CN116582314A

CN116582314A - Optimal hidden double-protection text method

Info

Publication number: CN116582314A
Application number: CN202310505552.7A
Authority: CN
Inventors: 张菊; 张涛; 张渝
Original assignee: Southwest University
Current assignee: Southwest University
Priority date: 2023-05-06
Filing date: 2023-05-06
Publication date: 2023-08-11

Abstract

The invention discloses an optimal hidden double-protection text method, which comprises the following steps: encrypting the carrier text by using an SHA256 algorithm to generate a hash digest a; step two: embedding the secret information and the hash digest a into three components of a color pixel value R, G, B of the carrier text by using an information hiding algorithm to form a steganographic text; step three: sending the steganographic text to a recipient; step four: the receiver receives a file, wherein the file is a steganographic text or a legal modification steganographic text or an illegal tampering steganographic text; step five: the receiver uses SHA256 hash algorithm to extract hash digest b from the file; step six: whether the hash digest b is equal to the hash digest a or not, if not, indicating that the secret information has been illegally tampered; if equal, the recipient extracts the secret information. The invention combines the hash encryption technology with the text information hiding technology of the minimum modification pixels, thereby ensuring the integrity and the safety of the file during transmission to a greater extent.

Description

Optimal hidden double-protection text method

Technical Field

The invention relates to the technical field of encryption information, in particular to an optimal hidden double-protection text method.

Background

With the rapid development of multimedia technology and the wide popularization of internet application, the trend of digitization and networking of information is unavoidable, which greatly promotes the revolution of social production life and information propagation. The Internet provides a more convenient and rapid transmission channel for information interaction, so that people can exchange and share information on the network at any time and any place. A large amount of digital information is transmitted through the internet, wherein important sensitive data such as military information, electronic commerce information, personal privacy and the like are not spent. The problems of illegal copying and spreading of digital works, personal privacy disclosure, confidential information tampering and the like are endlessly compounded by the influence of the openness of the Internet environment and the vulnerability of the digital information and the risk of the information security. How to ensure the data security in the transmission process has become one of the challenges to be solved in the information security field.

Encryption techniques [8,15] are an important support in the field of information security. The numbers in brackets refer to the numbers of the following references, and are the same. Encryption technology refers to a method for converting plaintext to be transferred into ciphertext which is difficult to understand by common people by utilizing a secret key and an encryption algorithm, thereby protecting data security, and is essentially data transformation under a specific mapping rule. Encryption techniques are mainly divided into three categories: symmetric cryptographic Algorithm [16] (Symmetric-key Algorithm), asymmetric cryptographic Algorithm [5] (Asymmetric-key Algorithm), digest Algorithm [6] (Digest Algorithm). The symmetric algorithm refers to the same cryptographic algorithm for encrypting and decrypting keys, and comprises AES, SM1, SM4, DES and 3DES, IDEA, RC2, the asymmetric algorithm refers to the fact that the encrypting and decrypting keys are different cryptographic algorithms, and common asymmetric algorithms comprise RSA, SM2, DH, DSA, ECDSA, ECC and the like. The digest algorithm refers to a cryptographic algorithm that converts any arbitrary length of input message data into fixed length of output data, also known as a hash function. Digest algorithms are commonly used to make a determination of data integrity, i.e., hash the data and then compare the digest values for consistency. Summary algorithms are mainly divided into three main categories: MD (Message Digest) series, SHA (Secure Hash Algorithm ) series, MAC (Message Authentication Code, message authentication code algorithm) series.

The encryption technology can effectively hide the semantic content of the secret information, but the ciphertext appearance is usually presented as a pile of meaningless messy codes, which clearly prompts the existence of the secret information and is easy to excite the cracking enthusiasm of an attacker. Even if an attacker cannot reversely extract the plaintext information, the attacker can track, tamper and destroy the plaintext information, so that a receiver cannot smoothly extract the original plaintext information, and the aim of disturbing the hidden communication is fulfilled. This makes it easy to see that relying solely on encryption algorithms is not able to mask the communication behavior itself and it is difficult to ensure data security under open channel conditions.

To reduce the likelihood of personal attacks on the secret information, the information hiding technique [9,11,18] embeds the secret information in an imperceptible manner into the selected carrier, enabling covert communications by overt transmission of the carrying carrier. The information hiding can effectively hide the existence of secret information, so that the secret information is changed from 'hard to understand' to 'imperceptible', thereby avoiding the attention of an attacker and achieving the effect of avoiding theft or damage. Information hiding utilizes the ubiquitous redundancy characteristic of multimedia information to secretly hide meaningful secret information such as software serial number, secret text or copyright information in the multimedia information through a certain algorithm. In general, the carrier may be text, image, audio, video, etc., and the most studied and deepest is information hiding with image as carrier at present, mainly due to the existence of larger redundant information in the image, and the larger hiding capacity, on the other hand, due to the intuitiveness of image processing, based on these advantages of the image carrier, some secret information can be hidden therein without doubt. Text files are the most popular and convenient popular information media tools, and secret communication by using text is the most convenient way. However, the text file is formed by directly encoding text data, and data redundancy hardly exists, so that information hiding cannot be realized by modifying the effective data of the original file, the difficulty of hiding information by taking the text as a carrier is relatively high, but the text with hidden secret information is often not easy to doubt, and the text file has relatively good safety, so that the text-based information hiding has important practical significance and application prospect. The encryption technology aims at encrypting communication content and generating a set of meaningless messy codes by the information, and the information hiding technology is more focused on hiding communication behaviors, so that the information hiding technology has more ideal security in the field of hidden communication.

