CN109547663B - Improved LSB image steganography method combined with cryptography - Google Patents

Abstract

The invention discloses a cryptograph-combined improved LSB image steganography method, which comprises the following steps: (1) and (3) encryption process: inputting a carrier image and secret information, and carrying out encryption preprocessing to obtain the lowest k effective bit of a carrier image block and binary information of a secret information array block; applying cryptographic encryption coding to the secret information array block according to the carrier image block to generate a secret key for each secret information array block; replacing the least-significant-k bits of the carrier image with the obtained encryption information, thereby outputting an encrypted image, and taking a key address in the encrypted image as an output; (2) and (3) decryption process: inputting an encrypted image and a key address, and dividing the encrypted image into nxn pixel blocks; and then, decrypting the encrypted image by using the secret key, and finally, applying a decoding algorithm to the decrypted information to obtain the secret information. Compared with the traditional method, the method increases the information hiding capacity and has the advantages of good hiding performance and good robustness.

Description

Improved LSB image steganography method combined with cryptography

Technical Field

The invention relates to the field of information security and cryptography, in particular to an improved LSB (least significant bit) image steganography method combining cryptography.

Background

With the rapid development of information technology and the widespread use of the internet, digital media has become an important carrier for military, commercial, etc. organizations and individuals to acquire and transfer information. Meanwhile, digital communication in the internet is vulnerable to eavesdropping, malicious interference and the like, so people pay more attention to the communication security problem than ever before. The traditional encryption technology converts information into ciphertext to hide information content, but has the defect that the ciphertext after encryption is meaningless messy code and easily attracts the attention of an attacker, so that the information is interfered or intercepted, even damaged. In this context, a new communication security concept is gradually formed: communication security not only means hiding the content of information but also requires the existence of hidden information transmission behavior. Therefore, more covert digital Steganography (Steganography) with "camouflage" features is gaining increasing attention.

The basic modes of information hiding include transmission hiding, carrier hiding and storage hiding, and the implementation methods include an information hiding method based on replacement, an information hiding method based on transformation and an information hiding method based on spread spectrum, at present, steganography plays an increasingly important role in the field of information security, and is summarized into three aspects of secret communication, integrity and qualification authentication, and illegal disclosure of data, (1) secret communication is mainly used for secure communication of information, secret information is hidden in common multimedia information for transmission by steganography in network communication, and eavesdroppers have difficulty in detecting multimedia information really hidden with secret information when facing massive multimedia information on a network, (2) an important aspect of computer system security is data integrity.

The basic principle of digital steganography is to hide secret information to be transmitted into redundant information by utilizing the characteristic of the redundant information which is insensitive to a human perception system and exists in digital carriers such as images, videos, audios and texts, and the secret information is transmitted by means of transmission of the carriers. Because the surface of the information-embedded secret carrier is the same as that of a common carrier, a possible attacker can hardly perceive the existence of secret information, and the safe and concealed transmission of the information is ensured.

The Least Significant Bit (LSB) algorithm belongs to the spatial domain information hiding algorithm, which is one of the most widely used hiding techniques. Each image can be uniquely represented by its bit-plane, while the human visual system is very insensitive to the lowest few bits in the bit-plane, and replacing these corresponding bits with secret messages is a very confusing means of information hiding, and the amount of information hiding is relatively large. In this type of information hiding method, a lossless image format is mainly used and data can be directly processed and restored. The main disadvantages of the conventional image steganography based on the LSB algorithm are low security, poor detection resistance and poor robustness.

Disclosure of Invention

The invention aims to overcome the defects and shortcomings in the prior art, and provides an improved LSB image steganography method combined with cryptography.

In order to realize the purpose, the invention adopts the following technical scheme:

a method for improved LSB image steganography incorporating cryptography, comprising the steps of:

(1) and (3) encryption process: inputting a carrier image and secret information, and carrying out encryption preprocessing to obtain the lowest k effective bit of a carrier image block and a binary code of a secret information array block; applying cryptographic encryption coding to the secret information array block according to the carrier image block to generate a secret key for each secret information array block; carrying out encryption operation on the secret information array block according to the obtained secret key, then replacing the least-k significant bit of the carrier image with the encrypted secret information array, thereby outputting an encrypted image, and taking the address of the secret key in the encrypted image as output;

(2) and (3) decryption process: firstly, inputting an encrypted image and a secret key address, then decrypting the encrypted image by using the secret key, and finally applying a decoding algorithm to the decrypted information to obtain secret information.

As a preferred technical solution, in the step (1), the encryption preprocessing is: dividing an input carrier image into blocks of non-overlapping n × n pixels, and then extracting the least significant k bits of each block; meanwhile, a string table compression algorithm is applied to carry out compression coding on the input secret information, then the coded information is converted into binary information, the binary information is read into a secret information array, and the secret information array is divided into n multiplied by n bit blocks, so that a secret information array block can be obtained.

As a preferred technical solution, in the step (1), the specific process of generating the key for each secret information array block is as follows: carrying out XOR processing on the binary codes of the carrier image block and the secret information array block to obtain a result array; then, the total number t of each row of binary codes in the result array being 1 is calculated, and a key is generated for each secret information array block, namely if t > n/2, the corresponding key is 1, otherwise, the corresponding key is 0.

As a preferred technical solution, in the step (1), the encrypting operation on the secret information array block according to the key specifically includes: if the secret key corresponding to the binary column of the secret information array block is 1, each bit of the column is inverted, and if the corresponding secret key is 0, the column is kept as it is.

As a preferred technical scheme, the specific process of the step (2) is as follows:

firstly, inputting an encrypted image and a key address, dividing the encrypted image into blocks of n multiplied by n pixels, and extracting encryption information bits from the least k significant bits of the encrypted image blocks according to the key address; then, carrying out decryption operation on the encrypted information of each encrypted image block according to the secret key; and finally, applying a string table decompression algorithm to the decrypted information to obtain the secret information.

