EP3818459A1

EP3818459A1 - Method and system for authenticating the computer-aided manufacturing of a three-dimensional part

Info

Publication number: EP3818459A1
Application number: EP19733827.0A
Authority: EP
Inventors: Perez PELAGE
Original assignee: Viaccess SAS
Current assignee: Viaccess SAS
Priority date: 2018-07-03
Filing date: 2019-07-02
Publication date: 2021-05-12
Also published as: US20210264041A1; CN112352236A; WO2020007867A1; FR3083626A1; FR3083626B1

Abstract

The invention relates to a method and system for authenticating the computer-aided manufacturing of a three-dimensional part by a manufacturing device, using at least one predetermined manufacturing material, said three-dimensional part to be manufactured being defined by a three-dimensional model obtained by computer-aided design and shown in a predetermined file format, said manufacturing device being controlled for manufacturing from said three-dimensional model and from a comprehensive set of manufacturing parameters. The method comprises the steps of: - generating (46) a cryptographic key (K') according to the parameter values of a non-empty parameter subset (SP') of the comprehensive set of manufacturing parameters, comprising at least one parameter of a set of configuration parameters of the manufacturing device, or at least one parameter of a set of parameters relating to the manufacturing method or at least one parameter of a set of characteristic parameters of the manufacturing material, - detecting (48) a watermark in said three-dimensional model by applying a predetermined watermark detection algorithm which is initialised with the generated cryptographic key (K'), - comparing (52) the detected watermark to an expected watermark, and authenticating the computer-aided manufacturing of said three-dimensional part in case of a positive comparison.

Description

Method and system for authentication of computer-aided manufacturing of three-dimensional parts

The present invention relates to a method and a system for authentication of computer-aided manufacturing of three-dimensional parts.

The invention is in the field of computer-aided manufacturing, using three-dimensional models obtained by computer-aided design.

In the field of computer-aided manufacturing there is, on the one hand, additive manufacturing, for example 3D printing, which consists of manufacturing a part by depositing successive layers of one or more predetermined materials, and d on the other hand, subtractive manufacturing, in which a 3D part is made by removing material from a block of material.

In addition, computer-aided manufacturing includes the physical manufacturing of physical objects and so-called virtual manufacturing, which involves generating a digital twin of a physical object. The digital twin of a physical object is an object, simulated in a computer system, having the same shape and the same physical properties, and is used in simulation phases, for example to test performance and robustness properties of the object before its actual physical manufacture, or to perform predictive maintenance of the part manufactured or to be manufactured itself, or of the manufacturing device. Virtual manufacturing is advantageous especially in industrial prototyping phases, where it makes it possible to reduce manufacturing costs by avoiding the manufacture of multiple expensive prototypes. It is also advantageous for predictive maintenance purposes, under which it makes it possible to anticipate the occurrence of faults or failures, and therefore the need for maintenance interventions, of the part manufactured or to be manufactured itself, or of the manufacturing device.

In all cases, computer-aided manufacturing is carried out according to a manufacturing process, on the one hand from a three-dimensional model obtained by computer-aided design and represented in a predetermined file format, and on the other part by using a global set of manufacturing parameters which includes a set of parameters relating to the manufacturing process, a set of parameters relating to the materials used, and a set of configuration parameters of the device for manufacturing the part.

In the case of additive manufacturing, and more specifically 3D printing, the manufacturing process designates the technique used for the formation of a layer of material. It can for example be selective laser melting, or "Selective Laser Melting" (SLM), in which a laser beam is directed towards a bed of powder. previously deposited, or powder projection, or “Directed Energy Deposition” (DED), in which a laser beam is directed towards a jet of material to melt it as it is deposited. Other methods are known, and the invention applies in their contexts. For each of these processes, corresponding parameters are to be set.

The values of the parameters of the global set of manufacturing parameters contribute to the final properties of the manufactured object, in terms of robustness and more generally, compliance with the specifications of the part to be manufactured.

The development of parameters relating to the manufacturing process and configuration parameters of the manufacturing device, in particular, requires the intervention of qualified operators and can, in certain applications, be long and costly.

Particularly in the field of industrial production of three-dimensional parts using computer-aided manufacturing processes, it is important to be able to validate the authenticity of the manufacturing process for a given part.

The authenticity of the manufacturing process is used here to denote the authenticity of the association of the three-dimensional model and at least one non-empty subset of the global set of parameters.

Various methods of inserting a watermark, known as watermarking in English, are known in three-dimensional model description files or in associated digital images, with the aim of making it possible to detect possible hacks or illegitimate appropriation by a third party. 'a 3D model. However, such methods are only used to authenticate the 3D model used, or to ensure access to the only manufacturing machines authorized to the 3D model.

One of the objectives of the invention is to improve the security of computer-aided manufacturing of three-dimensional parts, in particular for the industrial manufacture of such parts.