Description of related Art

1.Character feature methods[7] by changing a certain characteristic of the text, such as a font size, or style of font, etc. The secret information is hidden, for example, by changing the style of the font, by changing the lengthening or shortening of the points of i and j, the ends of h, d, b. This approach is visually more concealed because the individual letter change readers may not be aware of it. But since fewer objects are available for format modification in the carrier, the secret information embedded in the imported carrier text is fewer, and the hiding capacity is low. And the text encounters an operation of modifying the text format or re-entering the text during the transfer, secret information is lost. And this approach may require creating a new font, which is difficult.

2.Syntactic Methods syntax method [1] aims at making some transformations to the text structure to embed secret information, such as the location of mobile adverbs, add formal subjects, or change initiative to passive. By changing the text structure to embed the secret information, for example, using different grammars to represent the same meaning, the sender sets rules to convert the secret information into a binary stream, one grammar represents embedded data "0", the other grammar embeds data "1", and if multiple grammars exist, more than two binary bits can be embedded at the same time, so that the embedding capacity of the hiding method can be increased. Although more than two binary bits can be embedded, there are few, perhaps a few, of the thousands of words of text bytes, where different syntax structures can be used to express the same meaning, and his opportunities for use are very limited. Therefore, the embedding capacity of the method is not high, but the concealment is good, the grammar results are various, and readers cannot perceive that secret information is concealed inside even if the grammar structures are different.

3.Semantic Methods semantic method [23] aimed at changing text content to insert secret information. The following describes a method of embedding secret information by changing text contents. The method specifically includes the steps that two synonyms are designated as primary or secondary values, a sender sets rules, one word represents embedded data of 1, one word represents embedded data of 0, and when the synonyms are many, a group of synonyms can be embedded with secret information of two or more bits. The method has low use frequency and small embedding capacity. And too many synonyms used may be perceived by the reader. But the method has good robustness performance and cannot be easily changed by people.

4.Double Space Methods (DS 96), open Space method [1,23] conceals secret information by processing of a space, and conceals secret information in a cover text by using the position of the space. As shown in fig. 2, an example of text content using the sentence spacing steganography method. The method is to control the space between each sentence of carrier text to hide information, to convert the secret information into binary bit stream, to place one or two spaces behind the termination character of each sentence, to set rules, such as one space hiding binary bit 0, two space hiding binary bit 1, and to extract the secret information according to the rules after the receiver receives the carrier text. This method has a problem of inefficiency in that the amount of text that can be hidden depends on how many sentences. However, a large amount of text is required to hide a small amount of secret information. And many word processors automatically set inter-sentence spaces, which also results in the hidden secret information being completely corrupted. And the different spaces are observable by human vision, the concealment of the method is also relatively low.

5.Regular Space with Unicode Space (RSUS 15), kumar et al [10] proposes a USC15 text steganography method that uses Unicode space characters to hide secret data information in Microsoft word files, normalizes the width of Unicode characters by reducing the font size to make them equal to the width of the pair or Six-Per-Em Unicode characters, and hides 4-bit secret data in the interword and intersentence spaces and 3-bit secret information in the interparagraph or interline spaces.

6. Steganography and encryption techniques, color Coding Approach (CC 17), malik et al [14] proposes a CC17 text steganography method that uses Move To Front (MTF) encoding, huffman compression, and color encoding, and conceals secret data by forwarding an email platform. The method can reach the coverage text capacity of more than 1 bit/character. Input: confidential information, cover text; and (3) outputting: steganographic text, a set of email addresses. Extracting secret information binary bits according To a color coding table, extracting an email address, decompressing by using Huffman, and then obtaining original secret information by using Move To Front (MTF) coding.

7.Hybrid text steganography (HT 17), aman et al [2] proposed an HT text steganography method, which performs a series of operations such as random arrangement (Permulation), bit filling, compression, etc. on secret information, and then encodes the blank space of the cover text by using the minimum width Unicode to achieve the purpose of information hiding.

8.Minimum Pixel Modification(MPM2022)[21]The method is to embed secret information in a cover image carrier, which maintains good picture quality while having a large capacity hiding capability by modifying picture pixels and minimizing modifications to image pixels using an optimization function. Input: cover pixel group g= (G) ₀ ,g ₁ ,…,g _n-1 ) And 2k+1 bits of secret information; and (3) outputting: steganographic pixel group G '= (G' ₀ ,g ₁ ′,…,g′ _n-1 ) The method comprises the steps of carrying out a first treatment on the surface of the Step1: finding a cover pixel with a specified index using the formula;

g _h ＝q Mod n (4)；

step2: converting binary secret information into decimal number d, and grouping the secret information, and (b) _k b _k-1 …b ₁ b ₀ ) ₂ Conversion to decimal d ₀ Will (b) _yk …b _yk+2 b _yk+1 ) ₂ Conversion to decimal d _y ,y∈[1,n-1]The method comprises the steps of carrying out a first treatment on the surface of the Step3: finding x in optimization problem _h And x _i ；

Embedding information g 'in a steganographic pixel' _h ＝x _h +g _h ，g _i ′＝x _i +g _i . Step4: combining g' _h And g _i ' get G ' = (G ' ₀ ,g ₁ ′,…,g′ _h ,…,g′ _n-1 ) Through d _h ＝g′ _h mod m ₀ And d _i ＝g _i ′mod m ₁ Acquisition of d _h And d _i Merging d _h And d _i Secret information is obtained.

Reference to the literature

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Therefore, the conventional encryption technology has the defect that although the conventional encryption technology can effectively hide the semantic content of the secret information, the appearance of the ciphertext generally shows a meaningless messy code, clearly prompts the existence of the secret information, and is easy to trace, tamper and destroy. The existing text hiding technology has low secret information hiding capacity; the ciphertext is easily modified to damage the ciphertext in the transmission process; a defect of low concealment.

