The application of cryptography in information hiding technology is reflected in:

1 Copyright protection

With the rapid development of communication technology, information security issues have also become very serious. It is highlighted that the copyright protection of digital works (such as computer art, scanned images, digital music, videos, and three-dimensional animations) has become a current hot topic. Since digital works can be copied and modified very easily, and can be exactly the same as the original work, the original author has to use some methods that seriously damage the quality of the work to add copyright marks, but this clearly visible mark can easily be tampered with. The emergence of digital watermarks uses the principle of data hiding to make copyright signs invisible or inaudible, which does not damage the original work and achieves the purpose of copyright protection. In other words, digital watermark technology directly embeds some marking information related or irrelevant to the multimedia content into the multimedia content, but it does not affect the use value of the original content and is not easily noticed or noticed by others. Through this information hidden in multimedia content, people can confirm the creator and purchaser of the content and whether the viewing information is true and complete. Digital audio watermarking technology is an important research direction in information hiding technology.

The information to be kept confidential is embedded into the audio through a special algorithm without affecting the normal listening effect (that is, it has auditory transparency), making it impossible for people to detect and destroy such information. When you want to use it, extract it on the computer in the same way. Through this information hidden in the audio content, we can determine whether the object is protected, monitor the spread of protected data, identify authenticity, resolve copyright disputes, and provide certification evidence for the court. The current digital audio watermarking technology has the function of tracking illegal copying, but it cannot prevent piracy. Technically speaking, when buying a sound product, you have to enter your basic information during the invoicing process. The payee can even take a photo of the purchaser and embed this information into the song. Of course, this involves privacy issues, so this information can only be used when piracy occurs and copyright protection occurs, and cannot be used in other circumstances. This is the same reason that telecommunications companies need customer information. If there is a pirated copy in the market, the judicial authorities will buy one and extract the watermark inside, and then they will know who is the source of the dissemination. If this can be realized legally, people will have to go through an additional procedure when purchasing audio works, just like they need to register when going to the hospital, or fill out a form when going to a telecommunications company to make a phone call. It may take some time for people to agree with this procedure and to jointly combat piracy.

2 Digital signature

Digital signature is established on the basis of public key encryption system. The calculation method involved in the generation of digital signature is the well-known hash function function. , also called "Hash Function". The hash function function is actually a mathematical calculation process. This computational process is based on a computational method that creates a numerical representation or compressed form of information in the form of a "hash function value" or "hash function result" (often referred to as a "message digest" or "message identifier") above. In the case of a secure hash function (sometimes called a one-way hash function), it is virtually impossible to deduce the original information from the known hash function results. Therefore, the hash function function allows the software to operate on a smaller and predictable amount of data to generate digital signatures, but maintains a high degree of correlation with the original information content, and effectively guarantees that the information has not been modified in any way after being digitally signed. .

The so-called digital signature is a digital string that can only be generated by the sender of the information and cannot be forged by others. It is also a proof of the authenticity of the information sent by the sender. When signing a document or any other piece of information, the signer must first accurately define the scope of what is to be signed. The hash function function in the signer's software will then calculate a unique hash function value for the signed message (for practical purposes). Finally, the signer's private password is used to convert the hash function result value into a digital signature. The resulting digital signature is unique to both the message being signed and the private password used to create the digital signature.

A digital signature (a digital signature of the hash function result of a message) is attached to the message and is stored and transmitted along with the message. However, it can also be stored and transmitted as a separate unit of data, as long as a reliable link to the corresponding information is maintained. Because a digital signature is unique to the information it signs.

3 Digital fingerprint

Digital fingerprint technology is a new digital product copyright protection technology developed in recent years. Digital fingerprinting refers to the use of redundant data and randomness prevalent in digital works to introduce a certain error into each copy of the data distributed, making the copy unique, so that when an illegal redistribution copy is discovered, A copyright protection technology for digital works that traces errors in the copy back to the dishonest original purchaser.