To this end, the invention proposes a method of authentication of computer-aided manufacturing of a three-dimensional part by a manufacturing device, using at least one predetermined manufacturing material, said three-dimensional part to be manufactured being defined by a three-dimensional model obtained by computer-aided design and represented in a predetermined file format, said manufacturing device being adapted to be controlled to manufacture said part from said three-dimensional model and from a global set of manufacturing parameters. This process includes steps of: generation of a cryptographic key as a function of the values of the parameters of a non-empty subset of parameters of the global set of manufacturing parameters of said three-dimensional part, said non-empty subset of parameters comprising at least one parameter a set of configuration parameters of the manufacturing device, or at least one parameter of a set of parameters relating to the manufacturing process or at least one parameter of a set of parameters characteristic of the at least one manufacturing material,

- detection of a watermark in said three-dimensional model by applying a predetermined watermark detection algorithm initialized with the generated cryptographic key,

-comparison of the detected watermark with an expected watermark, and authentication of the computer-aided manufacture of said three-dimensional part in the event of a positive comparison.

Advantageously, the method of the invention makes it possible to authenticate the computer-aided manufacture of three-dimensional parts by validating in a linked manner the three-dimensional model defining the part and a non-empty subset of the global set of parameters comprising at least one parameter. of a set of configuration parameters of the manufacturing device, and / or at least one parameter of a set of parameters relating to the manufacturing process and / or at least one parameter of a set of parameters characteristic of the at least one material Manufacturing,

The computer-aided manufacturing authentication method for a three-dimensional part according to the invention may have one or more of the characteristics below, taken independently or according to any acceptable combination.

The method further includes inhibiting a step of manufacturing said three-dimensional part in the event of a negative comparison.

The non-empty subset of parameters is determined prior to the generation of a cryptographic key and comprises said set of parameters relating to the manufacturing process, and a predetermined subset of configuration parameters of the manufacturing device and a predetermined subset characteristic parameters of the at least one manufacturing material.

The generation of a cryptographic key is also dependent on a secret key.

The method further comprises extracting said set of parameters relating to the method for manufacturing metadata associated with the received three-dimensional model. The method further comprises receiving said set of configuration parameters from the manufacturing device, from a man-machine interface of the manufacturing device, or from an external control device.

The detected watermark is formed from a series of N bits, N being a non-zero positive integer, the method comprising a step of obtaining the expected watermark from a memory.

According to another aspect, the invention relates to a method of inserting a digital watermark for the authentication of computer-aided manufacturing of three-dimensional parts by a manufacturing device using at least one predetermined manufacturing material, said three-dimensional part to be manufactured being defined by a three-dimensional model obtained by computer-aided design and represented in a predetermined file format, said manufacturing device being adapted to be controlled to manufacture said part from said three-dimensional model, the method comprising a step of obtaining a three-dimensional model of a three-dimensional part to be manufactured. This digital watermark insertion process includes steps of:

determination of a non-empty subset of a global set of manufacturing parameters for said part to be manufactured, said non-empty subset of parameters comprising at least one parameter from a subset of device configuration parameters manufacturing, or at least one parameter from a set of parameters relating to the manufacturing process or at least one parameter from a subset of parameters characteristic of the at least one manufacturing material,

- generation of a cryptographic key as a function of the values of the parameters of said non-empty subset of parameters,

insertion according to said cryptographic key of a watermark formed by a series of N bits, N being a non-zero positive integer, by applying a predetermined watermark insertion algorithm, in said three-dimensional model to obtain a model three-dimensional watermarked of said workpiece.

The method of inserting a digital watermark for the authentication of computer-aided manufacturing of a three-dimensional part according to the invention may have one or more of the characteristics below, taken independently or according to any acceptable combination.

The generation of a cryptographic key is also dependent on a secret key.

The non-empty subset of parameters includes the manufacturing device configuration parameter subset, and the parameter set relating to the manufacturing process and the subset of parameters characteristic of the at least one manufacturing material,

The method includes storing watermark data associated with the watermark inserted into said three-dimensional model.

The method includes storing all of the manufacturing parameters in association with the watermarked model in a file in predetermined file format, said set of manufacturing parameters being stored in the form of metadata.

According to another aspect, the invention relates to a digital watermark insertion device for the authentication of computer-aided manufacturing of three-dimensional parts by a manufacturing device using at least one predetermined manufacturing material, said three-dimensional part to be manufactured being defined by a three-dimensional model obtained by computer-aided design and represented in a predetermined file format, said manufacturing device being adapted to be controlled to manufacture said part from said three-dimensional model, said device comprising a module adapted to receive a three-dimensional model of a three-dimensional part to be manufactured. This device includes modules adapted to:

-determining a non-empty subset of a global set of manufacturing parameters for said part to be manufactured, said non-empty subset of parameters comprising at least one parameter from a subset of configuration parameters of the manufacturing device , or at least one parameter from a set of parameters relating to the manufacturing process or at least one parameter from a subset of parameters characteristic of the at least one manufacturing material,

- generate a cryptographic key as a function of the values of the parameters of said non-empty subset of parameters,

inserting, as a function of said cryptographic key, a watermark formed by a series of N bits, N being a non-zero positive integer, by applying a predetermined watermark insertion algorithm, into said three-dimensional model to obtain a watermarked three-dimensional model of said part to be manufactured.

