Cryptography – Particular algorithmic function encoding – Nbs/des algorithm
Patent
1995-05-17
1997-12-02
Gregory, Bernarr E.
Cryptography
Particular algorithmic function encoding
Nbs/des algorithm
380 4, 380 9, 380 25, 380 49, H04L 900
Patent
active
056944705
DESCRIPTION:
BRIEF SUMMARY
In general, this invention concerns a computer system for reading encrypted information, as well as a decrypting unit for use in such a system.
To be more specific, the computer system according to the invention is of the type defined in claim 1, i.e. comprising a decrypting unit for receiving encrypted information and being operable either in a converting state (referred to as an "open" state) in which it converts said encrypted information into corresponding decrypted information, or in a non-converting state (referred to as a "locked" state) in which no decryption of said encrypted information is possible by said decryption unit, said decryption unit being operable in the converting state only if it receives a predetermined external decryption key; and a display tool for displaying said decrypted information to a user.
In the following description and the appended claims, the term "display tool" will be used for designating the applications software for displaying the decrypted information to the user.
As a rule, prior-art cryptographic computer systems are designed for safe transmission of information from an emitter to a receiver, in which case the information is first encrypted by the encrypting unit of the emitter with the aid of an encryption key and then, after being transmitted in encrypted form on a communication link, decrypted by the decrypting unit of the receiver with the aid of a decryption key corresponding to the encryption key.
The decrypting unit can be implemented as software or hardware, or a combination thereof. For instance, a decrypting unit available on the market consists of a so-called cryptocard (by which is meant that the unit has an encrypting as well as a decrypting function) which is to be mounted in a personal computer or the like and be connected to an external bar code reader for reading a separate bar code constituting the decryption key.
In such prior-art systems, the encryption serves to prevent unauthorised monitoring of the information being transmitted on the communication link. Once the receiver has decrypted the information, no security requirements are normally placed on the receiver's management of the decrypted information.
Behind the invention lies a demand for the possibility of decrypting the encrypted information and displaying it to a user in a secure and reliable manner, so that the user is unable to manage or process the decrypted information in an unauthorised way. A special, however not compulsory, object of the invention is to prevent unauthorised copying, storage and the like of the decrypted information, such that the decrypted information is not stored in decrypted form once the user that has employed the display tool for reading the decrypted information has stopped reading. Printout of the decrypted information may, however, be allowed to some extent, especially if the user needs to take the decrypted information with him to some other location.
Today's cryptographic computer systems do not meet this demand. In, say, a personal computer operating under the operating systems DOS/Windows.TM. and having a cryprocard of the above type, the user has, as soon as the cryptocard has been unlocked by the decryption key, perfect control over the decrypted information provided by the decrypting unit. If the encrypted information is stored on e.g. a CD-ROM and is read by means of a CD-ROM reader connected to the personal computer, the reader may constitute a specific "unit", say unit d. By using conventional DOS commands (XCOPY, COPY, etc.) or conventional copying functions of application programs under DOS or Windows.TM., the user has every possibility, as soon as the cryptocard has been unlocked, to copy the decrypted information from unit d to any other unit, for instance unit c (hard disc) or unit a (floppy disc), and/or to request a printout of all the decrypted information.
The object of the invention is, therefore, to meet the above demand.
According to the invention, this object is achieved by a computer system in which if it receives a predetermine
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Gregory Bernarr E.
Telub Teknik AB
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