Compared with the prior art, the invention has the following advantages and effects:

1. the image steganography method of the invention applies the principle of cryptography, reduces the difference between the bits of the carrier image and the bits of the secret information, and enhances the robustness and the anti-detection performance;

2. the invention combines the string table compression algorithm to compress and encode the secret information, thereby increasing the capacity of the secret information.

Drawings

FIG. 1 is a flow chart of the improved LSB image steganography method of the present invention incorporating cryptography;

fig. 2(a) -2 (h) are exemplary diagrams of the improved LSB image steganography method in combination with cryptography in an encryption phase of the present invention, wherein fig. 2(a) is an input carrier image; FIG. 2(b) is an input secret; FIG. 2(c) shows the result array obtained by XOR processing the information array block; FIGS. 2(d) and 2(e) are processes for generating a key from a result array; FIGS. 2(f) and 2(g) are processes for encrypting an array of information according to a key; fig. 2(h) shows an output encrypted image.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention.

Examples

Fig. 1 shows a cryptogra phic improved LSB image steganography method, which includes the following steps:

and (3) an encryption stage:

inputting: carrier image, secret information;

and (3) outputting: encrypting the image and the secret key.

The first step is as follows: inputting a standard carrier image; as shown in fig. 2 (a);

the second step is that: dividing the carrier image into small blocks of n × n pixels without overlap;

the third step: extracting the least-k significant bit (Im _ b) of each tile;

the fourth step: inputting secret information; as shown in FIG. 2 (b);

the fifth step: applying a string table compression algorithm (LZW compression algorithm) to carry out compression coding on the secret information;

and a sixth step: converting the encoded information into binary information;

the seventh step: reading the binary information into an information array;

eighth step: dividing the information array into small blocks (mess _ b) of n × n bits;

the ninth step: applying cryptographic encryption coding to the information array block according to the carrier image block (i.e. performing exclusive or processing on the binary codes of the carrier image block and the secret information block) to obtain a result array (res _ b), as shown in fig. 2 (c); calculating the total number t of each row of binary codes in the result array as 1, as shown in fig. 2(d), generating a key (Keys) for each small block, i.e. if t > n/2, the corresponding key is 1, otherwise, the corresponding key is 0, as shown in fig. 2 (e);

the tenth step: encrypting the secret information array block according to the secret key, specifically operating as follows: if the key corresponding to the binary column of the secret information array block is 1, each bit of the column is inverted, and if the corresponding key is 0, the column is kept as it is, as shown in fig. 2 (f); replacing the least-k significant bit (Im _ b) with the encrypted secret information array block, as shown in fig. 2 (g);

the eleventh step: finding out the key address in the image as output;

the twelfth step: the encrypted image is output as shown in fig. 2 (h).

And a decryption stage:

inputting: encrypting the image, the key address;

and (3) outputting: carrier image, secret information.

The first step is as follows: inputting an encrypted image;

the second step is that: dividing the encrypted image into small blocks of n x n pixels;

the third step: extracting encryption information bits from the least k significant bits of the encryption image block according to the position of the secret key;

the fourth step: carrying out decryption operation on each small block according to the secret key;

the fifth step: a string table decompression algorithm (LZW decompression algorithm) is applied to obtain the secret information.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the claims.

Claims (3)

1. A method for improving LSB image steganography in combination with cryptography, comprising the steps of:

(1) and (3) encryption process: inputting a carrier image and secret information, and carrying out encryption preprocessing to obtain the lowest k effective bit of a carrier image block and a binary code of a secret information array block; applying cryptographic encryption coding to the secret information array block according to the carrier image block to generate a secret key for each secret information array block; carrying out encryption operation on the secret information array block according to the obtained secret key, then replacing the least-k significant bit of the carrier image with the encrypted secret information array, thereby outputting an encrypted image, and taking the address of the secret key in the encrypted image as output;

(2) and (3) decryption process: firstly, inputting an encrypted image and a secret key address, then decrypting the encrypted image by using the secret key, and finally applying a decoding algorithm to decrypted information to obtain secret information;

the encryption preprocessing comprises the following steps: dividing an input carrier image into blocks of non-overlapping n × n pixels, and then extracting the least significant k bits of each block; meanwhile, a string table compression algorithm is applied to carry out compression coding on the input secret information, then the coded information is converted into binary information, the binary information is read into a secret information array, and the secret information array is divided into n multiplied by n bit blocks, so that a secret information array block can be obtained;

the specific process of generating the secret key for each secret information array block is as follows: carrying out XOR processing on the binary codes of the carrier image block and the secret information array block to obtain a result array; then, the total number t of each row of binary codes in the result array being 1 is calculated, and a key is generated for each secret information array block, namely if t > n/2, the corresponding key is 1, otherwise, the corresponding key is 0.

2. The method for improving the LSB image steganography in combination with cryptography according to claim 1, wherein in step (1), the encrypting operation on the secret information array block according to the secret key specifically comprises: if the secret key corresponding to the binary column of the secret information array block is 1, each bit of the column is inverted, and if the corresponding secret key is 0, the column is kept as it is.

3. The improved LSB image steganography method in combination with cryptography according to claim 1, wherein the specific process of step (2) is as follows:

firstly, inputting an encrypted image and a key address, dividing the encrypted image into blocks of n multiplied by n pixels, and extracting encryption information bits from the least k significant bits of the encrypted image blocks according to the key address; then, carrying out decryption operation on the encrypted information of each encrypted image block according to the secret key; and finally, applying a string table decompression algorithm to the decrypted information to obtain the secret information.

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