FR2640794A1 - Process for monitoring access to an information item or to a monitored area, access key for the implementation of the process and process for manufacturing this key - Google Patents

Abstract

Access monitoring process implementing a non-ambiguous recognition of an access information item memorised on an information carrier 10 called an "access key", characterised in that a carrier 10, one at least of whose memorising properties is partially and definitively corrupted in a random fashion, is used as the access key, and a transcription of one portion at least of the structure S1, P0, S2, P0, S2, P39 of the corruption 12 is used, at least partially, as access information; in that the said transcription is memorised in at least one uncorrupted part of the said carrier 10; and in that, when monitoring access, the state of the carrier 10 is evaluated, at least partially, and the result of this evaluation is compared with the transcription memorised in the carrier. Application to the protection of software and to the monitoring of access to areas whose access is controlled.

Description

 The present invention relates to a method for controlling access to information or to a controlled area using unambiguous recognition of access information stored on an information medium called an "access key". It also relates to such an access key and to a method for manufacturing this key.

 In general, a method is known for identifying non-falsifiable data carriers.

Such a method is described in particular in documents GB-1,535,340 and FR-2,473,758. An area is provided on the non-falsifiable data carrier, comprising optical information. This optical information can consist of a physical property of the materials in a random design or not on this same material. Information corresponding to said optical information is recorded on a magnetic part of the support.

When the support is recognized, the optical information is measured or checked and this measurement is then compared with the information recorded in the magnetic support. It is only when there is a coincidence that the support is then recognized as valid.

 This known method has the drawback in particular of the fact that it is necessary successively to measure optical information with optical measurement means and then to read magnetic information with magnetic reading means. It is therefore necessary to use two distinct types of measuring or reading devices and, in certain cases, a particularly sophisticated optical measuring device. It follows that this process is particularly expensive in its implementation.

 Another method is known, known as the "laser hole", which is supposed to make a data medium unforgeable and unbreakable, especially in the computer field.

This method consists, on flexible discs used as a data carrier, of drilling the discs considered with a hole. This hole must be very fine, theoretically invisible to the naked eye. To do this, a laser beam is used as a means of drilling. This hole is located at a predetermined location on the flexible disk, on a well-defined sector of the latter. Special information is recorded on this sector. When reading such a flexible disk, and more particularly when reading the sector in question, we come to check whether, at the precise location of this sector, there is an alteration of the information. particularly fine and of the 512 unitary information contained in this sector only one or a small number of them is altered; we just come to check that this precise information is missing.

 This process has a number of drawbacks. First of all, it is supposed to make the flexible disc considered unique and non-reproducible. However, in use, it has been found that counterfeiters can identify the positioning of the hole and reproduce this hole by simply drilling another flexible disk, sometimes even using less sophisticated means than a laser beam: has been found that a simple needle can do the trick in some cases. It then only remains to copy the information written on this sector in particular and on the entire flexible disk in general. We then obtain a counterfeit model of the flexible disk considered.

 The present invention aims in particular to propose a method of medium identification or access control making it possible to guarantee, even better than the prior art mentioned above, counterfeiters, and making it possible in particular to avoid a simple copying of the flexible disk serving as an access key as in the case of the perforated flexible disks mentioned # above. Furthermore, the present invention aims to provide such a method implementing an access key having, in each application, a unique and particular character. In addition, the present invention aims to solve the drawbacks of the technique disclosed in the GB-1 535 340 and FR-2 473 758 analyzed above, so that we avoid having to use for the same support to identify readers or different types of measuring devices.

 The present invention therefore relates to an access control method implementing an unambiguous recognition of access information stored on an information medium called "access key characterized in that uses a medium of which one at least of its memorizing properties is partially and definitively degraded in a random manner as access key, and a transcription of at least a portion of at least partially is used as access information the structure of the degradation; in that said transcription is stored in at least one non-degraded part of said medium; and in that, during access control, the state of the medium is evaluated, at least partially, and we compare the result of this transcription evaluation stored in the medium.

 Similarly, the present invention relates to an access key comprising an information medium in which information relating to its structure is memorized, characterized in that at least one of the memorizing properties of the medium is partially and definitively degraded randomly , in that said information partially consists at least of a transcription of the structure of the degradation and in that this transcription is stored in at least one non-degraded part of the support.

 The method according to the invention can advantageously be used to control the access of the key holder to protected places (national defense, banks, etc.) or to control the access of a user to software, in particular to prevent unlawful duplication of such software. In general, the method, according to the inventive succinctly defined above, makes it possible to control access to any type of protected information.