Disclosure of Invention

In view of at least one defect in the prior art, the invention aims to provide an optimal hidden double-protection text method, which combines a hash encryption technology with a text information hiding technology for minimizing modification pixels, thereby ensuring the integrity and the safety of files during transmission to a greater extent and realizing double-hidden communication; the text information hiding technology using RGB three-channel pixels for modifying the text font is proposed for the first time, the embedding capacity is greatly increased, the non-detectability of the text is improved, and the technology is innovative.

In order to achieve the above purpose, the invention adopts the following technical scheme: an optimally hidden double-protection text method comprises the following steps: step one: encrypting the carrier text by using an SHA256 hash algorithm to generate a hash digest a; step two: embedding the secret information and the hash digest a into R, G, B components of the color pixel values of the carrier text by using an information hiding algorithm to form a steganographic text; step three: sending the steganographic text to a recipient; step four: the receiver receives a file, wherein the file is a steganographic text or a legal modified steganographic text or an illegally tampered steganographic text; step five: the receiver uses SHA256 hash algorithm to extract hash digest b from the file; step six: judging whether the regenerated hash digest b is equal to the extracted hash digest a or not, and if not, judging whether the regenerated hash digest b is equal to the extracted hash digest a or not; indicating that the secret information is illegally tampered by an attacker, and discarding the file by a receiver; if the two types of the files are equal, the files are indicated to belong to the steganographic text or the legal modified steganographic text, and the step seven is shifted; step seven: the recipient extracts the secret information.

Embedding secret information and a hash digest a into R, G, B components of color pixel values of a carrier text by adopting the following information hiding algorithm;

input: carrier text font color RGB three channel G ₁ ，G ₂ ，G ₃ And 3nk+3 bits of secret information;

and (3) outputting: steganographic text G ₁ ′,G ₂ ′,G ₃ ′；

The embedding process comprises the following steps:

step 21: processing the carrier text information; step 21 further comprises:

step 211: acquiring pixel values of each letter of the carrier text, and representing pixel values of R, G, B three components of an ith letter by P (i, 1), P (i, 2) and P (i, 3); denoted P (i, a), a=1, 2,3;

step 212: acquiring pixel values of R, G, B channels of each letter of the carrier text by using G respectively ₁ ，G ₂ ，G ₃ A representation; will G ₁ ，G ₂ ，G ₃ Merging into G; g is the total number of pixel values of the carrier text;

step 213: grouping the total number of the obtained pixel values, wherein n pixels are a group;

step 22: processing the secret information; step 22 further comprises:

step 221: 3nk+3 bits of secret information are divided into 3 groups, and each group of nk+1 bits is respectively:

B ₃ ＝(b _3nk+3 b _3nk+2 …b _2nk+3 b _2nk+2 )2；

B ₂ ＝(b _2nk+1 b _2nk …b _nk+2 b _nk+1 )2；

B ₁ ＝(b _nk b _nk-1 …b ₁ b ₀ ) ₂ ；

wherein n represents that a group of pixels contains n pixels, k is the embedding degree, and the larger k represents the more secret information is embedded;

step 222: to binary confidential information B of each group ₁ 、B ₂ 、B ₃ Respectively converting into decimal numbers D;

D ₃ ＝2 ^nk b _3nk+3 +2 ^nk-1 b _3nk2 +…+2 ¹ b _2nk+3 +2 ⁰ b _2nk+2 ；D ₂ ＝2 ^nk b _2nk+1 +2 ^nk-1 b _2nk +…+2 ¹ b _nk+2 +2 ⁰ b _nk+1 ；

D ₁ ＝2 ^nk b _nk +2 ^nk-1 b _nk-1 +…+2 ¹ b ₁ +2 ⁰ b ₀ ；

step 223: will B ₁ Dividing into n groups, the first group comprising k+1 bits, (b) _k b _k-1 …b ₁ b ₀ ) ₂ Conversion to decimal number d ₀ The remaining n-1 groups are: (b) _(y+1)k …b _yk+2 b _yk+1 ) ₂ Conversion to decimal number d _y ,y∈[1,n-1]The method comprises the steps of carrying out a first treatment on the surface of the Likewise will B ₂ ,B ₃ These operations are also performed;

step 23: embedding secret information; step 23 further comprises:

will B ₁ ,B ₂ ,B ₃ Decimal numbers of each group are embedded in each group of pixel values, B ₁ The embedding process is as follows:

step 231: q represents the index of the vector text color pixel value, and equation (6) is used to index the hidden k+1 bit pixel value, g _i Pixel value, g, representing original carrier text font _h Refers to the h pixel in a set of carrier text font pixels; use g _i ' pixel value, g ', representing the embedded steganographic text font ' _h Refers to the h pixel value in a set of steganographic text font pixel sets;

g _h ＝q mod n (6)；

step 232: finding x in optimization problem _h ，x _h Representing the searched optimized value corresponding to the h pixel value;

using g' _h ＝x _h +g _h Embedding secret information;

step 233: at the same time, in the optimization problem, find x _i ，x _i Representing the found optimized value corresponding to the ith pixel value;

using g' _i ＝x _i +g _i Embedding secret information;

step 234: likewise will B ₂ ,B ₃ The operations of steps 231-233 of step 23 are also performed; step 235: will g' _h And g' _i Combining to obtain a steganographic text font R, G and a B-channel pixel G' ₁ ,G′ ₂ ,G′ ₃ 。

The step seven of the receiver extracting the secret information includes: obtain input G' ₁ ,G′ ₂ ,G′ ₃ Outputting 3nk+3 bits of secret information; the seventh step comprises the following steps: step 71: using index g' _i =q mod n, finding the pixel value of the hidden k+1 bits binary secret information; step 72: resume d ₀ ＝g′ _h mod 2 ^k+1 ；

Step 73: resume d _i ＝g′ _i mod2 ^k The method comprises the steps of carrying out a first treatment on the surface of the Step 74: will d ₀ ，d _i And combining to obtain secret information d, and converting the secret information d into binary bits.

