JPS62284582A - Encipherment method for image data - Google Patents

Abstract

PURPOSE:To store and transmit image data with high efficiency by providing a step wherein the configuration of the transposition of data blocks of tree- encoded image data by layers or data block groups is specified according to a cipher key and a step wherein the tree-encoded image data is transposed in to the specified configuration. CONSTITUTION:The cipher key specifies the configuration of the transposition of data blocks or data block groups of block structure of respective layers through the transposition configuration specification step as they are or after certain conversion processing. In the transposition step, data blocks or block groups of the tree-encoded image data in respective layers are transposed according to the specified configuration. Consequently, the respective blocks of the original tree-encoded image data are moved to different positions and when they are decoded on a tree basis, a quite different image from the original image is obtained and thus encipherment is performed. Consequently, image data are stored and transmitted with high efficiency.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to processing of image data, and particularly to a subsequent encryption method for one image data.

[Conventional technology]

Although there are many documents on encryption methods for ordinary data, there are very few documents on encryption methods for single image data. As a rare example, the Institute of Electronics and Communication Engineers branch axis IE82-
Based on the ``98r cryptographic encoding method that utilizes the characteristics of graphic information,'' this f'L is a method that repeatedly applies a second-order dispersion operation to the image data.

Incidentally, one image data has a large amount of data, and when storing, transmitting, etc. the next one image data, it is common to suppress data redundancy (so-called image compression) by high-efficiency encoding. Therefore, it is desirable that the encryption method for one image data be compatible with such a high-efficiency encoding method. The encrypted data is similar to noise and has low redundancy patterns and leaks.Therefore, this method is suitable.

Accumulation of one image data is not compatible with high-efficiency encoding method.

There is a problem that the cost of transmission etc. increases. The present invention is intended, in particular, to realize an image data encryption method that is compatible with high-efficiency encoding methods and can take full advantage of their advantages.

This is called a tree encoding method, a layered encoding method, etc. [Means for solving the problem] According to the present invention, a single painter data processing device is used.

After tree encoding, there is a step of specifying a form M4 of transposition of hierarchical data blocks or data block groups for the tree-encoded image data based on the cryptographic key, and a step of specifying the form M4 of transposition of the data block or data block group by layer for the tree-encoded image data, and converting the specified form of transposition to the tree-encoded image. A step is added to the data. [Operation] Tree-encoded image data has a hierarchical block structure corresponding to a tree structure. The cryptographic key can be passed through a transpose format specification step, either as is or after a certain transformation process.
Each specifies the form of transposition of a data block or a group of blocks in the n-layer block structure. In the transposing step, data blocks or block groups in each hierarchy are transposed (rearranged) for the tree-encoded image data according to this specification. As a result, each block of original tree-encoded image data.

As with the shuffle f'Lfc, if the image is moved to a different position and then tree-decoded as it is, the resulting image will be completely different from the original image, thus achieving encryption. Decoding can be performed by performing a transposition opposite to that used in encryption for each layer.

〔Example〕

FIG. 1 shows an example of an apparatus for implementing an embodiment of the present invention under the quadrant tree (Qsad-Tram) encoding method.
- The 044-tree encoding mechanism itself for converting into quadtree-encoded data is well known;
alCad(sg of B<5ary Inha
gaa' IEEE Trasa.

Pattars Analysis and M
ac le sea I outside talNgasaa.

Voj, PAMI-7Na3 (May 1985),
The % mellowness described on pages 284 to 298 may be as shown in Japanese Patent Application No. 60-241218, and a round one may be used. Simply put, this encoding method uses original image data,
Depending on the density or presence of luminance change points in each part, for example, as shown in Figure 2, the luminance data in each block is divided into multiple blocks of different sizes by repeating 4 divisions. There is something to encode each of them. The order of the quadrant (
(number of times) is called the hierarchy of that block or block group. For example, in Fig. 2 (4), the hierarchy of the entire image is #O''', the block group of blocks 1 to 7 generated in the first @th quadrant, block 8% blocks 9 to 12
The hierarchy of the block group and the block group of blocks 13 to 19 is 111, which is 69, and the blocks 1. Block 2, block groups 3 to 6 between blocks, block 7, etc. at level "2" and 6
Block 3 occurs in the third quarter division. Book 4.
Block 5. This is layer '3', such as block 6.

Hierarchical transposition@2 transposes a block or a group of blocks in each layer excluding -o't- for quadtree-encoded picture data. The transposition rule for each layer is given by the replacement information generated by the replacement information generation unit 3 based on the encryption key. The output of the layered transpose unit 2 is encrypted image data, which is represented by block 4 and sent to an flt storage device or communication system. The storage device referred to herein is not limited to a commonly-called data storage device, but also includes a laser card, an IC card, and other data holding means.

As an example, the encryption of image data that has been subjected to quadtree encoding as shown in FIG. 2 will be described in detail. The block structure in Figure 2 can be represented by the quadtree structure shown in Figure 2). Each leaf of the quadtree corresponds one-to-one to each of blocks 1 to 19, and the root node The hierarchy of R is "0", and the hierarchy value of the following 1% nodes increases by a1" toward the end. Each hierarchy j (f = 1, 2
1...), specify replacement: and according to this, the node (!) belonging to the corresponding hierarchy (!
2 (block or group of blocks) in Figure 2 (4) is transposed. For example, when the permutation r shown in Figure 3 (5) is given to a certain hierarchy, the four nodes in the hierarchy with the same parent node will have the node in the first position as the third honorary node. The trap node at the second position is moved to the first position and placed in the same manner as shown in FIG. 3 (CB). The transposition of this node is shown in Figure 3 (C
) corresponds to the transposition of the block shown in 1 for each of layers #1" to "J3" for the quadtree structure of the 21st field)
11 Transmutation: is specified and transposed, and the result is shown in Figure 4 (4).

