KR20080095030A - Watermarking for 3d cad drawings - Google Patents

Abstract

A method of watermarking 3D CAD(Computer Aided Design) image is provided to improve subjective texture and objective texture and extract a watermark without error against attacks such as file format conversion, RST(Rotation, Scaling, Translation), component removal and layer removal. Information to be embedded in a 3D CAD image is generated in the form of a binary bit watermark. An object line into which the watermark is inserted is set among line components. A watermark insertion intensity of the object line is obtained. The length of the object line is varied in the range of the insertion intensity according to the binary bit watermark. It is confirmed whether the varied line satisfies an insertion angle condition.

Description

How to insert watermark in 3D CAD drawing {Watermarking for 3D CAD Drawings}

The present invention relates to a watermarking technique for preventing illegal copying and distribution of 3D CAD design drawings, and more particularly, by inserting a watermark according to the distribution of line, arc and 3DFACE components based on 3D vector data. And 3D CAD drawing watermarking techniques that have robustness against geometric attack and file conversion attack.

Recently, various forms of digital works have appeared in accordance with the provision and distribution of information using the Internet. However, digital works have many problems in copyright protection due to their characteristics. It is easy to store or convert information, so that a large amount of copying is possible in open spaces such as the Internet without any restrictions, and it is possible to maintain the same data information as the original even after copying and to distribute it without the author's consent, thus protecting the copyright of the author. Difficult to do

This problem of copyright infringement is increasing in seriousness, and many legal, institutional and technical solutions have been invented. To this end, encryption is performed on the data so that only specific users can use the information, and digital watermarking hides copyright information from the data and delivers it to the user so that the data is not externally modified. Watermarking) is a technical solution that can solve the above-mentioned problems.

Among them, watermarking is a copyright protection technology for digital data, and may be referred to as a copyright display and verification technology for digital content. By concealing copyright information into data and re-detecting hidden copyright information, it is possible to detect data tampering and forgery, and to claim the author's ownership.

In this watermark embedding method, a spatial method, which is a method of adding a small change to data such as a pixel value of a screen and using it as a watermark, converts data in a digital form into an analog signal of frequency components, and converts the same. As a technique for transforming and inserting a watermark, the Discrete Cosine Transform (DCT), the Fast Fourier Transform (FFT), or the Frequency Domain Method using the Wavelet Transform, etc. There is this. This method is divided into visible, ie, visible watermarking technology and invisible watermarking technology.

Visible watermarking technology is a form of overlaying copyright information on the original, which generally prevents the user from erasing the copyright information. However, it is difficult to preserve the original value because the copyright information is visible on the original. Technically, visible watermarking technology is easy to implement, but it is difficult to use for e-commerce because the content is damaged.

On the other hand, invisible watermarking technology is invisible, so it is possible to protect the copyright without damaging the original, and if a copyright problem occurs, it is possible to extract it and claim its copyright based on it. Currently, most watermarking techniques use invisible methods. Therefore, when invisible watermarking is used, even if images, audio, and video files are distributed over the Internet, users cannot detect whether or not a watermark is in the distributed work.

However, the above-mentioned watermark insertion / extraction method is for two-dimensional images, and there is a drawback that cannot be directly applied to three-dimensional images, which are widely used in CAD, animation, and virtual reality, which are widely used recently. . Therefore, there is an active research into inserting information that can be decoded only by the author into the 3D image and using it as a basis of copyright.

A widely used method of expressing 3D images is a mesh structure. The mesh structure basically consists of vertices and information connecting them. In order to insert information into the mesh structure, some modifications are made to the vertices and the connection information. By the way, even if the 3D image is the same model, the combination of the expression method, that is, the coordinates of the vertices and the connection information is infinite. It is also possible to convert rotations and translations. It is a big challenge to ensure that watermarks embedded in such high degree of freedom 3D images survive everyday transformations and intentional attacks.

In particular, when a watermark is inserted in a rectangular coordinate system based on a coordinate point with respect to the 3D image, watermarking the direction of the 3D image to extract the watermark when the 3D image is rotated or translated. A reorientation process is needed to bring it back to the state it was in. However, this reorientation process requires a lot of information about the 3D image. Moreover, the reorientation process for the 3D image has a disadvantage in that the extraction of the watermark requires the existence of the original in which the watermark is inserted.