 Thanks to the characteristics mentioned above, the method according to the invention uses only one measurement and reading apparatus. Indeed, it will be observed that, according to the invention, one degrades at least one of the memorizing properties of said support. Thanks to this characteristic, the same reader can be used to control the degradation of the support and to read the information on this support.

Compared to the “laser hole” method analyzed above, the method according to the present invention has the following advantages
First of all, unlike the laser hole method, the invention is not limited to the use of flexible disks as an access key, although the latter can very advantageously be used for this purpose as well as it will emerge from the explanations given below. Thus, any information medium is likely to be suitable a priori.

 Then, whatever the medium used, the degradation of the latter is done completely randomly. This makes the reproducibility of the support protected by this process delicate. Indeed, in the laser hole method, the laser hole is always located on the same sector of the flexible disk. In the method according to the present invention, the support considered is randomly degraded, the degradation zone therefore not being predetermined.

 Advantageously, in a preferred embodiment, the invention uses a magnetic medium, such as a flexible disc, as an access key.

 In a first variant, to degrade this support, the magnetic properties of this support are randomly, irreversibly and permanently altered. In addition, during the manufacture of the key, the magnetic state of each sector of the disc is determined; a set of encrypted information corresponding to the position of the altered sectors is recorded on some of the unaltered sectors. During an access control, the state of at least a portion of the sectors of the flexible disk is determined and the result obtained is compared with the information stored on the flexible disk during its manufacture.

 The invention lends itself particularly well to its implementation on magnetic media, and in particular on flexible disks commonly used in computer science. Degradation can be easily done there in a random manner, for example by scraping the surface of this disc, by passing a solvent over this surface such as acetone or by magnetizing portions of the sectors of this disc by means of a magnetic field. particularly high. This randomness already makes the reproducibility of the flexible disk thus degraded particularly difficult.

In addition, it is possible to make this degradation more or less strongly so that certain portions of the flexible disk apparently degraded (for example by scratching) are not actually. The reproducibility of such a flexible disk is made even more delicate since it must then be verified that each portion of the apparently visible degradation is actually a degradation of the memorizing properties of the flexible disk.

 Conventionally, a 5.25 inch flexible disk has 720 sectors distributed on two sides. If you scratch randomly one side of such a flexible disk, you actually degrade a number of the sectors considered. The recognition of degraded sectors can then be done by means of a simple flexible disk reader whose software is fitted, this reader being able to determine the valid sectors (whether or not they have been scratched) from the sectors invalidated by scratching. .We therefore observe that, thanks to the invention, a single magnetic reader is used whereas in the process set out in the prior art documents cited above, an optical reader must be used on the one hand and on the other hand a magnetic reader: in this respect, the method according to the present invention is particularly simpler in its implementation when a magnetic medium such as a flexible disk is used as an access key.

 In addition, compared to the so-called "laser hole" method, it will be observed that in these flexible disks the number of possibilities of degradations is of the order of 4.105 possibilities (corresponding to the number of possible positions for holes), while, in the method according to the present invention, there are 2360 # l possibilities of degradation of one face and 2720 # l possibilities of degradation of the two faces. It will be appreciated that, thanks to the present invention, the task of falsifiers is considerably complicated.

 Indeed, thanks to the method according to the present invention, it does not matter how the degradation is carried out. On the other hand, from the point of view of the counterfeiter, it is important for him to degrade again in a strictly identical manner another flexible disk. However, to achieve this result, it must degrade on the copy only the sectors which are degraded in the original flexible disk. It must therefore carry out a particularly fine and precise degradation of the flexible disc constituting the counterfeit key.

 Furthermore, advantageously according to a second variant of the preferred embodiment of the invention, it is possible to use as access key certain flexible discs rejected during manufacture during quality control. Indeed, some flexible discs are rejected because the magnetic qualities of some of their sectors are degraded. However, such poor workmanship is generally eminently random, which makes these flexible disks particularly well suited for their use as access keys in accordance with the invention, all the more so as very often these original faults or "degradations" are invisible to the naked eye; this characteristic makes their reproducibility even more difficult. The use of flexible disks thus "degraded" of origin also makes it possible to avoid, during the manufacture of access keys, the operation of random degradation, which further reduces plus the cost of implementing the process according to the invention.

 It will also be observed that a degraded flexible disk according to the invention is illegible by means of a commonly used flexible disk reader. You must either modify the reading program, or use this reader manually, which obviously complicates the task of counterfeiters.