According to another aspect, the invention relates to a computer-assisted manufacturing authentication system for a three-dimensional part by a manufacturing device, using at least one predetermined manufacturing material, said three-dimensional part to be manufactured being defined by a three-dimensional model obtained. by computer-aided design and represented in a predetermined file format, the system comprising a device suitable for controlling said manufacturing device to fabricate said part from said three-dimensional model and a global set of manufacturing parameters. This system includes modules adapted to:

-generate a cryptographic key as a function of the values of the parameters of a non-empty subset of parameters of the global set of manufacturing parameters of said three-dimensional part, said non-empty subset of parameters comprising at least one parameter of a set of configuration parameters of the manufacturing device, or at least one parameter of a set of parameters relating to the manufacturing process or at least one parameter of a set of parameters characteristic of the at least one manufacturing material,

- detect a watermark in said three-dimensional model by applying a predetermined watermark detection algorithm initialized with the generated cryptographic key,

- compare the detected watermark to an expected watermark, and authenticate the computer-aided manufacture of said three-dimensional part in the event of a positive comparison.

According to one embodiment, the system comprises a module adapted to inhibit a step of manufacturing said three-dimensional part in the event of a negative comparison.

Other characteristics and advantages of the invention will emerge from the description which is given below, for information and in no way limitative, with reference to the appended figures, among which:

- Figure 1 schematically illustrates the main steps of a computer-aided manufacturing process of three-dimensional part according to an embodiment of the invention;

- Figure 2 is a block diagram of the main steps of inserting a watermark according to one embodiment;

- Figure 3 is a block diagram of the main steps of authentication of computer-aided manufacturing;

- Figure 4 schematically illustrates a computer-assisted manufacturing authentication system of three-dimensional part according to one embodiment.

The invention will be more particularly described in detail in the case of additive manufacturing of three-dimensional parts by 3D printing, from predetermined materials. However, as already explained, the invention also applies to a computer-aided manufacturing of a digital twin of a real 3D part, for example for the purposes of prototyping or predictive maintenance.

The invention also applies in the case of computer-aided subtractive manufacturing.

FIG. 1 illustrates the main steps involved in a process 1 of computer-aided production of three-dimensional part in which the invention applies. In a particular case, this process implements 3D printing of a part, for example an industrial part or a part intended for the consumer market.

This process includes a first step 2 of computer-aided design (acronym CAD), conventionally implemented using software dedicated to computer-aided design making it possible to obtain a model of the part to be produced expressed in a predetermined format.

The design is carried out by a first player, for example a design office or an industrialist.

For example, a format called 3D CAD (for Computer Aided Design) is used, this format expressing the three-dimensional geometry of the 3D part to be manufactured. In general, the parts to be manufactured have complex shapes, expressed from geometric shapes: lines, arcs, B-spline curves. The design step 2 receives as input an initial specification C relating to the part to be manufactured, comprising physical, thermal and mechanical properties. For example, these specifications include the desired shape of the part, the mass, the resistance, the temperature range of use.

In addition, at the input of step 2, there are a few manufacturing parameters: the manufacturing device, for example the type of 3D printer that will be used for manufacturing, as well as the characteristics of the printing process and the parameters of the material (s). The values of these parameters are obtained from the initial specifications C or from one or more external databases.

At the end of design step 2, a file is obtained in selected format comprising an initial Modjnit model of the 3D part to be manufactured.

The initial Modjnit model is provided at the input of a step 6 of preprocessing of this initial model, which includes a last watermark insertion operation specific to the invention. For example, the initial Modjnit model is stored on a non-volatile electronic recording medium, readable by a computer, this electronic recording medium being supplied to a device which implements step 6 of preprocessing.

According to a variant, the initial Modjnit model is stored in a file and transmitted via a communications network, according to a chosen communications protocol, to a device which implements step 6 of preprocessing.

The pretreatment step 6 is implemented by a second actor, for example a methods office, which may be different from the first actor, and which uses, for the insertion of watermark, a trusted third party for assisted manufacturing by computer. This trusted third party ensures the sharing of secrets, as described in more detail below, and provides the algorithm for calculating the cryptographic keys K and K ’, as described below, from shared secrets.

Step 6 includes, before the watermark is inserted, an operation to transform the initial Modjnit model, into a final model, and a set of metadata.

