CN103942284B - File fingerprint information extracting method based on sine function - Google Patents

Abstract

A file fingerprint information extraction method based on a sine function, which uses a sine function to generate a position sequence, which is used as a position value when extracting file fingerprint information from the file content, and after the value is taken out, it is replaced by a replacement matrix to obtain the final File fingerprints to achieve a certain degree of confidentiality of the plaintext of the file. Among them, the permutation matrix can be set to a default value or specified by the user. This strategy is simple to implement and highly scalable. It can provide fingerprints of any bit length. The fingerprint information can be scattered in the file content in any form, which is very suitable for stream ciphers. In the scenario of encrypting and decrypting data.

Description

A File Fingerprint Information Extraction Method Based on Sine Function

technical field

The invention belongs to the field of computer applications, and relates to a method for acquiring file encryption information.

Background technique

In computer applications, especially in the field of information security, file fingerprint information is a very important method and strategy. The so-called file fingerprint refers to the feature that can uniquely identify a certain file, and each different file will have different fingerprint information. File fingerprints play a pivotal role in protecting data integrity, identification and many other aspects. In many scenarios, it is necessary to adopt a simpler and more effective file fingerprint information extraction mechanism.

Existing file fingerprint information extraction methods mainly focus on finding relevant hash functions to process file content. For example, in terms of verifying data integrity, the data publisher first hashes the content of the file, and attaches the hash value to the head or tail of the file. The hash value is compared to determine whether the data has been tampered with or damaged. In the industry, relatively mature and widely used hash functions include MDx and SHA-x.

However, in the stream cipher mechanism, each file needs to be encrypted and decrypted with a different key. The commonly used method of using file fingerprints to identify different files is not suitable, because a fingerprint information needs to be attached to the file header or tail , affects the length of the file, and the fingerprint information is public, once it is destroyed, the file has the risk of being unable to decrypt. Therefore, it is very necessary to study a file fingerprint information extraction method that can be used in stream ciphers.

Contents of the invention

The problem solved by the technology of the present invention is to overcome the deficiencies of the prior art and provide a method for extracting file fingerprint information based on a sinusoidal function, which is especially suitable for encrypting and decrypting data in a stream cipher system.

The technical solution of the present invention is: a kind of file fingerprint information extraction method based on sinusoidal function, comprises the following steps:

(1) Use a random sequence generator to generate a random sequence with a length of n bits; the random sequence is only generated once and will not be generated repeatedly.

(2) Obtain the file content and the file size A calculated by bit, use the following formula to calculate the location information, and extract the corresponding bit from the file content as the initial fingerprint information,

In the formula, S is an integer between 1 and n, F(S) is the Sth position extracted from the file content, L is the diffusion coefficient determined by the file size A, when A is less than 16KB, L=2 ¹⁷ bit, when A is greater than or equal to 16KB, L=A;

(3) Extract the corresponding bit information from the file content to generate n-bit initial fingerprint information; when the number of extraction positions calculated in step (2) is equal to n, the bit information extracted from n corresponding positions is the initial fingerprint information information, when the number of extraction positions calculated in step (2) is less than n, the random sequence generated in step (1) is replaced sequentially from the highest bit by using the bit information extracted from the corresponding position, thus obtaining n bit initial fingerprint information;

(4) Use the permutation matrix to replace the n-bit initial fingerprint information to obtain the final file fingerprint information. The permutation matrix is a 16*16 two-dimensional array, each element in the array is different, but the value of each element belongs to a value from 0 to 255. The permutation matrix is a fixed default matrix or randomly selected by the user.

The advantage of the present invention compared with prior art is:

(1) Simple to implement. Use the sine function to generate a position sequence, which is used as the position value when extracting the file fingerprint information from the file content. After the value is taken out, it is replaced with a permutation matrix to obtain the final file fingerprint. Compared with the traditional HASH method, this The inventive method does not need to make any changes to the source file to be encrypted (the traditional HASH method needs to append the hash value of the file to the file), which is easy to implement;

(2) It is very suitable for the user stream cipher system. Without changing the content of the file, the identity function of identifying each file is realized, and different key streams are generated for different files. The traditional method must change the content of the source file. If an error occurs in the transmission process of the file, the source file cannot be decrypted. The method of the present invention can avoid the above problems;

(3) Higher security. A random array is used to make it suitable for files of different sizes and provide good security. Traditional methods are less secure for small files, because small files can be cracked by brute force using traditional methods, and using file fingerprints and supplementing random data can ensure that even when the file content is small, it can provide more secure guarantee.

Description of drawings

Fig. 1 is a flowchart of the method of the present invention.

detailed description

As shown in Figure 1, it is a flow chart of the file fingerprint information extraction method based on the sine function of the present invention, which mainly includes the following steps:

1. Initial Fingerprint Generation

According to the file content and file length (calculated by bit length), combined with the sine function and fingerprint position calculation formula, the initial fingerprint information of the corresponding number of digits is extracted from the file content.

