Cryptography – Particular algorithmic function encoding – Nbs/des algorithm
Patent
1994-10-11
1997-03-04
Tarcza, Thomas H.
Cryptography
Particular algorithmic function encoding
Nbs/des algorithm
380 23, 380 24, 380 21, 39518701, H04L 908, H04L 914, H04K 100
Patent
active
056088000
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention provides a method of checking transmitted encrypted data for unauthorized introduction of data.
2. Description of the Related Art
It is known to protect the data to be transmitted by a transmitter to a receiver against unauthorized attack by the data being enciphered. For example, H. Sedlak, U. Golze, Ein Public-Key-Code Kryptographie-Prozessor (A Public-Key-Code Cryptography Processor), Informationstechnik it, 28th year, Issue 3/1986, pages 157, 158 gives an introductory description of the possibilities of safeguarding data to be transmitted by a transmitter to a receiver. In this case, both the transmitter and the receiver may be a computer. The enciphering or safeguarding is intended to have the result that the authenticity of the sender and protection of the message or of the data against manipulation are achieved. For this purpose, the messages to be transmitted can be enciphered, or encrypted, for example on the basis of an asymmetric or symmetric enciphering method. Asymmetric encryption or enciphering means in this case that two different keys are used for enciphering and deciphering. It is similarly possible to use the same key both in the case of the receiver and in the case of the transmitter, a symmetric enciphering thereby being achieved. In the case of the asymmetric methods, it is possible that a key cannot be calculated from the other key without additional information. Therefore, one of the two keys may be published. This method is also known as the public-key method.
The message to be transmitted usually comprises useful data and a signature developed from the useful data.
The signature is an extract of the useful data enciphered with the sender key. With the aid of the receiver key, it can then be established whether the deciphered signature can be developed from the transmitted useful data. FIG. 1 shows this principle. At the transmitter SE, the useful data D are digitally appended with a signing key before sending. The signature S is obtained. The useful data are then transmitted together with the signature to the receiver EM. With the aid of the corresponding verification key, the receiver EM checks the integrity of the message comprising useful data and signature and the authenticity of the appended signature.
A potential attacker may tap the data traffic and spuriously reintroduce the tapped data together with the signature at the recipient's premises or at some other place in possession of the verification key. The recipient has no possible way of detecting from the signature whether the data are original or are spuriously introduced data.
SUMMARY OF THE INVENTION
The problem underlying the invention is to provide a process in which the recipient can detect whether the data received are data transmitted directly from the transmitter or are data introduced by an attacker without authorization. This problem is solved by a process for detecting unauthorized introduction of any data transmitted by a transmitter to a receiver, useful data, this purpose is dependent on coupling data designating the transmission between transmitter and receiver.
The process according to the invention is substantially based on a symmetric enciphering of the signature. By this enciphering, a forgery-proof coupling of the signature to a particular data exchange between transmitter and receiver can be achieved.
For this purpose, it is advantageous to allow so-called coupling data, from which unauthorized reintroduction can be detected, to go into the key used in the enciphering of the signature. Such coupling data may, for example, be an identification of the recipient or the time of the data transmission. The coupling data may be transmitted in addition to the useful data and the enciphered signature to the recipient in plain text for checking.
In order furthermore to prevent unauthorized recovery of the original signature, random data additionally generated by the transmitter go into the key for enciphering the signature. These
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Baumgartner Helmut
Hoffmann Gerhard
Lechner Stephan
Leclerc Matthias
Lohmann Ekkehard
Sayadian Hrayr A.
Siemens Aktiengesellschaft
Siemens Nixdorf Informationssysteme AG
Tarcza Thomas H.
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