 And finally, even if we manage to read a degraded flexible disk according to the method of the invention and to reproduce the latter, it will be necessary, in order to be able to completely reproduce an access key, to decode and even decrypt the information recorded on the original floppy disk and reproduce the same information on the counterfeit floppy disk which is a particularly complicated job.

The characteristics and advantages of the present invention will emerge from the description which follows with reference to the appended drawings in which
- Figure 1 is a schematic view of a flexible disk used as an information medium according to the invention
FIG. 2 is a simplified algorithm illustrating a preferred coding and encryption method making it possible to code the information relating to the structure of the flexible disk illustrated in FIG. 1;
- Figure 3 is a simplified algorithm for an access key validity test, integrated in the protected software;
- Figure 4 is a block diagram of a method of protection against the diversion of validity test orders given by the subroutine according to the simplified algorithm of Figure 3
FIGS. 5, respectively 6, illustrate a commented listing of a program written in C language for an IBM PC compatible computer, implementing the simplified algorithm of FIG. 2, respectively 3.

In the description of the preferred embodiment which will follow, there will be described successively
- the access key used and the manufacturing thereof
- evaluation and comparison operations carried out during access control.

Access key used and manufacture of
this one
According to the embodiment chosen and shown in the figures, the invention implements as an information medium, intended to serve as an access key, a flexible disc 10 of 5.25 inches.

 Basically this flexible disk is formatted and divided into tracks, themselves divided into sectors, so that the flexible disk is cut out spatially as illustrated in FIG. 1. The tracks are arranged concentrically from the edge towards the center.

They are numbered from p0 to p39. In FIG. 1, only the tracks p0 and p39 are shown diagrammatically. Each track is divided into sectors (9 sectors in the case of formatting to IBM PC standards, under the MS-DOS operating system).

The sectors are in the form of angular sectors and they have been numbered in FIG. 1 from 51 to 59.

 We also know that there are two types of flexible disc, those called "double-sided" and those called "single-sided". In the case of a double-sided flexible disk, cutting of the same type is carried out on the other face of the flexible disk. In the description which follows, it will be a question of “double-sided” flexible disks, but it will be observed that, obviously, all that is described can also apply, to “single-sided” flexible disks.

Conventionally, these flexible disks are read by a disk drive comprising a control mechanism associated with a control logic written in the read-only memory of the central unit. The flexible disc player has two magnetic read heads for alternately reading each side.

 According to one aspect of the invention, the information medium used, here the flexible disk 10, is partially and permanently degraded randomly.

 The degradation, shown diagrammatically in FIG. 1, consists here of a trace 12 left by a solvent such as acetone in the visible face of the flexible disk 10 illustrated in FIG. 1. In the embodiment presently described the solvent has been applied from a stick comprising a cloth soaked in acetone which has been treated, randomly on a part of the flexible disc so that it has left, in the magnetic material on the surface of the flexible disc, the trace 12. Theoretically the sectors crossed by the trace 12 have been degraded, that is to say that their memorizing properties have been altered so that no information can be written or read there. This deterioration is also final because it is irreversible.

 In the disc illustrated in Figure 1 the following sectors have been altered - sector 51 of track p0. In fact, the trace 12 enters at 13 in the sector sl of the track p0.

- sector 52 of track p0 (portion 14 of track 12) - and, in the example considered, sector 52 of each of the subsequent tracks p1 to P3s-
It should be noted here that trace 12 can have any shape and that any number of sectors can be altered. Such a trace, carried out randomly, is obviously unique, that is to say that it is distinct from one damaged flexible disk to another.

A simple calculation shows that there are 2360 # l possibilities of degradation of a 5.25 inch flexible disk face formatted as presently described and 2720 # l possibilities of degradation of the sectors on both sides
The degradations can be obtained by other means than that described here. Thus, for example, a scratching of the surface of the disk is liable to alter the memorizing properties of the sectors of this flexible disk. As a variant, the flexible disc 10 constituting the key may very well be in the form of a flexible disc whose memorizing properties are altered, invisible to the naked eye.

This will for example be the case with certain flexible discs rejected during quality control by the disc manufacturer for lack of magnetization in certain sectors. Choosing such disks as access keys has several advantages
- degradation invisible to the naked eye which complicates the task of counterfeiters
- Random degradation of the disc from the start, which makes it possible to avoid having to carry out this degradation by a process such as those explained above. It follows a low cost of manufacturing the access key
- improvement of the profitability of flexible disc production lines.