The invention provides the optimal hidden double-protection text method, combines the hash encryption technology with the text information hiding technology of the minimum modification pixels, thereby ensuring the integrity and the safety of the file during transmission to a greater extent and realizing double-hidden communication; the text information hiding technology using RGB three-channel pixels for modifying the text font is proposed for the first time, the embedding capacity is greatly increased, the non-detectability of the text is improved, and the technology is innovative.

Drawings

FIG. 1 is a general flow chart of the present invention;

FIG. 2 is a schematic diagram of text content using a sentence spacing steganography method;

FIG. 3 is a diagram of a process of encrypting data using SHA256 algorithm to generate a digest;

FIG. 4 is 8 hash initial values in the SHA256 algorithm;

FIG. 5 is a 64-bit hash constant in the SHA256 algorithm;

FIG. 6 is a schematic diagram of a hash digest generated in the SHA256 algorithm;

fig. 7 is an example of text used by the SHA256 algorithm.

FIG. 8 is a secret digest obtained using the SHA256 algorithm;

FIG. 9 is a binary stream into which a 256-bit secret digest is translated;

FIG. 10 is an original text file and a generated digest value; wherein (a) is the content of the original text file; (b) a summary value generated for the cover text file;

FIG. 11 is a diagram of a legal modified text file and a generated digest value; wherein (a) is legal modification of text file content; (b) generating a digest value for the legally modified text file;

FIG. 12 is a diagram of illegally tampered text file and a generated digest value; wherein (a) is illegally tampering with the text file content; (b) a digest value generated for illegally tampering with the text file;

FIG. 13 is a graph of security level comparison analysis of the present invention with other algorithms;

FIG. 14 is a schematic diagram of a comparison of original text and steganographic text; wherein (a) is the content of the original text file; (b) Content of a cover text file containing steganographic text;

FIG. 15 is a RGB comparison of original text letters to steganographic text letters; wherein (a) is an RGB diagram of original text letters; (b) An RGB diagram of cover text letters containing steganographic text;

FIG. 16 is a graph comparing the hiding power of the present invention with other algorithms;

FIG. 17 is a graph comparing the number of characters required to conceal the same data as other algorithms in accordance with the present invention.

Detailed Description

The invention will be described in further detail with reference to the drawings and the specific examples.

As shown in fig. 2, open Space method hides secret information by processing of the blank, and hides secret information in the cover text by using the position of the blank. Is an example of text content using a sentence spacing steganography method. The method is to control the space between each sentence of carrier text to hide information, to convert the secret information into binary bit stream, to place one or two spaces behind the termination character of each sentence, to set rules, such as one space hiding binary bit 0, two space hiding binary bit 1, and to extract the secret information according to the rules after the receiver receives the carrier text. This method has a problem of inefficiency in that the amount of text that can be hidden depends on how many sentences.

The information hiding technology is one of embedding secret information into multimedia carrier waves such as words, images, audio and video. In recent years, researchers have proposed many concealment schemes for images, but there have been insufficient researches on text information concealment techniques. Based on the idea of combining an encryption algorithm and a text information hiding algorithm, the invention provides an optimal hidden double protection text method (TPM), thereby improving the hiding capacity and tamper resistance of the text. The main idea of the TPM is to generate 256-bit binary system from the text file through a Sha256 hash algorithm, divide the pixel values of three channels of n+1 text fonts R, G, B into one group, perform specific modulo operation on each group, and embed 256-bit binary system and secret information therein. In this embodiment, by comparing the performance of the TPM with the text information hiding algorithm proposed in recent years, the performance of embedding capability (bpp), security, imperceptibility, visual attack, and the like of the TPM are all very good, and the overall performance is the highest. In order to realize safer information communication, the invention provides that the encryption technology is combined with text information hiding, so that double hidden communication is realized. The invention provides a safe contract protection scheme aiming at formatted text files (such as doc files generated by a tablet or word, and the like), and the scheme organically combines an encryption technology and an information hiding technology. Firstly, encrypting the contract file by using a hash function to obtain a fixed abstract value, hiding the abstract value in the contract file by using a text information hiding technology, and then sending the abstract value to a target receiver, thereby realizing double-hidden communication. In this embodiment, it is proved that the pixel value of the text color carries the secret information as a feasible scheme, so that a text information hiding method for modifying the pixels of the text font is proposed to protect the file, when the destination receiver receives the file, only the same hash function is used to generate the abstract, if the abstract is consistent with the extracted secret information, the file is not tampered and destroyed by the person, and meanwhile, some more confidential information can be hidden in the text file to prevent the secret data from being revealed. The innovation and contribution of the invention are as follows:

1. the hash encryption technology is combined with the text information hiding technology of the minimum modification pixels, so that the integrity and the safety of the file during transmission are ensured to a greater extent, and double hidden communication is realized.

2. The text information hiding technology using RGB three-channel pixels for modifying the text font is proposed for the first time, the embedding capacity is greatly increased, the non-detectability of the text is improved, and the technology is innovative.

3. The text hiding technology is used for hiding confidential secret data, so that the privacy of the file is protected.

As shown in fig. 1-17, an optimally hidden double protected text approach, TPM (Text pixels Modification); the invention provides a text information hiding method combining cryptography and steganography, which is carried out in two stages. The first stage uses a hash function to encrypt the carrier text to generate a digest, and when delivered to the receiver, the receiver uses the hash to generate a digest to verify the integrity of the transmission process, and the second stage embeds the encrypted information and the information to be hidden into the R, G, B components of the color pixel values of the carrier text. Fig. 1 shows an overall flow chart of the proposed algorithm.

