CN114491667A - Electronic seal anti-counterfeiting method based on seal frame codes - Google Patents

Abstract

The invention discloses an anti-counterfeiting coding method for a frame of an electronic seal, which comprises the following steps: step 1, encrypting the information text of a plaintext by using a key to generate an encrypted bit string, and then forming an encoded binary string by the encrypted bit string; step 2, representing the coded binary string as a strip line with alternate colors and white colors; and 3, drawing the strip lines on the frame of the electronic seal to generate an electronic seal image with codes.

Description

Electronic seal anti-counterfeiting method based on seal frame codes

Technical Field

The invention relates to the technical field of electronic seal anti-counterfeiting, in particular to an electronic seal anti-counterfeiting method based on seal frame coding.

Background

With the continuous development of electronic commerce, commerce and trade behaviors of conducting transactions through electronic commerce are accepted by more and more enterprises, however, the development of business models also brings a series of problems, and the anti-counterfeiting of electronic seals is a focus of attention. Although the existing electronic seal provides a basic anti-counterfeiting scheme by means of conventional watermarking and the like, when a contract, a document and the like printed by the electronic seal are scanned and then printed or copied, the authenticity of the seal is very difficult to distinguish.

Therefore, the invention provides an electronic seal anti-counterfeiting method based on seal frame codes, when a document containing a seal after primary printing is copied or scanned and then printed, encrypted information contained in the seal is damaged, so that the encrypted information is failed to decode, and the anti-copying effect is achieved.

Disclosure of Invention

In order to realize the purpose of the invention, the following technical scheme is adopted for realizing the purpose:

an anti-counterfeiting coding method for a frame of an electronic seal comprises the following steps:

step 1, encrypting the information text of the plaintext by using a key to generate an encrypted bit string, and then forming the encrypted bit string into a coding binary string;

step 2, representing the coded binary string as a strip line with alternate colors and white colors;

and 3, drawing the strip lines on the frame of the electronic seal to generate an electronic seal image with codes.

The anti-counterfeiting encoding method for the electronic seal frame comprises the following steps: the key is a combined key and comprises a user key and a random key.

The anti-counterfeiting encoding method for the electronic seal frame comprises the following steps: the coded binary string comprises 5 data fields, wherein the data field A is a random key, the data field B is a checksum of the random key, the data field C is a character number of an information text, the data field D is a checksum of the data field E, and the data field E is an encrypted bit string.

The anti-counterfeiting coding method for the electronic seal frame comprises the following steps of: color bar NL, representing a binary 0; a colored wide bar WL representing a binary 1; the start symbols SS, SS are much longer than NL and WL; the white space SL is a space between NL, WL, and SS, and is white.

The anti-counterfeiting coding method for the electronic seal frame comprises the following coding structures of strip lines: starting with SS, followed by a coded binary string or a number of cyclic coded binary strings.

The anti-counterfeiting encoding method for the electronic seal frame comprises the following steps: before generating the stripe line, adding a bit 0 after every 4 bits of the coded binary string to form an extended coded string, wherein the coding structure of the stripe line is as follows: starting with SS, followed by a number of cyclic coded binary strings, which are separated by wall symbols, denoted by "01111110".

The anti-counterfeiting encoding method for the electronic seal frame comprises the following steps: in the step 1, a plurality of keys are used for encrypting the information text of the plaintext to generate a plurality of encrypted bit strings, and then the encrypted bit strings form a plurality of coding binary strings; in step 2, each coding binary string is represented as a strip line with alternate colors and white colors to form a strip group; and 3, drawing the strip line group on the frame of the electronic seal to generate an electronic seal image with codes, wherein the adjacent strip lines in the strip generation group are spaced by a preset distance.

The anti-counterfeiting encoding method for the electronic seal frame comprises the following steps of:

assuming equal probabilities of 0 and 1 occurrence in the stripe, the width of the average 1bit is:

wherein W_NL、W_WLAnd W_SLThe widths of the coding primitives NL, WL and SL, respectively.

The anti-counterfeiting encoding method for the electronic seal frame comprises the following steps: a plurality of rows of tape are pieced together into groups of tape in rows with the spacing between rows being LD, the gaps between rows being filled with red, and then each row is cyclically shifted by a random length.