In addition to the initial model Modjnit, which is a classic CAD model, this operation takes as input a set P _fab of parameters of the manufacturing process, and subsets P _mat 'and P _{¥ nf} ' of the sets P _mat and P _mac , respectively parameters relating to the materials and configuration parameters of the manufacturing device used in the actual manufacturing phase 8 described below.

The values of the parameters of the set P _fab of parameters of the manufacturing process are obtained from experts in the methods office via a man-machine interface, or an external control device, from the device which implements step 6 of pretreatment. The values of the parameters of the subsets P _mat 'and P _cont ' of the sets P _mat and P _mac , are obtained from one or more external databases.

The set P _mat of characteristic parameters of the manufacturing material (s) comprises for example physical characteristics of the materials, for example polymer or metal, particle size, humidity and oxidation rate, melting temperature.

For example, the parameters of size (granulometry) or of shape of the material are known during step 6, and therefore belong to the subset P _mat 'of P _mat . On the other hand, the moisture content of the material, or the fact of knowing whether the material (its possible excess) is or cannot be reused, are examples of parameters of P _mat which do not belong to the subset P _mat ' . The set of configuration parameters of the manufacturing device P _mac includes all the parameters to be set for the device to operate, that is to say both physical parameters (eg physical characteristics of the laser rays), and environmental parameters (atmosphere, humidity).

For example, the temperature parameter of the laser beam must also be known during step 6, and therefore belongs to the subset P _{¥ nf} 'of P _mac · On the other hand, the parameters relating to the manufacturing environment such as the oxygen or radon level in the manufacturing enclosure, are examples of parameters of P _mac which do not belong to the subset R _{¥ h} L

The set P _fab of parameters relating to the manufacturing process includes information relating to the manufacture of the desired part, according to the specifications, for example information relating to the positioning of the part, to the support (s) to use when depositing material or the laser strategy (scanning direction, etc.) to be implemented for each layer to be manufactured. They also include controls of the manufacturing device for each layer of material to be deposited.

Of course, the set of parameters P _fab depends on the manufacturing process S LM, DED.

In addition, the sets of parameters P _mat , P _mac and P _fab are partly interdependent, all being linked to the part to be manufactured and to the means to be used to manufacture it.

The final model is a 3D model, describing the geometry of the part to be manufactured, but in a format, called exchange, different from that of the initial model, such as, for example, IGES (“Initial Graphics Exchange Specification”), STEP (“Standard for Exchange of ProducT Model Data”), STL (“Stereolitography”) or AMF (“Additive Manufacturing File Format”).

In one embodiment, in this final model, the geometry of the part is very slightly modified as a function of some of the parameters taken into account of the overall set of manufacturing parameters.

The metadata produced by the transformation operation includes the manufacturing parameters P _fab .

Step 6 of preprocessing ends with a watermark insertion operation in this model, according to a non-empty subset of the global set of manufacturing parameters, in the 3D model to obtain a watermarked model Mod_WM of the 3D part to be manufactured. A detailed embodiment of the insertion operation will be described in detail below with reference to FIG. 2. In one embodiment, the watermarked model is stored in a file of given format, and the associated manufacturing parameters P _fab are also stored in this file in the form of metadata.

Process 1 also includes a manufacturing step 8 implemented by a computer-aided manufacturing device, for example a 3D printer.

In the case of a material manufacturing of the 3D part, the manufacturer, the third actor in the process, receives the material (s) 4 to be used and all of the characteristic parameters of the materials P _mat , the watermarked model Mod_WM obtained in step 6 pre-treatment, as well as the expected values of the parameters relating to the manufacturing process P _fab .

The manufacturing device also receives, for example by means of a man-machine interface which it comprises or an external control device, a complete set of configuration parameters P _mac , that is to say say values for all of the configuration parameters to operate the manufacturing device.

In the case of virtual manufacture of the digital twin of the 3D part, with the only difference from the above, the manufacturer does not receive the material (s) 4, but only the set of parameters characteristic of the materials P _mat and l set of parameters from sets P _fab and P _mac .

In order to ensure the safety of manufacturing and the production of 3D parts having the characteristics provided for by the specifications, the manufacturing step implements an authentication according to the invention implementing a detection of the watermark inserted in the model watermarked Mod_WM.

Indeed, it is a question of securing the production in relation to cases where the 3D model itself or the manufacturing parameters have been modified, maliciously or not.

An embodiment of the authentication is detailed below with reference to FIG. 3.

The manufacturing step 8 is implemented by the manufacturer, in cooperation with the trusted third party who contributed to the pretreatment step, more precisely by ensuring the watermark insertion operation.

In case of non-authentication of the overall manufacturing process, it is planned to inhibit the printing of the 3D part or its digital twin, that is to say not to trigger it. Advantageously, manufacturing security is then ensured, any use of configuration parameters which can induce a malfunction of the manufacturing device being prevented. In addition, advantageously, this makes it possible to reduce costs by avoiding the production of potentially defective parts, or to commit resources in the predictive maintenance of such parts or of devices illegally or improperly used to produce them.