Encryption process: the basic process of data encryption is to process the original file or data in plaintext according to algorithm to make it an unreadable ciphertext. The method achieves the purpose of protecting data from being stolen and read by illegal persons. The encryption technique employed herein is the SHA256 (Secure Hash Algorithm) algorithm, which is a cryptographic hash function algorithm. The algorithm comprises three stages, namely constant initialization, information preprocessing and digest value calculation. The process of generating the summary is shown in fig. 3.

1. Constant initialization, fetchThe first 8 prime numbers in the natural numbers, for which square roots are calculated, the 32bits from which the fractional part of the result is taken are converted into 16-ary numbers, and a hash initial value is generated. For example, the number of the cells to be processed, the 32bits of the decimal fraction are converted to a 16-ary number by equation (71). Prime number 2 corresponds to an initial value of 6a09e667.

0.41421356237309504880168872420970≈6*16 ^-1 +a*16 ^-2 +0*16 ^-3 +…(1)；

The 8 hash initial values are shown in fig. 4. And then taking the first 64 prime numbers of the natural number, calculating the cube roots of the prime numbers, and taking 32bits of the decimal part to convert the decimal part into 16-system numbers to generate a hash constant K. Similar to the above hash initial value, the 64-bit hash constant is shown in fig. 5.

2. Information preprocessing refers to supplementing a message after calculating a hash with a required message so that the message meets a required structure. The preprocessing of the information is divided into two steps.

Step1: additional padding bits.

Let the binary coding bit number of the message be l, complement one bit "1" after the coding bit, then complement k bit "0", k is the minimum non-negative integer satisfying the following equation.

l+1+k≡448mod512 (2)；

Step2: additional length values. The length l of the original information is encoded in a 64-bit binary form, appended to the filled message, so that the length of the entire message becomes 512bits or multiples of 512 bits.

3. The digest value is calculated.

Step1: dividing the preprocessed message into 512bits of blocks, assuming that message M can be decomposed into n blocks, i.e., M ₁ ～M _n 。

Step2: will M ₁ The block is constructed as 64 words, the first 16 words are words that directly decompose the block into 16 32bits of wordsDenoted as w 0],w[1],…,w[15]The next 48 words w _t Generated by iterative calculation of equation (3).

w _t ＝σ ₁ (w _t-2 )+w _t-7 +σ ₀ (w _t-15 )+w _t-16 (3)；

Wherein sigma ₀ Sum sigma ₁ The bit operation for logic:

step3: for M ₁ The block calculates M ₁ Each word of the block is subject to an encryption loop. h is a ₀ ～h ₇ The encryption process is as shown in fig. 6: ch. Sigma 1, ma, sigma 0 are nonlinear logic functions whose representations are shown in formulas (61) - (64), with "+" boxes representing the addition of numbers together, and mod2 ³² Pair 2 ³² And taking the rest. h is a ₀ ～h ₇ The initial value at the beginning is the hash initial value calculated before, K ₀ Represented is a first hash constant, also known as a hash key. As can be seen from FIG. 6, M will be ₁ W 0 of the first block of (2)]And K is equal to ₀ Add mod2 ³² Calculating the obtained value and h ₇ Again add mod2 ³² Calculating the obtained value and h ₄ ～h ₆ Adding mod2 by the value calculated by Ch nonlinear logic function ³² Calculating, and then the obtained value is combined with h ₄ The value obtained by the sigma 1 nonlinear logic function is added to mod2 ³² Calculating the obtained value and h ₃ Add mod2 ³² Calculating, namely assigning the obtained value to h ₄ According to FIG. 6, new h is obtained in sequence ₀ ～h ₇ 。

Step4: each block is calculated circularly until M is calculated _n . And finally obtaining the 256bits hash digest.

4. An example of the encryption, an example of the text used by the SHA256 algorithm is shown in FIG. 7.

The secret digest obtained using the SHA256 encryption algorithm is shown in fig. 8. The text is converted into a 256-bit digest and then the digest is converted into binary bits, and fig. 9 is a binary stream into which the 256-bit digest is converted.

5. Embedding process, input: carrier text font color RGB three channel G ₁ ，G ₂ ，G ₃ And 3nk+3 bits of secret information; and (3) outputting: steganographic text G' ₁ ,G′ ₂ ,G′ ₃ ；

Step1: and processing the carrier information.

1. Each letter pixel value of the carrier text is obtained, and P (i, 1), P (i, 2), P (i, 3) are used to represent the pixel values of the R, G, B three components of the ith letter. Denoted P (i, a), a=1, 2,3.

2. Acquiring pixel values of R, G, B channels of each letter of the carrier text by using G respectively ₁ ，G ₂ ，G ₃ Representation, G ₁ ，G ₂ ，G ₃ And are combined into G. G is the total number of pixel values of the cover text.

2. The obtained pixel values are grouped, and n pixels are a group.

Step2: processing the secret information.

1. 3nk+3 bits of secret information are divided into 3 groups, and each group of nk+1 bits is respectively:

B ₃ ＝(b _3nk+3 b _3nk+2 …b _2nk+3 b _2nk+2 ) ₂ ；

B ₂ ＝(b _2nk+1 b _2nk …b _nk+2 b _nk+1 ) ₂ ；

B ₁ ＝(b _nk b _nk-1 …b ₁ b ₀ ) ₂ ；

where n represents that a group of pixels contains n pixels, k is the degree of embedding, and the larger k represents the more secret information is embedded.