The anti-counterfeiting encoding method for the electronic seal frame comprises the following steps: if total N row of bands on the frame, then the minimum width of frame is:

W_m(N)＝N×H_LH+(N+1)×H_LD (2)

n is a natural number of 1 to 3, H_LHAnd H_LDRespectively row height and row spacing.

The anti-counterfeiting encoding method for the electronic seal frame comprises the following substeps S1-S6:

s1, creating a new image, wherein the image of the new image is the same as the stamp image in the stamp die file, the background is set to be transparent, and the image is called as a stamp base image;

s2, judging whether each non-transparent pixel point on the stamp base map is on the frame or not, wherein the judging method comprises the following steps:

expressing the inner and outer rings and the central ellipse equation of the ellipse frame of the seal image as

Wherein a, b > | s | (3)

Equation (9) is a family of elliptic curves with s as a parameter, a is the length of the major axis of the central ellipse, b is the length of the minor axis of the central ellipse, and s is the distance from the major axis and the minor axis of one of the elliptic curves to the major axis and the minor axis of the central ellipse respectively, (x)_c,y_c) Is the center coordinate of the ellipse; the curve when s is 0 corresponds to the central ellipse, (x, y) is the coordinate of each point on the frame of the seal image ellipse;

for given point coordinates (x, y) in the stamp image, solving the equation (9) to obtain s, and if | s | < W, indicating that the point W on the stamp frame is the stamp frame width W_mHalf of the total amount of (N) is,

if the point (x, y) is on the stamp border, continuing to the next step S3, otherwise, repeating the substep S2 for the next point;

s3, finding the point nearest to the point on the central ellipse, determining the centrifugal angle of the nearest point,

the ellipse equation is expressed as the eccentric angle

Where t is the angle of the eccentricity,

the distance from a point (x, y) outside the ellipse to the ellipse is then expressed as

Numerically calculating the centrifugal angle t at which D is minimal_min(D)；

S4, calculating the arc length by the centrifugal angle

The arc length from the right end point of the major axis of the central ellipse in the clockwise direction to the centrifugal angle t is represented as

S5, calculating coordinates (x ', y') in the flat strip group according to equations (3) to (6) for points (x, y) on the stamp frame, wherein the value of x 'is equal to the arc length S (t), and the value of y' is equal to the distance s from the points (x, y) to the central ellipse; taking the color value of the point from the flat strip group and drawing the color value to the (x, y) point of the seal base map;

then returning to substep S2, processing the next point of the stamp base image until all points on the stamp image have completed substep S2;

and 4, outputting the encoded electronic seal image, wherein the seal image comprises a frame containing the encoded watermark and the rest of the seal.

And 5, printing the seal image with the code, and printing the electronic seal image on a paper document in the seal application system.

An anti-counterfeiting decryption method for a frame of an electronic seal comprises the following steps:

step 1, scanning a seal part of a file to obtain a seal scanning image, wherein the seal is printed by a seal image formed by one of the encoding methods;

step 2, identifying a seal frame;

step 3, stretching the frame into strip rows or strip groups;

step 4, identifying bit sequences in the strip lines to obtain a coded binary string;

and 5, decoding by using the key sequence to obtain the hidden character string.

Drawings

Fig. 1, (a) a schematic diagram of a stamp image with frame encoding; (b) a frame-coded locally enlarged image schematic, wherein: the black in the figure represents the color of the stamp, which is actually red, blue or purple;

FIG. 2 is a schematic diagram of the encoding and decoding flow of the frame encoding seal printing anti-counterfeiting technology;

FIG. 3 is a schematic diagram of a stripe row encoding structure;

FIG. 4 is a schematic view showing the boundary of the code pattern aligned with the stamp frame in a zigzag pattern;

FIG. 5 is a schematic diagram of the inside and outside ellipse equations of the stamp frame;

fig. 6 is a schematic diagram of the correspondence between the flat (flattened) strip group and the strip group which is totally curved into an ellipse.