Generally, the introduced error refers to information related to the user and a certain purchase process. When a publisher discovers illegally distributed authorization information, it can track the illegally distributed users based on this information.

The digital fingerprint system can be divided into two parts: algorithm and protocol. The algorithm includes fingerprint encoding, decoding, embedding, extraction and data distribution strategies, etc., while the protocol part specifies how entities interact to achieve various functions. Characteristic data distribution and tracking system.

4 Broadcast Monitoring

The watermarking system developed by the Korea Broadcasting Corporation Technical Research Institute (KBS TRI) embeds copyright information into uncompressed video streams before MPEG-2 compression. And detect the watermark in the received video without the original video. Use a secure key to generate the watermark and the watermark embedding location. The intensity of the embedded watermark for each pixel is determined by the invisible human visual system. KBS's watermark technology meets the requirements of invisibility, robustness and security. Watermarks in broadcast content identify the original broadcaster and can detect illegal copies and unauthorized reuse of content.

For standard-definition videos, the information embedded as a watermark in the video is a 64-bit copyright identifier; for high-definition videos, it is a 128-bit copyright identifier. The watermark bits of the copyright identifier are generated by a security key used for watermarking system security. The watermark is embedded in the spatial domain of the video sequence prior to MPEG-2 compression for digital television transmission. Therefore, the watermark must withstand MPEG-2 compression. The imperceptibility of a watermark is determined by the strength of the watermark. For imperceptibility, the watermark intensity is expected to be as low as possible, while for robustness, the watermark intensity is expected to be as high as possible. Therefore, the design of watermarking systems always involves a compromise between imperceptibility and robustness. Therefore, according to the human visual system, the watermark intensity is designed to be different on each pixel. Watermarks are detected in the transmitted MPEG-2 stream. The detection algorithm requires more than 30 frames of video. Illegal users may carry out various attacks on digital content containing watermarks. Therefore, the watermarking system of KBS Company is designed to meet the requirements of robustness.

With the advancement of IT and digital technology, the copyright protection of digital TV content is becoming increasingly important in the digital TV broadcast environment. Watermark technology is considered the most feasible solution for terrestrial digital television.

5 Secure Communication

Digital watermark technology can also be applied to secure communication of information. Secret communication has important uses in intelligence, military and other fields. The system must ensure that both parties can communicate normally and the communication content will not be stolen by the enemy. Traditionally, secret communications have been primarily achieved through cryptographic techniques. Therefore, for the sake of national security, various countries are sparing no effort to develop their own cryptographic technologies to ensure the security of secret communications. With the development of network technology, ordinary users also hope that their online communications will not be eavesdropped by third parties. Therefore, cryptography technology has come out of the military's black box and is increasingly used in the network. But even if the password algorithm is carefully designed, it may still be cracked by the enemy. What is more serious is that it is difficult for us to detect that the password has been cracked. It will be extremely dangerous to continue to use this password to send intelligence. On the other hand, if the enemy detects that ciphertext is being transmitted on the channel, even if it cannot be cracked in a short time, it will deliberately destroy our communication channel to prevent our communication. If our intelligence personnel are collecting information abroad, using passwords to transmit files can easily reveal their identities. Therefore, in addition to meeting the basic requirement of confidentiality, secret communications should also be extremely concealed and difficult to detect.

With the development of the Internet, people from all over the world can easily send emails and various files through the Internet. The Internet is extremely open and unsafe. If we can hide secret information in some ordinary files such as pictures, MP3, and WAV. The carrier of information hiding can be regarded as a communication channel, the information to be hidden can be regarded as a signal that needs to be transmitted, and the embedding and extraction of information can be regarded as the modulation and demodulation processes in communication respectively.

Since it is difficult to detect the existence of digital watermark information in multimedia data, some important information can be hidden in ordinary multimedia data during the transmission process, thereby avoiding third-party eavesdropping and monitoring. . Through ordinary Internet transmission, it will be difficult for the enemy to discover the existence of secret information, and therefore will not actively destroy the communication channel, thus ensuring communication security.