In addition, with the development of 3D graphics techniques, many design drawings are created by 3D CAD tools in the industrial field, but the watermarking studies on 3D CAD design drawings are inadequate compared to 3D shape models. Distribution is increasing day by day industrial and economic losses.

The present invention has been proposed to solve the above problems, by inserting a watermark according to the distribution of the three-dimensional vector data-based line, arc and 3DFACE components, while satisfying the invisibility, file conversion, movement, scaling, rotation, To provide robustness against component and layer cutting.

In order to achieve the above object, the present invention provides a method for inserting a watermark into line components of a 3D CAD drawing consisting of lines connecting a pair of points, the binary bit information to be inserted into the 3D CAD drawing Generating a watermark, setting a target line to insert a watermark among line components, obtaining a watermark embedding intensity of the target line, and within the range of the embedding intensity according to the binary bit watermark And changing the length of the target line and checking whether the changed line meets the condition of the insertion angle.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the reference numerals to the components of the drawings it should be noted that the same reference numerals as possible even if displayed on different drawings.

1 illustrates a general digital watermarking process.

Digital watermarking technology is largely divided into watermark generation, insertion target selection, embedding, and detecting stage technologies. Various methods for various purposes are proposed, but there are four common considerations. This is always followed. The first is imperceptibility, and digital watermarks should be inserted so that they do not affect the quality of the original content. The second is robustness, so that no watermark should be detected, no matter what manipulation or counterfeiting is done on the digital content. Third, security should be developed so that even if a watermark embedding and detection algorithm is known, it cannot help to detect or remove the presence of a watermark. Fourth, the use of the original should be considered whether or not to use the original when detecting the watermark. In particular, a technique for detecting with an original during the classification of digital watermarking algorithms is called a blind watermarking method, and a technique for detecting without an original is called a non-blind watermarking method.

Referring to FIG. 1, the watermark generation process is a method of determining how to insert a watermark to be inserted into target content. As the watermark, a binary image, a binary image converted by a key value, a character string encrypted by key information, or a psuedonoise signal is used. Such a watermark may include copyright, owner, content contents, etc. as well as watermark presence information.

The watermark embedding process is a process of inserting a watermark generated in an original image. As a general watermarking process inserting method of FIG. 1, a method of adding and defining an insertion strength in a spatial domain or a transformation domain is used. The transform domain is a Discrete Fourier Transform (DFT), Discrete Cosine Trnasform (DCT), Discrete Wavelet Transform (DWT), Fourier-Mellin Transform (FMT), etc. Various domains are used depending on the purpose of use.

In the watermark detection process, the non-blind detection method using the original has a watermark detection method based on a difference from the original content, and the blind detection method obtains an autocorrelation of the watermark signal, and a matched filter. ) Or a method using a MAP (Maximun A-Posteriori) applying a stochastic method.

2 is a conceptual diagram of a general 3D CAD data structure.

The basic structure of a 3D CAD drawing consists of sections of a header, a table, a block, an entity, and an EOF. The header section contains various conditions for the drawing, the version of AutoCAD, parameters for dimension lines, and the like. The table section describes names of lines and layers. The block section is a collection of several figures and named with one name. The entity section specifically describes coordinate values, layer names, and the like for an actual figure. The IF section describes the end of the file.

The shape of the figure is designed by the basic components of lines, arcs, circles, and 3DFACEs that are based on vector data in the entity section. The line component consists of a start point and an end point, and the arc component consists of two points: the start point and the end point, and the midpoint of the circumference, the radius of the circumference, two angles, and the reference point of the angle. Where the first angle is the angle from the starting point and the reference point of the angle, and the second angle is the angle from the end point and the reference point of the angle. The circle component consists of the radius and midpoint, and the 3DFACE consists of vertices representing the 3D surface.

3 is a block diagram of a 3D CAD watermark embedding technique according to the present invention.