Detailed Description

The invention is applied to the seal with the circular and elliptical frame. The information is hidden on the frame by dense arrangement coding, and the following describes the detailed implementation of the present invention with reference to fig. 1-5.

As shown in fig. 1, the codes are arranged along the frame in a ring shape, and there are a plurality of rows from inside to outside, the number of rows is determined by the width of the frame of the stamp, at least 1 row, and at most 3 rows. Because the basic unit forming the code is small in size and only has a few pixels, when the code is copied or scanned and printed again, the dot matrix of the coding unit is rearranged, so that the decoding fails, and the effect of preventing copying is achieved.

As shown in fig. 2, the electronic stamp anti-counterfeiting method based on stamp frame encoding includes encryption and decryption, wherein the encryption includes the following steps (see E1 to E5 in fig. 2):

step 1, encrypting a plaintext information text (InfoText) by using a plurality of different associated keys (CombKey) to generate a plurality of encrypted bit strings (EncodedBits), and then further forming a plurality of coded binary strings (Codestring).

Each character in the plaintext info text InfoText occupies 6 bits and may represent 64 printable characters, including upper and lower case letters, numbers, underlining, and spaces. InfoText allows a maximum length of 24, whose content is given by the user, which may be a set of numbers, a piece of text, or a unit name on the stamp.

The federated key CombKey consists of a user key (UserKey) and a random key (RandomKey). Wherein UserKey is a configuration item of the code generation program and the decoding program. The decoding program must use the same UserKey as the encoding program to decode correctly. There are 3 UserKey, corresponding to 3 circular bands from inside to outside. And the RandomKey is dynamically generated during encryption. Each user has a unique set of UserKey. Due to the existence of the Random Key, even if the InfoText is the same, the bit strings EncodedBits after each encryption are completely different.

RandomKey and EncodeBits together form a coded binary string (codeString). The coded binary string CodeString includes 5 data fields, see table 1. The total length of the coded binary string CodeString is a multiple of 4, as known from the sum of the number of bits of each field.

Data field	Number of bits	Description of the invention
			A	6	Random key (Randomkey)
B	2	Checksum of random key
			C	8	Number of characters of information text (InfoText). The effective range is 1-24.
D	8	Checksum of data field E
			E	4n	EncodeBits, the number of bits of which is padded to an integer multiple of 4.

TABLE 1 data field definitions of Codestring

And 2, representing each CoDesring as strip lines with red and white intervals, wherein the length of each strip line exceeds the perimeter of the seal frame, then splicing a plurality of rows (1-3 rows) of strip lines into strip groups in parallel, and the length of the spliced strip groups is equal to the perimeter of the seal frame.

Each stripe line is composed of a color stripe (usually red, and possibly blue or purple, hereinafter referred to as red stripe for descriptive convenience) and a white stripe arranged in sequence. The width of the white bar is fixed to separate the code bits. The width of the red stripes is divided into three categories: wide bars, narrow bars and starting symbols. The color bars and the white bars with different widths are collectively called as picture elements. The meanings of the different graphical elements are given in Table 2

Primitive type	For short	Full scale	Means of
				Narrow strip	NL	narrow line	Representing a binary digit of 0, red
Wide strip	WL	wide line	Representing a binary digit of 1, red
				Initial symbol	SS	start sign	Representing the starting point of recognition of the circular band, red
Blank space	SL	space line	Spacing between NL, WL, SS, white
				Line height	LH	Line height	Height of strip line
Line spacing	LD	Line distance	Line spacing of strip lines

TABLE 2 primitive meanings that constitute strip lines

Before generating the stripe line, add a bit 0 after every 4 bits of the CoDesring, to form an extended code string (ExCoDesring). This makes it impossible to have more than 4 consecutive 1 s in the ExCodeString, and "01111110" is taken as a Wall Sign (WS) of the interval ExCodeString. In a stripe line, ExCoDestring loops occur, separated by WS.

The coding structure of a stripe line is shown in fig. 3. Starting with SS, and repeating ExCoDestring for multiple times until the total length of the strip line is equal to the perimeter of the seal frame, and cutting off the redundant part. WS spaces are used between ExCodeString. An 8-bit random code is inserted between the SS and WS immediately adjacent to the SS to confuse the fixed pattern formed when the SS and WS are connected together.

