Digital signature technology is a typical application of asymmetric encryption algorithm. The application process of digital signature is that the sender of the data source encrypts the data checksum or other variables related to the data content with his own private key to complete the legal "signature" of the data, and the receiver of the data interprets the received "digital signature" with the public key of the other party, and uses the interpretation result to check the integrity of the data to confirm the legality of the signature. Digital signature technology is an important technology to confirm identity in the virtual environment of network system, which can completely replace the "autograph" in the real process and get technical and legal protection. In the management of public and private keys, the application of digital signature is just the opposite of PGP technology for encrypting emails. In the application of digital signature, the sender's public key is easy to obtain, but his private key needs to be kept strictly confidential.
The main functions of digital signature are: to ensure the integrity of information transmission, to authenticate the identity of the sender, and to prevent denial in transactions.
Digital signature includes general digital signature and special digital signature. Common digital signature algorithms include RSA, ElGmal, Fiat-Shamir, Guillou-quiqour, Schnorr, Ong-Schnorr-Shamir, Des/DSA, elliptic curve digital signature algorithm and finite automaton digital signature algorithm. Special digital signatures include blind signature, proxy signature, group signature, undeniable signature, fair blind signature, threshold signature, signature with message recovery function and so on. It is closely related to the specific application environment.
Digital signature technology encrypts abstract information with the sender's private key and sends it to the receiver together with the original text. The receiver can decrypt the encrypted digest information with only the transmitted public key, and then use a hash function to generate digest information for the received original text and compare it with the decrypted digest information. If they are the same, it means that the received information is complete and has not been modified during transmission, otherwise it means that the information has been modified, so the digital signature can verify the integrity of the information.
Digital watermarking technology is to embed some identification information (digital watermarking) directly into digital carriers (including multimedia, documents, software, etc.). ), but it does not affect the use value of the original carrier, and it is not easy to be perceived or noticed by human perception systems (such as visual or auditory systems). Through these hidden information in the carrier, we can confirm the creator and buyer of the content, transmit secret information or judge whether the carrier has been tampered with. Digital watermarking is an important research direction of information hiding technology.
As a digital watermarking technology, it mainly has the following characteristics:
-Security: The information of digital watermark should be secure and difficult to tamper with or forge. At the same time, there should be a low false detection rate. When the original content changes, the digital watermark will also change, so as to detect the change of the original data; Of course, digital watermarking also has strong anti-duplication ability.
-Concealment: Digital watermarking should be imperceptible and should not affect the normal use of protected data; Will not be downgraded;
-Robustness: It means that the digital watermark can still maintain partial integrity and be accurately identified after going through various unintentional or intentional signal processing processes. Possible signal processing processes include channel noise, filtering, digital-to-analog and analog-to-digital conversion, resampling, clipping, displacement, scale change and lossy compression coding. Fragile watermark, a digital watermark mainly used for copyright protection, is mainly used for integrity protection. This watermark also embeds invisible information in the content data. When the content changes, the watermark information will also change, so that we can identify whether the original data has been tampered with.
Watermark capacity: refers to the amount of watermark information that can be embedded without deformation of the carrier. The embedded watermark information must be enough to represent the identification information of the creator or owner of multimedia content or the serial number of the buyer, which is beneficial to solving copyright disputes and protecting the interests of the legitimate owner of digital property rights. Especially in the field of covert communication, there is a great demand for watermark capacity.
Classification of digital watermarking
-1. Divided by characteristics
According to the characteristics of watermarking, digital watermarking can be divided into robust digital watermarking and fragile digital watermarking. Robust digital watermarking is mainly used to identify copyright information in digital works. By using this watermarking technology, the identification information of the creator and owner or the identification of the buyer (that is, the serial number) is embedded in the data of multimedia content. In the event of copyright disputes, the information of the creator or owner is used to identify the copyright owner of the data, while the serial number is used to track the users who violate the agreement and provide multimedia data for piracy. Digital watermarking for copyright protection requires strong robustness and security. Besides surviving in general image processing (such as filtering, adding noise, replacing and compressing), it also needs to be able to resist some malicious attacks.
Fragile watermarking, contrary to the requirement of robust watermarking, is mainly used for integrity protection. This watermark also embeds invisible information in the content data. When the content changes, the watermark information will also change, so that we can identify whether the original data has been tampered with. Vulnerable watermark should have strong immunity (robustness) to general image processing (such as filtering, noise adding, replacement, compression, etc.). ), at the same time, it must have strong sensitivity, that is, it must allow a certain degree of distortion and be able to detect distortion. It must be sensitive to the change of signal, and people can judge whether the data has been tampered with according to the state of fragile watermark.
Fingerprints are no longer just a means to hunt down criminals. Now more and more people use digital fingerprints in their daily lives. Fingerprint identification has been widely used in the checkout counter of a supermarket chain in California and the lockers near the Statue of Liberty, which can reduce the waiting time.
Now digital fingerprints are applied to passwords of mobile phones and personal computers, and fingerprints are also used to open safes.
But today's fingerprints are not the fingerprints that were printed on paper with fingers. At present, the finger is pressed on the glass window connected to the computer, and the attribute of the fingerprint is usually confirmed by optical reading equipment.
Digital fingerprint technology will become the dominant technology in the near future. The reason for the development of digital fingerprint security technology is that the progress of science and technology is reducing the production cost of this technology. Recently, software companies put a cheap automatic digital fingerprint interpretation software on the market. In addition, they also put in products such as digital fingerprint keyboard and mouse.
Using digital fingerprints, people can avoid a big headache and don't have to bother to remember digital passwords.