The digital signature is carried out using an asymmetric cryptographic method, called the RSA method. Here is encrypted with a secret key known only to the user the file. It is using a public key corresponding to the secret key, it is possible to decrypt the encrypted file, whereby the proof is provided that the file has been encrypted by the owner of the secret key. In a variant, it is known not to sign the file yourself with the secret key, but to form a hash value of the file using a hash function and encrypting the hash value formed with the secret key and the corresponding public key decrypt and verify the digital signature using the same hash function.
An overview of hash functions can be found in . Under a hash function is a function to understand when it is not possible to calculate a function value given an appropriate input value. Further, an arbitrary length input string is assigned to an output string of fixed length. Further may be required for the hash function additional properties.
Such additional property is collision-free, ie it must not be possible to find two different input strings that give the same output string. Examples of a hash function are the method in accordance with the MD-2 standard, the method according to the MD-5 standard, the method SHA-1, the Data Encryption Standard DES , which is performed without using a key, or even any other arbitrary hash function.
An overview of asymmetric cryptographic methods can be found in . With the method known from  process, although it is possible to ensure that the electronic file has actually been signed by the owner of the secret key, however, is not necessarily guaranteed by this method that the user has actually signed what his example has been shown via a data presentation device. Thus, there is a possibility that a user information has not been shown, but is still in the electronic file. Wenn der Benutzer nun die gesamte elektronische Datei signiert, so unterschreibt der Benutzer damit auch einen Teil der elektronischen Datei, der ihm gar nicht zur Kenntnis gebracht worden ist.
If the user sign the entire electronic file, the user signs therefore also part of the electronic file that has been it not brought to the attention.
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Thus, satisfying  known methods by no means to the safety requirements that are placed in the field of electronic commerce, or generally an electronic activities in a computer network, such as the Internet. It is imperative that it is ensured in the case when a digital signature is to be binding under an electronic file for the undersigned, that the user has actually signed what has been presented to the user on the data display device. It should therefore be detectable at any one time, which representation has been presented to the signatory at the time of signature generation.
Das Originaldokument, welches von dem Benutzer unterzeichnet worden ist, soll dabei maschinell durch den Rechner weiter verarbeitbar bleiben. The original document that has been signed by the user is intended to remain workable machine by the computer. Thus, the invention is based on the problem of forming a proof variable, the proof of a digital signing of an electronic file, and to demonstrate that an electronic file has been digitally signed, unforgeable possible. The problem is solved by the method having the features according to the independent patent claims and with the devices having the features according to the independent claims.
The invention makes it possible to ensure that the user has actually signed the electronic file that has been presented to him on the data display. This is done even required under considerable saving storage space requirement or required data transfer rate in the storage and transmission of proof variable. Under the first file format, a file format is to be understood in this context, which can not be readily ensured that the user is actually shown that all matter contained in the file information in the first file format information shown.
This means that it is possible in principle for a file in the first file format information in the file from the user to "hide", so as to bring the user to sign information of which he never becomes aware. An example of such a file format is to be understood in a standard Microsoft Winword file or a Microsoft Excel file.
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By setting characteristics configurations of the program used to display the data can be ensured even when data in the first file format that the user is actually represented the entire information contained in the file. An example of such a program is Microsoft Winword, the display options can be clearly defined in which, in an initialization file or in a database record registry.
Under the second file format, a file format is to understand where it is not readily possible for the user or a third party to add additional information to the file that is not shown to the user. Dies bedeutet, dass die gesamte Information, die in der Datei in dem zweiten Dateiformat enthalten ist, auch dem Benutzer dargestellt wird.
This means that all the information that is included in the file in the second file format, and the user is shown. Examples of files in the second file format are PDF files that are presented to the user on a screen, or PostScript files that can be printed to a user directly to a printer.
Preferred developments of the invention emerge from the dependent claims. By this development, the data rate required for transmitting the detection size and the memory required to store the detection size is further reduced. Bevorzugt basiert das Verfahren zur Bildung der digitalen Signaturen auf dem Prinzip der asymmetrischen Kryptographie. Preferably, the method is based to form the digital signatures on the principle of asymmetric cryptography. In this manner the achievable level of safety is further enhanced with the signing. In diesem Fall ist das erste Dateiformat gleich dem zweiten Dateiformat.
In this case, the first file format is equal to the second file format. Embodiments of the invention are illustrated in the figures and are explained in more detail below. Es zeigen Show it.
The processor is arranged such that the method steps described in the following are feasible. The first processor further includes a bus connected to the display component over which the first computer is connected to peripheral units. The first computer is connected to a monitor and a printer as a data output devices.
