Principle of Digital Signature

The base of digital signature is Messages Digest Algorithm and Dissymmetric Key Encryption Algorithm.

Messages Digest Algorithm

It is a kind of algorithm by which we can get a characteristic character string (message digest) from a electronic file. If any change in this electronic file occurs, the message digest obtained by messages digest algorithm will be changed greatly. It almost has no possibility that two different electronic file have same message digest. Messages Digest Algorithm is also known as Digital Fingerprint.

Dissymmetric Key Encryption Algorithm (DKEA)

In DKEA system, every user have a pair of digital key: a public key and a private key. Public key is published and the private key is kept by the owner. When encrypt by one of the two keys, the other key must be used to decrypt. DKEA can solve the problem of key publish and management. Also, it can be used to provide the identification of the two sides of data transportation. DKEA has become the core of commerce cipher system.

Process of Digital Signature

Signing

Encrypt the message digest of a electronic file by the private key. The result is the signature.

Verify

Calculate and get the message digital (m1) of the electronic file again. Decrypt the signature by user's publish key then get the original message digest (m2). Compare m1 and m2. If m1 equals to m2, the signature is proved to be valid and the identity of the encrypting person is confirmed.