 According to the invention, a transcription is carried out of at least a portion of the structure of the degradation, and this transcription which is stored in an undegraded part of the medium is used as access information.

 In practice, in this embodiment, it is a matter of carrying out a coding giving the position of the sectors altered by the trace 12 and of storing this coding in an undegraded part of the support.

 Materially, in this embodiment, to manufacture an access key, there is a degraded flexible disk as explained above and a flexible disk player connected to a computer implementing the simplified algorithm illustrated in the figure 2 using the program illustrated in figures 5. To facilitate understanding of the program, titles, subtitles and comments have been inserted in italics between the various groups of instructions.

 Classically, the program is divided into three chapters - Chapter I: definition of the variables, - Chapter II: definition of the specific procedures, - Chapter III. main procedure statement.

 The main procedure comprises three specific procedures (FIGS. 2 and 5d) - a procedure 110 during which a so-called "state table" is described, describing the state of the surface of the disk, sector by sector - a procedure 120 of search for sectors on which the encryption table corresponding to the state table determined at 110 will be written - a procedure 130 for writing said state table on the sectors determined at 120.

 The procedure 110 for constituting a state table essentially comprises a loop during which all the sectors of the flexible disk are tested to determine whether each of these is valid or altered. Test 111 checks whether the sector being analyzed is the last of the flexible disk (the one numbered: fl, 59 P39 last sector of the last track on side 2 of the flexible disk).

 If the test 111 is negative, a first test 112 is executed during which one comes to check whether the sector being analyzed is indeed the first of the track being examined (sector numbered sl). If this test is positive, the track considered is formatted. To do this, the procedure 113 described in FIG. 5d under point 2.9 is implemented.

 At the end of the formatting procedure 113, or if the test 112 proves to be negative, a procedure 114 of analysis of the state of the sector considered is executed. This procedure is called by the program under point 2.3.4.

in Figure 5b and set out under point 2.7 in Figure 5c. At the end of this procedure, we therefore have information allowing us to know if the sector considered is valid or altered.

 A procedure 115 is then executed (described under point 2.3.4., FIG. 5b). The procedure 115 is a procedure making it possible to store the information obtained at the end of the procedure 114 in a state table.

 During the test loop 111, a storage operation 116 is also executed in a variable called "anchoring" during which the coordinates of the first altered sector encountered during analysis are put.

This operation is explained in the listing under point 2.3.5.

 The test 111 is executed for each of the sectors of the flexible disk. When all the sectors have been examined, and the test 111 proves positive, a state table describing the state of the surface of each face of the flexible disc is then available. The coordinates of the first defective annular sector encountered during the analysis are also available.

 The procedure 120 for searching encryption writing sectors is then carried out.

 This procedure includes operations 121-124 which are mentioned under point 2.2. of the listing in figure Sa.

 The procedure 120 essentially consists in searching for three valid sectors on the flexible disk in order to write the encrypted table of the state of the surface thereof.

 The search for valid sectors is done here by examining the sectors one by one concentrically following the tracks, following their natural order along each track.

 Those skilled in the art, user of the method, can plan to do the research using a different algorithm, capable of covering all or part of the surface of the flexible disk.

 The procedure 120 for determining three valid sectors begins with a test 121 which makes it possible to determine if one is at the end of the search procedure, that is to say if one has found the three valid sectors.

(point 2.2.1 of the listing in figure 5b).

 If the test 121 proves to be negative, a test 122 is then executed during which it is determined whether the sector examined is valid or not. If this test is negative, a procedure 124 for searching for a new sector is then executed. In the presently described embodiment, the surface of the flexible disk is moved as described above.

 Under point 2.8 (FIG. 5d) the test 122 and the procedure 124 for searching for free sectors used in the embodiment described here are illustrated, the call to the procedure 124 being mentioned in 2.2.2.

of Figure 5b.

 When the test 122 is positive, that is to say that the sector examined is valid, the position of this sector is stored in a table called "localization".

 When the three valid sectors have been found and their coordinates written in the "localization" table, the procedure 130 of writing the state table of the flexible disk on the three sectors considered is executed (point 2.4 of FIG. 5c).

 Under point 2.5, a procedure for transforming the linear coding (from 0 to 719) of the coordinates of the sectors of the flexible disk into "cylindrical" coordinates (face fl, f2; tracks: p0 to p39 sectors: s1 to s9) is illustrated. .

 Under point 2.7 there is illustrated a procedure for measuring the state of the sector considered implemented in the test loop 111 of the procedure 110 for constituting a state table.

