METHOD AND DEVICE FOR PREVENTING UNAUTHORISED ACCESS TO A COMPUTER SYSTEM

Abstract: In a method and a device for preventing unauthorised access to a computer system comprising at least one processing unit (1) or the like, a disc unit (3), a display (5), and a keyboard (7), use is made of a floppy disc (9). Information in the form of a personal identification code containing the name of an authorised user and an access code encrypted by means of a one-way encrypting function, and an authenticity code formed by a system access code and at least the personal identification code are recorded on the floppy disc. After insertion of the floppy into the disc unit, the computer system is adapted, in starting-up, to read at least the personal identification code and the authenticity code; to check the authenticity code by means of the system access code and the information recorded on the floppy disc and used to form the authenticity code; to request, via the display, the user to enter his name and access code in non-encrypted form via the keyboard; to encrypt the access code entered by the user; to check the read name against the entered name and, respectively, the read, encrypted access code against the entered access code which is then encrypted by the computer system; and to give the user access to the computer system merely in case of a positive result of all three checks.

Description: METHOD AND DEVICE FOR PREVENTING UNAUTHORISED ACCESS TO A COMPUTER SYSTEM The present invention relates generally to protection against unauthorised use of a computer system, e.g. a per¬ sonal computer, comprising a processing unit or the like, a disc unit for floppy discs, a display and a keyboard. There are prior art techniques of preventing such unauthorised access. A first variant means that the user has to identify himself by a personal code via the keyboard, which code is checked by software stored in the computer system against one or more corresponding codes stored in the computer system. When the personal code and the corresponding code or one of the corresponding codes stored in the computer system conform to each other, the user is allowed to use the computer system, i.e. data or instructions entered by the user are accepted and processed. However, the security of this technique is not satisfactory. A second, more reliable variant has therefore been developed. This requires the use of a card with a magnetic strip or an integrated circuit in which the identity in¬ formation is stored. This requires, however, a special card reader reading the identity information into the computer system, which decides, based on either this information only or a combination of this information and a personal code entered via the keyboard, whether the user is authorised or not. One drawback of this solution is that it requires a special card reader. A third variant, see DK-A-6229/89, tries to eliminate the last-mentioned drawback by providing a floppy disc with an integrated circuit containing a processing part and a memory part, and an interface via which the read and write equipment in a disc unit for floppy discs can trans¬ fer information between the integrated circuit and the computer system in which the disc unit is included. Of course, this eliminates the need of a separate card reader, but the special floppy disc will be complicated because of the arrangement of the integrated circuit and the associated interface, and since it requires a source of current supply of its own, for example a built-in battery. The object of the present invention therefore is to provide a method for preventing unauthorised access to a computer system, and a device for carrying out the method, which assure high security but do not require any addi¬ tional equipment in the form of e.g. cards, a card reader or special integrated circuits. More precisely, according to the invention a personal identification code should be recorded on the floppy disc, said identification code preferably containing the user's name and an access code which is encrypted while using a one-way encrypting function. By name is here, of course, meant the user's name or the like which is unique for the user. The floppy disc may contain further information in addition to the personal identification code, as will be exemplified below. The floppy disc should also contain an authenticity code which is formed by means of a system access code which is, in turn, stored in a permanent memory in which it is not accessible to any user but the system administrator, i.e. the permanent memory is lock- able by the system administrator. More precisely, the authenticity code is developed as a function of all the information recorded on the floppy disc (exclusive of the actual authenticity code), while using the system access code as a key. The function itself may be a one-way en¬ crypting function. In the method and the device according to the inven¬ tion, the floppy disc with the above-mentioned codes is first inserted into the disc unit. Subsequently, the computer system is started and reads via its BIOS (Basic Input Output System) all the information of the floppy disc as well as the authenticity code which for authenti- cation of the information read is checked by means of the system access code stored in the permanent memory, and all the information read, while using the same function as is used to produce the authenticity code recorded on the floppy disc. At least in case of a positive result of this check, the BIOS of the system initiates a request to the user to enter, via the keyboard, his personal identification code. Next, the name in this entered code is checked against the one read from the floppy disc and stored thereon as plain text, and after being encrypted by the one-way en¬ crypting function, the entered access code is checked against the access code read from the floppy disc. If one or some of the checks described above turn out negative, the user is not allowed to use the computer system. If, however, all checks turn out positive, the user is allowed to use the system. In a preferred embodiment, if all three checks turn out positive, use is made of information which is read from the floppy disc and which defines the extent of the user's authorisation and is stored on the floppy disc in encrypted form, after decryption to then control what the user is allowed to do. The used encrypting/decrypting key suitably is based on the user's name and the system access code stored in the lockable, permanent memory. This technique is above all applicable if not all users of the computer sys¬ tem should be allowed to perform all operations that are possible in the system. Thus, the