As a variant, the production is not interrupted but the parts produced are not approved because they do not correspond to the manufacturing conditions provided for to satisfy the initial specifications.

The production process 1 optionally includes a post-treatment step 10, comprising for example an operation for finishing the 3D part, for example by milling, sanding, polishing, electropolishing, heat treatment, surface treatment, removal of supports, as well as 'a 3D part test operation. This post-processing step is carried out according to methods known in the state of the art.

Finally, the process includes the supply 12 of the parts to a final recipient, who applies, for example, tests of conformity with the initial specifications.

It should be noted that in the case of virtual manufacturing, the supply 12 of the part is for example the supply of the digital twin of a 3D part to be manufactured to a software application which performs tests and / or predictive maintenance .

It is also envisaged to carry out both a hardware manufacturing of 3D parts and an associated virtual manufacturing, so as to simulate the use and to perform predictive maintenance on the digital twin of actually used 3D hardware parts.

FIG. 2 is a block diagram of an embodiment of the insertion of a watermark in the pretreatment step 6 described above.

In one embodiment, the watermark insertion is performed by an executable program code instruction module implemented by a programmable electronic device. . Preferably, the watermark insertion module is saved and executed in a secure memory and by a processor, such as for example existing in a smart card.

In this embodiment described with reference to FIG. 2, the insertion of the watermark comprises a first step 20 of receiving a final 3D model of the part to be manufactured, resulting from all of the pre-processing operations of a initial 3D model, except for watermark insertion.

Step 20 is followed by a step 22 of determining at least one non-empty subset SP of the global set of manufacturing parameters.

In this step forming part of the preprocessing 6, we have the set of preprocessing parameters consisting of the set P _fa b of parameters relating to the manufacturing process, and sub-assemblies P _mat 'and P _{¥ nf} ' of the sets P _mat and P _mac , respectively parameters relating to the materials and configuration parameters of the manufacturing device.

The determination 22 consists in determining a non-empty subset SP of the set of preprocessing parameters.

In one embodiment, the non-empty subset SP consists of the set of parameters P _mat 'and / or P _{¥ nf} ' and / or P _fab

Preferably, the non-empty subset SP consists of all the parameters of the sets P _mat 'and P _conf ' and P _fab .

According to a variant, the non-empty SP subset consists of only one of the P _mat ', P _conf ' and P _fab subsets. For example, the non-empty SP subset is formed by the P _fab subset. .

According to another variant, the non-empty subset SP consists of a predetermined number P of parameters of each of the subsets P _mat ', P _conf ' and P _fab

The method also includes a step 24 of obtaining a secret key K ₀ . The secret key K ₀ is shared between the methods office and the manufacturer. This sharing is ensured by the trusted third party.

According to a variant, the secret key K ₀ is associated with an identifier of the initial 3D model Modjnit and shared by all the manufacturers, if there are several, of the part defined by the 3D model Modjnit.

Then, a cryptographic key calculation K is performed in step 26, by applying a cryptographic function parameterized by the secret key K ₀ and the non-empty subset SP of parameters chosen in step 22.

For example, a hash function is first applied to the set of concatenated values of the parameters of the chosen subset, to obtain a fingerprint. Any known hash function, such as MD5 (Message Digest 5), SHA-1 or SHA-256 (Secure Hash Algorithm 1 or 256), RIPEMD-160 (RACE Integrity Primitives Evaluation Message Digest 160) or Whirlpool is applicable here. The fingerprint obtained is then encrypted using a symmetric encryption algorithm and the key K ₀ , to obtain the cryptographic key K. Any known algorithm, such as AES (Advanced Encryption Standard), MARS, RC6, Serpent , Twofish or Blowfish is applicable here.

Alternatively, the cryptographic key K is calculated as a key fingerprint message authentication code, or HMAC, for "keyed-hash message authentication code", that is to say using a cryptographic hash function. in combination with the key K ₀ . Any iterative hash function can be used to calculate an HMAC. This is for example the case of MD5 or SHA-1, the algorithm resulting from the calculation of HMAC being respectively noted HMAC-MD5 or HMAC-SHA1.

The step 26 of generating a cryptographic key K is followed by a step of inserting a watermark 28 in the final 3D model, the insertion of the watermark being dependent on the cryptographic key K.

For example, in one embodiment, the watermark is formed from a series of N bits {wi, ..., w _N }, each w, being equal to 0 or 1, N being a predetermined number or dependent on the final 3D model. The series of N bits is predetermined or randomly generated. It can also include both a predetermined series of bits and a randomly generated series of bits. In known manner, when it comprises a predetermined series of bits, this may for example include an identifier of a methods office, of a manufacturer, or of a manufacturing device.