Referring to FIG. 3, watermarks are inserted into lines, arcs, and 3DFACE components, respectively. In the present invention, after converting the copyright information of the 3D CAD drawing into ASCII code, it is generated as a binary bit and used as a watermark. The watermark bit represents one bit of the total binary bit string. In the present invention, one watermark bit is inserted into one line, arc, or 3DFACE component, respectively.

If the number of the insertion object is smaller than the number of the watermark bits, the watermark is inserted by the number of the insertion object. If the number of the insertion object is larger than the number of the watermark bits, the watermark is repeated by the number of the insertion object. Insert it.

First of all, three components are obtained from the entity section of the 3D CAD data. The watermark embedding component is determined according to the structure and distribution of the 3D CAD drawing or the user's preference. In the present invention, the insertion object for each component is the ratio of the length in the line component, the circumferential radius in the arc component, and the two side lengths in the 3DFACE component.

4 and 5 show a watermark embedding object and a result in a line component according to the present invention.

Line components within a 3D CAD file are connected in multiple pairs of start and end points. That is, a pair of points represents one line component. One line may or may not be connected to another line. Thus, when a point in a line component is changed by a watermark, the other line components connected to the point are also changed. Therefore, the lines connected to the line where the watermark is inserted should be excluded from the insertion target. In the present invention, a plurality of connected lines are first selected and used as a target line for embedding a watermark.

That is, by repeatedly selecting a line and excluding a line connected to the line, the target lines to which the watermark for the line component is inserted are constructed. Subsequently, any one of the insertion target lines configured in the above process is selected to insert the watermark.

In order to embed the watermark, the watermark embedding strength of the target line is first obtained. The insertion strength is a limit for invisible adjustment when the length of the target line is changed. The insertion strength is half the value of the absolute value of the absolute difference in distance between the vertex coordinates of the target line and the vertices connected to the vertex.

Referring to FIG. 4, vertex v ₀ is connected to vertex v ₁ , and two vertices v ₃ and v ₄ are connected to vertex v ₂ . The insertion strengths 420 of the two vertices v ₁ and v ₂ of the target line 410 are respectively determined invisibly according to the coordinate values of the connected vertices. That is, the insertion strength 420 of one vertex v is [v-Δv, v + Δv], and Δv is determined by the minimum distance between the coordinates of the vertex v and the coordinates of the vertices connected to the vertex v.

The target line is then changed in length within the range of the insertion strength by checking the watermark bit. The change criterion is that when the watermark bit is 1, the length of the watermark target line is larger than the average length of the connected lines, and when the watermark bit is 0, the length of the target line is smaller than the average length of the connected lines.

In this case, changing the length of the target line increases or decreases the value according to the insertion angle condition. The condition of the insertion angle is that the difference between the angle between the two modified vertices and the vertices connected to the vertices and the angle between the vertices connected to the original two vertices must be less than an arbitrary threshold.

For example, referring to FIG. 5, when the watermark bit is 1, coordinate values of two vertices v ₁ and v ₂ of the target line 410 are increased by 0.0001 units until the change criterion is satisfied within an insertion strength. Let's do it. Where the angle between the increased vertices v ₁ ′, v ₂ ′ and the vertices connected to these vertices θ ₁ ′ and θ ₂ ′ (530) and the vertices connected to the original two vertices v ₁ , v ₂ , Difference between the angle θ ₁ and θ ₂ 520 between | θ ₁ '-θ ₁ | And | θ ₂ '-θ ₂ | Must be less than the user-selected value.

If the watermark bit is 0, the coordinate values of two vertices v ₁ and v ₂ of the target line 410 are decreased by 0.001 units until the change criterion is satisfied within the insertion strength. Where the angle between the increased vertices v ₁ ′, v ₂ ′ and the vertices connected to these vertices θ ₁ ′ and θ ₂ ′ (530) and the vertices connected to the original two vertices v ₁ , v ₂ , Difference between the angle θ ₁ and θ ₂ 520 between | θ ₁ '-θ ₁ | And | θ ₂ '-θ ₂ | are both less than a certain threshold.

6 and 7 illustrate a watermark embedding object and its result in an arc component according to the present invention.