(1) Obtain the file length;

(2) According to the length of the file, calculate the corresponding position of the fingerprint information in the file content according to the following fingerprint calculation formula;

Formula description: The length of the file fingerprint information is n bits, S is an integer between [1,n], indicating the Sth bit of the fingerprint to be extracted; L is the diffusion coefficient, determined by the size of the file, when the file size is less than 16KB L is 2 ¹⁷ , and in other cases L is the size of the file (calculated in bits); F(S) indicates the specific location of the file corresponding to the S-th bit.

The derivation process of the above formula is as follows:

Since the relationship function adopts a sine function, the subscript of the bit in the file starts from 0, so

Therefore, the following formula is obtained:

The reason why the above formula uses the sine function as the basis to realize the generation of file fingerprint bits is that: 1) Because the position information generated by the sine function is more concealed than the position information generated by the linear function, and it is better than the high-order function and exponential function. The /logarithmic function is simple; 2) The coefficient of the function is associated with the file content to ensure that different files have different location information. Even if the file length is the same, its fingerprint information value is different; 3) In order to solve the problem of small files, The security guarantee measures are taken in the form of supplementing random arrays.

(3) Read the corresponding initial fingerprint information bit from the file content according to the calculated position (position counted in bits). If the file length is too small, fill the initial fingerprint with a bit string of corresponding length from the complementary array as needed information.

2. Complementary array generation

A bit array is generated by a random sequence generator (a random sequence generating function), which is a bit string with the same length as the file fingerprint information, and is generated once and used permanently.

(1) Use the random sequence generator to calculate a random sequence equal to the length of the fingerprint information;

(2) Use the pre-set randomness detection rules to check whether the randomness of the generated random sequence meets the requirements, if not, regenerate the random sequence; if it meets the requirements, the generated random sequence is a complementary array;

3. Fingerprint Information Replacement

The developer can set a default permutation matrix, and provide an interface for the user to choose whether to specify the permutation matrix, and use the permutation matrix to replace the initial fingerprint information to obtain the final file fingerprint information.

(1) Determine whether to use the default permutation matrix or use the user-specified permutation matrix;

(2) Use the permutation matrix to replace the initial fingerprint information to obtain the final file fingerprint information.

The permutation matrix is a 16*16 two-dimensional array. Each element in the array is different and belongs to a value from 0 to 255. That is to say, the permutation matrix is an arrangement of 0 to 255. The so-called default permutation matrix is automatically and randomly generated by the algorithm; and the user-specified permutation matrix, that is, the user can also generate a permutation by himself and input it in the form of algorithm parameters.

The permutation matrix is used to transform the initial file fingerprint information, making the relationship with the file data more complex, and improving the confidentiality of file fingerprint information acquisition. The function of the permutation matrix is to disturb the position of the bits in the file fingerprint information. Elements in the array cannot be repeated.

The content that is not described in detail in the description of the present invention belongs to the well-known technology of those skilled in the art.

Claims (3)

1. a kind of file fingerprint information extracting method based on SIN function, it is characterised in that comprise the steps：

(1) random sequence generator is utilized, random sequences of the length for n bit are generated；

(2) file size A for obtaining file content and calculating by bit, using following formula positional information is calculated,

$F\left(S\right)=(L+1)\·sin\frac{\mathrm{\π}(S-1)}{2(n-1)}$

In formula, S is that 1 to the integer between n, F (S) is the S position extracted from file content, and L is to be determined by file size A Fixed diffusion coefficient, when A is less than 16KB, L=2¹⁷Bit, when A is more than or equal to 16KB, L=A；

(3) information that corresponding bit is extracted from file content generates the initial fingerprint information of n bit；When calculating in step (2) When the extraction position number for arriving is equal to n, the bit information extracted from n correspondence position is initial fingerprint information, when step (2) In calculated extraction position number when being less than n, using the bit information extracted from correspondence position, to what is generated in step (1) Immediately sequence proceeds by order and replaces from highest order, thus obtains the initial fingerprint information of n bit；

(4) the initial fingerprint information of n bit is entered into line replacement using permutation matrix, so as to obtain final file fingerprint information； Described permutation matrix is the two-dimensional array of a 16*16, and each element in array is different from, but each element Value belongs to a value in 0～255.

2. a kind of file fingerprint information extracting method based on SIN function according to claim 1, it is characterised in that：Institute The random sequences stated are only generated once, are not repeated to generate.

3. a kind of file fingerprint information extracting method based on SIN function according to claim 1, it is characterised in that：Institute The permutation matrix stated is fixed default matrix or is randomly selected by user.