For example, the watermark insertion method used is the method described in the article "Digital Watermark of 3D CAD Product Model" by X. Feng et al, published in International Journal of Security and Its Applications ", vol. 9, n ° 9, 2015. This method consists in modifying certain coordinates of geometric entities defining the 3D model, while preserving the final geometry of the part.

According to one embodiment, the points whose coordinates are modified which are randomly selected, the random walk function being initialized by the cryptographic key K.

According to a variant, the series of N bits {\ -, ..., \ _n } forming the inserted watermark, it is the points whose coordinates are modified which are selected randomly ,. In other words, in this embodiment, the watermark generated is a hazard generated using the cryptographic key K.

Of course, this is an example of an embodiment of the watermark insertion. There are many known methods known as blind, that is to say in which the watermark is detectable from the watermarked model, without the need to use the initial 3D model. Any known method of inserting a watermark in a 3D model of this type can be used. Advantageously, the calculated cryptographic key K is used as a cryptographic hazard in the insertion of the watermark.

Thus, a watermarked Mod_WM model is obtained. Note that when using the watermark insertion method described above, the metadata of the file in which the 3D model is stored is not modified by the watermark insertion.

The method also includes a step 30 of storing the watermark data F, for example of the series of N bits {\ -, ..., \ _n } forming the watermark in the case where the watermark is predetermined. According to one embodiment, the watermark data F are stored by the trusted third party, for example in a file. Alternatively, the watermark data is also inserted into the metadata of the file in which the 3D model is stored.

In the case where the watermark is the hazard generated using the cryptographic key K, the storage step 30 is omitted.

FIG. 3 is a block diagram of the main steps of a manufacturing process authentication method, implemented by a computer controlling a manufacturing device, typically of 3D printing.

The authentication method comprises, in this manufacturing phase, a first step 40 of receiving a 3D model comprising code instructions for the manufacture of a 3D part by a manufacturing device.

For example, this 3D model is received as a file in exchange format as described above, comprising metadata.

A legitimate file is a file with a watermark inserted by a method as described above with reference to Figure 2.

The method also includes a step 42 of receiving a global set of parameters and of determining a non-empty subset SP ’of parameters.

The global set of parameters includes the set P _fab of parameters relating to the manufacturing process, obtained for example by extracting these parameters from the metadata of the file received, the set P _mat of parameters characteristic of the material (s) provided by the supplier of raw materials, and the set P _mac of configuration parameters of the manufacturing device itself, received from a man-machine interface of this device, or from an external control device.

The set of parameters P _mat characteristic of the material (s) is a superset of the parameters P _mat 'used in the pretreatment step.

The set of parameters P _mac for configuring the manufacturing device is a superset of the parameters P _conf ′ used in the pretreatment step.

The determination 42 of the non-empty subset SP ′ comprises the determination of the parameters which are homologous to those determined in step 22 implemented during the insertion of the watermark, from the sets of parameters P _fab , P _mat and P _mac .

Thus, if the non-empty subset SP of parameters of step 22 was composed of a concatenation of the parameters P _mat 'and P _conf ' and P _fab , the subset of parameters SP 'is formed from the parameters , corresponding to the parameters P _mat 'and P _conf ' and P _fab , extracts from P _mat , P _mac and P, _ab . Without modification of the watermarked model Mod_WM, and if the values of the non-empty subset SP 'of the parameters received counterparts of the non-empty subset SP of parameters chosen for the watermark insertion are equal to those used for the watermark insertion , the watermark data used for its insertion, is equal to that of the watermark extracted from the watermarked model during the manufacturing phase.

The authentication process involves obtaining the key K ₀ 44 used for the insertion of the watermark. Indeed, in this case, the secret key K ₀ is a shared secret in order to improve the confidence level of the authentication.

The secret key is obtained from the trusted third party.

For example, it is stored, for example on a secure device such as a secure smart card, provided by the trusted third party.

Then in step 46 a cryptographic key K 'is calculated by applying the same algorithm as that used in step 26, that is to say the same cryptographic function parameterized by the secret key K ₀ , to the concatenated values of the SP 'subset of the set of parameters received homologous to the non-empty SP subset of the global set of parameters chosen for watermark insertion.

A watermark F 'is detected or extracted in the watermark detection step 48 from the watermark model received using the cryptographic key K', by applying a detection method associated with the watermark insertion method applied to the watermark insertion step 28. The cryptographic key K 'is used analogously to the use of the cryptographic key K during the insertion.

For example, the cryptographic key K ’is used to determine the points whose coordinates are supposed to be modified by the insertion of a watermark.

Alternatively, the cryptographic key K ’is used to generate the expected watermark data.

At the end of the detection step 48, a series of N binary values (0 or 1) is extracted from the watermarked model.

The expected watermark data F is obtained in step 50. The expected watermark data is the watermark data inserted in the authentic file during step 6 of pre-processing of the initial model, which was stored in the watermark insertion step 30.