The arc component is composed of two vertices 612, 614, a midpoint 620, a radius 630, an angle between two vertices and a reference point 640, as shown in FIG. 6. In the present invention, a watermark is inserted at a radius 630 using two vertices 612 and 614 of a randomly selected target arc among the arc components of the 3D CAD drawing and a midpoint 620 of a circle.

In order to embed the watermark, the watermark embedding strength of the target arc is first obtained. The insertion strength is a value for invisibly adjusting when the radius of the target arc is changed. When the insertion strength α is larger than 0 and the radius 630 R is larger than the insertion strength α, the range of the insertion strength α is Becomes In the present invention, the insertion strength α is the median of these ranges. Determined.

In embedding the watermark, the insertion criterion checks the watermark bit, and if the watermark bit is 1, adds it to the radius of the target arc, and if the watermark bit is 0, subtracts the embedding strength to the radius of the target arc.

In the present invention, in order to change the radius of the target arc in accordance with the above criteria, the center of the circle is moved in the midpoint direction or the midpoint direction of the two vertices. That is, as shown in FIG. 7, when the watermark bit is 1, the center point 620 of the circle is shifted by the insertion strength in the direction of the center point 650 of the two vertices, and when the watermark bit is 0, the center point of the circle ( 620 is moved by the insertion strength in the direction opposite the midpoint 650 of the two vertices. The difference between the curvature of the target arc before the change and the curvature of the target arc changed by the watermark should be smaller than an arbitrary threshold.

8 and 9 illustrate a watermark embedding object and a result in a 3DFACE component according to the present invention.

The 3DFACE component represents a 3D polygonal surface for surface modeling in a 3D CAD drawing and consists of vertices that determine the polygonal surface.

First, a set of lengths of a randomly selected target 3DFACE among 3DFACE components of a 3D CAD drawing for obtaining a watermark is obtained. Referring to FIG. 8, the length set of the target 3DFACE is {l ₀ , l ₁ , l ₂ , 1 ₃ }. Then randomly select any length pair without shared vertices from the length set. For example, selecting l ₀ selects the length l _2, with no shared vertices. Here, one length is used as the reference length 810 and the other length is used as the symmetry length 820.

In the present invention, FIG. 8 is an independent 3DFACE, which is not connected to another 3DFACE, but is changed by a watermark when the 3DFACE is connected to another 3DFACE, and thus includes a length of 3D polygonal faces connected to a symmetric length where a watermark is inserted. Should be excluded from insertion.

Subsequently, the magnitude and direction of the first displacement vector and the second displacement vector of the symmetric length are obtained according to the binary bit watermark. The direction of the first displacement vector and the second displacement vector should be parallel to the reference length, and the magnitudes of the first displacement vector and the second displacement vector are determined to satisfy the following two conditions simultaneously.

First, if the watermark bit is 1, the sum of the two displacement vectors must be greater than the difference between the reference length 810 and the symmetry length 820, and if the watermark bit is 0, The sum of the two displacement vectors should be smaller than the difference between the reference length 810 and the symmetry length 820.

Secondly, two vertices within symmetry length 820 must move within an invisible region. The difference from between the θ ₁ 'and θ _2' when the ratio is poetry area as shown in FIG. 9, the symmetry length 820 and between the two lengths connected changes by the angle θ ₁ and θ ₂ and the watermark | θ ₁ - θ ₁ '| And | θ ₂ - θ ₂ '| should be less than any threshold.

Subsequently, a watermark is inserted into the target 3DFACE. In embedding the watermark, the embedding criterion checks the watermark bit so that if the watermark bit is 1, the length ratio of the length pair is greater than 1, and if the watermark bit is 0, the length ratio of the length pair is greater than 1. Make it small.

In order to change the length ratio according to the watermark embedding criterion, two vertices in the symmetric length 820 are changed in parallel with the reference length 810. That is, if the watermark bit is 1, one vertex is added by the first displacement vector in the symmetry length 820 and the other vertex is subtracted by the second displacement vector. If the watermark bit is 0, one vertex is subtracted from the symmetry length 820 by the first displacement vector, and the other vertex is added by the second displacement vector.

