A set of digital signatures usually defines two complementary operations, one for signing and the other for verification. Electronic signature and digital signature have different meanings in legal terms.
Electronic signature refers to the person who is attached to and associated with an electronic document and used to identify and confirm the identity, qualification and authenticity of the electronic document; Digital signature is an electronic signature formed by encrypting it by mathematical algorithm or other means. This means that not all electronic signatures are digital.
Digital signature is not to scan the signature into a digital image, or to obtain the signature with a touch screen, let alone a signature.
The integrity of the digital signature document is easy to verify (riding seal, riding signature or handwriting identification is not required), and the digital signature is undeniable (that is, undeniable), without handwriting expert verification.
principle
Usually the public key is used for encryption and the private key is used for decryption. In digital signature, private key encryption (equivalent to generating signature) and public key decryption (equivalent to verifying signature) are used.
The message can be signed directly (that is, encrypted with the private key, and the purpose of encryption at this time is to sign, not to keep secret), and the verifier can decrypt the message correctly with the public key. If it is consistent with the original message, the signature is verified successfully. But the hash value of the message is usually signed, because the length of the hash value is usually much smaller than the original message, which greatly improves the efficiency of signing (asymmetric encryption). Note that computing the hash value of a message is not a necessary step for digital signature.
In practical use, we want to encrypt and sign the message, so we should combine encryption and signature. For example, TLS combines encryption and signature.