For example, they are obtained on request from the methods office based on a unique identifier of the watermarked model received, or are supplied with it by the methods office.

In one embodiment, the watermark data F are therefore obtained in step 50 by request from a memory where they have been stored by the office. methods, or on a removable medium where they were provided by him in conjunction with the watermarked model.

This watermark F data is compared in the comparison step 52 with the watermark F data extracted from the received file.

In the event of a negative comparison in step 52, it is deduced that the overall manufacturing process is not authenticated. As a security measure, it is then possible to inhibit, that is to say not to trigger, the step of manufacturing the 3D part in step 54.

In the event of a positive comparison, the authenticity of the manufacturing process is certified and therefore the production of the part is authorized (step 56).

FIG. 4 schematically illustrates an authentication system for manufacturing 3D parts according to one embodiment.

The system 60 includes a watermark insertion device 62 and a 3D part manufacturing subsystem 64, both of which are connected to a communications network 66.

The insertion device 62 is a programmable electronic device, for example a computer, or an electronic device produced in the form of programmable logic components, such as an FPGA (from the English Field-Programmable Gate Array), or also in the form dedicated integrated circuits, type ASIC (from the English Appiication- Specific Integrated Circuit). The device 62 is typically integrated into a device for preparing the manufacturing of the methods office, not shown.

It comprises in particular a central computing unit 68, or CPU, comprising one or more electronic processors, capable of executing computer program instructions when the device 62 is powered up.

The device 62 also includes an electronic memory unit 70 adapted to store information, in particular registers. In particular, executable code instructions able to implement the methods according to the invention are stored.

The device 62 includes a control interface 72 making it possible to update parameters and to receive commands from an operator, as well as a communication module 74 making it possible to receive and communicate data via the network 66 according to communication protocols. communication given. The various functional blocks of the device 62 described above are connected via a communication bus.

The device 62 is suitable for implementing the insertion of a watermark in a file representing an initial model of a 3D part to be manufactured, making it possible to obtain a file with watermark 76. The file 76 is transmitted via the communication network 66 or via an electronic non-volatile data storage medium to a watermark authentication device 80 forming part of a manufacturing subsystem 64.

The device 80 is also suitable for controlling a device 82 for manufacturing 3D parts, for example a 3D printer.

The device 80 is a programmable electronic device, for example a computer, or an electronic device produced in the form of programmable logic components, such as an FPGA (from the English Field-Programmable Gâte Arraÿ), or also in the form of integrated circuits. dedicated, type ASIC (from the English Application -Specifies Integrated Circuit).

It comprises in particular a central computing unit 84, or CPU, comprising one or more electronic processors, capable of executing computer program instructions when the device 80 is powered up.

The device 80 also includes an electronic memory unit 86 adapted to store information, in particular registers. In particular, executable code instructions able to implement the authentication method according to the invention are stored.

The device 80 comprises a control interface 88 making it possible to update parameters and to receive commands from an operator, as well as a communication module 90 making it possible to receive and communicate data via the network 66 according to a communication protocol. communication given. The various functional blocks of the device 80 described above are connected via a communication bus.

Claims

1.- Method for authentication of computer-aided manufacturing of a three-dimensional part by a manufacturing device, using at least one predetermined manufacturing material, said three-dimensional part to be manufactured being defined by a three-dimensional model obtained by computer-aided design and represented in a predetermined file format, said manufacturing device being adapted to be controlled for manufacturing said part from said three-dimensional model and from a global set of manufacturing parameters, the method being characterized in that it comprises steps of:

-generation (46) of a cryptographic key (K ') as a function of the values of the parameters of a non-empty subset (SP') of parameters of the global set of manufacturing parameters of said three-dimensional part, said sub non-empty set (SP ′) of parameters comprising at least one parameter from a set (P _mac ) of configuration parameters of the manufacturing device, or at least one parameter from a set (P _fab ) of parameters relating to the process manufacturing or at least one parameter from a set (P _mat ) of characteristic parameters of the at least one manufacturing material,

- detection (48) of a watermark in said three-dimensional model by applying a predetermined watermark detection algorithm initialized with the generated cryptographic key (K ’),

comparison (52) of the detected watermark with an expected watermark, and authentication of the computer-aided manufacture of said three-dimensional part in the event of a positive comparison.

2.- Method according to claim 1, further comprising an inhibition (54) of a step of manufacturing said three-dimensional part in the event of a negative comparison.

3.- Method according to one of claims 1 or 2, wherein said non-empty subset (SP ') of parameters is determined (42) prior to the generation (46) of a cryptographic key and comprises said set ( P _fab ) parameters relating to the manufacturing process, and a predetermined subset (P _{¥ nf} ') of configuration parameters of the manufacturing device and a predetermined subset (P _mat ') of parameters characteristic of the at least one material of manufacturing.