Watermark extraction is extracted from each component of the watermarked 3D CAD drawing using the key stored in the insertion process. The key information stores the index of the target line generated in the line component watermark embedding process as key information, the index of the target arc generated in the arc component watermark embedding process as key information, and the 3DFACE component watermark embedding process. Stores the index of the target 3DFACE generated by the as key information. The extraction process is similar to the above insertion process.

10 are drawings designed in AutoCAD 2002 tool for performance evaluation of the present invention.

Referring to FIG. 10, a line component is distributed in FIG. 10A, an arc component in FIG. 10B, a 3DFACE component in FIG. 10C, and a line and 3DFACE component are distributed in FIG. 10D. Can be seen. In the performance evaluation of the present invention, 500 components among the components of the drawing were selected as the watermark insertion object.

FIG. 11 is a 3D CAD diagram in which a watermark is inserted according to the present invention. FIG.

Referring to FIG. 11, it can be confirmed that the watermark is invisibly inserted. In addition, in the performance evaluation of the present invention, the SNR (Signal to Noise Ratio) of each component in which a watermark is inserted is used for objective quality evaluation.

The SNR is a value of a constant format expressing how much noise is mixed in a signal received at a receiver with a signal sent from a transmitter, and the SNR is expressed by Equation 1 below.

Where v represents the vertex coordinate value in the line and 3DFACE components and the radius in the arc component, and M is the mean value of v. var (v) represents the variance of v. The SNRs of the watermarked drawings are about 39.89 to 42.50 dB, as shown in Table 1 below, indicating good image quality.

<Table 1> SNR of each component in 3D CAD drawing with watermark embedded

3D CAD Drawings (a) (b) (c) (d) Insertion Components and Number of Components 1,130 lines 1,770 arcs 551 3DFACE 8,738 lines 3DFACE 3,927 SNR 40.12 dB 41.05 dB 39.89 dB 42.50dB41.33dB

In the performance evaluation of the robustness, we attacked the watermarked 3D CAD drawings such as file format conversion, translation, scaling, rotation, component removal, and layer cutting. The bit error rate (BER) of the watermark extracted for each attack is shown in Table 2 below. In the diagram of Fig. 11D, a watermark is inserted into two components, a line and a 3DFACE. The BER is an average of watermark BER extracted in two components.

<Table 2> BER of extracted watermark

3D CAD Drawing Attack (a) (b) (c) (d) File format conversion (DXF, DWG, DWT, DWS) - - - - RST - - - - 30% cutting 0.13 0.08 0.22 0.03 Layer cutting 0.24 0.15 0.28 0.07

In the performance evaluation of file format conversion, we converted to DXF, DWG, DWT, and DWS using AutoCAD tools. However, it can be seen that the watermark is extracted without error in any file format conversion. In the performance evaluation for the geometrical attack, referring to FIG. 12, the watermarked drawings were moved to an arbitrary position, expanded and contracted by an arbitrary scaling factor, and rotated by an arbitrary angle. FIG. 12 (a) is about 30% of the line components removed from the diagram of FIG. 11 (a), FIG. 12 (b) is a three times magnification of the diagram of FIG. 11 (b), and FIG. Any layer in the diagram of FIG. 11 (b) has been removed, and FIG. 12 (d) is a diagram in which any layer of the diagram of FIG. 11 (c) has been removed. In the present invention, however, the watermark is inserted into the length ratio in the line component, the radius of curvature in the arc component, and the length ratio of the two surfaces in the 3DFACE component, and thus is irrelevant to movement and rotational attacks.

Looking at Table 2, it can be seen that all watermarks are extracted without error for the RST attack. Cleavage experiments removed about 30% of each component on any layer in the figure. Removing the layer is the same as removing all components in any layer. At this time, the extracted watermark has a BER of 0.15 to 0.28. The BER varies depending on the number of components in which a watermark is inserted in one layer. From the above results, it can be confirmed that the watermark inserted by the proposed method is extracted without error for the attack.