invention eliminates the possibility of copying a different user's access disc, and the possibility of changing the extent of the one's own authorisation. Moreover, the access disc can contain information in the form of data that are necessary for preparing the computer system for operation to the extent of the user's valid authorisation, e.g. log-on information and other user-specific information. Furthermore, the floppy disc can contain information in the form of service routines which make it possible to read and update the information on the floppy disc, if the system access code is known. The method and the device for preventing unauthorised access to a computer system comprising at least one proces sing unit or the like, a disc unit, a display and a key¬ board, have thus according to the invention the features a defined in claims 1 and 6, respectively. Preferred embodi¬ ments are defined in the dependent claims. The invention will now be described in more detail with reference to the accompanying drawing which illus¬ trates a computer system to which the invention is applic¬ able. The invention is useful in an off-line computer, for example a personal computer, which may also be included in a network. The network system illustrated in the drawing com¬ prises personal computers 1, 2, each accommodating a disc unit 3, 4 and each having a display 5, 6 and a keyboard 7, 8. A floppy disc 9 is shown to be inserted into the disc unit 3. Joint resources in the network system are exem¬ plified by a printer 10 and a data base unit or server 11. According to the invention, use is made of a special floppy disc, below called access disc, for checking a user's authorisation to use the computer system via e.g. the computer 1. More precisely, the user's name or the like, which is unique for the user, is recorded on the access disc as plain text, i.e. non-encrypted. Moreover, access code is recorded on the same access disc. In con¬ trast to the name, this access code is recorded in en- crypted form, a one-way encrypting function being used fo the encryption, i.e. a function which does not allow or allows, this, however, being most unlikely, decryption of the result of the encryption. In practice, it should thus be impossible to derive the non-encrypted access code fro the encrypted access code. The name and the access code form a personal identi¬ fication code which is unique for the user. On the access disc there is also recorded an authen¬ ticity code formed by means of a system access code which, in turn, is stored in an available permanent memory in which it is not accessible to any user but the system ad¬ ministrator. The permanent memory can thus be locked by the system administrator. Moreover, the access disc can advantageously contain information which is recorded in encrypted form and states to what extent the authorised user may use the computer system. The question whether the user should have access to e.g. serial or parallel ports, as well as the length of the access time and the allowed software may here be involved. In each personal computer 1, 2, there is thus a lock- able memory for storing the system access code which can be unique for the system administrator preparing the access discs, and which can be combined with the authorised user's name for forming an encrypting/decrypting key for said in- formation stating to what extent the authorised user should be allowed to use the computer system. The device described above functions as follows. 1. An authorised user who wishes to use e.g. the personal computer 1 inserts his access disc 9 into the disc unit 3 before start-up of the computer 1. 2. In the subsequent start-up of the computer 1, its BIOS will provide reading of the authenticity code from the access disc 9 inserted into the disc unit 3, and all the information recorded thereon, possibly except the above- mentioned data for permitting operation of the computer system to the extent of the user's authorisation. 3. The BIOS of the computer 1 then checks the authen¬ ticity of the information read, by authenticating this with the system access code as a key. The authentication func- tion can be a one-way encrypting function. The authentica¬ tion thus results in an authenticity code which is compared with the authenticity code read from the floppy disc. If the result of the comparison and, thus, the check is nega¬ tive, the user is informed via the display 5 that access to the system is not allowed. Alternatively, this message can be delivered only after execution of all the checks. 4. The BIOS of the computer 1 then generates, at least in case of a positive result of the first check, a request to the user via the display 5 tbat he should enter his name or the like, as well the access code in non-encrypted form via the keyboard 7. 5. The BIOS of the computer 1 then checks whether the entered name conforms with the name read from the access disc, and encrypts the entered, non-encrypted access code and, subsequently, checks whether the result of this en¬ cryption conforms with the encrypted access code read from the access disc. 6. Merely if all three described checks or comparisons yield a positive result, i.e. conformity prevails, the user is given access to the computer 1, and this is preferably shown via the display 5. Since different users of the computer system should normally not have access to all the equipment thereof, the access disc suitably also contains the above-mentioned information stating to what extent the authorised user will be allowed to use the computer system. This information can be read from the access disc at the same time as the au¬ thenticity code and the personal identification code or, alternatively, be read only after these have been checked with a positive result. After establishing that the user is authorised and said information has been read, the informa- tion is decrypted by means of the decrypting key described above. The BIOS of the computer 1 subsequently uses the information to prepare the computer 1 for operation to the extent stated by said information. Additional necessary data for such preparing can also be recorded on the access disc. It will be appreciated that the method and the device according to the invention afford high security against unauthorised use of the computer system, both regarding the access thereto and regarding the extent of the access. By means of the special access disc and the method of using it, the invention also ensures that this high security can be achieved without necessitating any additional equipment. Several modifications of the particular embodiment described above are obvious to a person skilled in the art.