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From the processor , the electronic file , which is present in a first file format, in a first step step is transformed into a second file format being ensured for the file in the second file format, a file, the second in the file format is presented to a user, clearly the whole in the file information contained the user also represents. However, the secret key information may already be stored in the first computer th.
Using a hash function step to form a first hash value of the file in the second file format in a second step. Der erste Hashwert wird unter Verwendung eines Verfahrens zur Erstellung einer digitalen Signatur digital signiert Schritt , womit eine Transformationssignatur gebildet wird. The first hash value by using a method for creating a digital signature digitally signed step , whereby a transformation signature is formed th.
Die elektronische Datei in dem ersten Dateiformat wird ebenfalls unter Verwendung einer Hash-Funktion einer Hashwertbildung unterzogen Schritt The electronic file in the first file format is also using a hash function of a hash value subjected to step The hash value formed over the file in the first file format is digitally signed step , whereby a document signature is formed th. A detection size includes the electronic file in the first file format and the document signature formed by the signature formation via the hash value of the electronic file in the first file format as well as the transformation signature , the signature formed over the hash value of the electronic file in the second file format, equivalent.
The proof variable is stored in the memory of the first computer th. The detection size is transmitted from the first computer to a second computer via a communication network th. The second computer also includes a memory , a processor , which is connected via a bus to the memory on. The proof variable is stored in the memory of the second computer th. A detection that the user has actually signed the electronic file in the first file format, and no hidden information is contained in the electronic file in the first file format is carried out, according to the following procedure.
It is used for the electronic file in the first file format, in turn, transform into the second file format is performed step About the file in the second file format, a hash value is formed using a hash function step In a further step the transformation signature is decrypted step Since the digital signature is carried out according to the RSA method, the transform signature was formed such that the hash value that has been encrypted using the file in the second file format using the secret key of the user th.
The decryption of the signature transformation is now carried out with the corresponding to the secret key of public key. Schritt The result of the decryption, the hash value of the file in the second file format, as it is formed in the first computer see. Step In a comparison step step , it is checked whether the decrypted signature matches transform to the computer formed in the second hash value of the file in the second file format step Ist dies der Fall, so ist durch diesen Verifikationsschritt nachgewiesen, dass die Darstellung der bei der Signatur-Erstellung gezeigten, dem Benutzer dargestellten Anzeige und somit dem Inhalt der elektronischen Datei , entspricht Schritt If this is the case, it is detected by this verification step that the image of the step shown at the signature creation, the user display and illustrated thus the content of the electronic file corresponds to.
Continue thereby by decrypting the document signature that has been formed according to the RSA method by encrypting the hash value of the electronic file in the first file format using the secret key of the user , decrypted with the corresponding to the secret key of the public key, a is formed of received hash value of the electronic file in the first file format step Furthermore, in a further step step on the electronic file in the first file format is made, a hash value.
Yield both verification steps steps and a positive result, so is therefore detected that the user has actually get the electronic file are shown in in the first file format with its contents and it thus also the entire contents of the electronic file in has signed the first file format.
Somit kann die elektronische Datei in dem ersten Dateiformat weiterverarbeitet werden Schritt Thus, the electronic file can be processed in the first file format step Bei negativer Verifikation wird ein Signal generiert, mit dem angezeigt wird, dass die Datei in dem ersten Dateiformat entweder nicht digital signiert worden ist oder modifiziert worden ist nicht dargestellt. In case of negative verification a signal is generated, is displayed with the that the file has not been digitally signed in the first file format either or modified not shown.
Zur einfacheren Darstellung sind die Komponenten des in Fig. For ease of illustration, the components of the embodiment shown in Figure 2, corresponding to the components of Figure 1, is provided in Figure 2 with the same reference numerals as in Fig. After transformation of the electronic file from the first file format into the second file format step and the following hash value calculation for the file in the second file format step , a concatenated hash value using another hash value on other sizes step formed step The formation of the concatenated hash value is performed such that the hash value of the file in the second file format described in the following sizes is concatenated and a hash value is performed on the concatenation.
Is for the indicator component , a configuration is set, which ensures that the user is actually represented the entire information contained in the file, even though it is present in the first file format, and this configuration is included in the transformation signature, the first file format may be equal to be the second file format. In this case, the step is eliminated and the concatenated hash value formed in step is identical to that formed in step , hash value. The concatenated hash value is digitally signed step and it is an extended signature transformation is stored in an enlarged size detection , instead of the signature transformation th.
Furthermore, in an enlarged size detection according to this embodiment, the sizes described above, which have been taken into account in the formation of the concatenated hash value, further referred to as configuration data included. The shamans used the voodoo doll in a way to communicate with the Loa spirits , like their dead ancestor, for guidance. It can be used to summon the spirit through the Loa so that it hears your plea and makes manifest your desires, wishes and wants. This project was set by Cordwainer's, London.
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