 Finally, as explained above, the listing illustrated in figure Sa includes a chapter I of definition of the variables. The following variables are defined there - number of tracks per side (point 1.1) - number of sectors per track (point 1.2) - number of heads per flexible disk drive (point 1.3); - total number of sectors (point l.-4) - table of "linear" coordinates of the storage sectors of the surface state table of the flexible disk localization (point 1.5.) - pointer to the first damaged sector of the flexible disk: anchoring (point 1.6) - table describing the surface condition of the flexible disk: mapping (point 1.7).

Evaluation and comparison operations
performed during access control
In general, according to the invention, during access control, at least partially evaluating the state of the medium and comparing the result of this evaluation with the transcription stored on the medium.

 Thus, in the embodiment presently described, when the flexible disk 10, the manufacture of which has been described above, is used as an access key allowing access to information or to a controlled area, the means putting in works the process according to the invention must evaluate the state of the surface of the disc, that is to say in this case determine which sectors are altered and, then, compare the result of this evaluation with the information memorized on the support, in this case the transcription of the structure of the degradation recorded on the flexible disk by the process described above.

 The following description relates to an embodiment of this double step, the method according to the invention being used here to allow the protection of software against excessive duplication of the latter, only the bearer of a key access as described above being capable of being able to use the software in question. Thus, if this user duplicates the software, the copies can only be implemented by a computer by holders of the access key; however, as this is unique, it follows that at a given moment only either the original of the software, or a copy, can be used, which obviously reduces considerably the interest for the user to make copies. (Note however that this - process still allows the user of the protected software to make a so-called backup copy).

 Thus, the protection of the software is carried out by obliging the user to read, at the start of the protected software, the access key formed here by the degraded flexible disk 10 and to have it checked by the protected software. The conformity of the "key" actually introduced into the reader with the key actually manufactured and delivered with the software, by making a comparison between the evaluation of the surface condition of the flexible disk used as a key with the transcription of the structure of the degradation recorded there.

 It will be noted that one or more conformity tests can also be carried out during the operation of the software.

 We will now describe, in support of FIG. 4, a simplified algorithm 200 of a subroutine intended to be included for this purpose in the software that it is sought to protect.

 Figures 6a-6e illustrate a program written in C language implementing the algorithm 200.

As in Figures 5, to facilitate understanding of the program, titles, subtitles and comments have been inserted in italics between the various groups of instructions,
Conventionally, the program is divided into three chapters - Chapter I - Definition of variables, - Chapter II - Definition of specific procedures, - Chapter III - Statement of the main procedure.

 In the embodiment shown, the program first performs a test procedure for the absence of a software filter capable of having been implemented by a counterfeiter in order to thwart the conformity test procedure. This absence test procedure is described below in support of Figure 4 and exposed under point 2.11 of Figure 6d. In the event of the presence of such a software filter, the program ends because of a high probability that the flexible disk (access key) which will be examined next by the procedures 220, 230 and 240 is a counterfeit.

 In the other case, the procedure 220 exposed under point 2-9, figure 6d) is executed which essentially comprises a loop (point 2.9.1., Figure 6d) during which all the sectors of the flexible disk are tested for determine the first damaged sector of the examined flexible disk. As soon as the latter is encountered thanks to the test 222, the sequence of instructions 223 is executed (exposed in point 2.9.3., FIG. 6d) which stores in a variable called "anchoring" of the program 200 the coordinates of this first invalid sector .

 Procedure 230 is then carried out for finding the sectors containing the table describing the surface condition of the flexible disk.

 This procedure is exposed under 2.2, figure 6a: it includes operations 231 to 235.

 The procedure 230 essentially consists in searching for three valid sectors on the flexible disk in order to read the table of the presumed state of the surface of the flexible disk.

 The search is done in the same way as that exposed during the constitution of an access key.

 The procedure 230 (point 2.2 of FIG. 6a) for determining the three valid sectors begins with a test 231 (point 2.2.1 of FIG. 6a) which makes it possible to determine whether one is at the end of the search procedure, that is to say ie if we found three valid sectors.

 If the test 231 proves to be negative, a test 232 is then executed (point 2.7 of FIG. 6c) during which it is determined whether the sector examined is valid or not. If this test is negative, a procedure 233 (point 2.2.2 of FIG. 6a) is executed to search for a new sector. We move on the surface of the flexible disk following the natural order of the sectors as described in the section on building an access key. If the test is positive, the position of this sector is stored in a table called "localization".

