Digital signature (also known as public key digital signature and electronic signature) is an ordinary physical signature, similar to the signature written on paper, but it is realized by using the technology in the field of public key encryption, which is used to identify digital information. A set of digital signatures usually defines two complementary operations, one for signing and the other for verification.

A digital signature is a digital string, which can only be generated by the sender of the information, and others cannot forge it. This number string is also an effective proof of the authenticity of the information sent by the information sender.

Digital signature is the application of asymmetric key encryption technology and digital digest technology.

Digital envelope is a method of distributing symmetric keys through asymmetric encryption (that is, there are two kinds of public keys and private keys). Digital envelope is a technology to realize information integrity verification.

In PKCS#7, digital envelope is defined as a term, but in the text, it is explained as follows: digital envelope contains encrypted content and encryption key used to encrypt the content.

Although the public key of the receiver is often used to encrypt the "encryption key", it is not necessary, and it can also be encrypted by using the symmetric key enjoyed by the sender and the receiver in advance. When receiving the digital envelope, the receiver first decrypts it with the private key or pre-shared key to obtain the "encryption key", and then decrypts the ciphertext with this key to obtain the original text. Digital envelope technology uses a two-layer encryption system.