Assuming equal probability of 0 and 1 occurrence in the stripe, the width of the average 1bit is

Wherein W_NL、W_WLAnd W_SLThe widths of the coding primitives NL, WL and SL, respectively.

And (3) splicing a plurality of (1-3 rows) of strip rows into a strip group consisting of a plurality of rows, wherein the space between the rows is LD, and the gaps between the rows are filled with red. Each row is then cyclically shifted by a random length to avoid a fixed pattern caused by the alignment of SS symbols of different rows.

The number of strip lines in the strip group depends on the width of the physical seal frame, and the number of the strip lines is at least 1 and at most 3. The frame is provided with N rows of strips. The minimum width of the frame is:

W_m(N)＝N×H_LH+(N+1)×H_LD (14)

n is a natural number of 1 to 3, H_LHAnd H_LDRespectively row height and row spacing.

And 3, drawing the strip group on the frame of the electronic seal to generate an electronic seal image with codes.

And drawing the strip group on the stamp frame along the central line of the frame in the clockwise direction. The strip group is a horizontal strip, the coding pattern in the strip group is a rectangle, and the stamp frame is a curve, so when the strip group is drawn, the strip group needs to be locally deformed, and the horizontal edge and the vertical edge of the coding pattern in the strip group are respectively aligned with the tangent line and the normal line of the stamp frame. This alignment operation theoretically changes a rectangle into a curved trapezoid, however, since the encoding pattern has a size of only a few pixels, its boundary appears jagged after the alignment operation. As shown in fig. 4.

The process of generating the seal image with the seal code watermark is to draw a strip group on the seal frame. The round and oval are common stamp frames. Since a circle can be regarded as a special case of an ellipse, only the generation algorithm of the ellipse needs to be considered. The premise for drawing the strip groups onto the oval frame is that the stamp image already exists, and the parameters of the frame of the stamp image, including the center coordinates of the oval, the major and minor semi-axes of the oval, have been determined, and it is ensured that the stamp image has been adjusted to have its major axis horizontal. This stamp image is saved, along with the associated parameters, in a configuration file, referred to as a stamp model file. Based on the prepared stamp model file, the stamp containing the code can be drawn. Specifically, the method includes 6 substeps (S1 to S6).

S1, creating a new image, wherein the image of the new image is the same as the stamp image in the stamp model file, and only setting the background to be transparent. This image is referred to as a stamp base image.

And S2, judging whether each non-transparent pixel point on the stamp base map is on the frame.

The judgment method comprises the following steps:

as shown in FIG. 5, the elliptical equations of the inner and outer rings and the center of the elliptical frame of the stamp image can be expressed as

Wherein a, b > | s | (15)

Equation (15) is a family of elliptic curves with s as a parameter, a being the length of the major axis of the central ellipse, b being the length of the minor axis of the central ellipse, and s being the distance from the major axis and the minor axis of one of the elliptic curves to the major axis and the minor axis of the central ellipse, respectively, (x)_c,y_c) Is the center coordinate of the ellipse. The curve when s is 0 corresponds to the central ellipse. When a and b are determined, any point on the plane can belong to a certain ellipse uniquely identified by s in the curve family. And (x, y) is the coordinate of each point on the oval frame of the stamp image.

For given point coordinates (x, y) in the stamp image, solving equation (15) to obtain s, if | s | ≦ W, indicating that the point is on the stamp frame, where W is the width W of the stamp frame_mHalf of (N).

If the point (x, y) is on the stamp border, proceeding to the next step S3, otherwise, repeating the substep S2 for the next point,

s3, finding the point closest to the point on the central ellipse, and determining the centrifugal angle of the closest point.

The ellipse equation is expressed as the eccentric angle

Where t is the angle of eccentricity.

The distance from a point (x, y) outside the ellipse to the ellipse is then expressed as

Numerically calculating the centrifugal angle t at which D is minimal_min(D)。

And S4, calculating the arc length by the centrifugal angle.

