Only the sender of information can produce a digital string that others can't forge, and this digital string is also an effective proof of the authenticity of the information sent by the information sender. It is a method to authenticate digital information, which is similar to the ordinary physical signature written on paper, but it is realized by using the technology in the field of public key encryption.

A set of digital signatures usually defines two complementary operations, one for signing and the other for verification. Digital signature is the application of asymmetric key encryption technology and digital digest technology.

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When sending a message, the sender uses a hash function to generate a message digest from the message text, and then encrypts the digest with the sender's private key. The encrypted digest will be sent to the receiver as the digital signature of the message. The receiver first uses the same hash function as the sender to calculate the message digest from the received original message.

The public key is then used to decrypt the digital signature attached to the message. If the two digests are the same, the receiver can confirm that the message belongs to the sender. Digital signature can ensure that the message is indeed signed by the sender, because others can't forge the sender's signature, and digital signature can ensure the integrity of the message.

Because the characteristic of digital signature is that it represents the characteristics of the file, if the file changes, the value of the digital abstract will also change. Different files will get different digital summaries. Digital signature includes hash function, receiver's public key and sender's private key.