4.- Method according to any one of claims 1 to 3, wherein the generation of cryptographic key is also a function of a secret key (K ₀ ).

5.- Method according to any one of claims 1 to 4, further comprising an extraction of said set of parameters relating to the method of manufacturing metadata associated with the received three-dimensional model.

6.- Method according to any one of claims 1 to 5, further comprising receiving said set (P _mac ) of configuration parameters of the manufacturing device, a man-machine interface of the manufacturing device, or an external control device.

7.- Method according to any one of claims 1 to 6, wherein said detected watermark is formed by a series of N bits, N being a non-zero positive integer, the method comprising a step of obtaining (50 ) of the watermark expected from a memory.

8.- Method of inserting a digital watermark for the authentication of computer-aided manufacturing of a three-dimensional part by a manufacturing device using at least one predetermined manufacturing material, said three-dimensional part to be manufactured being defined by a three-dimensional model obtained by computer-aided design and represented in a predetermined file format, said manufacturing device being adapted to be controlled to manufacture said part from said three-dimensional model, the method comprising a step of obtaining (20) a three-dimensional model of a three-dimensional part to manufacture,

characterized in that it comprises stages of:

-determination (22) of a non-empty sub-assembly (SP) of a global set of manufacturing parameters for said part to be manufactured,

said non-empty subset (SP) of parameters comprising at least one parameter of a subset (P _conf ') of configuration parameters of the manufacturing device, or at least one parameter of a set (P _fab ) of parameters relating to the manufacturing process or at least one parameter from a subset (P _mat ') of characteristic parameters of the at least one manufacturing material,

- generation (26) of a cryptographic key (K) as a function of the values of the parameters of said non-empty subset (SP) of parameters, -insertion (28) as a function of said cryptographic key of a watermark formed by a series of N bits, N being a non-zero positive integer, by applying a predetermined watermark insertion algorithm, in said three-dimensional model for obtain a watermarked three-dimensional model of said workpiece.

9.- Method according to claim 8, wherein the generation of cryptographic key is also a function of a secret key (K ₀ ).

10.- Method according to any one of claims 8 or 9, wherein said non-empty sub-assembly (SP) comprises the sub-assembly (P _{¥ nf} ') of configuration parameters of the manufacturing device and the assembly ( P _fab ) of parameters relating to the manufacturing process and the subset (P _mat ') of parameters characteristic of the at least one manufacturing material,

1 1.- Method according to any one of claims 8 to 10, comprising a storage (30) of watermark data associated with the watermark inserted in said three-dimensional model.

12.- Method according to any one of claims 8 to 1 1, comprising a storage of all the manufacturing parameters (P _fab ) in association with the watermarked three-dimensional model in a file in predetermined file format, said set of manufacturing parameters being stored in the form of metadata.

13.- Digital watermark insertion device for the computer-aided manufacturing authentication of a three-dimensional part by a manufacturing device using at least one predetermined manufacturing material, said three-dimensional part to be manufactured being defined by a three-dimensional model obtained by computer-aided design and represented in a predetermined file format, said manufacturing device being adapted to be controlled to manufacture said part from said three-dimensional model, said device comprising a module adapted to receive a three-dimensional model of a three-dimensional part to be manufactured ,

characterized in that it includes modules adapted to:

-determine a non-empty subset (SP) of a global set of manufacturing parameters for said part to be manufactured,

said non-empty subset (SP) of parameters comprising at least one parameter of a subset (P _{¥ nf} ') of configuration parameters of the manufacturing, or at least one parameter of a set (P _fab ) of parameters relating to the manufacturing process or at least one parameter of a subset (P _mat ') of parameters characteristic of the at least one manufacturing material,

- generate a cryptographic key (K) as a function of the values of the parameters of said non-empty subset (SP) of parameters,

14.- Computer-aided manufacturing authentication system for a three-dimensional part by a manufacturing device, using at least one predetermined manufacturing material, said three-dimensional part to be manufactured being defined by a three-dimensional model obtained by computer-aided design and represented. in a predetermined file format, the system comprising a device suitable for controlling said manufacturing device to manufacture said part from said three-dimensional model and from a global set of manufacturing parameters, the system being characterized in that it comprises modules suitable for:

-generate a cryptographic key (K ') as a function of the values of the parameters of a non-empty subset (SP') of parameters of the global set of manufacturing parameters of said three-dimensional part, said subset (SP ' ) not empty of parameters comprising at least one parameter from a set (P _mac ) of configuration parameters of the manufacturing device, or at least one parameter from a set (P _fab ) of parameters relating to the manufacturing process or at least a parameter from a set (P _mat ) of parameters characteristic of the at least one manufacturing material,

- detect a watermark in said three-dimensional model by applying a predetermined watermark detection algorithm initialized with the generated cryptographic key (K ’),

15.- The system of claim 14, comprising a module adapted to inhibit a step of manufacturing said three-dimensional part in the event of a negative comparison.