2. To binary confidential information B of each group ₁ 、B ₂ 、B ₃ Converted into decimal numbers D, D ₃ ＝2 ^nk b _3nk+3 +2 ^nk-1 b _3nk+2 +…+2 ¹ b _2nk+3 +2 ⁰ b _2nk+2 ,D ₂ ＝2 ^nk b _2nk+1 +2 ^nk-1 b _2nk +…+2 ¹ b _nk+2 +2 ⁰ b _nk+1 ,D ₁ ＝2 ^nk b _nk +2 ^nk-1 b _nk-1 +…+2 ¹ b ₁ +2 ⁰ b ₀ 。

3. Will B ₁ Dividing into n groups, the first group comprising k+1 bits, (b) _k b _k-1 …b ₁ b ₀ ) ₂ Conversion to decimal number d ₀ The remaining n-1 groups are: (b) _(y+1)k …b _yk+2 b _yk+1 ) ₂ Conversion to decimal number d _y ,y∈[1,n-1]. Likewise will B ₂ ,B ₃ These operations are also performed.

Step3: embedding secret information, B ₁ The decimal numbers of each group are embedded into each group of pixel values, and the embedding process is as follows:

1.q represents the index of the vector text color pixel value, using equation 6 to index the pixel value of the hidden k+1 bits, where g is used _i To represent the pixel values, g, of the original carrier text font _h Refers to the h-th pixel value in a set of original carrier text font pixels. Use g _i ' to represent embedded steganographic text fontsPixel value, g' _h Refers to the h-th pixel value in a set of steganographic text font pixel sets.

g _h ＝q mod n (6)；

2. Finding x in optimization problem _h ：

Using g' _h ＝x _h +g _h Secret information is embedded.

3. At the same time, in the optimization problem, find x _i ：

Using g' _i ＝x _i +g _i Secret information is embedded.

4. Likewise will B ₂ ,B ₃ The above operations 1 to 3 are also performed.

5. Will g' _h And g _i ' combining results in a steganographic text font R, G and a B-three channel pixel G ₁ ′,G ₂ ′,G ₃ ′。

Extraction process, input: g ₁ ′,G ₂ ′,G ₃ 'A'; and (3) outputting: 3nk+3 bits of secret information.

1. Using index g' _h =q mod n, finding the pixel value of the hidden k+1 bit binary secret information.

2. Resume d ₀ ＝g′ _h mod 2 ^k+1 The method comprises the steps of carrying out a first treatment on the surface of the 3. Resume d _i ＝g _i ′mod2 ^k ；

4. Will d ₀ ，d _i And combining to obtain secret information d, and converting the secret information d into binary bits.

Experimental analysis in this example, experiments were used to evaluate the performance of the proposed method, which was performed by python and run on a computer equipped with Intel (R) Core (TM) i7-10700 CPU@2.90GHz and 16GB memory. The operating system is Windows 10Professional 64 bits. Performance evaluation metrics of the scheme include embedding capability, protection index, and text quality.

1. Security analysis, the security of information hiding refers to the property of information to ensure non-modification, non-destruction and non-loss during transmission, exchange, storage and processing. In the present invention, secret information is hidden in letter color pixels of transmitted cover text, and only designated recipients can extract the secret information by a specific extraction method. The text after embedding the secret information is not so different from the original cover text that it cannot be observed by the naked human eye. And the method encodes the entire text file using the SHA256 function, generating a 256-bit digest that is embedded into the cover text along with the secret information. The receiver only needs to perform SHA256 operation on the received text once and then compares the received text with the extracted original abstract. If the two digest values are not identical, indicating that the information has been illegally tampered with by an attacker, the receiver should discard the file in time and feed back to the sender. This process ensures the integrity and security of text transmissions.

FIG. 10 is an original text file and a generated digest value; wherein (a) is the content of the original text file; (b) a summary value generated for the cover text file.

This embodiment considers two types of tampering: legal modification and illegal tampering. Legal modifications include changes in font format, font size, and color, which do not affect the understanding and transmission of the file content, so that such modifications are not detected and the resulting digest value is unchanged. Illegal tampering includes adding a character to the text, deleting a character, replacing a character with a visually different character, replacing a character with a visually similar character, and tampering with the character, which affects interpretation of the text content, so that tampering is detected, and the generated text digest value is different from the previous original text digest value. FIG. 11 is a diagram of a legal modified text file and a generated digest value; wherein (a) is legal modification of text file content; (b) generating a digest value for the legally modified text file;

the original cover text is modified in fig. 11 (a) by the color of a letter "a", which belongs to legal modification, and the abstract generated after the modification is:

bacdbd027c5660eb068790920aef de6d127bf9888264fc71c6ce077801dbdc, consistent with the summary generated by the original text, as shown in (b) of fig. 11. FIG. 12 is a diagram of illegally tampered text file and a generated digest value; wherein (a) is illegally tampering with the text file content; (b) a digest value generated for illegally tampering with the text file; one character "a" of the original cover text is modified to "e" in (a) of fig. 12, and then the illegally tampered digest value is obtained in (b) of fig. 12 as follows:

6fa5a61685228a82cc19222733ffe774a8b578f75f901967b9208ab9354b5302, which is quite different from the previous original digest value. In the DS96, RSUS15, HT17 schemes, once a suspect file is hidden from secret information, it is easily found. In the CC17 scheme, too, it is easily found due to the rich colors. Thus, these methods have a lower security level than the TPM method. The method proposed by the invention is very sensitive to illegal tampering, and fig. 13 shows the security level comparison analysis of the invention relative to other algorithms, and the method proposed by the invention has a higher security level than other encryption technologies.

