Electronic signature refers to the data contained in the data message in electronic form and accompanied by data used to identify the identity of the signer and show that the signer approves its content. Generally speaking, electronic signature is an electronic signature of electronic documents through cryptographic technology, which is not a digital visualization of written signature, but similar to handwritten signature or seal, and can also be said to be an electronic seal. The purpose of electronic signature is to sign the electronic version of Mid-Autumn Festival greeting cards, invitations and construction contracts.

An electronic signature is not a digital image of a written signature. It is actually an electronic code, through which the recipient can easily verify the identity and signature of the sender on the Internet. It can also verify whether the original text of the file has changed during transmission. If someone wants to send an important document to a foreign person through the network, both the receiver and the sender need to apply for an electronic license from the licensing authority CA first.

This encryption certificate includes the applicant's public key on the Internet, that is, the "public computer password", which is used for file verification. The sender encrypts the file with the public key of the receiver issued by CA, and signs the file with its own key. When the recipient receives the file, he first analyzes the signature with the sender's public key to prove that the file is indeed sent by the sender. Then use your own private key to decrypt the file and read it.