Simply put, the so-called digital signature is some data attached to the data unit, or the cryptographic transformation of the data unit. This kind of data or transformation allows the receiver of the data unit to confirm the source and integrity of the data unit, and protects the data from being forged by people (such as the receiver). This is a method of signing an electronic message, and the signed message can be transmitted in a communication network. Digital signature can be obtained based on both public key cryptosystem and private key cryptosystem. At present, digital signature is mainly based on public key cryptosystem. Include general digital signature and special digital signature. Common digital signature algorithms include RSA, ElGamal, Fiat-Shamir, Guillou-Quisqour, 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. Obviously, the application of digital signature involves legal issues, and the federal government of the United States has formulated its own digital signature standard (DSS) based on the discrete logarithm problem over a finite field. Some countries, such as France and Germany, have enacted digital signature laws.