 When the three valid sectors have been found and their coordinates stored in the corresponding table, the procedure 235 reads the state table of the flexible disk (point 2.10, figure 6d).

 In the last phase, the conformity of the access key is tested through the 240 procedure (point 2.12, figure 6e).

 In the presently described embodiment, the philosophy of the conformity test is as follows. We choose to check if there is an almost perfect correspondence between the surface condition of the disk measured during the conformity procedure and that announced by the state table read and decrypted during the same conformity test. The applicants' experience has revealed that it would suffice to test that a small proportion of all the sectors present on one side (here fifteen sectors taken at random from the three hundred and sixty that comprise a 5.25 inch flexible disk face ). Experience has also shown that, during this verification, one could only tolerate a small margin of conformity error (in this case, out of fifteen sectors, at least twelve must prove to be in conformity).

 The 240 procedure therefore begins with a test aimed at determining whether fifteen sectors of the flexible disk have been tested. If this is not the case, procedure 242 randomly draws the linear coordinate of a new sector to be tested (point 2.3, figure 6b). The test 243 allows to know if the sector is a priori damaged (described under point 2.12.3, figure 6e). If this is the case, the track containing this sector is formatted by the procedure 224 (point 2.12.5, figure 6e).

 Indeed, the formatting of a sector makes it possible to rectify a purely logical, therefore reversible "degradation", which could have been caused by a counterfeiter.

It is therefore only after the fact that the state of this sector is tested by calling procedure 245 (point 2.12.6, figure 6e). If this test is in accordance with the information collected in the surface state table of the flexible disk, a success counter is incremented by procedure 247 (exposed under points 2.12.6, 2.12.7, FIG. 6e).

 At the end of this loop 241, the flexible disk is declared to conform if more than 11 sectors have been found to conform to the description of the surface state table of the flexible disk (described under point 2.12.8, FIG. 6e).

On examination of FIGS. 6, it will be observed that certain procedures or variables are identical to the procedures or variables already described in support of FIGS. 5. These identical elements which will not be described again here are the following - procedure for transforming the linear coding of the coordinates of the sectors of the flexible disk, in cylindrical coordinates (point 2.5 figure 5C and point 2.4 figure 6b), - procedure for measuring the state of the sector considered (point 2.7 figure 5.C and point 2.6 figure 6.C ), - the following variables are to be repeated
- number of tracks per side (point 1.1 figures
5a and 6a),
- number of sectors per track (point 1.2
Figures Sa and 6a),
- number of heads per reader (point 1.3
Figures Sa and 6a)
- total number of sectors (point 1.4 figures
Sa and 6a),
- table of linear coordinates (point 1.5
Figures Sa and 6a),
- pointer to the first altered sector
(point 1.6 figures Sa and 6a),
- surface state table of the flexible disk
(point 1.7 figures Sa and 6a).

 We will now describe in support of FIG. 4 the procedure 210 for testing the absence of a filter mentioned during the description of FIG. 3 and referred to in point 2.11 of FIG. 6d. This control procedure is implemented when the user of the software that is to be protected has direct control over the computer implementing this software, in particular when the user of the software in question runs it on the IBM PC type personal computer.

 Indeed, it is known that one of the simplest means to circumvent an excess control procedure, and in particular that known as the "laser hole", consists in recording in the memory of the computer used by the counterfeiter or the user of the counterfeit software, a resident program intended to filter the orders sent by the access control procedure in the software. Thus, in the so-called "laser hole" method, this resident program intercepts the order to check the presence of the hole in the sector considered in the flexible disk and simulates the presence of such a hole.

 The inventor sought a way to avoid the diversion of the access control procedure in the protected software.

Conventionally, we know that a computer has two memory areas, one called random access memory (RAM /
Random Access Memory) and the other known as ROM
Read Only Memory). The application software is stored in the computer's RAM while the read-only part includes, in a non-modifiable form all the input-output procedures, the interfaces with the computer's peripherals. In particular, in the read-only memory of the computer the procedures for managing the floppy disk drives are recorded. These management procedures consist of successive instructions controlling in particular the position of the read heads, the movement of the latter, etc. In FIG. 4, the RAM part of the computer is shown diagrammatically under the reference RAM and under the reference
ROM the read only part of the computer. Application software is stored in a portion of memory
RAM referenced in 30. This software includes an access control program. The latter comprises a series of instructions 31 implementing the program described in support of FIG. 3.