The arc length from the right end point of the major axis of the central ellipse in the clockwise direction to the centrifugal angle t is represented as

S5, as shown in FIG. 6, a point (x, y) on the seal ellipse corresponds to a point (x ', y') on the flat strip group. Where x 'has a value equal to the arc length S (t) and y' has a value equal to the distance s of the point (x, y) from the central ellipse. Thus, for each point (x, y) on the stamp frame, the coordinates (x ', y') corresponding to the flat strip group can be calculated according to equations (15) to (18), and then the color value is extracted from the point (x ', y') on the flat strip group and is drawn on the (x, y) point of the stamp base map.

Then, returning to substep S2, the next point of the stamp base image is processed until all points on the stamp image have completed substep S2.

And 4, outputting the coded electronic seal image. The stamp image includes a frame containing the encoded watermark and the rest of the stamp.

And 5, printing the seal image with the code. In a stamp application system, an electronic stamp image is printed onto a paper document.

Decryption includes the following steps (see fig. 2, D1 through D5):

step 1, scanning the seal part of the file to obtain a seal scanning image

Step 2, automatically identifying the stamp frame through an image processing algorithm;

for the stamp image, the red part is firstly obtained, and other colors (mainly black characters) are filtered. And then, thinning the red line by adopting a skeleton generation algorithm. Finally, an ellipse detection algorithm is adopted to automatically extract parameters of the ellipse, including a central coordinate (x)_c,y_c) The major semi-axis a, the minor semi-axis b and the clockwise angle alpha between the major semi-axis and the horizontal. Because the paper placement may be slightly incorrect during scanning, it is necessary to consider that the semimajor axis of the ellipse and the horizontal line have a small included angle when performing ellipse detection.

The ellipse detection algorithm can adopt a random Hough transform algorithm based on symmetrical point search, and the algorithm reduces 5 parameters of an ellipse to 1 dimension by utilizing the geometric characteristics of the ellipse, thereby greatly reducing the operation amount.

Step 3, stretching the frame into a strip group;

and (3) expanding the elliptical frame into a strip group by using the elliptical parameters obtained in the step (2). The process is an inverse process of drawing a strip group to a frame when generating a seal coding watermark, and is specifically divided into a plurality of small steps (Q1-Q3):

q1. the scanned image is rotated in a counter clockwise direction by a to produce a scanned image with a horizontal semi-major axis of the ellipse.

Q2. construct a rectangular strip with a width equal to the perimeter of the central ellipse and a height equal to 2 d. This strip will be used to store the set of strips in a flattened state. Where 2d is the width of the stamp frame shown in fig. 6.

Q3. similar to S5, for each point (x ', y') in the flattened band set, the coordinates (x, y) corresponding to the scanned image are calculated according to equations (15) - (18), and then the color value of the point (x, y) is extracted from the scanned image and plotted on the point (x ', y') in the flattened band set.

Step 4, identifying a bit sequence in the band group to obtain codeString;

the stripe group is split into a plurality of stripe rows. For each stripe row, the SS flag is searched from left to right. The stripe row is then cyclically shifted horizontally so that the SS flag is at the left end of the stripe row. The CodeString is then extracted according to the coding rules for that stripe line.

And 5, decoding the CoDesring sequence by combining the UserKey so as to obtain the hidden character string.

UserKey is obtained from the decoded configuration file. It must be the same as the UserKey used in the encoding. RandomKey and EncodedBits can be extracted from CodeString. And after the RandomKey and the UserKey are combined into a CombKey, decoding EncodedBits in the Codestring to obtain InfoText. Since a plurality of CodeString can be extracted from one band row, the watermark has certain capability of resisting local contamination.

Claims (2)

1. An electronic seal frame anti-counterfeiting coding method is characterized by comprising the following steps:

step 1, encrypting the information text of a plaintext by using a key to generate an encrypted bit string, and then forming an encoded binary string by the encrypted bit string;

step 2, representing the coded binary string as a strip line with alternate colors and white colors;

and 3, drawing the strip lines on the frame of the electronic seal to generate an electronic seal image with codes.

2. The electronic seal frame anti-counterfeiting encoding method according to claim 1, characterized in that: the key is a combined key and comprises a user key and a random key.

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