones, the chip card comprising a signing device which can store the secret key of the user. Advantageously, the signing device of the chip card is also able to create a signed message from a message received by the mobile radio telephone, that is to say a message to be signed. In the context of the present invention, the signing device of a chip card according to the invention is therefore a device which stores the secret key of the user and, in an advantageous embodiment, also performs signing. However, the performance of the signing does not have to take place directly on the chip card, but can be carried out by a software and / or hardware component in the mobile radio telephone.

p0029Further advantageous embodiments of the invention result from the subclaims.

p0030The invention is explained in more detail with reference to the figures and the corresponding exemplary embodiment.

p0031The figures show:<ul><li><figref idrefs="f0001">FIG</figref> Shows the sequence of the method according to the invention,</li><li><figref idrefs="f0002">FIG</figref> Schematically the structure of a mobile radio telephone according to the invention and FIG</li><li><figref idrefs="f0003">FIG</figref> 6 shows a schematic representation of a chip card according to the invention.</li></ul>

p0032The <figref idrefs="f0001">FIG</figref> The transmitting device 1, which can be implemented in the form of a computer having a texteritor or a homebanking program, can designate a message 3 to be signed, a receiving device 5 which is implemented in the form of a message server, a mobile radio telephone 7, a signed message 9 And an addressee 11.

p0033By means of a homebanking program contained in the transmitting device 1, a message 3 to be signed is sent, for example by e-mail, to the receiving device 5. The receiving device 5 converts the received message 3 to be signed into a message which can be sent to the mobile radio 7, in particular by means of a mobile radio network, in an advantageous embodiment by means of the SMS. The receiving device 5 assigns the message 3 to be signed to the mobile telephone 7, for example, by means of information stored in the receiving device 5. It may also be provided that the assignment takes place by means of an information transmitted by the transmitting device 1 together with the message 3 to be signed. This information is generally the mobile radio telephone number.

p0034In the mobile radio telephone 7, the received message 3 is displayed in a display device 13. The precise procedure will be described in the description<figref idrefs="f0002">FIG</figref> In more detail. After display of the message 3 to be signed in the display device 13, the message 3 to be signed is signed on the user's instruction and the signed message 9 is forwarded to the receiving device 5 or also to another receiver. The transmission of the signed message 9 from the mobile telephone 7 to the receiving device 5 also takes place by means of SMS. The receiving device 5 can compare the signed message 9 with the original message 3 to be signed and then transmit it to an addressee 11. The transmission to the addressee 11 can be effected in any desired way.

p0035The <figref idrefs="f0002">FIG</figref> Represents a mobile radio telephone 7. The mobile radio telephone 7 comprises a display device 13, a transmitting and receiving device 15, a chip card device 17, a touch device 19 and a signing device 21.

p0036The message 3 to be signed by the receiving device 5 is received by the transmitting and receiving device 15 of the mobile radio telephone 7 and, if necessary, is forwarded to the signing device 21, The signing device 21 ensures the internal management of the signature sequence. The signing device 21 contains software components for activating the display device 13 so that the message 3 to be signed can be visualized. Furthermore, the message 3 to be signed is signed within the signing device 21. In order to be able to perform the signing process, the signing device 21 must communicate with the chip card device 17. Furthermore, it is necessary for the signing device 21 to receive either the secret key directly or the PIN via the touch device 19. If the PIN, which is generally shorter than the secret key, is entered by means of the operating device of a chip card 25 by means of an operating system of a chip card 25, the user can virtually release the unwieldy, secret key for the signing operation . The signing device 21 can communicate with the chip card 25 via a bidirectionally configured connecting line 23. The chip card device 27 ensures that the commands or commands of the signing device 21 are executed and the signed message 9 is passed on to the transmitting and receiving device 15 via the signing device 21. That is, the chip card device 27 represents an interface between the signing device 21 and the chip card 25.

p0037The <figref idrefs="f0003">FIG</figref> Shows a chip card 25 according to the invention in a very simplified schematic illustration. This essentially comprises a contact pad 31 as well as a memory unit 27 and a cryptography module 29. The secret key necessary for the generation of the signed message 9 is stored in the memory unit 27. In this case, The cryptography module 29 serves to encrypt the message 3 to be signed, for example by means of an RSA method. The memory unit 27 or the cryptography module 29 can be in communicative connection with the chip card device 27 via the contact pad 31. For the sake of clarity, further elements necessary for the operation of the chip card 25, such as, for example, a controller are shown in the illustration of FIG<figref idrefs="f0003">FIG</figref> not shown.