2. Imperceptibility analysis, because the method provided by the invention uses Sha256 cryptography, the integrity of the transmitted text file is ensured, but others do not know that we hide the text abstract in the text, so the imperceptibility of the transmission process is ensured. When an illegal molecule is unknowingly tampered with a text file, then the file is transmitted to a receiver, but in fact, the file can be found tampered. And the steganographic text obtained by using the method provided by the invention is not very different from the cover text (as shown in fig. 14), and is difficult to be perceived by naked eyes. The difference between one letter before and after steganography is shown in fig. 15, where the RGB differences are not large and are not easily perceived. FIG. 14 is a schematic diagram of a comparison of original text and steganographic text; wherein (a) is the content of the original text file; (b) Content of a cover text file containing steganographic text; FIG. 15 is a RGB comparison of original text letters to steganographic text letters; wherein (a) is an RGB diagram of original text letters; (b) RGB diagram of cover text letters containing steganographic text.

3. The data hiding power analysis, the data hiding power refers to the number of secret data bits (bpc) that each character can hide, and the following expression represents the data hiding power HC of the cover text.

A higher bpc indicates more secret data that can be embedded in one character, and a lower bpc indicates less efficient embedding. The method provided by the invention can achieve the data hiding capability of 6-9bpc, and successfully achieve the aim of enhancing the text data hiding capability. Fig. 16 shows the data hiding and hiding capacities of n=1, 2,3, 4, k=3, 4, 5 of the method, respectively, and the data hiding and hiding capacities of the method proposed by the present invention are higher compared with those of the methods proposed by the previous related works. Table 1 summarizes the proposed characteristics of several text steganography, including the number of carrier text characters in a group, the number of embedded bits per group, and the data hiding capability, we set 5 characters as one word and 10 words as one sentence. In this table, n is the number of texts in a group, and k is the degree to which secret data is embedded.

Table 1 comparison of data hiding ability

For the test, the above method is applied to secret information with the same size, the embedded secret information is 16bits, and the cover text information is "Akbar acid," How many crows are there in this city? "Without even a moment's thoughts, birbal reply" There are fifty thousand five hundred and eighty nine crows, my hard "," How can you be so sure? The experimental results are presented in fig. 17 by "asked akbar. Birbal acid," Make your men count, my long. If you find more crows it means some have come to visit their relatives here. If you find less number of crows it means some have gone to visit their relatives elsewhere ". Akbar was pleased very much by Birbal's wit", when 16bits of secret information need to be hidden, 77 cover text characters are required for the DS96 method, 18 cover text characters are required for the RSUS15 method, 16 cover text characters are required for the CC17 method, 18 cover text characters are required for the HT17 method, 8 text characters are required for the UC19, and only 2 cover text characters are required for the method we propose. FIG. 17 is a graph comparing the number of characters required to conceal the same data with other algorithms, and the number of characters required to conceal the same data is minimized.

4. Visual similarity and protection against visual attacks. The method provided by the invention changes R, G and B three channels of the text font RGB, and the change of each channel is very small, so that the human eyes cannot see the difference. Fig. 14 is a cover text and a steganographic text with little distinction. Open Space method by using the size of the blank to hide the secret information, there is a case where the sizes of the spaces between words or sentences are not uniform, and a reader who is careful to read them finds the difference, so the method is not resistant to visual attacks. The USC15 text steganography method uses Unicode space characters to normalize the width of Unicode characters, which can be observed by naked eyes, so that the method cannot resist visual attacks. The CC17 method uses rich color changes in steganographic text, whose cover text is distinct from steganographic text, and thus is not resistant to visual attacks. The HT17 method performs a series of operations such as random arrangement (Permulation), bit filling, compression and the like on secret information, and then encodes the blank space of the cover text by using the minimum width Unicode to achieve the purpose of information hiding. This concealment is also very difficult to find with the naked eye and is therefore resistant to visual attacks. The UC19 method performs three-level encryption on confidential data, then uses Unicode characters to embed generated binary data into a cover text, and is also difficult to observe by naked eyes, so that the method can resist visual attacks. As in table 2, we compared whether or not to defend against visual attacks.

Table 2 comparison against visual attacks

Conclusion: the invention uses the combination of encryption technology and information hiding technology to protect the text file and secret data, wherein the information hiding method also uses the optimization function to achieve the aim of least cover text modification and most secret information hiding. The method not only increases the security of the transmitted file, but also improves the embedding capability of secret information. From the experimental results, it can be seen that since the pixels of each word can be divided into R, G, B three channels, and each channel of one word can hide 3-bit secret information, and an optimization algorithm is adopted for the word, so that the pixels of the word are minimally modified, the performance of payload and visual attack is superior to other technologies. Most importantly, the method presented herein ensures the integrity of the transmitted document, and once the document is illegally tampered with by an lawbreaker, the recipient can very alert to observe and discard the document.

Finally, it should be noted that: the above description is only illustrative of the specific embodiments of the invention and it is of course possible for those skilled in the art to make modifications and variations to the invention, which are deemed to be within the scope of the invention as defined in the claims and their equivalents.

Claims

1. An optimally hidden double-protection text method is characterized by comprising the following steps:

step one: encrypting the carrier text by using an SHA256 hash algorithm to generate a hash digest a;

step two: embedding the secret information and the hash digest a into R, G, B components of the color pixel values of the carrier text by using an information hiding algorithm to form a steganographic text;

step three: sending the steganographic text to a recipient;

step four: the receiver receives a file, wherein the file is a steganographic text or a legal modified steganographic text or an illegally tampered steganographic text;

step five: the receiver uses SHA256 hash algorithm to extract hash digest b from the file;

step six: judging whether the regenerated hash digest b is equal to the extracted hash digest a or not, and if not, judging whether the regenerated hash digest b is equal to the extracted hash digest a or not; indicating that the secret information is illegally tampered by an attacker, and discarding the file by a receiver; if the two types of the files are equal, the files are indicated to belong to the steganographic text or the legal modified steganographic text, and the step seven is shifted;

step seven: the recipient extracts the secret information.