The result of transposing the corresponding block or block group is shown in item 41). In other words, the image data in FIG. 2 (4) is transformed into the image data arranged as shown in item 41 by performing the transposition s2 based on the above-mentioned permutation 1rl ``'' C. This is the image data that has been encoded.

The information representing the permutation f (for each layer) is supplied by the permutation information generation unit 3 to the per-layer transposition unit 2 based on the encryption key. In such a case, the replacement information generation s3 only transfers the input information to the hierarchical transposition unit 2 after decoding or decoding.
It is not easy to manage encryption keys when the number of floors is large. A good way to solve this problem is to use a pseudo-random number generator to generate a series of hierarchical permutation information from a short cryptographic key. For example, in the case of a quadtree, 4! for each layer!
= 61 permutations of 24 times.

These are coded with numbers from "1" to "24". An appropriate numerical value is adopted as the encryption key, and pseudorandom numbers in the range of 1 to 24 are generated based on the well-known M sequence. For an image of 512 x 512 pixels, 2' = 5
Since the number is 12, it is only necessary to generate nine random numbers. By treating the nine random number sequences obtained in this manner as a permutation code sequence and sequentially decoding them, it is possible to sequentially obtain permutation information for friends in each layer.

Decoding is achieved by substituting its inverse permutation: r4 for each permutation r4 in the process described above. For example, the inverse substitution of f1 is as follows. The decryption key may be the reverse substitution information itself or its code, but since there is a one-to-one correspondence between substitution and its reverse substitution, the decryption key may be the same as the encryption key.

The reverse permutation information generating section 6 supplies information representing the reverse permutation of the permutation for each layer used in the if encoding based on the decryption key to the layer-by-layer reversal fR section 5. The reverse replacement information generation unit 6 generates the replacement information that is exactly the same as the replacement information generation s3 when information indicating reverse replacement is given as the decryption key, and generates replacement information or code when the decryption key is the same as the encryption key. It is the same as the replacement information generation unit except that it converts the information into the corresponding reverse replacement information or code. The hierarchical inverse transposition unit 5 performs the reverse transposition of the received nine-encrypted image data to that performed in the hierarchical transposition unit 2 to obtain original quadtree encoded data. As a matter of fact, the configurations of the transposing section 2 and the reverse transposing section 5 are the same.

The output of the layer-by-layer inverse transposition unit 5 is decoded by the quadtree decoding unit 7, and the output from the layer-by-layer transmission 'f! The section 2 and the replacement information generating section 3 can also be realized by a single processor with an appropriate program. The same applies to W5 to W7.

Data is read illegally from the storage device or communication system 1
Even if it is intercepted or intercepted, the original image will not be obtained unless the decryption key is found. 4 images of 512x512 pixels
When tree encoding n, permutation permutation is (4!)'# 2.6 X I 0
There are 12 ways to do this, and since image evaluation requires the assistance of human recognition and human functions, it is possible to obtain a sufficient concealment effect for English use.

The quadtree encoding method adopted in the above embodiment is as follows.

The encoded data of a block is stored only in the corresponding nest of the quadtree, but Fukan #J is a tree code Kitagata E that stores encoded data in nodes other than the first leaf (branch nodes). Ic 41 can be used. In this type of encoding method, after decoding the encoded data of the parent node and subtracting the resulting luminance data from the image data of the corresponding block, the process is divided into four sub-blocks, each of which is divided into four sub-blocks. Encode it.

Since this encoding method also uses a quadtree structure, it is possible to perform encryption by performing the above-mentioned hierarchical transposition.

It is defined by a permutation of the form.

〔Effect of the invention〕

According to the present invention, since encryption is achieved by adding transposition processing to tree encoding for image compression, the image compression effect of tree encoding is completely maintained.
Thus, it is possible to realize a cryptographic system that enables highly efficient storage and transmission of image data at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a tl-transfer processing apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a quadtree encoding system.
Figure 3 is a schematic diagram of transposition processing, and Figure 4 is a schematic diagram of hierarchical transposition for the quadrant in Figure 2. Part, 3・
... Replacement Information Generation Department Representative Patent Attorney Mamoru Nohagi (1 person) 1st Yuka Tsuji 1st Ward, I3 (CB)...? PM 56t
yttttbtbCA) (C)

Claims (1)

[Scope of Claims] 1. In an image data processing device having a tree encoding means for converting original image data into tree-encoded image data having a hierarchical block structure, data for each layer of the tree-encoded image data is The method comprises the steps of specifying a form of transposition of a block or a group of data blocks based on an encryption key, and a step of transposing the tree-encoded image data for each layer according to the specified transposition form. image data encryption method. 2. The image data encryption method according to claim 1, wherein the transposition form specifying step includes a step of generating information specifying the transposition form for each layer from an encryption key by a pseudo-random number generation process.