Claims: CLAIMS 1. Method for preventing access to a computer system, comprising a processing unit or the like, a disc unit for floppy discs, a display and a keyboard, c h a r a c ¬ t e r i s e d by the steps of recording, on a floppy disc, information at least in the form of an identification code which is personal for the user and includes the user's name and an encrypted access code, the encryption being carried out by means of a one-way encryption function, recording, on the same floppy disc, an authenticity code which is formed as a function of at least the personal identification code, while using a system access code stored in a permanent memory and accessible but to a system administrator, inserting the floppy disc into the disc unit before the start-up of said computer system, in starting-up, said computer system reading at leasΕ " the personal identification code in said information and the authenticity code from the floppy disc, said computer system then checking the authenticity of the read information by means of said function which uses the system access code stored in a permanent memory, said computer system subsequently, at least in case of a positive result of said check, requesting the user via the display to enter his name and his access code in non- encrypted form via the keyboard, said computer system checking, after the entering has been carried out, the read name against the entered name, the computer system encrypting the entered access code, while using said one-way encrypting function and, subsequently, checking the result against the read, en- crypted access code, and said computer system giving the user access to the computer system merely in case of a positive result of all three checks. 2. Method as claimed in claim 1, c h a r a c t e r - i s e d in that information stating the extent of the authorisation is recorded in encrypted form on said floppy disc together with the personal identification code, that said computer system decrypts the information in case of a positive result of all three checks, and that said computer system gives the user access to the extent stated by the information. 3. Method as claimed in claim 2, c h a r a c t e r ¬ i s e d in that the information about the extent of the authorisation is encrypted and decrypted, while using the user's name and the system access code lockably stored in the computer system. 4. Method as claimed in claim 3, c h a r a c t e r ¬ i s e d in that the encryption and decryption are carried out by means of en encrypting key which is a function of the user's name and the system access code. 5. Method as claimed in any one of claims 1-4, c h a r a c t e r i s e d by recording, on the floppy disc, information which in combination with the system access code permits reading and up-dating of the contents of said floppy disc. 6. Device for preventing unauthorised access to a computer system, comprising at least one processing unit (1) or the like, a disc unit (3), a display (5), and a key¬ board (7), c h a r a c t e r i s e d in that it includes a floppy disc (9), on which information is recorded at least in the form of a personal identification code in¬ cluding an authorised user's name and an access code en¬ crypted by means of a one-way encrypting function, and an authenticity code formed by means of a system access code, which is stored in a permanent memory and accessible but to a system administrator, and at least the personal identi¬ fication code, and that the computer system is adapted, after insertion of the floppy disc into the disc unit, to read, in starting-up, at least the personal identification code of the information recorded on the floppy disc, and the au- thenticity code, to check the authenticity of the read information by means of the system access code and a func¬ tion used to form the authenticity code, to request via the display, at least in case of a positive result of said check, the user to enter his name and his access code in non-encrypted form via the keyboard, to encrypt the access code entered by the user, to check the read name against the entered name and, respectively, the read, encrypted access code against the access code which is entered and then encrypted by the computer system, and, only in case o a positive result of all three checks, to give the user access to the computer system. 7. Device as claimed in claim 6, c h a r a c t e r ¬ i s e d in that on the floppy disc, information about the extent of the authorisation is also recorded, in addition to the personal identification code, and that the computer system is adapted to decrypt the information about the extent of the authorisation in case of a positive result o all three checks, and to give the user access to the computer system to the extent stated by the information. 8. Device as claimed in claim 7, c h a r a c t e r ¬ i s e d in that it includes a permanent memory for lock¬ ably storing the system access code, and that the computer system is adapted to encrypt and decrypt the information about the extent of the authorisation, while using the lockably stored system access code. 9. Device as claimed in claim 6, c h a r a c t e r ¬ i s e d in that the computer system is adapted to encrypt and decrypt the information about the extent of the author isation by means of a key which is a function of the user' name and the system access code. 10. Device as claimed in any one of claims 6-9, c h a r a c t e r i s e d in that on the floppy disc (9), information is also recorded, which in combination with the system access code permits reading and updating of the contents of said floppy disc.

Inventors: SJOEQUIST TOM, SJOEQUIST, TOM
Applicants: ICL SYSTEMS AB, SJOEQUIST TOM
Application year: 1993
Main classification: G06F1
IPC codes: G06F21