2. The optimally hidden double protection text method of claim 1, wherein: embedding secret information and a hash digest a into R, G, B components of color pixel values of a carrier text by adopting the following information hiding algorithm;

and (3) outputting: steganographic text G' ₁ ,G′ ₂ ,G′ ₃ ；

The embedding process comprises the following steps:

step 21: processing the carrier text information; step 21 further comprises:

step 212: acquiring pixel values of R, G, B channels of color of each letter of the carrier text by respectively usingG ₁ ，G ₂ ，G ₃ A representation; will G ₁ ，G ₂ ，G ₃ Merging into G; g is the total number of pixel values of the carrier text;

step 22: processing the secret information; step 22 further comprises:

B ₃ ＝(b _3nk+3 b _3nk+2 …b _2nk+3 b _2nk+2 ) ₂ ；

B ₂ ＝(b _2nk+1 b _2nk …b _nk+2 b _nk+1 ) ₂ ；

B ₁ ＝(b _nk b _nk-1 …b ₁ b ₀ ) ₂ ；

step 222: to binary confidential information B of each group ₁ 、B ₂ 、B ₃ Converting into decimal numbers;

D ₃ ＝2 ^nk b _3nk+3 +2 ^nk-1 b _3nk+2 +…+2 ¹ b _2nk+3 +2 ⁰ b _2nk+2 ；

D ₂ ＝2 ^nk b _2nk+1 +2 ^nk-1 b _2nk +…+2 ¹ b _nk+2 +2 ⁰ b _nk+1 ；

D ₁ ＝2 ^nk b _nk +2 ^nk-1 b _nk-1 +…+2 ¹ b ₁ +2 ⁰ b ₀ ；

step 223: will B ₁ Dividing into n groups, the first group comprising k+1 bits, (b) _k b _k-1 …b ₁ b ₀ ) ₂ Conversion to decimal number d ₀ The remaining n-1 groups are: (b) _(y+1)k …b _yk+2 b _yk+1 ) ₂ Conversion to decimal number d _y ,y∈[1,n-1]The method comprises the steps of carrying out a first treatment on the surface of the Likewise, theWill B ₂ ,B ₃ These operations are also performed;

step 23: embedding secret information; step 23 further comprises:

will B ₁ ,B ₂ ,B ₃ The decimal numbers of each group are embedded into each group of pixel values, and the embedding process is as follows:

step 231: q represents the index of the vector text color pixel value, and equation (6) is used to index the hidden k+1 bit pixel value, g _i Pixel values g representing the original carrier image _h Refers to the h pixel in a group of pixels; using g' _i Representing pixel values, g ', of the embedded steganographic picture' _h Refers to the pixel value of the h steganographic picture in a group of pixels;

g _h ＝q mod n (6)；

using g' _h ＝x _h +g _h Embedding secret information;

using g' _i ＝x _i +g _i Embedding secret information;

step 234: likewise will B ₂ ,B ₃ The operations of steps 231-233 of step 23 are also performed;

step 235: will g' _h And g' _i Combining to obtain a steganographic text font R, G and a B-channel pixel G' ₁ ,G′ ₂ ,G′ ₃ 。

3. The optimal hidden double protected text method according to claim 2, wherein said step seven receiver extracts the secret information comprising: obtain input G' ₁ ,G′ ₂ ,G′ ₃ Outputting 3nk+3 bits of secret information;

the seventh step comprises the following steps:

step 71: using index g' _i =q mod n, finding the pixel value of the hidden k+1 bits binary secret information;

step 72: resume d ₀ ＝g′ _h mod 2 ^k+1 ；

Step 73: resume d _i ＝g′ _i mod2 ^k ；

Step 74: will d ₀ ，d _i And combining to obtain secret information d, and converting the secret information d into binary bits.

4. The optimal hidden double protected text method according to claim 1, wherein legal modifications include steganographic text font format changes, font size, color changes; illegal tampering includes adding a character to the steganographic text, deleting a character, replacing a character with a visually different character, replacing a character with a visually similar character to tamper with the steganographic text.

5. The optimal hidden double protected text method according to claim 1, wherein the SHA256 hash algorithm comprises three phases, constant initialization, information preprocessing and calculation of digest values, respectively.

6. The optimal hidden double protected text method according to claim 5, wherein the constant initialization comprises: taking the first 8 prime numbers in the natural numbers, calculating square root for the prime numbers, and taking out 32bits of the decimal part of the result to convert the decimal part into 16-system numbers to generate a hash initial value;

then taking the first 64 prime numbers of the natural number, calculating the cube roots of the prime numbers, and taking 32bits of the decimal part to convert the decimal part into 16-system numbers to generate a hash constant K;

the information preprocessing refers to supplementing the information needed after the information with the hash is calculated, so that the information meets the needed structure; the preprocessing of the information is divided into two steps:

step 11: adding padding bits;

setting the binary coding bit number of the information as l, supplementing a bit of '1' after the coding bit, and supplementing k bits of '0', wherein k is a minimum non-negative integer meeting the following equation;

l+1+k≡448mod512(2)；

step 12: adding a length value;

encoding the length l of the original information into a 64-bit binary form, and attaching the original information to the back of the filled information, so that the length of the whole information becomes 512bits or multiples of 512 bits;

step 13: and calculating the digest value to obtain a 256-bit hash digest.