In the foregoing description of the present invention, specific embodiments such as CAD drawings have been described, but various modifications can be made without departing from the scope of the present invention. Therefore, the scope of the present invention is not to be determined by the embodiments described above, but will be apparent in the claims as well as equivalent scope.

As described above, the present invention has excellent subjective image quality and shows good image quality by confirming that the component SNR is 39.89 to 42.50 dB in terms of objective image quality. In addition, over 80% of watermarks were extracted without errors for attacks such as file format conversion, RST, component removal, and layer removal. The result is robustness against invisibility and geometric attacks and file conversion attacks.

1 illustrates a general digital watermarking process.

2 is a conceptual diagram of a general 3D CAD data structure.

3 is a block diagram of a 3D CAD watermark embedding technique according to the present invention.

4 shows a watermark embedding object in a line component according to the present invention.

5 shows a result of embedding a watermark in a line component according to the present invention.

6 shows a watermark embedding object in an arc component according to the present invention.

7 shows the result of embedding a watermark in the arc component according to the present invention.

8 shows a watermark embedding object in a 3DFACE component according to the present invention.

9 shows the result of embedding a watermark in the 3DFACE component according to the present invention.

Figure 10 shows the drawings designed in the AutoCAD 2002 tool for performance evaluation of the present invention.

FIG. 11 is a result of inserting a watermark in FIG. 10 according to the present invention.

FIG. 12 is a view showing an attack performed such as component removal and layer cutting for performance evaluation of the present invention.

* Description of the symbols for the main parts of the drawings *

410: target line 420: insertion strength

510: changed target line 620: the center of the circle

630: radius 640: reference point

810: reference length 820: symmetry length

Claims (22)