 The computer's RAM comprises a portion referenced as 32 comprising a series of addresses making it possible to call in the ROM read-only memory procedures dedicated to the management of the peripherals, in particular of the flexible reader (s). The instructions contained in part 32 of the RAM memory are called vectors because they point to addresses of the ROM memory and determine the start of the procedures for managing the peripherals and in particular the floppy disk drives.

In the computer RAM, these vectors are always written to the same addresses, all of these constituting the part referenced at 32 in FIG. 4. As we know, this device makes it possible to ensure the compatibility of the different computers "IBM compatible
PC ". In addition, in accordance with the same standards, the addresses which the vectors registered in zone 32 may point to are always between two terminals (namely, in hexadecimal, the FFFF numbers: 0000 and
FFFF: FFFF). The ROM zone considered has been referenced at 33 in FIG. 5. Thus, when it is desired to have the presence of a conforming access key checked in the flexible disk reader, the program 30 sends the series of instructions 31 which makes it possible to designate an address vector 34 in the area 32 of the RAM, the vector 34 pointing to a predetermined address in the ROM, lying between the two aforementioned terminals. In the ROM begins at this address the series of instructions managing the flexible disk.

 Thanks to the presence of other parameters in registers not represented in FIG. 4 but conventional in the art considered, the read head comes to be positioned above the sectors of the disc, indicated in the sequence of instructions 31 of the software. protected. Thus the test procedure described above with the support of FIG. 3 is then correctly carried out.

 In the case where an infringer wishes to divert the control procedure, it is known to modify the instruction of the address vector 34 in the part 32 of the RAM so that instead of pointing an instruction in the ROM 33, this vector points to an address of a filtering program developed by the counterfeiter and saved in portion 35 of the RAM.

In this filtering program, the counterfeiter may have reproduced, if he has the means, in software form the topography of the flexible disk of access key and in particular that illustrated in FIG. 1. This is how he can have recorded, in the hypothesis where he would have a flexible disc reader to read a flexible disc such as that illustrated in FIG. 1, the position of the altered sectors, namely the sector sl of track p0 and the sector 52 of track p0 to p39.

 Thus, in response to a read order given by the following instructions 31, the filtering program can let read a flexible disk 10 'containing all the encrypted information recorded in the valid sectors of the flexible disk 10. This information will return to the program 30 by the normal path shown diagrammatically by the link 36. On the other hand, when the sequence of instructions 31 instructs the reading of an invalidated sector, the filtering program recorded at 35 may compensate for the lack of invalidation of the sector in the disk. flexible 10 'by sending information corresponding to an invalidation of the sector considered directly to the program 30 (arrow in bold line 37).

According to the invention, when it is implemented on a personal computer, in particular of the IBM PC type, at the start of the test procedure (see FIG. 3 in particular), that is to say upstream of the instructions recorded at 31 in program 30, it is tested whether the content of vector 34 is well between the upper and lower limits of the addresses of the read-only memory 33 (in the current state of the PC FFFF standard: 0000 and
FFFF: FFFF). If this is the case, it is known that the vector 34 then points to an address in a ROM part of the memory which is non-reprogrammable and which imperatively commands reading of a flexible disc. If this is not the case, it is deduced therefrom that the vector 34 points to a different address in random access memory and this can then only be a filtering program.

 Of course, the present invention is in no way limited to the embodiment described and shown, but on the contrary quite encompasses any variant within the reach of ordinary skill in the art.

 In particular, in the embodiment presently described, the information medium used as an access key is a flexible disk of which part of its memorizing magnetic properties is permanently and randomly degraded. It is obvious that the present invention can be implemented with any other information medium known to those skilled in the art.

 Similarly, in accordance with the invention, to implement it it is not necessary to store on the information medium used as an access key all of the degradation. Memorizing a transcription of only a portion of the degradation may be sufficient.

Claims (11)