A method of embedding a watermark in line components of a 3D CAD drawing consisting of lines connecting a pair of points, Generating a binary bit watermark of information to be inserted into the 3D CAD drawing; Setting a target line into which a watermark is to be inserted among the line components; Obtaining a watermark embedding strength of the target line; Changing a length of a target line within the range of the insertion strength according to the binary bit watermark; Checking whether the changed line satisfies a condition of an insertion angle; Watermark embedding method of 3D CAD drawings. The method of claim 1, wherein the setting of the target line to be inserted comprises: First selecting a line with many connected lines, Excluding the lines connected to the selection line, Repeating the selection step and the exclusion step to set the target line to be inserted among the line components of the 3D CAD drawing watermark. The method of claim 1, wherein the obtaining of the insertion strength comprises: And inserting the insertion strength into a half value at which the absolute value of the distance difference between the vertex coordinates of the target line and the vertices connected to the vertex is the smallest value. The method of claim 1, wherein changing the length of the target line comprises: If the watermark bit is 1, the length of the target line to be inserted is larger than the average length of the connected lines. If the watermark bit is 0, the length of the target line to be inserted is smaller than the average length of the connected lines. The method of claim 1, wherein the step of checking whether the insertion angle is satisfied The target line is changed until the difference between the angle between the two modified vertices and the vertices connected to the vertices and the angle between the two vertices connected to the vertices before the change is less than an arbitrary threshold. How to insert watermarks in 3D CAD drawings. The method of claim 1, wherein the method of embedding a watermark in a line includes: When the number of the binary bit watermark bits is smaller than the number of the insertion target lines, the watermark bits are repeatedly inserted by the number of the insertion target lines, And if the number of bits of the binary bit watermark bit is larger than the number of the insertion target lines, watermark data is inserted only as much as the number of the insertion target lines. The watermark embedding method of claim 1, wherein the index of the target line generated in the watermark embedding process is stored as key information and used to extract the watermark. A method of embedding a watermark in arc components of a 3D CAD drawing consisting of two vertices, the midpoint of a circle, the radius, and the angle between two vertices and a reference point, Generating a binary bit watermark of information to be inserted into the 3D CAD drawing; Arbitrarily selecting a target arc into which a watermark is to be inserted among the arc components; Obtaining a watermark embedding strength from the curvature of the target arc; Changing a radius of a target arc by an insertion strength according to the binary bit watermark; Watermark embedding method of 3D CAD drawings. The method of claim 8, wherein the obtaining of the insertion strength comprises: The insertion strength is 0 <insertion strength < A method of embedding a watermark in a 3D CAD drawing, wherein R is an arbitrary value within a range of the radius of the target arc. The method of claim 9, wherein the insertion strength is, Is the median of the above range (R is the radius of the target arc). The method of claim 8, wherein the changing the radius of the target arc by the insertion strength, If the binary bit watermark bit is 1, the center of the circle of the target arc is shifted by the insertion strength in the midpoint direction of the two vertices, Binary Bit Watermark When the bit is 0, the watermark embedding method of the 3D CAD drawing comprising moving the center of gravity of the arc of the target arc by the insertion strength in the direction opposite to the midpoint of the two vertices. 10. The method of claim 8, wherein the method of embedding a watermark in an arc comprises: If the binary bit watermark bit number is smaller than the number of the insertion target arc, the watermark bit is repeatedly inserted by the number of the insertion target arc, And if the number of bits of the binary bit watermark bit is larger than the number of the arcs to be inserted, insert the watermark data only as much as the number of the arcs to be inserted. The watermark embedding method of claim 8, wherein the index of the target arc generated in the watermark embedding process is stored as key information and used to extract the watermark. A method of embedding a watermark in 3DFACE components of a 3D CAD drawing consisting of vertices that determine a polygonal surface, Generating a binary bit watermark of information to be inserted into the 3D CAD drawing; Randomly selecting a target 3DFACE to insert a watermark among 3DFACE components; Selecting an arbitrary length pair by obtaining a length set of the target 3DFACE; Selecting a reference length and a symmetry length among the selected length pairs; Obtaining the magnitude and direction of the first and second displacement vectors of the symmetric length according to the binary bit watermark; Changing the length ratio of the selected length pair by the displacement vector according to the binary bit watermark; Watermark embedding method of 3D CAD drawings. 15. The method of claim 14, wherein selecting the arbitrary length pairs comprises: A method for embedding a watermark in a 3D CAD drawing comprising selecting an arbitrary length pair having no shared vertices among a set of lengths of 3DFACE. The method of claim 14, wherein the step of randomly selecting the target 3DFACE, 3. The method of inserting a watermark in a 3D CAD drawing, characterized in that 3DFACEs connected to the symmetry length to which the watermark is inserted are excluded. 15. The method of claim 14, wherein the magnitude of the first displacement vector and the second displacement vector, If the binary bit watermark bit is 1, the sum of the first displacement vector and the second displacement vector must be greater than the difference between the reference length and the symmetry length, If the binary bit watermark bit is 0, the watermark embedding method of the 3D CAD drawing, which must satisfy the condition that the sum of the first displacement vector and the second displacement vector must be smaller than the difference between the reference length and the symmetry length. 15. The method of claim 14, wherein the magnitude of the first displacement vector and the second displacement vector, A method of inserting a watermark in a 3D CAD drawing comprising satisfying a condition that a difference between an angle between two or more lengths connected to a symmetry length and an angle when changed by a watermark must be smaller than an arbitrary threshold. The method of claim 14, wherein the direction of the first displacement vector and the second displacement vector, A method of inserting a watermark in a 3D CAD drawing, characterized in that it is parallel to a reference length. The method of claim 14, wherein changing the length ratio of the selected length pair by a displacement vector comprises: If the binary bit watermark bit is 1, add one vertex by the first displacement vector within the symmetry length, subtract the other vertex by the second displacement vector, If the binary bit watermark bit is 0, the watermark embedding method of the 3D CAD drawing comprises subtracting one vertex by the first displacement vector and adding another vertex by the second displacement vector within the symmetry length. 15. The method of claim 14, wherein the method of embedding a watermark in 3DFACE, If the number of watermark bits is smaller than the number of 3DFACEs to be inserted, the watermark bits are repeatedly inserted by the number of 3DFACEs to be inserted, And if the number of watermark bits is larger than the number of 3DFACEs to be inserted, inserting watermark data only by the number of 3DFACEs to be inserted. 15. The method of claim 14, wherein the index of the target 3DFACE generated in the watermark embedding process is stored as key information for use in extracting the watermark.