 1. Access key peddling an information carrier (10) in which information relating to its structure is stored. characterized in that at least one of the storage properties of the support is partially and definitively degraded in a random manner (12), in that said information partially consists at least of a transcription of the structure of the degradation ((S1, PO), (SX, P,), (S2, Pro,)) and in that this transcription is stored in at least an undegraded part of the support.  2. Flexible disk used as an access key according to claim 1  3. Flexible disk according to claim 2, divided into sectors, characterized in that a set of encrypted information corresponding to the position of the altered sectors is recorded on certain of the unaltered sectors ((S1, PO), ( S2, P0), (S2, PX  4 Method of manufacturing an access key of the kind comprising an information medium (10) in which related information. has its structure recorded, characterized in that an information medium is used (10) of which at least one of the memorizing properties is partially and definitively degraded in a random manner (12), in that, to constitute, partially at least, said information the structure ((S1, P0), (S2, P0). (S2, For)) of the degradation (12) is transcribed, and in that this transcription is stored in at least one non- degraded support (10).  5. Method according to claim 4, characterized in that a magnetic medium is used as information carrier, such as a flexible disk, the magnetic properties of which are partially. randomly and permanently altered.  6. Method according to claim 5, carac terris in that, to degrade this support, is altered randomly. irreversible and permanent magnetic properties of the support.  7. Method according to any one of claims 5, 6, characterized in that said magnetic support being a flexible disc (10) divided into sectors, the magnetic state of each sector of the disc is determined.  ((S2, P0) - (S0, P09)); a set of encrypted information corresponding to the position of the altered sectors ((S1, P0), (S2, P0), (S2, P09)) is recorded on some of the unaltered sectors.  6. Access control method implementing an unambiguous recognition of access information stored on an information medium (10) called access key ", characterized in that the key used is access a medium (10) one of which, in the care of its memorizing properties, is partially and definitively degraded in a random manner, and a transcription of at least a portion of at least the structure is used as access information ((S1, P0), (S2, P0), (S2, P09)))) of the degradation (12) in that said transcription is stored in at least one non-degraded part of said support (10): and in that that, during access control, the state of the medium (10) is evaluated, at least partially, and the result of this evaluation is compared to the transcription stored in the medium.  9. access control method, intended for the protection of software, implementing an unambiguous recognition of access information stored on an information medium (10) called "access key", characterized in that a support (10) is used as access key, at least one of its memorizing properties of which is partially and definitively degraded in a random manner, and use is made, in care partially, as access information, a transcription of at least a portion of the structure ((Sa, P.), (Ss, P.), (S2, P ##)) of the degradation (12); in that said transcription is stored in at least one non-degraded part of said support (10); in that, during the access control, the state of the medium (10) is evaluated, at least partially, and the result of this evaluation is compared with the transcription stored in the medium and in what is included in said software at Poins a series of instructions (200) controlling the implementation of said evaluation and executing said comparison.  10. Access control method, intended for software protection, implementing an unambiguous recognition of access information stored on an information medium (10) called "access key", characterized in that a support (10) is used as access key, at least one of its memorizing properties of which is partially and definitively degraded in a random manner, and at least partially, is used as access information, a transcription of at least a portion of the structure ((S1, P.), (5 =, P.>, (Sz, Pas)) of the degradation (12), in that said transcription is stored in at least an undegraded part of said medium (10); in that, during access control, the state of the medium (10) is evaluated, at least partially, and the result of this evaluation is compared with the transcription stored in the support and in that included in said software at least a series of instructions (200) comman during the implementation of said evaluation and executing said comparison and comprising a procedure (210! filter absence test.  11.Access control method, intended for the protection of software, implementing unambiguous recognition of access information stored on an information medium (10> called access elef ", characterized in that a support (10) is used as an access key, one of which at least one of its memorizing properties is partially and definitively degraded in a random manner, and one uses, at least partially, as access information, a transcription of at least a portion of the structure ((S1, P0), (S2, P0), (S2, P09)) of the degradation (12); in that said transcription is stored in at least one non- degraded from said medium (10); in that, during access control, the state of the medium (10) is evaluated, at least partially, and the result of this evaluation is compared to the transcription stored in the medium and what is included in said software at least a series of instructions (200) comma nd the implementation of said evaluation and executing said comparison and comprising a procedure (210) for testing the absence of a filter and test instructions according to which one checks mi the address vector (34) at the start of the disk management procedures flexible actually points into the computer's ROM.  12. Method according to any one of claims 4, 8 to 11, characterized in that a support is used which is partially and permanently degraded, randomly, at least one of the memorizing properties.  13. Method according to any one of claims 8 to 12, characterized in that a flexible disk (10) divided into sectors ((S1, P0) - (S9, P09)) is used as access key, including the magnetic properties are partially, randomly and definitively altered. a set of cryptic information corresponding to the position of the altered sectors ((Sa, P0), (S2, P0), (S2, P ..)> being recorded on some of the unaltered sectors, and in that during an access control, during the evaluation step, the state of at least a portion of the sectors of the flexible disk is determined and the result obtained is compared with the information stored on the flexible disk during the manufacture of the key.